My interest in ophthalmology started at a very early age, motivated by my own amblyopia and hyperopia. These led me to study physics and optics, with my first research experience at undergraduate and master?s level at the Applied Optics Group of the Universidad de la Repblica in Uruguay. I then pursued my PhD work and a first postdoctoral position at the Photonics Group in Imperial College London, where I worked on instrumentation to study the topography of the tear film and adaptive optics (AO). The desire to advance AO for retinal imaging took me to the University of Rochester, where the interaction with patients affected by blinding conditions provided me with the determination to go beyond the proof-of-principle experiments after which many technologies are abandoned. Therefore, since starting my research group at the University of Rochester first, and at the Medical College of Wisconsin later and now at Stanford we have focused on the development and translation of AO and microscopy techniques into tools that can be used to address real clinical problems.

Academic Appointments

Administrative Appointments

  • Honorary Lecturer of Ophthalmology, University College London (UK) (2013 - Present)
  • Associate Adjunct Professor of Ophthalmology, Medical College of Wisconsin (2016 - Present)

Honors & Awards

  • Overseas Research Student Award, Universities UK (Ex. Committee of Vice-Chancellors & Principals) (2000)
  • Career Award at the Scientific Interface, Burroughs Wellcome Fund (2008)
  • Career Development Award, Research to Prevent Blindness (2012)

Boards, Advisory Committees, Professional Organizations

  • Member, The International Society for Optics and Photonics (2011 - Present)
  • Member, Association for Research in Vision and Ophthalmology (2001 - Present)
  • Member, Optical Society of America (2008 - Present)

Professional Education

  • PhD, Imperial College London, UK, Physics (2004)
  • MSc, Universidad de la Repblica, Uruguay, Physics (2000)
  • BSc, Universidad de la Repblica, Uruguay, Physics (1998)


  • Alfredo Dubra. "United States Patent 8,226,236 Method and apparatus for imaging in an eye", University Of Rochester, May 18, 2006

Research & Scholarship

Current Research and Scholarly Interests

The optics of the eye can be thought of as an imperfect microscope objective through which the retina can be observed. Our lab uses adaptive optics, a technology originally developed to observe distant stars and galaxies to improve this microscope objective so that individual retinal and blood cells can be visualized. Moreover, we use and invent new microscopy imaging methods to reveal cellular and sub-cellular structures in the eye through a multidisciplinary approach that integrates optics, computer science, vision science, electrical engineering and other engineering disciplines.


2019-20 Courses

Stanford Advisees


All Publications

  • Intraobserver Repeatability and Interobserver Reproducibility of Foveal Cone Density Measurements in CNGA3- and CNGB3-Associated Achromatopsia TRANSLATIONAL VISION SCIENCE & TECHNOLOGY Georgiou, M., Litts, K. M., Singh, N., Kane, T., Patterson, E. J., Hirji, N., Kalitzeos, A., Dubra, A., Michaelides, M., Carroll, J. 2020; 9 (7)
  • Photoreceptor Structure in GNAT2-Associated Achromatopsia INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE Georgiou, M., Singh, N., Kane, T., Robson, A. G., Kalitzeos, A., Hirji, N., Webster, A. R., Dubra, A., Carroll, J., Michaelides, M. 2020; 61 (3): 40


    The purpose of this study was to report GNAT2-associated achromatopsia (GNAT2-ACHM) natural history, characterize photoreceptor mosaic, and determine a therapeutic window for potential intervention.Patients with GNAT2-ACHM were recruited from a single tertiary referral eye center (Moorfields Eye Hospital, London, UK). We performed longitudinal clinical evaluation and ophthalmic examination, and multimodal retinal imaging, including adaptive optics scanning light ophthalmoscopy, quantitative analysis of the cone mosaic, and outer nuclear layer (ONL) thickness, including cone densities evaluation in selected regions of interest and comparison with reported healthy controls.All nine subjects (3 women) presented with nystagmus, decreased visual acuity (VA), light sensitivity, and highly variable color vision loss. One patient had normal color vision and better VA. Mean VA was 1.01 (0.10) logarithms of the minimal angle of resolution (LogMAR) at baseline, and 1.04 (0.10) LogMAR after a mean follow-up (range) of 7.6 years (1.7-12.8 years). Optical coherence tomography showed preservation of the foveal ellipsoid zone (EZ; n = 8; 88.9%), and EZ disruption (n = 1; 11.1%). Mean ONL thickness (range, SD) was 84.72m (28.57-113.33, 25.46m) and 86.47m (28.57-113.33, 24.65m) for right and left eyes, respectively. Mean cone densities (SD) at 190m, 350m, and 500m from the foveal center, were 48.4 (24.6), 37.8 (14.7), and 30.7 (9.9), 103 cones/mm2, respectively. Mean cone densities were lower than these of unaffected individuals, but with an overlap.The cone mosaic in GNAT2-ACHM is relatively well preserved, potentially allowing for a wide therapeutic window for cone-directed interventions.

    View details for DOI 10.1167/iovs.61.3.40

    View details for Web of Science ID 000524168000040

    View details for PubMedID 32203983

  • Average gradient of Zernike polynomials over polygons Optics Express Akondi, V., Dubra, A. 2020; 28 (13): 18876-18886

    View details for DOI 10.1364/OE.393223

  • ANATOMIC, GENETIC AND FUNCTIONAL PROPERTIES OF THE RETINAL CIRCULATION IN PULMONARY HYPERTENSION Pulmonary Circulation Nickel, N. P., Shamskhou, E. A., Razeen, M., Condon, D., Messentier, L., Dubra, A., Liao, Y., Zamanian, R. T., Yuan, K., de Jesus Perez, V. A. 2020

    View details for DOI 10.1177/2045894020905508

  • Advances in Retinal Imaging NEUROPHOTONICS Yi, J., Dubra, A., Farsiu, S. 2019; 6 (4)
  • Special Section Guest Editorial: Advances in Retinal Imaging. Neurophotonics Yi, J., Dubra, A., Farsiu, S. 2019; 6 (4): 041101


    The guest editorial provides an introduction to the Special Section on Advanced Retinal Imaging: Instrumentation, Methods, and Applications.

    View details for DOI 10.1117/1.NPh.6.4.041101

    View details for PubMedID 31824978

  • RAC-CNN: multimodal deep learning based automatic detection and classification of rod and cone photoreceptors in adaptive optics scanning light ophthalmoscope images BIOMEDICAL OPTICS EXPRESS Cunefare, D., Huckenpahler, A. L., Patterson, E. J., Dubra, A., Carroll, J., Farsiu, S. 2019; 10 (8): 3815?32
  • Quantifying nystagmus in patients with Achromatopsia using image-based tracking with AOSLO Kane, T., Singh, N., Georgiou, M., Dubra, A., Michaelides, M., Kalitzeos, A. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2019
  • Reflectance adaptive optics scanning light ophthalmoscopy of epiretinal membranes Razeen, M. M., Leng, T., Dubra, A. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2019
  • Shack-Hartmann wavefront sensor bias at the pupil boundary: problem and solution Akondi, V., Dubra, A. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2019
  • Chromatic Shack-Hartmann wavefront sensor with adaptive optics correction of monochromatic aberrations Steven, S., Akondi, V., Dubra, A. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2019
  • Deep learning multimodal detection and classification of cone and rod photoreceptors in adaptive optics scanning light ophthalmoscope images Cunefare, D., Huckenpahler, A. L., Patterson, E. J., Dubra, A., Carroll, J., Farsiu, S. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2019
  • Adaptive Optics Findings in Vogt-Koyanagi-Harada Disease Pham, A., Halim, M., Razeen, M. M., Hassan, M., Ormaechea, M., Razeen, E., Uludag, G., Anh Ngoc Tram Tran, Al-Kirwi, K., Mahajan, S., Afridi, R., Dubra, A., Quan Dong Nguyen ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2019
  • Natural history of foveal cone structure in RPE65-associated Leber congenital amaurosis (LCA) Kalitzeos, A., Kumaran, N., Georgiou, M., Singh, N., Kane, T., Kasilian, M., Dubra, A., Carroll, J., Michaelides, M. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2019
  • Deep Phenotyping of PDE6C-Associated Retinopathy Georgiou, M., Robson, A. G., Hirji, N., Singh, N., Kane, T., Dubra, A., Carroll, J., Webster, A., Kalitzeos, A., Michaelides, M. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2019
  • Evaluating seasonal changes of cone photoreceptor structure in the 13-lined ground squirrel VISION RESEARCH Sajdak, B. S., Salmon, A. E., Litts, K. M., Wells, C., Allen, K. P., Dubra, A., Merriman, D. K., Carroll, J. 2019; 158: 90?99
  • Design of two spherical mirror unobscured relay telescopes using nodal aberration theory OPTICS EXPRESS Steven, S., Bentley, J., Dubra, A. 2019; 27 (8): 11205?26
  • CELLULAR IMAGING OF THE TAPETAL-LIKE REFLEX IN CARRIERS OF RPGR-ASSOCIATED RETINOPATHY RETINA-THE JOURNAL OF RETINAL AND VITREOUS DISEASES Kalitzeos, A., Samra, R., Kasilian, M., Tee, J. L., Strampe, M., Langlo, C., Webster, A. R., Dubra, A., Carroll, J., Michaelides, M. 2019; 39 (3): 570?80
  • Evaluating Seasonal Changes of Cone Photoreceptor Structure in the 13-Lined Ground Squirrel. Vision research Sajdak, B. S., Salmon, A. E., Litts, K. M., Wells, C., Allen, K. P., Dubra, A., Merriman, D. K., Carroll, J. 2019


    Cone photoreceptors of the 13-lined ground squirrel (13-LGS) undergo reversible structural changes during hibernation, including cone outer segment disc degeneration and inner segment mitochondria depletion. Here, we evaluated cone structure with adaptive optics scanning light ophthalmoscopy (AOSLO) before, during, and after hibernation. Also, intra-animal comparisons of cone structure were made at distinct physiological states (pre-hibernation, torpor, interbout euthermia, and post-hibernation) with AOSLO and transmission electron microscopy. Our results indicate that the 13-LGS cone mosaic is only transiently affected by structural remodeling during hibernation. Outer segment remodeling starts during torpid states during a period of fall transition in room temperature, with more severe structural changes during bouts torpor in cold temperature. Cones return to euthermic-like structure during brief periods of interbout euthermia and recover normal waveguiding properties as soon as 24 hours post-hibernation. Cone structure is visible with split-detector AOSLO throughout hibernation, providing evidence that intact outer segments are not necessary to visualize cones with this technique. Despite the changes to cone structure during hibernation, cone density and packing remained unchanged throughout the seasonal hibernation cycle. Pairing non-invasive imaging with ultrastructural assessment may provide insight to the biological origins of cone photoreceptor signals observed with AOSLO.

    View details for PubMedID 30826354

  • Adaptive Optics Retinal Imaging in CNGA3-Associated Achromatopsia: Retinal Characterization, Interocular Symmetry, and Intrafamilial Variability. Investigative ophthalmology & visual science Georgiou, M., Litts, K. M., Kalitzeos, A., Langlo, C. S., Kane, T., Singh, N., Kassilian, M., Hirji, N., Kumaran, N., Dubra, A., Carroll, J., Michaelides, M. 2019; 60 (1): 383?96


    Purpose: To investigate retinal structure in subjects with CNGA3-associated achromatopsia and evaluate disease symmetry and intrafamilial variability.Methods: Thirty-eight molecularly confirmed subjects underwent ocular examination, optical coherence tomography (OCT), and nonconfocal split-detection adaptive optics scanning light ophthalmoscopy (AOSLO). OCT scans were used for evaluating foveal hypoplasia, grading foveal ellipsoid zone (EZ) disruption, and measuring outer nuclear layer (ONL) thickness. AOSLO images were used to quantify peak foveal cone density, intercell distance (ICD), and the coefficient of variation (CV) of ICD.Results: Mean (SD) age was 25.9 (13.1) years. Mean ( SD) best corrected visual acuity (BCVA) was 0.87 (0.14) logarithm of the minimum angle of resolution. Examination with OCT showed variable disruption or loss of the EZ. Seven subjects were evaluated for disease symmetry, with peak foveal cone density, ICD, CV, ONL thickness, and BCVA not differing significantly between eyes. A cross-sectional evaluation of AOSLO imaging showed a mean (SD) peak foveal cone density of 19,844 (13,046) cones/mm2. There was a weak negative association between age and peak foveal cone density (r = -0.397, P = 0.102), as well as between EZ grade and age (P = 0.086).Conclusions: The remnant cone mosaics were irregular and variably disrupted, with significantly lower peak foveal cone density than unaffected individuals. Variability was also seen among subjects with identical mutations. Therefore, subjects should be considered on an individual basis for stratification in clinical trials. Interocular symmetry suggests that both eyes have comparable therapeutic potential and the fellow eye can serve as a valid control. Longitudinal studies are needed, to further examine the weak negative association between age and foveal cone structure observed here.

    View details for PubMedID 30682209

  • Deep Phenotyping of PDE6C-Associated Achromatopsia. Investigative ophthalmology & visual science Georgiou, M., Robson, A. G., Singh, N., Pontikos, N., Kane, T., Hirji, N., Ripamonti, C., Rotsos, T., Dubra, A., Kalitzeos, A., Webster, A. R., Carroll, J., Michaelides, M. 2019; 60 (15): 5112?23


    To perform deep phenotyping of subjects with PDE6C achromatopsia and examine disease natural history.Eight subjects with disease-causing variants in PDE6C were assessed in detail, including clinical phenotype, best-corrected visual acuity, fundus autofluorescence, and optical coherence tomography. Six subjects also had confocal and nonconfocal adaptive optics scanning light ophthalmoscopy, axial length, international standard pattern and full-field electroretinography (ERG), short-wavelength flash (S-cone) ERGs, and color vision testing.All subjects presented with early-onset nystagmus, decreased best-corrected visual acuity, light sensitivity, and severe color vision loss, and five of them had high myopia. We identified three novel disease-causing variants and provide phenotype data associated with nine variants for the first time. No subjects had foveal hypoplasia or residual ellipsoid zone (EZ) at the foveal center; one had an absent EZ, three had a hyporeflective zone, and four had outer retinal atrophy. The mean width of the central EZ lesion on optical coherence tomography at baseline was 1923 ?m. The mean annual increase in EZ lesion size was 48.3 ?m. Fundus autofluorescence revealed a central hypoautofluorescence with a surrounding ring of increased signal (n = 5). The mean hypoautofluorescent area at baseline was 3.33 mm2 and increased in size by a mean of 0.13 mm2/year. Nonconfocal adaptive optics scanning light ophthalmoscopy revealed residual foveal cones in only one of two cases. Full-field ERGs were consistent with severe generalized cone system dysfunction but with relative preservation of S-cone sensitivity.PDE6C retinopathy is a severe cone dysfunction syndrome often presenting as typical achromatopsia but without foveal hypoplasia. Myopia and slowly progressive maculopathy are common features. There are few (if any) residual foveal cones for intervention in older adults.

    View details for DOI 10.1167/iovs.19-27761

    View details for PubMedID 31826238

  • Centroid error due to non-uniform lenslet illumination in the Shack-Hartmann wavefront sensor Optics Letters Akondi, V., Steven, S., Dubra, A. 2019; 44 (17): 4167-4170


    Images formed by individual Shack-Hartmann wavefront sensor lenslets are displaced proportionally to the average wavefront slope over their aperture. This principle fails when the lenslet illumination is non-uniform. Here we demonstrate that the resulting error is proportional to the linear component of the illumination intensity, the quadratic wavefront component, and the lenslet size. For illustrative purposes, we compare the error due to centered Gaussian illumination decaying by 30% at the pupil edge against the error due to assuming the wavefront at the lenslet center being equal to the wavefront average across each lenslet. When testing up to ninth-order Zernike polynomial wavefronts and simulating nine lenslets across the pupil, the maximum centroid errors due to non-uniform illumination and sampling are 1.4% and 21%, respectively, and 0.5% and 6.7% when considering 25 lenslets across the pupil in the absence of other sources of error.

    View details for DOI 10.1364/OL.44.004167

  • Accounting for focal shift in the Shack-Hartmann wavefront sensor Optics Letters Akondi, V., Dubra, A. 2019; 44 (17): 4151-4154


    The Shack-Hartmann wavefront sensor samples a beam of light using an array of lenslets, each of which creates an image onto a pixelated sensor. These images translate from their nominal position by a distance proportional to the average wavefront slope over the corresponding lenslet. This principle fails in partially and/or non-uniformly illuminated lenslets when the lenslet array is focused to maximize peak intensity, leading to image centroid bias. Here, we show that this bias is due to the low Fresnel number of the lenslets, which shifts the diffraction focus away from the geometrical focus. We then demonstrate how the geometrical focus can be empirically found by minimizing the bias in partially illuminated lenslets.

    View details for DOI 10.1364/OL.44.004151

  • RAC-CNN: multimodal deep learning based automatic detection and classification of rod and cone photoreceptors in adaptive optics scanning light ophthalmoscope images. Biomedical optics express Cunefare, D., Huckenpahler, A. L., Patterson, E. J., Dubra, A., Carroll, J., Farsiu, S. 2019; 10 (8): 3815?32


    Quantification of the human rod and cone photoreceptor mosaic in adaptive optics scanning light ophthalmoscope (AOSLO) images is useful for the study of various retinal pathologies. Subjective and time-consuming manual grading has remained the gold standard for evaluating these images, with no well validated automatic methods for detecting individual rods having been developed. We present a novel deep learning based automatic method, called the rod and cone CNN (RAC-CNN), for detecting and classifying rods and cones in multimodal AOSLO images. We test our method on images from healthy subjects as well as subjects with achromatopsia over a range of retinal eccentricities. We show that our method is on par with human grading for detecting rods and cones.

    View details for DOI 10.1364/BOE.10.003815

    View details for PubMedID 31452977

    View details for PubMedCentralID PMC6701534

  • Long eye relief fundus camera and fixation target with partial correction of ocular longitudinal chromatic aberration BIOMEDICAL OPTICS EXPRESS Steven, S., Sulai, Y. N., Cheong, S. K., Bentley, J., Dubra, A. 2018; 9 (12): 6017?37
  • Fast adaptive optics scanning light ophthalmoscope retinal montaging BIOMEDICAL OPTICS EXPRESS Davidson, B., Kalitzeos, A., Carroll, J., Dubra, A., Ourselin, S., Michaelides, M., Bergeles, C. 2018; 9 (9): 4317?28
  • Cone Photoreceptor Cell Segmentation and Diameter Measurement on Adaptive Optics Images Using Circularly Constrained Active Contour Model INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE Liu, J., Jung, H., Dubra, A., Tam, J. 2018; 59 (11): 4639?52
  • Adaptive optics imaging of inherited retinal diseases BRITISH JOURNAL OF OPHTHALMOLOGY Georgiou, M., Kalitzeos, A., Patterson, E. J., Dubra, A., Carroll, J., Michaelides, M. 2018; 102 (8): 1028?35


    Adaptive optics (AO) ophthalmoscopy allows for non-invasive retinal phenotyping on a microscopic scale, thereby helping to improve our understanding of retinal diseases. An increasing number of natural history studies and ongoing/planned interventional clinical trials exploit AO ophthalmoscopy both for participant selection, stratification and monitoring treatment safety and efficacy. In this review, we briefly discuss the evolution of AO ophthalmoscopy, recent developments and its application to a broad range of inherited retinal diseases, including Stargardt disease, retinitis pigmentosa and achromatopsia. Finally, we describe the impact of this in vivo microscopic imaging on our understanding of disease pathogenesis, clinical trial design and outcome metrics, while recognising the limitation of the small cohorts reported to date.

    View details for PubMedID 29141905

    View details for PubMedCentralID PMC6059037

  • Deep learning based detection of cone photoreceptors with multimodal adaptive optics scanning light ophthalmoscope images of achromatopsia BIOMEDICAL OPTICS EXPRESS Cunefare, D., Langlo, C. S., Patterson, E. J., Blau, S., Dubra, A., Carroll, J., Farsiu, S. 2018; 9 (8)
  • Spatial summation in the human fovea: Do normal optical aberrations and fixational eye movements have an effect? JOURNAL OF VISION Tuten, W. S., Cooper, R. F., Tiruveedhula, P., Dubra, A., Roorda, A., Cottaris, N. P., Brainard, D. H., Morgan, J. W. 2018; 18 (8): 6


    Psychophysical inferences about the neural mechanisms supporting spatial vision can be undermined by uncertainties introduced by optical aberrations and fixational eye movements, particularly in fovea where the neuronal grain of the visual system is fine. We examined the effect of these preneural factors on photopic spatial summation in the human fovea using a custom adaptive optics scanning light ophthalmoscope that provided control over optical aberrations and retinal stimulus motion. Consistent with previous results, Ricco's area of complete summation encompassed multiple photoreceptors when measured with ordinary amounts of ocular aberrations and retinal stimulus motion. When both factors were minimized experimentally, summation areas were essentially unchanged, suggesting that foveal spatial summation is limited by postreceptoral neural pooling. We compared our behavioral data to predictions generated with a physiologically-inspired front-end model of the visual system, and were able to capture the shape of the summation curves obtained with and without pre-retinal factors using a single postreceptoral summing filter of fixed spatial extent. Given our data and modeling, neurons in the magnocellular visual pathway, such as parasol ganglion cells, provide a candidate neural correlate of Ricco's area in the central fovea.

    View details for PubMedID 30105385

  • High resolution imaging of retinal detachment in the cone-dominant ground squirrel Salmon, A. E., Sajdak, B. S., Connor, T. B., Dubra, A., Carroll, J. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2018
  • Characterization of Retinal Structure in CNGA3-associated Achromatopsia Georgiou, M., Langlo, C. S., Kalitzeos, A., Hirji, N., Kumaran, N., Dubra, A., Carroll, J., Michaelides, M. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2018
  • Interocular symmetry of foveal cone topography in achromatopsia (ACHM) Litts, K. M., Langlo, C. S., Patterson, E. J., Mastey, R., Cava, J. A., May, P., Lam, B. L., Fishman, G. A., Pennesi, M. E., Kay, C. N., Dubra, A., Hauswirth, W. W., Beasley, K. N., Chulay, J. D., Carroll, J. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2018
  • Non-confocal quad-detection adaptive optics scanning light ophthalmoscopy of the photoreceptor mosaic Sredar, N., Kowalski, B., Razeen, M. M., Steven, S., Dubra, A. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2018
  • High Resolution Imaging of Inner Retinal Microcystic Changes in Glaucoma Razeen, M. M., Steven, S., Sredar, N., Cheong, S., Yarp, J., Nunez, M., Goldberg, J. L., Dubra, A. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2018
  • Convolutional neural network based detection of cones in multimodal adaptive optics scanning light ophthalmoscope images of achromatopsia Cunefare, D., Patterson, E. J., Blau, S., Langlo, C. S., Dubra, A., Carroll, J., Farsiu, S. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2018
  • Achromatized visible light OCT for ultrahigh resolution retinal imaging Zhang, T., Chong, S., Kho, A., Bernucci, M., Dubra, A., Srinivasan, V. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2018
  • Adaptive optics retinal imaging in glaucoma Dubra, A. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2018
  • Automatic Cone Photoreceptor Localisation in Healthy and Stargardt Afflicted Retinas Using Deep Learning SCIENTIFIC REPORTS Davidson, B., Kalitzeos, A., Carroll, J., Dubra, A., Ourselin, S., Michaelides, M., Bergeles, C. 2018; 8: 7911


    We present a robust deep learning framework for the automatic localisation of cone photoreceptor cells in Adaptive Optics Scanning Light Ophthalmoscope (AOSLO) split-detection images. Monitoring cone photoreceptors with AOSLO imaging grants an excellent view into retinal structure and health, provides new perspectives into well known pathologies, and allows clinicians to monitor the effectiveness of experimental treatments. The MultiDimensional Recurrent Neural Network (MDRNN) approach developed in this paper is the first method capable of reliably and automatically identifying cones in both healthy retinas and retinas afflicted with Stargardt disease. Therefore, it represents a leap forward in the computational image processing of AOSLO images, and can provide clinical support in on-going longitudinal studies of disease progression and therapy. We validate our method using images from healthy subjects and subjects with the inherited retinal pathology Stargardt disease, which significantly alters image quality and cone density. We conduct a thorough comparison of our method with current state-of-the-art methods, and demonstrate that the proposed approach is both more accurate and appreciably faster in localizing cones. As further validation to the method's robustness, we demonstrate it can be successfully applied to images of retinas with pathologies not present in the training data: achromatopsia, and retinitis pigmentosa.

    View details for PubMedID 29784939

  • The Reliability of Cone Density Measurements in the Presence of Rods TRANSLATIONAL VISION SCIENCE & TECHNOLOGY Morgan, J. W., Vergilio, G. K., Hsu, J., Dubra, A., Cooper, R. F. 2018; 7 (3): 21


    Recent advances in adaptive optics scanning light ophthalmoscopy (AOSLO) have enabled visualization of cone inner segments through nonconfocal split-detection, in addition to rod and cone outer segments revealed by confocal reflectance. Here, we examined the interobserver reliability of cone density measurements in both AOSLO imaging modalities.Five normal subjects (nine eyes) were imaged along the horizontal and vertical meridians using a custom AOSLO with confocal and nonconfocal split-detection modalities. The resulting images were montaged using a previously described semiautomatic algorithm. Regions of interest (ROIs) were selected from the confocal montage at 190 ?m, and from split-detection and confocal montages at 900 and 1800 ?m from the fovea. Four observers (three experts, one nave) manually identified cone locations in each ROI, and these locations were used to calculate bound densities. Intraclass correlation coefficients and Dice's coefficients were calculated to assess interobserver agreement.Interobserver agreement was high in cone-only images (confocal 190 ?m: 0.85; split-detection 900 ?m: 0.91; split-detection 1800 ?m: 0.89), moderate in confocal images at 900 ?m (0.68), and poor in confocal images at 1800 ?m (0.24). Excluding the nave observer data substantially increased agreement within confocal images (190 ?m: 0.99; 900 ?m: 0.80; 1800 ?m: 0.68).Interobserver measurements of cone density are more reliable in rod-free retinal images. Moreover, when using manual cell identification, it is essential that observers are trained, particularly for confocal AOSLO images.This study underscores the need for additional reliability studies in eyes containing pathology where identifying cones can be substantially more difficult.

    View details for PubMedID 29946495

  • Non-invasive assessment of human cone photoreceptor function (vol 8, pg 5098, 2017) BIOMEDICAL OPTICS EXPRESS Cooper, R. F., Tuten, W. S., Dubra, A., Brainard, D. H., Morgan, J. W. 2018; 9 (4): 1842


    [This corrects the article on p. 5098 in vol. 8, PMID: 29188106.].

    View details for PubMedID 29676401

  • Ultrahigh resolution retinal imaging by visible light OCT with longitudinal achromatization BIOMEDICAL OPTICS EXPRESS Chong, S., Zhang, T., Kho, A., Bernucci, M. T., Dubra, A., Srinivasan, V. J. 2018; 9 (4): 1477?91


    Chromatic aberrations are an important design consideration in high resolution, high bandwidth, refractive imaging systems that use visible light. Here, we present a fiber-based spectral/Fourier domain, visible light OCT ophthalmoscope corrected for the average longitudinal chromatic aberration (LCA) of the human eye. Analysis of complex speckles from in vivo retinal images showed that achromatization resulted in a speckle autocorrelation function that was ~20% narrower in the axial direction, but unchanged in the transverse direction. In images from the improved, achromatized system, the separation between Bruch's membrane (BM), the retinal pigment epithelium (RPE), and the outer segment tips clearly emerged across the entire 6.5 mm field-of-view, enabling segmentation and morphometry of BM and the RPE in a human subject. Finally, cross-sectional images depicted distinct inner retinal layers with high resolution. Thus, with chromatic aberration compensation, visible light OCT can achieve volume resolutions and retinal image quality that matches or exceeds ultrahigh resolution near-infrared OCT systems with no monochromatic aberration compensation.

    View details for PubMedID 29675296

  • Sub-Airy Confocal Adaptive Optics Scanning Ophthalmoscopy TRANSLATIONAL VISION SCIENCE & TECHNOLOGY Sredar, N., Fagbemi, O. E., Dubra, A. 2018; 7 (2): 17


    To demonstrate the viability of improving transverse image resolution in reflectance scanning adaptive optics ophthalmoscopy using sub-Airy disk confocal detection.The foveal cone mosaic was imaged in five human subjects free of known eye disease using two custom adaptive optics scanning light ophthalmoscopes (AOSLOs) in reflectance with 7.75 and 4.30 mm pupil diameters. Confocal pinholes of 0.5, 0.6, 0.8, and 1.0 Airy disk diameters (ADDs) were used in a retinal conjugate plane before the light detector. Average cone photoreceptor intensity profile width and power spectrum were calculated for the resulting images. Detected energy using a model eye was recorded for each pinhole size.The cone photoreceptor mosaic is better resolved with decreasing confocal pinhole size, with the high spatial frequency content of the images enhanced in both the large- and small-pupil AOSLOs. The average cone intensity profile width was reduced by ?15% with the use of a 0.5 ADD pinhole when compared to a 1.0 ADD, with an accompanying reduction in signal greater than a factor of four.The use of sub-Airy disk confocal pinhole detection without increasing retinal light exposure results in a substantial improvement in image resolution at the cost of larger than predicted signal reduction.Improvement in transverse resolution using sub-Airy disk confocal detection is a practical and low-cost approach that is applicable to all point- and line-scanning ophthalmoscopes, including optical coherence tomographers.

    View details for PubMedID 29629239

  • Phenotypic diversity in autosomal-dominant cone-rod dystrophy elucidated by adaptive optics retinal imaging. The British journal of ophthalmology Song, H., Rossi, E. A., Stone, E., Latchney, L., Williams, D., Dubra, A., Chung, M. 2018; 102 (1): 136?41


    Several genes causing autosomal-dominant cone-rod dystrophy (AD-CRD) have been identified. However, the mechanisms by which genetic mutations lead to cellular loss in human disease remain poorly understood. Here we combine genotyping with high-resolution adaptive optics retinal imaging to elucidate the retinal phenotype at a cellular level in patients with AD-CRD harbouring a defect in theGUCA1Agene.Nine affected members of a four-generation AD-CRD pedigree and three unaffected first-degree relatives underwent clinical examinations including visual acuity, fundus examination, Goldmann perimetry, spectral domain optical coherence tomography and electroretinography. Genome-wide scan followed by bidirectional sequencing was performed on all affected participants. High-resolution imaging using a custom adaptive optics scanning light ophthalmoscope (AOSLO) was performed for selected participants.Clinical evaluations showed a range of disease severity from normal fundus appearance in teenaged patients to pronounced macular atrophy in older patients. Molecular genetic testing showed a mutation in inGUCA1Asegregating with disease. AOSLO imaging revealed that of the two teenage patients with mild disease, one had severe disruption of the photoreceptor mosaic while the other had a normal cone mosaic.AOSLO imaging demonstrated variability in the pattern of cone and rod cell loss between two teenage cousins with early AD-CRD, who had similar clinical features and had the identical disease-causing mutation inGUCA1A. This finding suggests that a mutation inGUCA1Adoes not lead to the same degree of AD-CRD in all patients. Modifying factors may mitigate or augment disease severity, leading to different retinal cellular phenotypes.

    View details for PubMedID 29074494

    View details for PubMedCentralID PMC5754866

  • Visible Light Optical Coherence Microscopy Imaging of the Mouse Cortex with Femtoliter Volume Resolution Merkle, C. W., Chong, S., Kho, A. M., Zhu, J., Kholiqov, O., Dubra, A., Srinivasan, V. J., Izatt, J. A., Fujimoto, J. G., Tuchin, V. V. SPIE-INT SOC OPTICAL ENGINEERING. 2018

    View details for DOI 10.1117/12.2292125

    View details for Web of Science ID 000453776500006

  • Long eye relief fundus camera and fixation target with partial correction of ocular longitudinal chromatic aberration. Biomedical optics express Steven, S., Sulai, Y. N., Cheong, S. K., Bentley, J., Dubra, A. 2018; 9 (12): 6017?37


    A combined 32 full field of view refractive fundus camera and fixation target with a -20 to +10 diopter sphere correction range is described and demonstrated. The optical setup partially corrects the average longitudinal chromatic aberration and spherical aberration of the human eye, while providing a long eye relief to allow integration with reflective adaptive optics ophthalmoscopes, as a viewfinder. The fundus camera operates with 940 nm light, using a maximum 2.9 mm diameter imaging pupil at the eye. The fixation target uses a light projector capable of delivering red, green and/or blue spatially and temporally modulated stimuli to the retina. The design and performance of each sub-system are discussed, and retinal imaging at various wavelengths is demonstrated.

    View details for PubMedID 31065410

    View details for PubMedCentralID PMC6491002

  • Deep learning based detection of cone photoreceptors with multimodal adaptive optics scanning light ophthalmoscope images of achromatopsia. Biomedical optics express Cunefare, D., Langlo, C. S., Patterson, E. J., Blau, S., Dubra, A., Carroll, J., Farsiu, S. 2018; 9 (8): 3740?56


    Fast and reliable quantification of cone photoreceptors is a bottleneck in the clinical utilization of adaptive optics scanning light ophthalmoscope (AOSLO) systems for the study, diagnosis, and prognosis of retinal diseases. To-date, manual grading has been the sole reliable source of AOSLO quantification, as no automatic method has been reliably utilized for cone detection in real-world low-quality images of diseased retina. We present a novel deep learning based approach that combines information from both the confocal and non-confocal split detector AOSLO modalities to detect cones in subjects with achromatopsia. Our dual-mode deep learning based approach outperforms the state-of-the-art automated techniques and is on a par with human grading.

    View details for PubMedID 30338152

    View details for PubMedCentralID PMC6191607

  • Cone Photoreceptor Cell Segmentation and Diameter Measurement on Adaptive Optics Images Using Circularly Constrained Active Contour Model. Investigative ophthalmology & visual science Liu, J., Jung, H., Dubra, A., Tam, J. 2018; 59 (11): 4639?52


    Cone photoreceptor cells can be noninvasively imaged in the living human eye by using nonconfocal adaptive optics scanning ophthalmoscopy split detection. Existing metrics, such as cone density and spacing, are based on simplifying cone photoreceptors to single points. The purposes of this study were to introduce a computer-aided approach for segmentation of cone photoreceptors, to apply this technique to create a normal database of cone diameters, and to demonstrate its use in the context of existing metrics.Cone photoreceptor segmentation is achieved through a circularly constrained active contour model (CCACM). Circular templates and image gradients attract active contours toward cone photoreceptor boundaries. Automated segmentation from in vivo human subject data was compared to ground truth established by manual segmentation. Cone diameters computed from curated data (automated segmentation followed by manual removal of errors) were compared with histology and published data.Overall, there was good agreement between automated and manual segmentations and between diameter measurements (n = 5191 cones) and published histologic data across retinal eccentricities ranging from 1.35 to 6.35 mm (temporal). Interestingly, cone diameter was correlated to both cone density and cone spacing (negatively and positively, respectively; P < 0.01 for both). Application of the proposed automated segmentation to images from a patient with late-onset retinal degeneration revealed the presence of enlarged cones above individual reticular pseudodrusen (average 23.0% increase, P < 0.05).CCACM can accurately segment cone photoreceptors on split detection images across a range of eccentricities. Metrics derived from this automated segmentation of adaptive optics retinal images can provide new insights into retinal diseases.

    View details for PubMedID 30372733

    View details for PubMedCentralID PMC6154284

  • Fast adaptive optics scanning light ophthalmoscope retinal montaging. Biomedical optics express Davidson, B., Kalitzeos, A., Carroll, J., Dubra, A., Ourselin, S., Michaelides, M., Bergeles, C. 2018; 9 (9): 4317?28


    The field of view of high-resolution ophthalmoscopes that require the use of adaptive optics (AO) wavefront correction is limited by the isoplanatic patch of the eye, which varies across individual eyes and with the portion of the pupil used for illumination and/or imaging. Therefore all current AO ophthalmoscopes have small fields of view comparable to, or smaller than, the isoplanatic patch, and the resulting images have to be stitched off-line to create larger montages. These montages are currently assembled either manually, by expert human graders, or automatically, often requiring several hours per montage. This arguably limits the applicability of AO ophthalmoscopy to studies with small cohorts and moreover, prevents the ability to review a real-time captured montage of all locations during image acquisition to further direct targeted imaging. In this work, we propose stitching the images with our novel algorithm, which uses oriented fast rotated brief (ORB) descriptors, local sensitivity hashing, and by searching for a 'good enough' transformation, rather than the best possible, to achieve processing times of 1-2 minutes per montage of 250 images. Moreover, the proposed method produces montages which are as accurate as previous methods, when considering the image similarity metrics: normalised mutual information (NMI), and normalised cross correlation (NCC).

    View details for PubMedID 30615701

    View details for PubMedCentralID PMC6157757

  • New Clinical Opportunities for Retinal Vascular Imaging Adaptive Optics to OCT Angiography Rosen, R., Chui, T., Weitz, R., Dubra, A., Carroll, J., Garcia, P., Pinhas, A., Scripsema, N., Mo, S., Agemy, S., Krawitz, B., Podoleanu, A., Bang, O. SPIE-INT SOC OPTICAL ENGINEERING. 2018

    View details for DOI 10.1117/12.2304296

    View details for Web of Science ID 000432466900001

  • Multimodal imaging of small hard retinal drusen in young healthy adults. The British journal of ophthalmology Pedersen, H. R., Gilson, S. J., Dubra, A., Munch, I. C., Larsen, M., Baraas, R. C. 2018; 102 (1): 146?52


    Small hard macular drusen can be observed in the retina of adults as young as 18 years of age. Here, we seek to describe the in vivo topography and geometry of these drusen.Retinal images were acquired in young, healthy adults using colour fundus photography, spectral domain optic coherence tomography (SD-OCT), reflectance flood-illuminated adaptive optic ophthalmoscopy (AO flood) and reflectance adaptive optic scanning light ophthalmoscopy (AOSLO) in both confocal and non-confocal split-detection modalities. Small bright yellow hard drusen within a 10 degree radius from the foveal centre were characterised.Small hard drusen were seen on colour photographs in 21 out of 97 participants and 26 drusen in 12 eyes in 11 participants were imaged using the full protocol. Drusen were easily identifiable in all modalities, except a few very small ones, which were not visible on SD-OCT. On AOSLO images, these drusen appeared as round, oval or lobular areas (up to three lobules) of diameter 22-61?m where cone photoreceptor reflectivity and density was decreased (p=0.049). This was usually associated with discrete thickening of the retinal pigment epithelium (RPE) complex.High lateral resolution imaging of small lobular hard retinal drusen suggests formation through the confluence of two or more smaller round lesions. The outline and size of these smaller lesions corresponds to 1-4 RPE cells. Prospective longitudinal studies are needed to determine the ultimate fate of small hard drusen and their potential relation to age-related macular degeneration.

    View details for PubMedID 29051326

    View details for PubMedCentralID PMC5754867

  • Visible light optical coherence microscopy of the brain with isotropic femtoliter resolution in vivo. Optics letters Merkle, C. W., Chong, S. P., Kho, A. M., Zhu, J., Dubra, A., Srinivasan, V. J. 2018; 43 (2): 198?201


    Most flying-spot optical coherence tomography and optical coherence microscopy (OCM) systems use a symmetric confocal geometry, where the detection path retraces the illumination path starting from and ending with the spatial mode of a single-mode optical fiber. Here we describe a visible light OCM instrument that breaks this symmetry to improve transverse resolution without sacrificing collection efficiency in scattering tissue. This was achieved by overfilling a water immersion objective on the illumination path while maintaining a conventional Gaussian mode detection path (1/e2intensity diameter ?0.82 Airy disks), enabling ?1.1???m full width at half-maximum (FWHM) transverse resolution. At the same time, a ?0.9???m FWHM axial resolution in tissue, achieved by a broadband visible light source, enabled femtoliter volume resolution. We characterized this instrument according to paraxial coherent microscopy theory and, finally, used it to image the meningeal layers, intravascular red blood cell-free layer, and myelinated axons in the mouse neocortex in vivo through the thinned skull.

    View details for DOI 10.1364/OL.43.000198

    View details for PubMedID 29328237

  • An Automated Reference Frame Selection (ARFS) Algorithm for Cone Imaging with Adaptive Optics Scanning Light Ophthalmoscopy. Translational vision science & technology Salmon, A. E., Cooper, R. F., Langlo, C. S., Baghaie, A., Dubra, A., Carroll, J. 2017; 6 (2): 9-?


    To develop an automated reference frame selection (ARFS) algorithm to replace the subjective approach of manually selecting reference frames for processing adaptive optics scanning light ophthalmoscope (AOSLO) videos of cone photoreceptors.Relative distortion was measured within individual frames before conducting image-based motion tracking and sorting of frames into distinct spatial clusters. AOSLO images from nine healthy subjects were processed using ARFS and human-derived reference frames, then aligned to undistorted AO-flood images by nonlinear registration and the registration transformations were compared. The frequency at which humans selected reference frames that were rejected by ARFS was calculated in 35 datasets from healthy subjects, and subjects with achromatopsia, albinism, or retinitis pigmentosa. The level of distortion in this set of human-derived reference frames was assessed.The average transformation vector magnitude required for registration of AOSLO images to AO-flood images was significantly reduced from 3.33 1.61 pixels when using manual reference frame selection to 2.75 1.60 pixels (mean SD) when using ARFS (P = 0.0016). Between 5.16% and 39.22% of human-derived frames were rejected by ARFS. Only 2.71% to 7.73% of human-derived frames were ranked in the top 5% of least distorted frames.ARFS outperforms expert observers in selecting minimally distorted reference frames in AOSLO image sequences. The low success rate in human frame choice illustrates the difficulty in subjectively assessing image distortion.Manual reference frame selection represented a significant barrier to a fully automated image-processing pipeline (including montaging, cone identification, and metric extraction). The approach presented here will aid in the clinical translation of AOSLO imaging.

    View details for DOI 10.1167/tvst.6.2.9

    View details for PubMedID 28392976

  • PHOTORECEPTOR INNER SEGMENT MORPHOLOGY IN BEST VITELLIFORM MACULAR DYSTROPHY. Retina (Philadelphia, Pa.) Scoles, D., Sulai, Y. N., Cooper, R. F., Higgins, B. P., Johnson, R. D., Carroll, J., Dubra, A., Stepien, K. E. 2017; 37 (4): 741-748


    To characterize outer retina structure in best vitelliform macular dystrophy (BVMD) and to determine the effect of macular lesions on overlying and adjacent photoreceptors.Five individuals with BVMD were followed prospectively with spectral domain optical coherence tomography and confocal and nonconfocal split-detector adaptive optics scanning light ophthalmoscopy (AOSLO). The AOSLO cone photoreceptor mosaic images were obtained within and around retinal lesions. Cone density was measured inside and outside lesions. In 2 subjects, densities were compared with published measurements acquired ?2.5 years before. One subject was imaged 3 times over a 5-month period.The AOSLO imaging demonstrated that photoreceptor morphology within BVMD retinal lesions was highly variable depending on the disease stage, with photoreceptor structure present even in advanced disease. The AOSLO imaging was repeatable even in severe disease over short-time and long-time intervals. Photoreceptor density was normal in retinal areas immediately adjacent to lesions and stable over ?2.5 years. Mobile disk-like structures possibly representing subretinal macrophages were also observed.Combined confocal and nonconfocal split-detector AOSLO imaging reveals substantial variability within clinical lesions in all stages of BVMD. Longitudinal cellular photoreceptor imaging could prove a powerful tool for understanding disease progression and monitoring emerging therapeutic treatment response in inherited degenerations such as BVMD.

    View details for DOI 10.1097/IAE.0000000000001203

    View details for PubMedID 27467379

    View details for PubMedCentralID PMC5362286

  • Assessing the spatial relationship between fixation and foveal specializations. Vision research Wilk, M. A., Dubis, A. M., Cooper, R. F., Summerfelt, P., Dubra, A., Carroll, J. 2017; 132: 53-61


    Increased cone photoreceptor density, an avascular zone (FAZ), and the displacement of inner retinal neurons to form a pit are distinct features of the human fovea. As the fovea provides the majority of our vision, appreciating how these anatomical specializations are related is important for understanding foveal development, normal visual function, and retinal disease. Here we evaluated the relationship between these specializations and their location relative to the preferred retinal locus of fixation (PRL). We measured foveal pit volume, FAZ area, peak cone density, and location of the PRL in 22 subjects with normal vision using optical coherence tomography and adaptive optics scanning light ophthalmoscopy. Foveal pit volume was positively correlated with FAZ area; however, peak cone density was not correlated with pit volume. In addition, there was no systematic offset of the location of any of these specializations relative to PRL, and there was no correlation between the magnitude of the offset from PRL and the corresponding foveal specialization measurements (pit volume, FAZ area, peak cone density). The standard deviation of our PRL measurements was consistent with previous measurements of fixational stability. These data provide insight into the sequence of events during foveal development and may have implications for visual function and retinal disease.

    View details for DOI 10.1016/j.visres.2016.05.001

    View details for PubMedID 27286921

    View details for PubMedCentralID PMC5164985

  • Vision science and adaptive optics, the state of the field. Vision research Marcos, S., Werner, J. S., Burns, S. A., Merigan, W. H., Artal, P., Atchison, D. A., Hampson, K. M., Legras, R., Lundstrom, L., Yoon, G., Carroll, J., Choi, S. S., Doble, N., Dubis, A. M., Dubra, A., Elsner, A., Jonnal, R., Miller, D. T., Paques, M., Smithson, H. E., Young, L. K., Zhang, Y., Campbell, M., Hunter, J., Metha, A., Palczewska, G., Schallek, J., Sincich, L. C. 2017


    Adaptive optics is a relatively new field, yet it is spreading rapidly and allows new questions to be asked about how the visual system is organized. The editors of this feature issue have posed a series of question to scientists involved in using adaptive optics in vision science. The questions are focused on three main areas. In the first we investigate the use of adaptive optics for psychophysical measurements of visual system function and for improving the optics of the eye. In the second, we look at the applications and impact of adaptive optics on retinal imaging and its promise for basic and applied research. In the third, we explore how adaptive optics is being used to improve our understanding of the neurophysiology of the visual system.

    View details for DOI 10.1016/j.visres.2017.01.006

    View details for PubMedID 28212982

  • REPEATABILITY AND LONGITUDINAL ASSESSMENT OF FOVEAL CONE STRUCTURE IN CNGB3-ASSOCIATED ACHROMATOPSIA. Retina (Philadelphia, Pa.) Langlo, C. S., Erker, L. R., Parker, M., Patterson, E. J., Higgins, B. P., Summerfelt, P., Razeen, M. M., Collison, F. T., Fishman, G. A., Kay, C. N., Zhang, J., Weleber, R. G., Yang, P., Pennesi, M. E., Lam, B. L., Chulay, J. D., Dubra, A., Hauswirth, W. W., Wilson, D. J., Carroll, J. 2017


    Congenital achromatopsia is an autosomal recessive disease causing substantial reduction or complete absence of cone function. Although believed to be a relatively stationary disorder, questions remain regarding the stability of cone structure over time. In this study, the authors sought to assess the repeatability of and examine longitudinal changes in measurements of central cone structure in patients with achromatopsia.Forty-one subjects with CNGB3-associated achromatopsia were imaged over a period of between 6 and 26 months using optical coherence tomography and adaptive optics scanning light ophthalmoscopy. Outer nuclear layer (ONL) thickness, ellipsoid zone (EZ) disruption, and peak foveal cone density were assessed.ONL thickness increased slightly compared with baseline (0.184 ?m/month, P = 0.02). The EZ grade remained unchanged for 34/41 subjects. Peak foveal cone density did not significantly change over time (mean change 1% per 6 months, P = 0.126).Foveal cone structure showed little or no change in this group of subjects with CNGB3-associated achromatopsia. Over the time scales investigated (6-26 months), achromatopsia seems to be a structurally stable condition, although longer-term follow-up is needed. These data will be useful in assessing foveal cone structure after therapeutic intervention.

    View details for DOI 10.1097/IAE.0000000000001434

    View details for PubMedID 28145975

  • Reliability and Repeatability of Cone Density Measurements in Patients With Stargardt Disease and RPGR-Associated Retinopathy. Investigative ophthalmology & visual science Tanna, P., Kasilian, M., Strauss, R., Tee, J., Kalitzeos, A., Tarima, S., Visotcky, A., Dubra, A., Carroll, J., Michaelides, M. 2017; 58 (9): 3608?15


    To assess reliability and repeatability of cone density measurements by using confocal and (nonconfocal) split-detector adaptive optics scanning light ophthalmoscopy (AOSLO) imaging. It will be determined whether cone density values are significantly different between modalities in Stargardt disease (STGD) and retinitis pigmentosa GTPase regulator (RPGR)-associated retinopathy.Twelve patients with STGD (aged 9-52 years) and eight with RPGR-associated retinopathy (aged 11-31 years) were imaged using both confocal and split-detector AOSLO simultaneously. Four graders manually identified cone locations in each image that were used to calculate local densities. Each imaging modality was evaluated independently. The data set consisted of 1584 assessments of 99 STGD images (each image in two modalities and four graders who graded each image twice) and 928 RPGR assessments of 58 images (each image in two modalities and four graders who graded each image twice).For STGD assessments the reliability for confocal and split-detector AOSLO was 67.9% and 95.9%, respectively, and the repeatability was 71.2% and 97.3%, respectively. The differences in the measured cone density values between modalities were statistically significant for one grader. For RPGR assessments the reliability for confocal and split-detector AOSLO was 22.1% and 88.5%, respectively, and repeatability was 63.2% and 94.5%, respectively. The differences in cone density between modalities were statistically significant for all graders.Split-detector AOSLO greatly improved the reliability and repeatability of cone density measurements in both disorders and will be valuable for natural history studies and clinical trials using AOSLO. However, it appears that these indices may be disease dependent, implying the need for similar investigations in other conditions.

    View details for PubMedID 28738413

    View details for PubMedCentralID PMC5525557

  • Open source software for automatic detection of cone photoreceptors in adaptive optics ophthalmoscopy using convolutional neural networks. Scientific reports Cunefare, D., Fang, L., Cooper, R. F., Dubra, A., Carroll, J., Farsiu, S. 2017; 7 (1): 6620


    Imaging with an adaptive optics scanning light ophthalmoscope (AOSLO) enables direct visualization of the cone photoreceptor mosaic in the living human retina. Quantitative analysis of AOSLO images typically requires manual grading, which is time consuming, and subjective; thus, automated algorithms are highly desirable. Previously developed automated methods are often reliant on ad hoc rules that may not be transferable between different imaging modalities or retinal locations. In this work, we present a convolutional neural network (CNN) based method for cone detection that learns features of interest directly from training data. This cone-identifying algorithm was trained and validated on separate data sets of confocal and split detector AOSLO images with results showing performance that closely mimics the gold standard manual process. Further, without any need for algorithmic modifications for a specific AOSLO imaging system, our fully-automated multi-modality CNN-based cone detection method resulted in comparable results to previous automatic cone segmentation methods which utilized ad hoc rules for different applications. We have made free open-source software for the proposed method and the corresponding training and testing datasets available online.

    View details for PubMedID 28747737

    View details for PubMedCentralID PMC5529414

  • Non-invasive assessment of human cone photoreceptor function. Biomedical optics express Cooper, R. F., Tuten, W. S., Dubra, A., Brainard, D. H., Morgan, J. I. 2017; 8 (11): 5098?5112


    Vision begins when light isomerizes the photopigments within photoreceptors. Noninvasive cellular-scale observation of the structure of the human photoreceptor mosaic is made possible through the use of adaptive optics (AO) enhanced ophthalmoscopes, but establishing noninvasive objective measures of photoreceptor function on a similar scale has been more difficult. AO ophthalmoscope images acquired with near-infrared light show that individual cone photoreceptor reflectance can change in response to a visible stimulus. Here we show that the intrinsic response depends on stimulus wavelength and intensity, and that its action spectrum is well-matched to the spectral sensitivity of cone-mediated vision. Our results demonstrate that the cone reflectance response is mediated by photoisomerization, thus making it a direct measure of photoreceptor function.

    View details for PubMedID 29188106

    View details for PubMedCentralID PMC5695956

  • CELLULAR IMAGING OF THE TAPETAL-LIKE REFLEX IN CARRIERS OF RPGR-ASSOCIATED RETINOPATHY. Retina (Philadelphia, Pa.) Kalitzeos, A., Samra, R., Kasilian, M., Tee, J. J., Strampe, M., Langlo, C., Webster, A. R., Dubra, A., Carroll, J., Michaelides, M. 2017


    To examine the features of the tapetal-like reflex (TLR) in female carriers of RPGR-associated retinopathy by means of adaptive optics scanning light ophthalmoscopy (AOSLO) and spectral domain optical coherence tomography.Nine molecularly confirmed RPGR carriers and three healthy controls underwent ocular examination and the following retinal imaging modalities: color photography, near-infrared reflectance, fundus autofluorescence, spectral domain optical coherence tomography, and AOSLO. After identifying TLR areas across all imaging modalities, normalized local contrast of outer retinal bands on spectral domain optical coherence tomography was calculated and AOSLO-acquired photoreceptor mosaic analysis was performed.Seven carriers had TLR areas, which colocalized with increased rod photoreceptor reflectivity on confocal AOSLO and reduced cone photoreceptor densities. Parafoveal TLR areas also exhibited reduced local contrast (i.e., increased reflectivity) of the outer retinal bands on spectral domain optical coherence tomography (inner segment ellipsoid zone and outer segment interdigitation zone). Healthy controls did not show TLR.The cellular resolution provided by AOSLO affords the characterization of the photoreceptor mosaic in RPGR carriers with a TLR. Features revealed include reduced cone densities, increased cone inner segment diameters, and increased rod outer segment reflectivity.This is an open access article distributed under the Creative Commons Attribution License 4.0 (CCBY), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

    View details for PubMedID 29190250

  • Automated Photoreceptor Cell Identification on Nonconfocal Adaptive Optics Images Using Multiscale Circular Voting. Investigative ophthalmology & visual science Liu, J., Jung, H., Dubra, A., Tam, J. 2017; 58 (11): 4477?89


    Adaptive optics scanning light ophthalmoscopy (AOSLO) has enabled quantification of the photoreceptor mosaic in the living human eye using metrics such as cell density and average spacing. These rely on the identification of individual cells. Here, we demonstrate a novel approach for computer-aided identification of cone photoreceptors on nonconfocal split detection AOSLO images.Algorithms for identification of cone photoreceptors were developed, based on multiscale circular voting (MSCV) in combination with a priori knowledge that split detection images resemble Nomarski differential interference contrast images, in which dark and bright regions are present on the two sides of each cell. The proposed algorithm locates dark and bright region pairs, iteratively refining the identification across multiple scales. Identification accuracy was assessed in data from 10 subjects by comparing automated identifications with manual labeling, followed by computation of density and spacing metrics for comparison to histology and published data.There was good agreement between manual and automated cone identifications with overall recall, precision, and F1 score of 92.9%, 90.8%, and 91.8%, respectively. On average, computed density and spacing values using automated identification were within 10.7% and 11.2% of the expected histology values across eccentricities ranging from 0.5 to 6.2 mm. There was no statistically significant difference between MSCV-based and histology-based density measurements (P = 0.96, Kolmogorov-Smirnov 2-sample test).MSCV can accurately detect cone photoreceptors on split detection images across a range of eccentricities, enabling quick, objective estimation of photoreceptor mosaic metrics, which will be important for future clinical trials utilizing adaptive optics.

    View details for PubMedID 28873173

    View details for PubMedCentralID PMC5586244

  • Unsupervised identification of cone photoreceptors in non-confocal adaptive optics scanning light ophthalmoscope images. Biomedical optics express Bergeles, C., Dubis, A. M., Davidson, B., Kasilian, M., Kalitzeos, A., Carroll, J., Dubra, A., Michaelides, M., Ourselin, S. 2017; 8 (6): 3081?94


    Precise measurements of photoreceptor numerosity and spatial arrangement are promising biomarkers for the early detection of retinal pathologies and may be valuable in the evaluation of retinal therapies. Adaptive optics scanning light ophthalmoscopy (AOSLO) is a method of imaging that corrects for aberrations of the eye to acquire high-resolution images that reveal the photoreceptor mosaic. These images are typically graded manually by experienced observers, obviating the robust, large-scale use of the technology. This paper addresses unsupervised automated detection of cones in non-confocal, split-detection AOSLO images. Our algorithm leverages the appearance of split-detection images to create a cone model that is used for classification. Results show that it compares favorably to the state-of-the-art, both for images of healthy retinas and for images from patients affected by Stargardt disease. The algorithm presented also compares well to manual annotation while excelling in speed.

    View details for PubMedID 28663928

    View details for PubMedCentralID PMC5480451

  • Progression of Local Glaucomatous Damage Near Fixation as Seen with Adaptive Optics Imaging. Translational vision science & technology Hood, D. C., Lee, D., Jarukasetphon, R., Nunez, J., Mavrommatis, M. A., Rosen, R. B., Ritch, R., Dubra, A., Chui, T. Y. 2017; 6 (4): 6


    Deep glaucomatous defects near fixation were followed over time with an adaptive optics-scanning light ophthalmoscope (AO-SLO) to better understand the progression of these defects and to explore the use of AO-SLO in detecting them.Six eyes of 5 patients were imaged with an AO-SLO from 2 to 4 times for a range of 14.6 to 33.6 months. All eyes had open-angle glaucoma with deep defects in the superior visual field (VF) near fixation as defined by 10-2 VFs with 5 or more points less than -15 dB; two of the eyes had deep defects in the inferior VF as well. AO-SLO images were obtained around the temporal edge of the disc.In 4 of the 6 eyes, the edge of the inferior-temporal disc region of the retinal nerve fiber (RNF) defect seen on AO-SLO moved closer to fixation within 10.6 to 14.7 months. In 4 eyes, RNF bundles in the affected region appeared to lose contrast and/or disappear.Progressive changes in RNF bundles associated with deep defects on 10-2 VFs can be seen within about 1 year with AO-SLO imaging. These changes are well below the spatial resolution of the 10-2 VF. On the other hand, subtle thinning of regions with RNF bundles is not easy to see with current AO-SLO technology, and may be better followed with OCT.AO-SLO imaging may be useful in clinical trials designed to see very small changes in deep defects.

    View details for DOI 10.1167/tvst.6.4.6

    View details for PubMedID 28713646

    View details for PubMedCentralID PMC5508541

  • Multimodal Imaging of Photoreceptor Structure in Choroideremia PLOS ONE Sun, L. W., Johnson, R. D., Williams, V., Summerfelt, P., Dubra, A., Weinberg, D. V., Stepien, K. E., Fishman, G. A., Carroll, J. 2016; 11 (12)


    Choroideremia is a progressive X-linked recessive dystrophy, characterized by degeneration of the retinal pigment epithelium (RPE), choroid, choriocapillaris, and photoreceptors. We examined photoreceptor structure in a series of subjects with choroideremia with particular attention to areas bordering atrophic lesions.Twelve males with clinically-diagnosed choroideremia and confirmed hemizygous mutations in the CHM gene were examined. High-resolution images of the retina were obtained using spectral domain optical coherence tomography (SD-OCT) and both confocal and non-confocal split-detector adaptive optics scanning light ophthalmoscope (AOSLO) techniques.Eleven CHM gene mutations (3 novel) were identified; three subjects had the same mutation and one subject had two mutations. SD-OCT findings included interdigitation zone (IZ) attenuation or loss in 10/12 subjects, often in areas with intact ellipsoid zones; RPE thinning in all subjects; interlaminar bridges in the imaged areas of 10/12 subjects; and outer retinal tubulations (ORTs) in 10/12 subjects. Only split-detector AOSLO could reliably resolve cones near lesion borders, and such cones were abnormally heterogeneous in morphology, diameter and density. On split-detector imaging, the cone mosaic terminated sharply at lesion borders in 5/5 cases examined. Split-detector imaging detected remnant cone inner segments within ORTs, which were generally contiguous with a central patch of preserved retina.Early IZ dropout and RPE thinning on SD-OCT are consistent with previously published results. Evidence of remnant cone inner segments within ORTs and the continuity of the ORTs with preserved retina suggests that these may represent an intermediate state of retinal degeneration prior to complete atrophy. Taken together, these results supports a model of choroideremia in which the RPE degenerates before photoreceptors.

    View details for DOI 10.1371/journal.pone.0167526

    View details for Web of Science ID 000389587100115

    View details for PubMedID 27936069

    View details for PubMedCentralID PMC5147929

  • Noninvasive imaging of the photoreceptor mosaic response to light stimulation. Proceedings of the National Academy of Sciences of the United States of America Srinivasan, V. J., Dubra, A. 2016

    View details for PubMedID 27810954

  • Imaging Foveal Microvasculature: Optical Coherence Tomography Angiography Versus Adaptive Optics Scanning Light Ophthalmoscope Fluorescein Angiography INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE Mo, S., Krawitz, B., Efstathiadis, E., Geyman, L., Weitz, R., Chui, T. P., Carroll, J., Dubra, A., Rosen, R. B. 2016; 57 (9): OCT130?OCT140


    To compare the use of optical coherence tomography angiography (OCTA) and adaptive optics scanning light ophthalmoscope fluorescein angiography (AOSLO FA) for characterizing the foveal microvasculature in healthy and vasculopathic eyes.Four healthy controls and 11 vasculopathic patients (4 diabetic retinopathy, 4 retinal vein occlusion, and 3 sickle cell retinopathy) were imaged with OCTA and AOSLO FA. Foveal perfusion maps were semiautomatically skeletonized for quantitative analysis, which included foveal avascular zone (FAZ) metrics (area, perimeter, acircularity index) and vessel density in three concentric annular regions of interest. On each set of OCTA and AOSLO FA images, matching vessel segments were used for lumen diameter measurement. Qualitative image comparisons were performed by visual identification of microaneurysms, vessel loops, leakage, and vessel segments.Adaptive optics scanning light ophthalmoscope FA and OCTA showed no statistically significant differences in FAZ perimeter, acircularity index, and vessel densities. Foveal avascular zone area, however, showed a small but statistically significant difference of 1.8% (P = 0.004). Lumen diameter was significantly larger on OCTA (mean difference 5.7 ?m, P < 0.001). Microaneurysms, fine structure of vessel loops, leakage, and some vessel segments were visible on AOSLO FA but not OCTA, while blood vessels obscured by leakage were visible only on OCTA.Optical coherence tomography angiography is comparable to AOSLO FA at imaging the foveal microvasculature except for differences in FAZ area, lumen diameter, and some qualitative features. These results, together with its ease of use, short acquisition time, and avoidance of potentially phototoxic blue light, support OCTA as a tool for monitoring ocular pathology and detecting early disease.

    View details for DOI 10.1167/iovs.15-18932

    View details for Web of Science ID 000383985400005

    View details for PubMedID 27409463

    View details for PubMedCentralID PMC4968918

  • Residual Foveal Cone Structure in CNGB3-Associated Achromatopsia INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE Langlo, C. S., Patterson, E. J., Higgins, B. P., Summerfelt, P., Razeen, M. M., Erker, L. R., Parker, M., Collison, F. T., Fishman, G. A., Kay, C. N., Zhang, J., Weleber, R. G., Yang, P., Wilson, D. J., Pennesi, M. E., Lam, B. L., Chiang, J., Chulay, J. D., Dubra, A., Hauswirth, W. W., Carroll, J. 2016; 57 (10): 3984-3995


    Congenital achromatopsia (ACHM) is an autosomal recessive disorder in which cone function is absent or severely reduced. Gene therapy in animal models of ACHM have shown restoration of cone function, though translation of these results to humans relies, in part, on the presence of viable cone photoreceptors at the time of treatment. Here, we characterized residual cone structure in subjects with CNGB3-associated ACHM.High-resolution imaging (optical coherence tomography [OCT] and adaptive optics scanning light ophthalmoscopy [AOSLO]) was performed in 51 subjects with CNGB3-associated ACHM. Peak cone density and inter-cone spacing at the fovea was measured using split-detection AOSLO. Foveal outer nuclear layer thickness was measured in OCT images, and the integrity of the photoreceptor layer was assessed using a previously published OCT grading scheme.Analyzable images of the foveal cones were obtained in 26 of 51 subjects, with nystagmus representing the major obstacle to obtaining high-quality images. Peak foveal cone density ranged from 7,273 to 53,554 cones/mm2, significantly lower than normal (range, 84,733-234,391 cones/mm2), with the remnant cones being either contiguously or sparsely arranged. Peak cone density was correlated with OCT integrity grade; however, there was overlap of the density ranges between OCT grades.The degree of residual foveal cone structure varies greatly among subjects with CNGB3-associated ACHM. Such measurements may be useful in estimating the therapeutic potential of a given retina, providing affected individuals and physicians with valuable information to more accurately assess the risk-benefit ratio as they consider enrolling in experimental gene therapy trials. (, NCT01846052.).

    View details for DOI 10.1167/iovs.16-19313

    View details for PubMedID 27479814

  • In Vivo Imaging of the Human Retinal Pigment Epithelial Mosaic Using Adaptive Optics Enhanced Indocyanine Green Ophthalmoscopy INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE Tam, J., Liu, J., Dubra, A., Fariss, R. 2016; 57 (10): 4376-4384


    The purpose of this study was to establish that retinal pigment epithelial (RPE) cells take up indocyanine green (ICG) dye following systemic injection and that adaptive optics enhanced indocyanine green ophthalmoscopy (AO-ICG) enables direct visualization of the RPE mosaic in the living human eye.A customized adaptive optics scanning light ophthalmoscope (AOSLO) was used to acquire high-resolution retinal fluorescence images of residual ICG dye in human subjects after intravenous injection at the standard clinical dose. Simultaneously, multimodal AOSLO images were also acquired, which included confocal reflectance, nonconfocal split detection, and darkfield. Imaging was performed in 6 eyes of three healthy subjects with no history of ocular or systemic diseases. In addition, histologic studies in mice were carried out.The AO-ICG channel successfully resolved individual RPE cells in human subjects at various time points, including 20 minutes and 2 hours after dye administration. Adaptive optics-ICG images of RPE revealed detail which could be correlated with AO dark-field images of the same cells. Interestingly, there was a marked heterogeneity in the fluorescence of individual RPE cells. Confirmatory histologic studies in mice corroborated the specific uptake of ICG by the RPE layer at a late time point after systemic ICG injection.Adaptive optics-enhanced imaging of ICG dye provides a novel way to visualize and assess the RPE mosaic in the living human eye alongside images of the overlying photoreceptors and other cells.

    View details for DOI 10.1167/iovs.16-19503

    View details for Web of Science ID 000383981600056

    View details for PubMedID 27564519

    View details for PubMedCentralID PMC5015921

  • Cone Photoreceptor Structure in Patients With X-Linked Cone Dysfunction and Red-Green Color Vision Deficiency INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE Patterson, E. J., Wilk, M., Langlo, C. S., Kasilian, M., Ring, M., Hufnagel, R. B., Dubis, A. M., Tee, J. J., Kalitzeos, A., Gardner, J. C., Ahmed, Z. M., Sisk, R. A., Larsen, M., Sjoberg, S., Connor, T. B., Dubra, A., Neitz, J., Hardcastle, A. J., Neitz, M., Michaelides, M., Carroll, J. 2016; 57 (8): 3853-3863


    Mutations in the coding sequence of the L and M opsin genes are often associated with X-linked cone dysfunction (such as Bornholm Eye Disease, BED), though the exact color vision phenotype associated with these disorders is variable. We examined individuals with L/M opsin gene mutations to clarify the link between color vision deficiency and cone dysfunction.We recruited 17 males for imaging. The thickness and integrity of the photoreceptor layers were evaluated using spectral-domain optical coherence tomography. Cone density was measured using high-resolution images of the cone mosaic obtained with adaptive optics scanning light ophthalmoscopy. The L/M opsin gene array was characterized in 16 subjects, including at least one subject from each family.There were six subjects with the LVAVA haplotype encoded by exon 3, seven with LIAVA, two with the Cys203Arg mutation encoded by exon 4, and two with a novel insertion in exon 2. Foveal cone structure and retinal thickness was disrupted to a variable degree, even among related individuals with the same L/M array.Our findings provide a direct link between disruption of the cone mosaic and L/M opsin variants. We hypothesize that, in addition to large phenotypic differences between different L/M opsin variants, the ratio of expression of first versus downstream genes in the L/M array contributes to phenotypic diversity. While the L/M opsin mutations underlie the cone dysfunction in all of the subjects tested, the color vision defect can be caused either by the same mutation or a gene rearrangement at the same locus.

    View details for DOI 10.1167/iovs.16-19608

    View details for Web of Science ID 000381729000039

    View details for PubMedID 27447086

    View details for PubMedCentralID PMC4968428

  • Assessing Photoreceptor Structure in Retinitis Pigmentosa and Usher Syndrome INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE Sun, L. W., Johnson, R. D., Langlo, C. S., Cooper, R. F., Razeen, M. M., Russillo, M. C., Dubra, A., Connor, T. B., Han, D. P., Pennesi, M. E., Kay, C. N., Weinberg, D. V., Stepien, K. E., Carroll, J. 2016; 57 (6): 2428-2442


    The purpose of this study was to examine cone photoreceptor structure in retinitis pigmentosa (RP) and Usher syndrome using confocal and nonconfocal split-detector adaptive optics scanning light ophthalmoscopy (AOSLO).Nineteen subjects (11 RP, 8 Usher syndrome) underwent ophthalmic and genetic testing, spectral-domain optical coherence tomography (SD-OCT), and AOSLO imaging. Split-detector images obtained in 11 subjects (7 RP, 4 Usher syndrome) were used to assess remnant cone structure in areas of altered cone reflectivity on confocal AOSLO.Despite normal interdigitation zone and ellipsoid zone appearance on OCT, foveal and parafoveal cone densities derived from confocal AOSLO images were significantly lower in Usher syndrome compared with RP. This was due in large part to an increased prevalence of non-waveguiding cones in the Usher syndrome retina. Although significantly correlated to best-corrected visual acuity and foveal sensitivity, cone density can decrease by nearly 38% before visual acuity becomes abnormal. Aberrantly waveguiding cones were noted within the transition zone of all eyes and corresponded to intact inner segment structures. These remnant cones decreased in density and increased in diameter across the transition zone and disappeared with external limiting membrane collapse.Foveal cone density can be decreased in RP and Usher syndrome before visible changes on OCT or a decline in visual function. Thus, AOSLO imaging may allow more sensitive monitoring of disease than current methods. However, confocal AOSLO is limited by dependence on cone waveguiding, whereas split-detector AOSLO offers unambiguous and quantifiable visualization of remnant cone inner segment structure. Confocal and split-detector thus offer complementary insights into retinal pathology.

    View details for DOI 10.1167/iovs.15-18246

    View details for PubMedID 27145477

  • Longitudinal imaging of microvascular remodelling in proliferative diabetic retinopathy using adaptive optics scanning light ophthalmoscopy OPHTHALMIC AND PHYSIOLOGICAL OPTICS Chui, T. Y., Pinhas, A., Gan, A., Razeen, M., Shah, N., Cheang, E., Liu, C. L., Dubra, A., Rosen, R. B. 2016; 36 (3): 290-302


    To characterise longitudinal changes in the retinal microvasculature of type 2 diabetes mellitus (T2DM) as exemplified in a patient with proliferative diabetic retinopathy (PDR) using an adaptive optics scanning light ophthalmoscope (AOSLO).A 35-year-old T2DM patient with PDR treated with scatter pan-retinal photocoagulation at the inferior retina 1 day prior to initial AOSLO imaging along with a 24-year-old healthy control were imaged in this study. AOSLO vascular structural and perfusion maps were acquired at four visits over a 20-week period. Capillary diameter and microaneurysm area changes were measured on the AOSLO structural maps. Imaging repeatability was established using longitudinal imaging of microvasculature in the healthy control.Capillary occlusion and recanalisation, capillary dilatation, resolution of local retinal haemorrhage, capillary hairpin formation, capillary bend formation, microaneurysm formation, progression and regression were documented over time in a region 2 superior to the fovea in the PDR patient. An identical microvascular network with same capillary diameter was observed in the control subject over time.High-resolution serial AOSLO imaging enables in vivo observation of vasculopathic changes seen in diabetes mellitus. The implications of this methodology are significant, providing the opportunity for studying the dynamics of the pathological process, as well as the possibility of identifying highly sensitive and non-invasive biomarkers of end organ damage and response to treatment.

    View details for DOI 10.1111/opo.12273

    View details for Web of Science ID 000378336600006

    View details for PubMedID 26803289

    View details for PubMedCentralID PMC4846498

  • Automatic detection of cone photoreceptors in split detector adaptive optics scanning light ophthalmoscope images. Biomedical optics express Cunefare, D., Cooper, R. F., Higgins, B., Katz, D. F., Dubra, A., Carroll, J., Farsiu, S. 2016; 7 (5): 2036-2050


    Quantitative analysis of the cone photoreceptor mosaic in the living retina is potentially useful for early diagnosis and prognosis of many ocular diseases. Non-confocal split detector based adaptive optics scanning light ophthalmoscope (AOSLO) imaging reveals the cone photoreceptor inner segment mosaics often not visualized on confocal AOSLO imaging. Despite recent advances in automated cone segmentation algorithms for confocal AOSLO imagery, quantitative analysis of split detector AOSLO images is currently a time-consuming manual process. In this paper, we present the fully automatic adaptive filtering and local detection (AFLD) method for detecting cones in split detector AOSLO images. We validated our algorithm on 80 images from 10 subjects, showing an overall mean Dice's coefficient of 0.95 (standard deviation 0.03), when comparing our AFLD algorithm to an expert grader. This is comparable to the inter-observer Dice's coefficient of 0.94 (standard deviation 0.04). To the best of our knowledge, this is the first validated, fully-automated segmentation method which has been applied to split detector AOSLO images.

    View details for DOI 10.1364/BOE.7.002036

    View details for PubMedID 27231641

    View details for PubMedCentralID PMC4871101

  • Correlating Photoreceptor Mosaic Structure to Clinical Findings in Stargardt Disease TRANSLATIONAL VISION SCIENCE & TECHNOLOGY Razeen, M. M., Cooper, R. F., Langlo, C. S., Goldberg, M. R., Wilk, M. A., Han, D. P., Connor, T. B., Fishman, G. A., Collison, F. T., Sulai, Y. N., Dubra, A., Carroll, J., Stepien, K. E. 2016; 5 (2): 6


    To demonstrate a method for correlating photoreceptor mosaic structure with optical coherence tomography (OCT) and microperimetry findings in patients with Stargardt disease.A total of 14 patients with clinically diagnosed Stargardt disease were imaged using confocal and split-detection adaptive optics scanning light ophthalmoscopy. Cone photoreceptors were identified manually in a band along the temporal meridian. Resulting values were compared to a normative database (n = 9) to generate cone density deviation (CDD) maps. Manual measurement of outer nuclear layer plus Henle fiber layer (ONL+HFL) thickness was performed, in addition to determination of the presence of ellipsoid zone (EZ) and interdigitation zone (IZ) bands on OCT. These results, along with microperimetry data, were overlaid with the CDD maps.Wide variation in foveal structure and CDD maps was seen within this small group. Disruption of ONL+HFL and/or IZ band was seen in all patients, with EZ band preservation in regions with low cone density in 38% of locations analyzed. Normality of retinal lamellar structure on OCT corresponded with cone density and visual function at 50/78 locations analyzed. Outer retinal tubulations containing photoreceptor-like structures were observed in 3 patients.The use of CDD color-coded maps enables direct comparison of cone mosaic local density with other measures of retinal structure and function. Larger normative datasets and improved tools for automation of image alignment are needed.The approach described facilitates comparison of complex multimodal data sets from patients with inherited retinal degeneration, and can be expanded to incorporate other structural imaging or functional testing.

    View details for DOI 10.1167/tvst.5.2.6

    View details for Web of Science ID 000388669300006

    View details for PubMedID 26981328

    View details for PubMedCentralID PMC4790429



    To compare images of photoreceptor layer disruptions obtained with optical coherence tomography (OCT) and adaptive optics scanning light ophthalmoscopy (AOSLO) in a variety of pathologic states.Five subjects with photoreceptor ellipsoid zone disruption as per OCT and clinical diagnoses of closed-globe blunt ocular trauma (n = 2), macular telangiectasia type 2 (n = 1), blue-cone monochromacy (n = 1), or cone-rod dystrophy (n = 1) were included. Images were acquired within and around photoreceptor lesions using spectral domain OCT, confocal AOSLO, and split-detector AOSLO.There were substantial differences in the extent and appearance of the photoreceptor mosaic as revealed by confocal AOSLO, split-detector AOSLO, and spectral domain OCT en face view of the ellipsoid zone.Clinically available spectral domain OCT, viewed en face or as B-scan, may lead to misinterpretation of photoreceptor anatomy in a variety of diseases and injuries. This was demonstrated using split-detector AOSLO to reveal substantial populations of photoreceptors in areas of no, low, or ambiguous ellipsoid zone reflectivity with en face OCT and confocal AOSLO. Although it is unclear if these photoreceptors are functional, their presence offers hope for therapeutic strategies aimed at preserving or restoring photoreceptor function.

    View details for PubMedID 26166796

  • Effects of Intraframe Distortion on Measures of Cone Mosaic Geometry from Adaptive Optics Scanning Light Ophthalmoscopy TRANSLATIONAL VISION SCIENCE & TECHNOLOGY Cooper, R. F., Sulai, Y. N., Dubis, A. M., Chui, T. Y., Rosen, R. B., Michaelides, M., Dubra, A., Carroll, J. 2016; 5 (1): 10


    To characterize the effects of intraframe distortion due to involuntary eye motion on measures of cone mosaic geometry derived from adaptive optics scanning light ophthalmoscope (AOSLO) images.We acquired AOSLO image sequences from 20 subjects at 1.0, 2.0, and 5.0 temporal from fixation. An expert grader manually selected 10 minimally distorted reference frames from each 150-frame sequence for subsequent registration. Cone mosaic geometry was measured in all registered images (n = 600) using multiple metrics, and the repeatability of these metrics was used to assess the impact of the distortions from each reference frame. In nine additional subjects, we compared AOSLO-derived measurements to those from adaptive optics (AO)-fundus images, which do not contain system-imposed intraframe distortions.We observed substantial variation across subjects in the repeatability of density (1.2%-8.7%), inter-cell distance (0.8%-4.6%), percentage of six-sided Voronoi cells (0.8%-10.6%), and Voronoi cell area regularity (VCAR) (1.2%-13.2%). The average of all metrics extracted from AOSLO images (with the exception of VCAR) was not significantly different than those derived from AO-fundus images, though there was variability between individual images.Our data demonstrate that the intraframe distortion found in AOSLO images can affect the accuracy and repeatability of cone mosaic metrics. It may be possible to use multiple images from the same retinal area to approximate a "distortionless" image, though more work is needed to evaluate the feasibility of this approach.Even in subjects with good fixation, images from AOSLOs contain intraframe distortions due to eye motion during scanning. The existence of these artifacts emphasizes the need for caution when interpreting results derived from scanning instruments.

    View details for DOI 10.1167/tvst.5.1.10

    View details for Web of Science ID 000388668800010

    View details for PubMedID 26933523

    View details for PubMedCentralID PMC4771077

  • Noninvasive imaging of the thirteen-lined ground squirrel photoreceptor mosaic VISUAL NEUROSCIENCE Sajdak, B., Sulai, Y. N., Langlo, C. S., Luna, G., Fisher, S. K., Merriman, D. K., Dubra, A. 2016; 33: e003


    Ground squirrels are an increasingly important model for studying visual processing, retinal circuitry, and cone photoreceptor function. Here, we demonstrate that the photoreceptor mosaic can be longitudinally imaged noninvasively in the 13-lined ground squirrel (Ictidomys tridecemlineatus) using confocal and nonconfocal split-detection adaptive optics scanning ophthalmoscopy using 790 nm light. Photoreceptor density, spacing, and Voronoi analysis are consistent with that of the human cone mosaic. The high imaging success rate and consistent image quality in this study reinforce the ground squirrel as a practical model to aid drug discovery and testing through longitudinal imaging on the cellular scale.

    View details for DOI 10.1017/S0952523815000346

    View details for Web of Science ID 000389715400003

    View details for PubMedID 26923645

    View details for PubMedCentralID PMC4793898

  • Retinal Architecture in RGS9- and R9AP-Associated Retinal Dysfunction (Bradyopsia) AMERICAN JOURNAL OF OPHTHALMOLOGY Strauss, R. W., Dubis, A. M., Cooper, R. F., Ba-Abbad, R., Moore, A. T., Webster, A. R., Dubra, A., Carroll, J., Michaelides, M. 2015; 160 (6): 1269?75


    To characterize photoreceptor structure and mosaic integrity in subjects with ?RGS9- and R9AP-associated retinal dysfunction (bradyopsia) and compare to previous observations in other cone dysfunction disorders such as oligocone trichromacy.Observational case series.setting: Moorfields Eye Hospital (United Kingdom) and Medical College Wisconsin (USA).Six eyes of 3 subjects with disease-causing variants in ?RGS9 or R9AP.Detailed retinal imaging using spectral-domain optical coherence tomography and confocal adaptive-optics scanning light ophthalmoscopy.Cone density at 100?m from foveal center ranged from 123 132 cones/mm(2) to 140 013 cones/mm(2). Cone density ranged from 30 573 to 34 876 cones/mm(2) by 600?m from center and from 15 987 to 16,253 cones/mm(2) by 1400?m from center, in keeping with data from normal subjects. Adaptive-optics imaging identified a small, focal hyporeflective lesion at the foveal center in both eyes of the subject with RGS9-associated disease, corresponding to a discrete outer retinal defect also observed on spectral-domain optical coherence tomography; however, the photoreceptor mosaic remained intact at all other observed eccentricities.Bradyopsia and oligocone trichromacy share common clinical symptoms and cannot be discerned on standard clinical findings alone. Adaptive-optics imaging previously demonstrated a sparse mosaic of normal wave-guiding cones remaining at the fovea, with no visible structure outside the central fovea in oligocone trichromacy. In contrast, the subjects presented in thisstudy with molecularly confirmed bradyopsia had a relatively intact and structurally normal photoreceptor mosaic, allowing the distinction between these disorders based on the cellular phenotype and suggesting different pathomechanisms.

    View details for DOI 10.1016/j.ajo.2015.08.032

    View details for Web of Science ID 000365243400024

    View details for PubMedID 26343007

    View details for PubMedCentralID PMC4653116

  • FELLOW EYE CHANGES IN PATIENTS WITH NONISCHEMIC CENTRAL RETINAL VEIN OCCLUSION Assessment of Perfused Foveal Microvascular Density and Identification of Nonperfused Capillaries RETINA-THE JOURNAL OF RETINAL AND VITREOUS DISEASES Pinhas, A., Dubow, M., Shah, N., Cheang, E., Liu, C. L., Razeen, M., Gan, A., Weitz, R., Sulai, Y. N., Chui, T. Y., Dubra, A., Rosen, R. B. 2015; 35 (10): 2028-2036


    Eyes fellow to nonischemic central retinal vein occlusion (CRVO) were examined for abnormalities, which might explain their increased risk for future occlusion, using adaptive optics scanning light ophthalmoscope fluorescein angiography.Adaptive optics scanning light ophthalmoscope fluorescein angiography foveal microvascular densities were calculated. Nonperfused capillaries adjacent to the foveal avascular zone were identified. Spectral domain optical coherence tomography, ultrawide field fluorescein angiographies, and microperimetry were also performed.Ten fellow eyes of nine nonischemic CRVO and 1 nonischemic hemi-CRVO subjects and four affected eyes of three nonischemic CRVO and one nonischemic hemi-CRVO subjects were imaged. Ninety percent of fellow eyes and 100% of affected eyes demonstrated at least 1 nonperfused capillary compared with 31% of healthy eyes. Fellow eye microvascular density (35 3.6 mm(-1)) was significantly higher than that of affected eyes (25 5.2 mm(-1)) and significantly lower than that of healthy eyes (42 4.2 mm(-1)). Compared with healthy controls, spectral domain optical coherence tomography thicknesses showed no significant difference, whereas microperimetry and 2/9 ultrawide field fluorescein angiography revealed abnormalities in fellow eyes.Fellow eye changes detectable on adaptive optics scanning light ophthalmoscope fluorescein angiography reflect subclinical pathology difficult to detect using conventional imaging technologies. These changes may help elucidate the pathogenesis of nonischemic CRVO and help identify eyes at increased risk of future occlusion.

    View details for DOI 10.1097/IAE.0000000000000586

    View details for Web of Science ID 000362219000014

    View details for PubMedID 25932560

    View details for PubMedCentralID PMC4816596

  • Details of Glaucomatous Damage Are Better Seen on OCT En Face Images Than on OCT Retinal Nerve Fiber Layer Thickness Maps INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE Hood, D. C., Fortune, B., Mavrommatis, M. A., Reynaud, J., Ramachandran, R., Ritch, R., Rosen, R. B., Muhammad, H., Dubra, A., Chui, T. P. 2015; 56 (11): 6208?16


    High-resolution images of glaucomatous damage to the retinal nerve fiber layer (RNFL) were obtained with an adaptive optics-scanning light ophthalmoscope (AO-SLO) and used as a basis for comparisons between en face slab images and thickness maps derived from optical coherence tomography (OCT) scans.Wide-field (9 12 mm) cube scans were obtained with swept-source OCT (DRI-OCT) from six eyes of six patients. All eyes had a deep defect near fixation as seen on a 10-2 visual field test. Optical coherence tomography en face images, based on the average reflectance intensity, were generated (ATL 3D-Suite) from 52-?m slabs just below the vitreal border of the inner limiting membrane. The RNFL thickness maps were generated from the same OCT data. Both were compared with the AO-SLO peripapillary images that were previously obtained.On AO-SLO images, three eyes showed small regions of preserved and/or missing RNFL bundles within the affected region. Details in these regions were seen on the OCT en face images but not on the RNFL thickness maps. In addition, in the healthier hemi-retinas of two eyes, there were darker, arcuate-shaped regions on en face images that corresponded to abnormalities seen on AO-SLO. These were not seen on RNFL thickness maps.Details of local glaucomatous damage, missing or easily overlooked on traditional OCT RNFL thickness analysis used in clinical OCT reports, were seen on OCT en face images based on the average reflectance intensity. While more work is needed, it is likely that en face slab imaging has a role in the clinical management of glaucoma.

    View details for PubMedID 26426403

  • Confocal Adaptive Optics Imaging of Peripapillary Nerve Fiber Bundles: Implications for Glaucomatous Damage Seen on Circumpapillary OCT Scans TRANSLATIONAL VISION SCIENCE & TECHNOLOGY Hood, D. C., Chen, M. F., Lee, D., Epstein, B., Alhadeff, P., Rosen, R. B., Ritch, R., Dubra, A., Chui, T. P. 2015; 4 (2): 12


    To improve our understanding of glaucomatous damage as seen on circumpapillary disc scans obtained with frequency-domain optical coherence tomography (fdOCT), fdOCT scans were compared to images of the peripapillary retinal nerve fiber (RNF) bundles obtained with an adaptive optics-scanning light ophthalmoscope (AO-SLO).The AO-SLO images and fdOCT scans were obtained on 6 eyes of 6 patients with deep arcuate defects (5 points ?-15 db) on 10-2 visual fields. The AO-SLO images were montaged and aligned with the fdOCT images to compare the RNF bundles seen with AO-SLO to the RNF layer thickness measured with fdOCT.All 6 eyes had an abnormally thin (1% confidence limit) RNF layer (RNFL) on fdOCT and abnormal (hyporeflective) regions of RNF bundles on AO-SLO in corresponding regions. However, regions of abnormal, but equal, RNFL thickness on fdOCT scans varied in appearance on AO-SLO images. These regions could be largely devoid of RNF bundles (5 eyes), have abnormal-appearing bundles of lower contrast (6 eyes), or have isolated areas with a few relatively normal-appearing bundles (2 eyes). There also were local variations in reflectivity of the fdOCT RNFL that corresponded to the variations in AO-SLO RNF bundle appearance.Relatively similar 10-2 defects with similar fdOCT RNFL thickness profiles can have very different degrees of RNF bundle damage as seen on fdOCT and AO-SLO.While the results point to limitations of fdOCT RNFL thickness as typically analyzed, they also illustrate the potential for improving fdOCT by attending to variations in local intensity.

    View details for DOI 10.1167/tvst.4.2.12

    View details for Web of Science ID 000388583500012

    View details for PubMedID 25909035

    View details for PubMedCentralID PMC4404969

  • Adaptive Optics Imaging of Healthy and Abnormal Regions of Retinal Nerve Fiber Bundles of Patients With Glaucoma INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE Chen, M. F., Chui, T. P., Alhadeff, P., Rosen, R. B., Ritch, R., Dubra, A., Hood, D. C. 2015; 56 (1): 674?81


    To better understand the nature of glaucomatous damage of the macula, especially the structural changes seen between relatively healthy and clearly abnormal (AB) retinal regions, using an adaptive optics scanning light ophthalmoscope (AO-SLO).Adaptive optics SLO images and optical coherence tomography (OCT) vertical line scans were obtained on one eye of seven glaucoma patients, with relatively deep local arcuate defects on the 10-2 visual field test in one (six eyes) or both hemifields (one eye). Based on the OCT images, the retinal nerve fiber (RNF) layer was divided into two regions: (1) within normal limits (WNL), relative RNF layer thickness within mean control values 2 SD; and (2) AB, relative thickness less than -2 SD value.As seen on AO-SLO, the pattern of AB RNF bundles near the border of the WNL and AB regions differed across eyes. There were normal-appearing bundles in the WNL region of all eyes and AB-appearing bundles near the border with the AB region. This region with AB bundles ranged in extent from a few bundles to the entire AB region in the case of one eye. All other eyes had a large AB region without bundles. However, in two of these eyes, a few bundles were seen within this region of otherwise missing bundles.The AO-SLO images revealed details of glaucomatous damage that are difficult, if not impossible, to see with current OCT technology. Adaptive optics SLO may prove useful in following progression in clinical trials, or in disease management, if AO-SLO becomes widely available and easy to use.

    View details for DOI 10.1167/iovs.14-15936

    View details for Web of Science ID 000351519800077

    View details for PubMedID 25574048

    View details for PubMedCentralID PMC4311778

  • Assessing photoreceptor structure after macular hole closure. Retinal cases & brief reports Hansen, S., Batson, S., Weinlander, K. M., Cooper, R. F., Scoles, D. H., Karth, P. A., Weinberg, D. V., Dubra, A., Kim, J. E., Carroll, J., Wirostko, W. J. 2015; 9 (1): 15-20


    To describe photoreceptor structure and recovery after macular hole (MH) closure with pars plana vitrectomy (PPV) using adaptive optics scanning light ophthalmoscopy and spectral domain optical coherence tomography.A pilot imaging study of four eyes from four subjects undergoing PPV for MH was conducted. Imaging with spectral domain optical coherence tomography and adaptive optics scanning light ophthalmoscopy was performed at varying time points after PPV.Despite successful MH closure, disruption of the foveal inner segment ellipsoid zone was seen in all patients when imaged at a mean of 117 days after PPV. Disruption of the photoreceptor mosaic was seen using adaptive optics scanning light ophthalmoscopy at locations corresponding to regions of ellipsoid zone disruption on spectral domain optical coherence tomography. Cone density immediately surrounding these disruptions was normal, except for one patient. In 2 patients who were imaged serially up to 516 days after PPV, recovery of cone cells within regions of mosaic disruption could be detected over time.Photoreceptor disruption exists even after apparent MH closure. Remodeling of the foveal cone mosaic continues for many months after surgery, perhaps accounting for the delayed postoperative improvements of visual acuity in some patients. Spectral domain optical coherence tomography and adaptive optics scanning light ophthalmoscopy are useful tools for monitoring photoreceptor recovery after surgical closure of MH.

    View details for DOI 10.1097/ICB.0000000000000117

    View details for PubMedID 25525907

  • Assessment of Perfused Foveal Microvascular Density and Identification of Nonperfused Capillaries in Healthy and Vasculopathic Eyes INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE Pinhas, A., Razeen, M., Dubow, M., Gan, A., Chui, T. Y., Shah, N., Mehta, M., Gentile, R. C., Weitz, R., Walsh, J. B., Sulai, Y. N., Carroll, J., Dubra, A., Rosen, R. B. 2014; 55 (12): 8056?66


    To analyze the foveal microvasculature of young healthy eyes and older vasculopathic eyes, imaged using in vivo adaptive optics scanning light ophthalmoscope fluorescein angiography (AOSLO FA).AOSLO FA imaging of the superficial retinal microvasculature within an 800-?m radius from the foveal center was performed using simultaneous confocal infrared (IR) reflectance (790 nm) and fluorescence (488 nm) channels. Corresponding IR structural and FA perfusion maps were compared with each other to identify nonperfused capillaries adjacent to the foveal avascular zone. Microvascular densities were calculated from skeletonized FA perfusion maps.Sixteen healthy adults (26 eyes; mean age 25 years, range, 21-29) and six patients with a retinal vasculopathy (six eyes; mean age 55 years, range, 44-70) were imaged. At least one nonperfused capillary was observed in five of the 16 healthy nonfellow eyes and in four of the six vasculopathic eyes. Compared with healthy eyes, capillary nonperfusion in the vasculopathic eyes was more extensive. Microvascular density of the 16 healthy nonfellow eyes was 42.0 4.2 mm(-1) (range, 33-50 mm(-1)). All six vasculopathic eyes had decreased microvascular densities.AOSLO FA provides an in vivo method for estimating foveal microvascular density and reveals occult nonperfused retinal capillaries. Nonperfused capillaries in healthy young adults may represent a normal variation and/or an early sign of pathology. Although limited, the normative data presented here is a step toward developing clinically useful microvascular parameters for ocular and/or systemic diseases.

    View details for DOI 10.1167/iovs.14-15136

    View details for Web of Science ID 000347222300040

    View details for PubMedID 25414179

    View details for PubMedCentralID PMC4266074

  • Genotype-Dependent Variability in Residual Cone Structure in Achromatopsia: Toward Developing Metrics for Assessing Cone Health INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE Dubis, A. M., Cooper, R. F., Aboshiha, J., Langlo, C. S., Sundaram, V., Liu, B., Collison, F., Fishman, G. A., Moore, A. T., Webster, A. R., Dubra, A., Carroll, J., Michaelides, M. 2014; 55 (11): 7303?11


    Gene therapy trials for inherited photoreceptor disorders are planned. Anatomical metrics to select the best candidates and outcomes are needed. Adaptive optics (AO) imaging enables visualization of photoreceptor structure, although analytical tools are lacking. Here we present criteria to assess residual photoreceptor integrity in achromatopsia (ACHM).Two AOSLOs, at the Medical College of Wisconsin and Moorfields Eye Hospital, were used to image the photoreceptor mosaic of 11 subjects with ACHM and 7 age-matched controls. Images were obtained, processed, and montaged using previously described methods. Cone density and reflectivity were quantified to assess residual cone photoreceptor structure.All subjects with ACHM had reduced numbers of cone photoreceptors, albeit to a variable degree. In addition, the relative cone reflectivity varied greatly. Interestingly, subjects with GNAT2-associated ACHM had the greatest number of residual cones and the reflectivity of those cones was significantly greater than that of the cones in the subjects with CNGA3/CNGB3-associated ACHM.We present cone reflectivity as a metric that can be used to characterize cone structure in ACHM. This method may be applicable to subjects with other cone disorders. In ACHM, we hypothesize that cone numerosity (and/or density) combined with cone reflectivity could be used to gauge the therapeutic potential. As gene replacement would not be expected to add cones, reflectivity could be a more powerful AO-metric for monitoring the cellular response to treatment and could provide a more immediate indicator of efficacy than behavioral measures, which may take longer to change.

    View details for DOI 10.1167/iovs.14-14225

    View details for Web of Science ID 000347217300036

    View details for PubMedID 25277229

    View details for PubMedCentralID PMC4235328

  • OUTER RETINAL STRUCTURE AFTER CLOSED-GLOBE BLUNT OCULAR TRAUMA RETINA-THE JOURNAL OF RETINAL AND VITREOUS DISEASES Flatter, J. A., Cooper, R. F., Dubow, M. J., Pinhas, A., Singh, R. S., Kapur, R., Shah, N., Walsh, R. D., Hong, S. H., Weinberg, D. V., Stepien, K. E., Wirostko, W. J., Robison, S., Dubra, A., Rosen, R. B., Connor, T. B., Carroll, J. 2014; 34 (10): 2133?46


    To evaluate outer retinal structural abnormalities in patients with visual deficits after closed-globe blunt ocular trauma.Nine subjects with visual complaints after closed-globe blunt ocular trauma were examined between 1 month after trauma and 6 years after trauma. Spectral domain optical coherence tomography was used to assess the outer retinal architecture, whereas adaptive optics scanning light ophthalmoscopy was used to analyze the photoreceptor mosaic integrity.Visual deficits ranged from central scotomas to decreased visual acuity. Spectral domain optical coherence tomography defects included focal foveal photoreceptor lesions, variable attenuation of the interdigitation zone, and mottling of the outer segment band, with one subject having normal outer retinal structure. Adaptive optics scanning light ophthalmoscopy revealed disruption of the photoreceptor mosaic in all subjects, variably manifesting as foveal focal discontinuities, perifoveal hyporeflective cones, and paracentral regions of selective cone loss.We observe persistent outer retinal disruption in subjects with visual complaints after closed-globe blunt ocular trauma, albeit to a variable degree. Adaptive optics scanning light ophthalmoscopy imaging allows the assessment of photoreceptor structure at a level of detail not resolvable using spectral domain optical coherence tomography or other current clinical imaging tools. Multimodal imaging seems to be useful in revealing the cause of visual complaints in patients after closed-globe blunt ocular trauma. Future studies are needed to better understand how photoreceptor structure changes longitudinally in response to various traumas.

    View details for DOI 10.1097/IAE.0000000000000169

    View details for Web of Science ID 000343048200036

    View details for PubMedID 24752010

    View details for PubMedCentralID PMC4175068

  • A Prospective Longitudinal Study of Retinal Structure and Function in Achromatopsia INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE Aboshiha, J., Dubis, A. M., Cowing, J., Fahy, R. A., Sundaram, V., Bainbridge, J. W., Ali, R. R., Dubra, A., Nardini, M., Webster, A. R., Moore, A. T., Rubin, G., Carroll, J., Michaelides, M. 2014; 55 (9): 5733?43


    To longitudinally characterize retinal structure and function in achromatopsia (ACHM) in preparation for clinical gene therapy trials.Thirty-eight molecularly confirmed ACHM subjects underwent serial assessments, including spectral domain optical coherence tomography (SD-OCT), microperimetry, and fundus autofluorescence (FAF). Foveal structure on SD-OCT was graded and compared for evidence of progression, along with serial measurements of foveal total retinal thickness (FTRT) and outer nuclear layer (ONL) thickness. Fundus autofluorescence patterns were characterized and compared over time.Mean follow-up was 19.5 months (age range at baseline, 6-52 years). Only 2 (5%) of 37 subjects demonstrated change in serial foveal SD-OCT scans. There was no statistically significant change over time in FTRT (P = 0.83), ONL thickness (P = 0.27), hyporeflective zone diameter (P = 0.42), visual acuity (P = 0.89), contrast sensitivity (P = 0.22), mean retinal sensitivity (P = 0.84), and fixation stability (P = 0.58). Three distinct FAF patterns were observed (n = 30): central increased FAF (n = 4), normal FAF (n = 11), and well-demarcated reduced FAF (n = 15); with the latter group displaying a slow increase in the area of reduced FAF of 0.03 mm(2) over 19.3 months (P = 0.002).Previously published cross-sectional studies have described conflicting findings with respect to the age-dependency of progression. This study, which constitutes the largest and longest prospective longitudinal study of ACHM to date, suggests that although ACHM may be progressive, any such progression is slow and subtle in most patients, and does not correlate with age or genotype. We also describe the first serial assessment of FAF, which is highly variable between individuals, even of similar age and genotype.

    View details for DOI 10.1167/iovs.14-14937

    View details for Web of Science ID 000343146900036

    View details for PubMedID 25103266

    View details for PubMedCentralID PMC4161486

  • Non-common path aberration correction in an adaptive optics scanning ophthalmoscope BIOMEDICAL OPTICS EXPRESS Sulai, Y. N., Dubra, A. 2014; 5 (9): 3059?73


    The correction of non-common path aberrations (NCPAs) between the imaging and wavefront sensing channel in a confocal scanning adaptive optics ophthalmoscope is demonstrated. NCPA correction is achieved by maximizing an image sharpness metric while the confocal detection aperture is temporarily removed, effectively minimizing the monochromatic aberrations in the illumination path of the imaging channel. Comparison of NCPA estimated using zonal and modal orthogonal wavefront corrector bases provided wavefronts that differ by ~?/20 in root-mean-squared (~?/30 standard deviation). Sequential insertion of a cylindrical lens in the illumination and light collection paths of the imaging channel was used to compare image resolution after changing the wavefront correction to maximize image sharpness and intensity metrics. Finally, the NCPA correction was incorporated into the closed-loop adaptive optics control by biasing the wavefront sensor signals without reducing its bandwidth.

    View details for DOI 10.1364/BOE.5.003059

    View details for Web of Science ID 000341650900017

    View details for PubMedID 25401020

    View details for PubMedCentralID PMC4230870

  • The reliability of parafoveal cone density measurements BRITISH JOURNAL OF OPHTHALMOLOGY Liu, B. S., Tarima, S., Visotcky, A., Pechauer, A., Cooper, R. F., Landsem, L., Wilk, M. A., Godara, P., Makhijani, V., Sulai, Y. N., Syed, N., Yasumura, G., Garg, A. K., Pennesi, M. E., Lujan, B. J., Dubra, A., Duncan, J. L., Carroll, J. 2014; 98 (8): 1126?31


    Adaptive optics scanning light ophthalmoscopy (AOSLO) enables direct visualisation of the cone mosaic, with metrics such as cone density and cell spacing used to assess the integrity or health of the mosaic. Here we examined the interobserver and inter-instrument reliability of cone density measurements.For the interobserver reliability study, 30 subjects with no vision-limiting pathology were imaged. Three image sequences were acquired at a single parafoveal location and aligned to ensure that the three images were from the same retinal location. Ten observers used a semiautomated algorithm to identify the cones in each image, and this was repeated three times for each image. To assess inter-instrument reliability, 20 subjects were imaged at eight parafoveal locations on one AOSLO, followed by the same set of locations on the second AOSLO. A single observer manually aligned the pairs of images and used the semiautomated algorithm to identify the cones in each image.Based on a factorial study design model and a variance components model, the interobserver study's largest contribution to variability was the subject (95.72%) while the observer's contribution was only 1.03%. For the inter-instrument study, an average cone density intraclass correlation coefficient (ICC) of between 0.931 and 0.975 was calculated.With the AOSLOs used here, reliable cone density measurements can be obtained between observers and between instruments. Additional work is needed to determine how these results vary with differences in image quality.

    View details for PubMedID 24855115

  • Microscopic Inner Retinal Hyper-Reflective Phenotypes in Retinal and Neurologic Disease INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE Scoles, D., Higgins, B. P., Cooper, R. F., Dubis, A. M., Summerfelt, P., Weinberg, D. V., Kim, J. E., Stepien, K. E., Carroll, J., Dubra, A. 2014; 55 (7): 4015?29


    We surveyed inner retinal microscopic features in retinal and neurologic disease using a reflectance confocal adaptive optics scanning light ophthalmoscope (AOSLO).Inner retinal images from 101 subjects affected by one of 38 retinal or neurologic conditions and 11 subjects with no known eye disease were examined for the presence of hyper-reflective features other than vasculature, retinal nerve fiber layer, and foveal pit reflex. The hyper-reflective features in the AOSLO images were grouped based on size, location, and subjective texture. Clinical imaging, including optical coherence tomography (OCT), scanning laser ophthalmoscopy, and fundus photography was analyzed for comparison.Seven categories of hyper-reflective inner retinal structures were identified, namely punctate reflectivity, nummular (disc-shaped) reflectivity, granular membrane, waxy membrane, vessel-associated membrane, microcysts, and striate reflectivity. Punctate and nummular reflectivity also was found commonly in normal volunteers, but the features in the remaining five categories were found only in subjects with retinal or neurologic disease. Some of the features were found to change substantially between follow up imaging months apart.Confocal reflectance AOSLO imaging revealed a diverse spectrum of normal and pathologic hyper-reflective inner and epiretinal features, some of which were previously unreported. Notably, these features were not disease-specific, suggesting that they might correspond to common mechanisms of degeneration or repair in pathologic states. Although prospective studies with larger and better characterized populations, along with imaging of more extensive retinal areas are needed, the hyper-reflective structures reported here could be used as disease biomarkers, provided their specificity is studied further.

    View details for DOI 10.1167/iovs.14-14668

    View details for Web of Science ID 000339487000003

    View details for PubMedID 24894394

    View details for PubMedCentralID PMC4078949

  • Relationship Between Foveal Cone Specialization and Pit Morphology in Albinism INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE Wilk, M. A., McAllister, J. T., Cooper, R. F., Dubis, A. M., Patitucci, T. N., Summerfelt, P., Anderson, J. L., Stepien, K. E., Costakos, D. M., Connor, T. B., Wirostko, W. J., Chiang, P., Dubra, A., Curcio, C. A., Brilliant, M. H., Summers, C., Carroll, J. 2014; 55 (7): 4186?98


    Albinism is associated with disrupted foveal development, though intersubject variability is becoming appreciated. We sought to quantify this variability, and examine the relationship between foveal cone specialization and pit morphology in patients with a clinical diagnosis of albinism.We recruited 32 subjects with a clinical diagnosis of albinism. DNA was obtained from 25 subjects, and known albinism genes were analyzed for mutations. Relative inner and outer segment (IS and OS) lengthening (fovea-to-perifovea ratio) was determined from manually segmented spectral domain-optical coherence tomography (SD-OCT) B-scans. Foveal pit morphology was quantified for eight subjects from macular SD-OCT volumes. Ten subjects underwent imaging with adaptive optics scanning light ophthalmoscopy (AOSLO), and cone density was measured.We found mutations in 22 of 25 subjects, including five novel mutations. All subjects lacked complete excavation of inner retinal layers at the fovea, though four subjects had foveal pits with normal diameter and/or volume. Peak cone density and OS lengthening were variable and overlapped with that observed in normal controls. A fifth hyper-reflective band was observed in the outer retina on SD-OCT in the majority of the subjects with albinism.Foveal cone specialization and pit morphology vary greatly in albinism. Normal cone packing was observed in the absence of a foveal pit, suggesting a pit is not required for packing to occur. The degree to which retinal anatomy correlates with genotype or visual function remains unclear, and future examination of larger patient groups will provide important insight on this issue.

    View details for DOI 10.1167/iovs.13-13217

    View details for Web of Science ID 000339487000022

    View details for PubMedID 24845642

    View details for PubMedCentralID PMC4098060

  • In Vivo Imaging of Human Cone Photoreceptor Inner Segments INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE Scoles, D., Sulai, Y. N., Langlo, C. S., Fishman, G. A., Curcio, C. A., Carroll, J., Dubra, A. 2014; 55 (7): 4244?51


    An often overlooked prerequisite to cone photoreceptor gene therapy development is residual photoreceptor structure that can be rescued. While advances in adaptive optics (AO) retinal imaging have recently enabled direct visualization of individual cone and rod photoreceptors in the living human retina, these techniques largely detect strongly directionally-backscattered (waveguided) light from normal intact photoreceptors. This represents a major limitation in using existing AO imaging to quantify structure of remnant cones in degenerating retina.Photoreceptor inner segment structure was assessed with a novel AO scanning light ophthalmoscopy (AOSLO) differential phase technique, that we termed nonconfocal split-detector, in two healthy subjects and four subjects with achromatopsia. Ex vivo preparations of five healthy donor eyes were analyzed for comparison of inner segment diameter to that measured in vivo with split-detector AOSLO.Nonconfocal split-detector AOSLO reveals the photoreceptor inner segment with or without the presence of a waveguiding outer segment. The diameter of inner segments measured in vivo is in good agreement with histology. A substantial number of foveal and parafoveal cone photoreceptors with apparently intact inner segments were identified in patients with the inherited disease achromatopsia.The application of nonconfocal split-detector to emerging human gene therapy trials will improve the potential of therapeutic success, by identifying patients with sufficient retained photoreceptor structure to benefit the most from intervention. Additionally, split-detector imaging may be useful for studies of other retinal degenerations such as AMD, retinitis pigmentosa, and choroideremia where the outer segment is lost before the remainder of the photoreceptor cell.

    View details for DOI 10.1167/iovs.14-14542

    View details for Web of Science ID 000339487000029

    View details for PubMedID 24906859

    View details for PubMedCentralID PMC4095721

  • Comparison of adaptive optics scanning light ophthalmoscopic fluorescein angiography and offset pinhole imaging BIOMEDICAL OPTICS EXPRESS Chui, T. P., Dubow, M., Pinhas, A., Shah, N., Gan, A., Weitz, R., Sulai, Y. N., Dubra, A., Rosen, R. B. 2014; 5 (4): 1173?89


    Recent advances to the adaptive optics scanning light ophthalmoscope (AOSLO) have enabled finer in vivo assessment of the human retinal microvasculature. AOSLO confocal reflectance imaging has been coupled with oral fluorescein angiography (FA), enabling simultaneous acquisition of structural and perfusion images. AOSLO offset pinhole (OP) imaging combined with motion contrast post-processing techniques, are able to create a similar set of structural and perfusion images without the use of exogenous contrast agent. In this study, we evaluate the similarities and differences of the structural and perfusion images obtained by either method, in healthy control subjects and in patients with retinal vasculopathy including hypertensive retinopathy, diabetic retinopathy, and retinal vein occlusion. Our results show that AOSLO OP motion contrast provides perfusion maps comparable to those obtained with AOSLO FA, while AOSLO OP reflectance images provide additional information such as vessel wall fine structure not as readily visible in AOSLO confocal reflectance images. AOSLO OP offers a non-invasive alternative to AOSLO FA without the need for any exogenous contrast agent.

    View details for DOI 10.1364/BOE.5.001173

    View details for Web of Science ID 000334078100017

    View details for PubMedID 24761299

    View details for PubMedCentralID PMC3985984

  • Classification of Human Retinal Microaneurysms Using Adaptive Optics Scanning Light Ophthalmoscope Fluorescein Angiography INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE Dubow, M., Pinhas, A., Shah, N., Cooper, R. F., Gan, A., Gentile, R. C., Hendrix, V., Sulai, Y. N., Carroll, J., Chui, T. P., Walsh, J. B., Weitz, R., Dubra, A., Rosen, R. B. 2014; 55 (3): 1299?1309


    Microaneurysms (MAs) are considered a hallmark of retinal vascular disease, yet what little is known about them is mostly based upon histology, not clinical observation. Here, we use the recently developed adaptive optics scanning light ophthalmoscope (AOSLO) fluorescein angiography (FA) to image human MAs in vivo and to expand on previously described MA morphologic classification schemes.Patients with vascular retinopathies (diabetic, hypertensive, and branch and central retinal vein occlusion) were imaged with reflectance AOSLO and AOSLO FA. Ninety-three MAs, from 14 eyes, were imaged and classified according to appearance into six morphologic groups: focal bulge, saccular, fusiform, mixed, pedunculated, and irregular. The MA perimeter, area, and feret maximum and minimum were correlated to morphology and retinal pathology. Select MAs were imaged longitudinally in two eyes.Adaptive optics scanning light ophthalmoscope fluorescein angiography imaging revealed microscopic features of MAs not appreciated on conventional images. Saccular MAs were most prevalent (47%). No association was found between the type of retinal pathology and MA morphology (P = 0.44). Pedunculated and irregular MAs were among the largest MAs with average areas of 4188 and 4116 ?m(2), respectively. Focal hypofluorescent regions were noted in 30% of MAs and were more likely to be associated with larger MAs (3086 vs. 1448 ?m(2), P = 0.0001).Retinal MAs can be classified in vivo into six different morphologic types, according to the geometry of their two-dimensional (2D) en face view. Adaptive optics scanning light ophthalmoscope fluorescein angiography imaging of MAs offers the possibility of studying microvascular change on a histologic scale, which may help our understanding of disease progression and treatment response.

    View details for DOI 10.1167/iovs.13-13122

    View details for Web of Science ID 000333036500013

    View details for PubMedID 24425852

    View details for PubMedCentralID PMC3943418

  • Visualization of retinal vascular structure and perfusion with a nonconfocal adaptive optics scanning light ophthalmoscope JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION Sulai, Y. N., Scoles, D., Harvey, Z., Dubra, A. 2014; 31 (3): 569?79


    Imaging of the retinal vascular structure and perfusion was explored by confocal illumination and nonconfocal detection in an adaptive optics scanning light ophthalmoscope (AOSLO), as an extension of the work by Chui et al. [Biomed. Opt. Express 3, 2537 (2012)]. Five different detection schemes were evaluated at multiple retinal locations: circular mask, annular mask, circular mask with filament, knife-edge, and split-detector. Given the superior image contrast in the reflectance and perfusion maps, the split-detection method was further tested using pupil apodization, polarized detection, and four different wavelengths. None of these variations provided noticeable contrast improvement. The noninvasive visualization of capillary flow and structure provided by AOSLO split-detection shows great promise for studying ocular and systemic conditions that affect the retinal vasculature.

    View details for DOI 10.1364/JOSAA.31.000569

    View details for Web of Science ID 000332227200016

    View details for PubMedID 24690655

    View details for PubMedCentralID PMC4465430

  • A Lensing Effect of Inner Retinal Cysts on Images of the Photoreceptor Mosaic RETINA-THE JOURNAL OF RETINAL AND VITREOUS DISEASES Langlo, C. S., Flatter, J. A., Dubra, A., Wirostko, W. J., Carroll, J. 2014; 34 (2): 421?22

    View details for DOI 10.1097/IAE.0b013e3182a2f50c

    View details for Web of Science ID 000336959400030

    View details for PubMedID 23974999

    View details for PubMedCentralID PMC3946899

  • Retinal Structure and Function in Achromatopsia Implications for Gene Therapy OPHTHALMOLOGY Sundaram, V., Wilde, C., Aboshiha, J., Cowing, J., Han, C., Langlo, C. S., Chana, R., Davidson, A. E., Sergouniotis, P. I., Bainbridge, J. W., Ali, R. R., Dubra, A., Rubin, G., Webster, A. R., Moore, A. T., Nardini, M., Carroll, J., Michaelides, M. 2014; 121 (1): 234?45


    To characterize retinal structure and function in achromatopsia (ACHM) in preparation for clinical trials of gene therapy.Cross-sectional study.Forty subjects with ACHM.All subjects underwent spectral domain optical coherence tomography (SD-OCT), microperimetry, and molecular genetic testing. Foveal structure on SD-OCT was graded into 5 distinct categories: (1) continuous inner segment ellipsoid (ISe), (2) ISe disruption, (3) ISe absence, (4) presence of a hyporeflective zone (HRZ), and (5) outer retinal atrophy including retinal pigment epithelial loss. Foveal and outer nuclear layer (ONL) thickness was measured and presence of hypoplasia determined.Photoreceptor appearance on SD-OCT imaging, foveal and ONL thickness, presence of foveal hypoplasia, retinal sensitivity and fixation stability, and association of these parameters with age and genotype.Forty subjects with a mean age of 24.9 years (range, 6-52 years) were included. Disease-causing variants were found in CNGA3 (n = 18), CNGB3 (n= 15), GNAT2 (n= 4), and PDE6C (n= 1). No variants were found in 2 individuals. In all, 22.5% of subjects had a continuous ISe layer at the fovea, 27.5% had ISe disruption, 20% hadan absent ISe layer, 22.5% had an HRZ, and 7.5% had outer retinal atrophy. No significant differences in age (P= 0.77), mean retinal sensitivity (P= 0.21), or fixation stability (P= 0.34) across the 5 SD-OCT categories were evident. No correlation was found between age and foveal thickness (P= 0.84) or between age and foveal ONL thickness (P= 0.12).The lack of a clear association of disruption of retinal structure or function in ACHM with age suggests that the window of opportunity for intervention by gene therapy is wider in some individuals than previously indicated. Therefore, the potential benefit for a given subject is likely to be better predicted by specific measurement of photoreceptor structure rather than simply by age. The ability to directly assess cone photoreceptor preservation with SD-OCT and/or adaptive optics imaging is likely to prove invaluable in selecting subjects for future trials and measuring the trials' impact.

    View details for DOI 10.1016/j.ophtha.2013.08.017

    View details for Web of Science ID 000329169500039

    View details for PubMedID 24148654

    View details for PubMedCentralID PMC3895408

  • Human Cone Visual Pigment Deletions Spare Sufficient Photoreceptors to Warrant Gene Therapy HUMAN GENE THERAPY Cideciyan, A. V., Hufnagel, R. B., Carroll, J., Sumaroka, A., Luo, X., Schwartz, S. B., Dubra, A., Land, M., Michaelides, M., Gardner, J. C., Hardcastle, A. J., Moore, A. T., Sisk, R. A., Ahmed, Z. M., Kohl, S., Wissinger, B., Jacobson, S. G. 2013; 24 (12): 993?1006


    Human X-linked blue-cone monochromacy (BCM), a disabling congenital visual disorder of cone photoreceptors, is a candidate disease for gene augmentation therapy. BCM is caused by either mutations in the red (OPN1LW) and green (OPN1MW) cone photoreceptor opsin gene array or large deletions encompassing portions of the gene array and upstream regulatory sequences that would predict a lack of red or green opsin expression. The fate of opsin-deficient cone cells is unknown. We know that rod opsin null mutant mice show rapid postnatal death of rod photoreceptors. Using in vivo histology with high-resolution retinal imaging, we studied a cohort of 20 BCM patients (age range 5-58) with large deletions in the red/green opsin gene array. Already in the first years of life, retinal structure was not normal: there was partial loss of photoreceptors across the central retina. Remaining cone cells had detectable outer segments that were abnormally shortened. Adaptive optics imaging confirmed the existence of inner segments at a spatial density greater than that expected for the residual blue cones. The evidence indicates that human cones in patients with deletions in the red/green opsin gene array can survive in reduced numbers with limited outer segment material, suggesting potential value of gene therapy for BCM.

    View details for DOI 10.1089/hum.2013.153

    View details for Web of Science ID 000328417900527

    View details for PubMedID 24067079

    View details for PubMedCentralID PMC3868405

  • In vivo imaging of retinal pigment epithelium cells in age related macular degeneration BIOMEDICAL OPTICS EXPRESS Rossi, E. A., Rangel-Fonseca, P., Parkins, K., Fischer, W., Latchney, L. R., Folwell, M. A., Williams, D. R., Dubra, A., Chung, M. M. 2013; 4 (11): 2527?39


    Morgan and colleagues demonstrated that the RPE cell mosaic can be resolved in the living human eye non-invasively by imaging the short-wavelength autofluorescence using an adaptive optics (AO) ophthalmoscope. This method, based on the assumption that all subjects have the same longitudinal chromatic aberration (LCA) correction, has proved difficult to use in diseased eyes, and in particular those affected by age-related macular degeneration (AMD). In this work, we improve Morgan's method by accounting for chromatic aberration variations by optimizing the confocal aperture axial and transverse placement through an automated iterative maximization of image intensity. The increase in image intensity after algorithmic aperture placement varied depending upon patient and aperture position prior to optimization but increases as large as a factor of 10 were observed. When using a confocal aperture of 3.4 Airy disks in diameter, images were obtained using retinal radiant exposures of less than 2.44 J/cm(2), which is ~22 times below the current ANSI maximum permissible exposure. RPE cell morphologies that were strikingly similar to those seen in postmortem histological studies were observed in AMD eyes, even in areas where the pattern of fluorescence appeared normal in commercial fundus autofluorescence (FAF) images. This new method can be used to study RPE morphology in AMD and other diseases, providing a powerful tool for understanding disease pathogenesis and progression, and offering a new means to assess the efficacy of treatments designed to restore RPE health.

    View details for DOI 10.1364/BOE.4.002527

    View details for Web of Science ID 000326582500021

    View details for PubMedID 24298413

    View details for PubMedCentralID PMC3829547

  • In vivo dark-field imaging of the retinal pigment epithelium cell mosaic BIOMEDICAL OPTICS EXPRESS Scoles, D., Sulai, Y. N., Dubra, A. 2013; 4 (9): 1710?23


    Non-invasive reflectance imaging of the human RPE cell mosaic is demonstrated using a modified confocal adaptive optics scanning light ophthalmoscope (AOSLO). The confocal circular aperture in front of the imaging detector was replaced with a combination of a circular aperture 4 to 16 Airy disks in diameter and an opaque filament, 1 or 3 Airy disks thick. This arrangement reveals the RPE cell mosaic by dramatically attenuating the light backscattered by the photoreceptors. The RPE cell mosaic was visualized in all 7 recruited subjects at multiple retinal locations with varying degrees of contrast and cross-talk from the photoreceptors. Various experimental settings were explored for improving the visualization of the RPE cell boundaries including: pinhole diameter, filament thickness, illumination and imaging pupil apodization, unmatched imaging and illumination focus, wavelength and polarization. None of these offered an obvious path for enhancing image contrast. The demonstrated implementation of dark-field AOSLO imaging using 790 nm light requires low light exposures relative to light safety standards and it is more comfortable for the subject than the traditional autofluorescence RPE imaging with visible light. Both these factors make RPE dark-field imaging appealing for studying mechanisms of eye disease, as well as a clinical tool for screening and monitoring disease progression.

    View details for DOI 10.1364/BOE.4.001710

    View details for Web of Science ID 000323889800022

    View details for PubMedID 24049692

    View details for PubMedCentralID PMC3771842



    To evaluate retinal structural and functional abnormalities in a patient with acute macular neuroretinopathy.An adaptive optics scanning light ophthalmoscope was used to image the photoreceptor mosaic and assess rod and cone structure. Spectral-domain optical coherence tomography was used to examine retinal lamination. Microperimetry was used to assess function across the macula.Microperimetry showed reduced function of localized areas within retinal lesions corresponding to subjective scotomas. Spectral-domain optical coherence tomography imaging revealed attenuation of two outer retinal bands typically thought to reflect photoreceptor structure. Adaptive optics scanning light ophthalmoscope images of the photoreceptor mosaic revealed a heterogeneous presentation within these lesions. There were areas containing non-waveguiding cones and other areas of decreased cone density where the remaining rods had expanded to fill in the vacant space. Within these lesions, cone densities were shown to be significantly lower than eccentricity-matched areas of normal retina, as well as accepted histologic measurements. A 6-month follow-up revealed no change in rod or cone structure.Imaging of acute macular neuroretinopathy using an adaptive optics scanning light ophthalmoscope shows a preferential disruption of cone photoreceptor structure within the region of decreased retinal sensitivity (as measured by microperimetry). Adaptive optics-based imaging tools provide a noninvasive way to assess photoreceptor structure at a level of detail that is not resolved by use of conventional spectral-domain optical coherence tomography or other clinical measures.

    View details for DOI 10.1097/IAE.0b013e31828cd03a

    View details for Web of Science ID 000330233200021

    View details for PubMedID 23615345

    View details for PubMedCentralID PMC4065781

  • Outer Retinal Structure in Best Vitelliform Macular Dystrophy JAMA OPHTHALMOLOGY Kay, D. B., Land, M. E., Cooper, R. F., Dubis, A. M., Godara, P., Dubra, A., Carroll, J., Stepien, K. E. 2013; 131 (9): 1207?15


    Demonstrating the utility of adaptive optics scanning light ophthalmoscopy (AOSLO) to assess outer retinal structure in Best vitelliform macular dystrophy (BVMD).To characterize outer retinal structure in BVMD using spectral-domain optical coherence tomography (SD-OCT) and AOSLO.Prospective, observational case series. Four symptomatic members of a family with BVMD with known BEST1 mutation were recruited at the Advanced Ocular Imaging Program research lab at the Medical College of Wisconsin Eye Institute, Milwaukee.Thickness of 2 outer retinal layers corresponding to photoreceptor inner and outer segments was measured using SD-OCT. Photoreceptor mosaic AOSLO images within and around visible lesions were obtained, and cone density was assessed in 2 subjects.Photoreceptor structure.Each subject was at a different stage of BVMD, with photoreceptor disruption evident by AOSLO at all stages. When comparing SD-OCT and AOSLO images from the same location, AOSLO images allowed for direct assessment of photoreceptor structure. A variable degree of retained photoreceptors was seen within all lesions. The photoreceptor mosaic immediately adjacent to visible lesions appeared contiguous and was of normal density. Fine hyperreflective structures were visualized by AOSLO, and their anatomical orientation and size were consistent with Henle fibers.AND RELEVANCE: The AOSLO findings indicate that substantial photoreceptor structure persists within active lesions, accounting for good visual acuity in these patients. Despite previous reports of diffuse photoreceptor outer segment abnormalities in BVMD, our data reveal normal photoreceptor structure in areas adjacent to clinical lesions. This study demonstrates the utility of AOSLO for understanding the spectrum of cellular changes that occur in inherited degenerations such as BVMD. Photoreceptors are often significantly affected at various stages of inherited degenerations, and these changes may not be readily apparent with current clinical imaging instrumentation.

    View details for DOI 10.1001/jamaophthalmol.2013.387

    View details for Web of Science ID 000325482400013

    View details for PubMedID 23765342

    View details for PubMedCentralID PMC3968428

  • In vivo imaging of human retinal microvasculature using adaptive optics scanning light ophthalmoscope fluorescein angiography BIOMEDICAL OPTICS EXPRESS Pinhas, A., Dubow, M., Shah, N., Chui, T. Y., Scoles, D., Sulai, Y. N., Weitz, R., Walsh, J. B., Carroll, J., Dubra, A., Rosen, R. B. 2013; 4 (8): 1305?17


    The adaptive optics scanning light ophthalmoscope (AOSLO) allows visualization of microscopic structures of the human retina in vivo. In this work, we demonstrate its application in combination with oral and intravenous (IV) fluorescein angiography (FA) to the in vivo visualization of the human retinal microvasculature. Ten healthy subjects ages 20 to 38 years were imaged using oral (7 and/or 20 mg/kg) and/or IV (500 mg) fluorescein. In agreement with current literature, there were no adverse effects among the patients receiving oral fluorescein while one patient receiving IV fluorescein experienced some nausea and heaving. We determined that all retinal capillary beds can be imaged using clinically accepted fluorescein dosages and safe light levels according to the ANSI Z136.1-2000 maximum permissible exposure. As expected, the 20 mg/kg oral dose showed higher image intensity for a longer period of time than did the 7 mg/kg oral and the 500 mg IV doses. The increased resolution of AOSLO FA, compared to conventional FA, offers great opportunity for studying physiological and pathological vascular processes.

    View details for DOI 10.1364/BOE.4.001305

    View details for Web of Science ID 000322618900006

    View details for PubMedID 24009994

    View details for PubMedCentralID PMC3756583

  • Automatic detection of modal spacing (Yellott's ring) in adaptive optics scanning light ophthalmoscope images OPHTHALMIC AND PHYSIOLOGICAL OPTICS Cooper, R. F., Langlo, C. S., Dubra, A., Carroll, J. 2013; 33 (4): 540?49


    An impediment for the clinical utilisation of ophthalmic adaptive optics imaging systems is the automated assessment of photoreceptor mosaic integrity. Here we propose a fully automated algorithm for estimating photoreceptor density based on the radius of Yellott's ring.The discrete Fourier transform (DFT) was used to obtain the power spectrum for a series of images of the human photoreceptor mosaic. Cell spacing is estimated by least-square fitting an annular pattern with a Gaussian cross section to the power spectrum; the radius of the resulting annulus provides an estimate of the modal spacing of the photoreceptors in the retinal image. The intrasession repeatability of the cone density estimates from the algorithm was evaluated, and the accuracy of the algorithm was validated against direct count estimates from a previous study. Accuracy in the presence of multiple cell types and disruptions in the mosaic was examined using images from four patients with retinal pathology and perifoveal images from two subjects with normal vision.Intrasession repeatability of the power spectrum method was comparable to a fully automated direct counting algorithm, but worse than that for the manually adjusted direct count values. In images of the normal parafoveal cone mosaic, we find good agreement between the power-spectrum derived density and that from the direct counting algorithm. In diseased eyes, the power spectrum method is insensitive to photoreceptor loss, with cone density estimates overestimating the density determined with direct counting. The automated power spectrum method also produced unreliable estimates of rod and cone density in perifoveal images of the photoreceptor mosaic, though manual correction of the initial algorithm output results in density estimates in better agreement with direct count values.We developed and validated an automated algorithm based on the power spectrum for extracting estimates of cone spacing, from which estimates of density can be derived. This approach may be used to estimate cone density in images where not every single cone is visible, though caution is needed, as this robustness becomes a weakness when dealing with images from patients with some retinal diseases. This study represents an important first step in carefully assessing the relative utility of metrics for analysing the photoreceptor mosaic, and similar analyses of other metrics/algorithms are needed.

    View details for DOI 10.1111/opo.12070

    View details for Web of Science ID 000320779800016

    View details for PubMedID 23668233

    View details for PubMedCentralID PMC3690144

  • Automatic cone photoreceptor segmentation using graph theory and dynamic programming BIOMEDICAL OPTICS EXPRESS Chiu, S. J., Lokhnygina, Y., Dubis, A. M., Dubra, A., Carroll, J., Izatt, J. A., Farsiu, S. 2013; 4 (6): 924?37


    Geometrical analysis of the photoreceptor mosaic can reveal subclinical ocular pathologies. In this paper, we describe a fully automatic algorithm to identify and segment photoreceptors in adaptive optics ophthalmoscope images of the photoreceptor mosaic. This method is an extension of our previously described closed contour segmentation framework based on graph theory and dynamic programming (GTDP). We validated the performance of the proposed algorithm by comparing it to the state-of-the-art technique on a large data set consisting of over 200,000 cones and posted the results online. We found that the GTDP method achieved a higher detection rate, decreasing the cone miss rate by over a factor of five.

    View details for DOI 10.1364/BOE.4.000924

    View details for Web of Science ID 000319798200013

    View details for PubMedID 23761854

    View details for PubMedCentralID PMC3675871

  • The Effect of Cone Opsin Mutations on Retinal Structure and the Integrity of the Photoreceptor Mosaic INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE Carroll, J., Dubra, A., Gardner, J. C., Mizrahi-Meissonnier, L., Cooper, R. F., Dubis, A. M., Nordgren, R., Genead, M., Connor, T. B., Stepien, K. E., Sharon, D., Hunt, D. M., Banin, E., Hardcastle, A. J., Moore, A. T., Williams, D. R., Fishman, G., Neitz, J., Neitz, M., Michaelides, M. 2012; 53 (13): 8006?15


    To evaluate retinal structure and photoreceptor mosaic integrity in subjects with OPN1LW and OPN1MW mutations.Eleven subjects were recruited, eight of whom have been previously described. Cone and rod density was measured using images of the photoreceptor mosaic obtained from an adaptive optics scanning light ophthalmoscope (AOSLO). Total retinal thickness, inner retinal thickness, and outer nuclear layer plus Henle fiber layer (ONL+HFL) thickness were measured using cross-sectional spectral-domain optical coherence tomography (SD-OCT) images. Molecular genetic analyses were performed to characterize the OPN1LW/OPN1MW gene array.While disruptions in retinal lamination and cone mosaic structure were observed in all subjects, genotype-specific differences were also observed. For example, subjects with "L/M interchange" mutations resulting from intermixing of ancestral OPN1LW and OPN1MW genes had significant residual cone structure in the parafovea (?25% of normal), despite widespread retinal disruption that included a large foveal lesion and thinning of the parafoveal inner retina. These subjects also reported a later-onset, progressive loss of visual function. In contrast, subjects with the C203R missense mutation presented with congenital blue cone monochromacy, with retinal lamination defects being restricted to the ONL+HFL and the degree of residual cone structure (8% of normal) being consistent with that expected for the S-cone submosaic.The photoreceptor phenotype associated with OPN1LW and OPN1MW mutations is highly variable. These findings have implications for the potential restoration of visual function in subjects with opsin mutations. Our study highlights the importance of high-resolution phenotyping to characterize cellular structure in inherited retinal disease; such information will be critical for selecting patients most likely to respond to therapeutic intervention and for establishing a baseline for evaluating treatment efficacy.

    View details for DOI 10.1167/iovs.12-11087

    View details for Web of Science ID 000313056000013

    View details for PubMedID 23139274

    View details for PubMedCentralID PMC3816954

  • Assessing Retinal Structure in Complete Congenital Stationary Night Blindness and Oguchi Disease AMERICAN JOURNAL OF OPHTHALMOLOGY Godara, P., Cooper, R. F., Sergouniotis, P. I., Diederichs, M. A., Streb, M. R., Genead, M. A., McAnany, J., Webster, A. R., Moore, A. T., Dubis, A. M., Neitz, M., Dubra, A., Stone, E. M., Fishman, G. A., Han, D. P., Michaelides, M., Carroll, J. 2012; 154 (6): 987?1001


    To examine retinal structure and changes in photoreceptor intensity after dark adaptation in patients with complete congenital stationary night blindness and Oguchi disease.Prospective, observational case series.We recruited 3 patients with complete congenital stationary night blindness caused by mutations in GRM6, 2 brothers with Oguchi disease caused by mutations in GRK1, and 1 normal control. Retinal thickness was measured from optical coherence tomography images. Integrity of the rod and cone mosaic was assessed using adaptive optics scanning light ophthalmoscopy. We imaged 5 of the patients after a period of dark adaptation and examined layer reflectivity on optical coherence tomography in a patient with Oguchi disease under light- and dark-adapted conditions.Retinal thickness was reduced in the parafoveal region in patients with GRM6 mutations as a result of decreased thickness of the inner retinal layers. All patients had normal photoreceptor density at all locations analyzed. On removal from dark adaptation, the intensity of the rods (but not cones) in the patients with Oguchi disease gradually and significantly increased. In 1 Oguchi disease patient, the outer segment layer contrast on optical coherence tomography was 4-fold higher under dark-adapted versus light-adapted conditions.The selective thinning of the inner retinal layers in patients with GRM6 mutations suggests either reduced bipolar or ganglion cell numbers or altered synaptic structure in the inner retina. Our finding that rods, but not cones, change intensity after dark adaptation suggests that fundus changes in Oguchi disease are the result of changes within the rods as opposed to changes at a different retinal locus.

    View details for DOI 10.1016/j.ajo.2012.06.003

    View details for Web of Science ID 000311878800011

    View details for PubMedID 22959359

    View details for PubMedCentralID PMC3498541

  • First-order design of a reflective viewfinder for adaptive optics ophthalmoscopy OPTICS EXPRESS Dubra, A., Sulai, Y. N. 2012; 20 (24): 26596?605


    Adaptive optics (AO) ophthalmoscopes with small fields of view have limited clinical utility. We propose to address this problem in reflective instruments by incorporating a viewfinder pupil relay designed by considering pupil and image centering and conjugation. Diverting light from an existing pupil optical relay to the viewfinder relay allows switching field of view size. Design methods that meet all four centering and conjugation conditions using either a single concave mirror or with two concave mirrors forming an off-axis afocal telescope are presented. Two different methods for calculating the focal length and orientation of the concave mirrors in the afocal viewfinder relay are introduced. Finally, a 2.2 viewfinder mode is demonstrated in an AO scanning light ophthalmoscope.

    View details for DOI 10.1364/OE.20.026596

    View details for Web of Science ID 000312452800049

    View details for PubMedID 23187514

    View details for PubMedCentralID PMC3601596

  • Repeatability of In Vivo Parafoveal Cone Density and Spacing Measurements OPTOMETRY AND VISION SCIENCE Garrioch, R., Langlo, C., Dubis, A. M., Cooper, R. F., Dubra, A., Carroll, J. 2012; 89 (5): 632?43


    To assess the repeatability and measurement error associated with cone density and nearest neighbor distance (NND) estimates in images of the parafoveal cone mosaic obtained with an adaptive optics scanning light ophthalmoscope (AOSLO).Twenty-one participants with no known ocular pathology were recruited. Four retinal locations, approximately 0.65 eccentricity from the center of fixation, were imaged 10 times in randomized order with an AOSLO. Cone coordinates in each image were identified using an automated algorithm (with or without manual correction) from which cone density and NND were calculated. Owing to naturally occurring fixational instability, the 10 images recorded from a given location did not overlap entirely. We thus analyzed each image set both before and after alignment.Automated estimates of cone density on the unaligned image sets showed a coefficient of repeatability of 11,769 cones/mm(2) (17.1%). The primary reason for this variability appears to be fixational instability, as aligning the 10 images to include the exact same retinal area results in an improved repeatability of 4358 cones/mm(2) (6.4%) using completely automated cone identification software. Repeatability improved further by manually identifying cones missed by the automated algorithm, with a coefficient of repeatability of 1967 cones/mm(2) (2.7%). NND showed improved repeatability and was generally insensitive to the undersampling by the automated algorithm.As our data were collected in a young, healthy population, this likely represents a best-case estimate for corresponding measurements in patients with retinal disease. Similar studies need to be carried out on other imaging systems (including those using different imaging modalities, wavefront correction technology, and/or image analysis software), as repeatability would be expected to be highly sensitive to initial image quality and the performance of cone identification algorithms. Separate studies addressing intersession repeatability and interobserver reliability are also needed.

    View details for DOI 10.1097/OPX.0b013e3182540562

    View details for Web of Science ID 000303654800023

    View details for PubMedID 22504330

    View details for PubMedCentralID PMC3348369

  • Adaptive optics retinal imaging in the living mouse eye BIOMEDICAL OPTICS EXPRESS Geng, Y., Dubra, A., Yin, L., Merigan, W. H., Sharma, R., Libby, R. T., Williams, D. R. 2012; 3 (4): 715?34


    Correction of the eye's monochromatic aberrations using adaptive optics (AO) can improve the resolution of in vivo mouse retinal images [Biss et al., Opt. Lett. 32(6), 659 (2007) and Alt et al., Proc. SPIE 7550, 755019 (2010)], but previous attempts have been limited by poor spot quality in the Shack-Hartmann wavefront sensor (SHWS). Recent advances in mouse eye wavefront sensing using an adjustable focus beacon with an annular beam profile have improved the wavefront sensor spot quality [Geng et al., Biomed. Opt. Express 2(4), 717 (2011)], and we have incorporated them into a fluorescence adaptive optics scanning laser ophthalmoscope (AOSLO). The performance of the instrument was tested on the living mouse eye, and images of multiple retinal structures, including the photoreceptor mosaic, nerve fiber bundles, fine capillaries and fluorescently labeled ganglion cells were obtained. The in vivo transverse and axial resolutions of the fluorescence channel of the AOSLO were estimated from the full width half maximum (FWHM) of the line and point spread functions (LSF and PSF), and were found to be better than 0.79 ?m 0.03 ?m (STD)(45% wider than the diffraction limit) and 10.8 ?m 0.7 ?m (STD)(two times the diffraction limit), respectively. The axial positional accuracy was estimated to be 0.36 ?m. This resolution and positional accuracy has allowed us to classify many ganglion cell types, such as bistratified ganglion cells, in vivo.

    View details for DOI 10.1364/BOE.3.000715

    View details for Web of Science ID 000302788200005

    View details for PubMedID 22574260

    View details for PubMedCentralID PMC3345801

  • Relationship between the Foveal Avascular Zone and Foveal Pit Morphology INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE Dubis, A. M., Hansen, B. R., Cooper, R. F., Beringer, J., Dubra, A., Carroll, J. 2012; 53 (3): 1628?36


    To assess the relationship between foveal pit morphology and size of the foveal avascular zone (FAZ).Forty-two subjects were recruited. Volumetric images of the macula were obtained using spectral domain optical coherence tomography. Images of the FAZ were obtained using either a modified fundus camera or an adaptive optics scanning light ophthalmoscope. Foveal pit metrics (depth, diameter, slope, volume, and area) were automatically extracted from retinal thickness data, whereas the FAZ was manually segmented by two observers to extract estimates of FAZ diameter and area.Consistent with previous reports, the authors observed significant variation in foveal pit morphology. The average foveal pit volume was 0.081 mm(3) (range, 0.022 to 0.190 mm(3)). The size of the FAZ was also highly variable between persons, with FAZ area ranging from 0.05 to 1.05 mm(2) and FAZ diameter ranging from 0.20 to 1.08 mm. FAZ area was significantly correlated with foveal pit area, depth, and volume; deeper and broader foveal pits were associated with larger FAZs.Although these results are consistent with predictions from existing models of foveal development, more work is needed to confirm the developmental link between the size of the FAZ and the degree of foveal pit excavation. In addition, more work is needed to understand the relationship between these and other anatomic features of the human foveal region, including peak cone density, rod-free zone diameter, and Henle fiber layer.

    View details for DOI 10.1167/iovs.11-8488

    View details for Web of Science ID 000302790700073

    View details for PubMedID 22323466

    View details for PubMedCentralID PMC3339921

  • Subclinical Photoreceptor Disruption in Response to Severe Head Trauma ARCHIVES OF OPHTHALMOLOGY Stepien, K. E., Martinez, W. M., Dubis, A. M., Cooper, R. F., Dubra, A., Carroll, J. 2012; 130 (3): 400?402
  • Retinal Crystals in Type 2 Idiopathic Macular Telangiectasia OPHTHALMOLOGY Sallo, F. B., Leung, I., Chung, M., Wolf-Schnurrbusch, U. K., Dubra, A., Williams, D. R., Clemons, T., Pauleikhoff, D., Bird, A. C., Peto, T., MacTel Study Grp 2011; 118 (12): 2461?67


    To characterize the phenotype and investigate the associations of intraretinal crystalline deposits in a large cohort with type 2 idiopathic macular telangiectasia (MacTel).Case-control study.Patients with and without retinal crystals from the Macular Telangiectasia Project, an international multicenter prospective study of type 2 MacTel.Grading of stereoscopic 30-degree color fundus (CF), confocal blue light reflectance (CBR), red-free (RF), and infrared (IR) images was performed according to the MacTel Natural History Study protocol and staged using the classification system devised by Gass and Blodi. Spectral domain-optical coherence tomography (SD-OCT) and adaptive optics imaging were used for a finer analysis of the phenotype. Associations between crystals and other characteristics of the disease, as well as potential risk factors, were investigated.Presence of crystals, fundus signs of MacTel, clinical characteristics, and presence of potential risk factors of MacTel.Of 443 probands enrolled in the MacTel study, 203 (46%) had crystalline deposits present; 60% of the cases were bilateral at baseline. Eyes with crystals had a mean letter score of 70.7 (standard deviation [SD] = 15.9), whereas those without crystals had a mean letter score of 66.5 (SD = 15.5, P < 0.001). Crystals were present at all stages of the disease and showed high reflectivity within a wide wavelength range. They were located at the anterior surface of the nerve fiber layer, arranged along the nerve fibers, within an annular area centered on the fovea. Significant associations of crystalline deposits were found with a loss of retinal transparency, macular pigment optical density (MPOD) loss, fluorescein leakage, retinal thickness, and a break in the inner segment/outer segment junction line. Associations with environmental risk factors were not found.Intraretinal crystals are a frequent phenomenon associated with type 2 MacTel. They may appear at all stages and aid in the early diagnosis of the disease. Their morphology further implicates Mller cells in the pathogenesis of the disease. Insight into their physical and chemical properties may provide clues to the metabolic pathways involved in the pathogenesis of the disease.Proprietary or commercial disclosure may be found after the references.

    View details for DOI 10.1016/j.ophtha.2011.05.022

    View details for Web of Science ID 000298138000023

    View details for PubMedID 21839520

    View details for PubMedCentralID PMC3433242

  • Spatial and temporal variation of rod photoreceptor reflectance in the human retina BIOMEDICAL OPTICS EXPRESS Cooper, R. F., Dubis, A. M., Pavaskar, A., Rha, J., Dubra, A., Carroll, J. 2011; 2 (9): 2577?89


    Using adaptive optics imaging tools to image the living retina, numerous investigators have reported temporal fluctuation in the reflectivity of individual cone photoreceptors. In addition, there is cone-to-cone (spatial) variation in reflectivity. As it has only recently become possible to image the complete rod photoreceptor mosaic in the living human retina, we sought to characterize the reflectivity of individual rods and compare their behavior to that of foveal/parafoveal cones. Across two subjects, we were able to successfully track the reflectance behavior of 1,690 rods and 1,980 cones over 12 hours. Rod and cone photoreceptors showed similar regional and temporal variability in their reflectance profiles, suggesting the presence of a common governing physiological process. Within the rod and cone mosaics, there was no sign of spatial clumping of reflectance profile behavior; that is, the arrangement of cells of a given archetypal reflectance profile within the mosaic was indistinguishable from random. These data demonstrate the ability to track the behavior of rod reflectivity over time. Finally, as these and other reflectance changes may be an indicator of photoreceptor function, a future extension of this method will be to analyze this behavior in patients with rod photoreceptor dysfunction (e.g., retinitis pigmentosa, Usher's syndrome, and congenital stationary night blindness).

    View details for DOI 10.1364/BOE.2.002577

    View details for Web of Science ID 000299883200013

    View details for PubMedID 21991550

    View details for PubMedCentralID PMC3184867

  • Photoreceptor Structure and Function in Patients with Congenital Achromatopsia INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE Genead, M. A., Fishman, G. A., Rha, J., Dubis, A. M., Bonci, D. O., Dubra, A., Stone, E. M., Neitz, M., Carroll, J. 2011; 52 (10): 7298?7308


    To assess photoreceptor structure and function in patients with congenital achromatopsia.Twelve patients were enrolled. All patients underwent a complete ocular examination, spectral-domain optical coherence tomography (SD-OCT), full-field electroretinographic (ERG), and color vision testing. Macular microperimetry (MP; in four patients) and adaptive optics (AO) imaging (in nine patients) were also performed. Blood was drawn for screening of disease-causing genetic mutations.Mean ( SD) age was 30.8 ( 16.6) years. Mean best-corrected visual acuity was 0.85 ( 0.14) logarithm of the minimal angle of resolution (logMAR) units. Seven patients (58.3%) showed either an absent foveal reflex or nonspecific retinal pigment epithelium mottling to mild hypopigmentary changes on fundus examination. Two patients showed an atrophic-appearing macular lesion. On anomaloscopy, only 5 patients matched over the entire range from 0 to 73. SD-OCT examination showed a disruption or loss of the macular inner/outer segments (IS/OS) junction of the photoreceptors in 10 patients (83.3%). Seven of these patients showed an optically empty space at the level of the photoreceptors in the fovea. AO images of the photoreceptor mosaic were highly variable but significantly disrupted from normal. On ERG testing, 10 patients (83.3%) showed evidence of residual cone responses to a single-flash stimulus response. The macular MP testing showed that the overall mean retinal sensitivity was significantly lower than normal (12.0 vs. 16.9 dB, P < 0.0001).The current approach of using high-resolution techniques to assess photoreceptor structure and function in patients with achromatopsia should be useful in guiding selection of patients for future therapeutic trials as well as monitoring therapeutic response in these trials.

    View details for DOI 10.1167/iovs.11-7762

    View details for Web of Science ID 000295467200035

    View details for PubMedID 21778272

    View details for PubMedCentralID PMC3183969

  • Noninvasive imaging of the human rod photoreceptor mosaic using a confocal adaptive optics scanning ophthalmoscope BIOMEDICAL OPTICS EXPRESS Dubra, A., Sulai, Y., Norris, J. L., Cooper, R. F., Dubis, A. M., Williams, D. R., Carroll, J. 2011; 2 (7): 1864?76


    The rod photoreceptors are implicated in a number of devastating retinal diseases. However, routine imaging of these cells has remained elusive, even with the advent of adaptive optics imaging. Here, we present the first in vivo images of the contiguous rod photoreceptor mosaic in nine healthy human subjects. The images were collected with three different confocal adaptive optics scanning ophthalmoscopes at two different institutions, using 680 and 775 nm superluminescent diodes for illumination. Estimates of photoreceptor density and rod:cone ratios in the 5-15 retinal eccentricity range are consistent with histological findings, confirming our ability to resolve the rod mosaic by averaging multiple registered images, without the need for additional image processing. In one subject, we were able to identify the emergence of the first rods at approximately 190 ?m from the foveal center, in agreement with previous histological studies. The rod and cone photoreceptor mosaics appear in focus at different retinal depths, with the rod mosaic best focus (i.e., brightest and sharpest) being at least 10 ?m shallower than the cones at retinal eccentricities larger than 8. This study represents an important step in bringing high-resolution imaging to bear on the study of rod disorders.

    View details for DOI 10.1364/BOE.2.001864

    View details for Web of Science ID 000299879500009

    View details for PubMedID 21750765

    View details for PubMedCentralID PMC3130574

  • Reflective afocal broadband adaptive optics scanning ophthalmoscope BIOMEDICAL OPTICS EXPRESS Dubra, A., Sulai, Y. 2011; 2 (6): 1757?68


    A broadband adaptive optics scanning ophthalmoscope (BAOSO) consisting of four afocal telescopes, formed by pairs of off-axis spherical mirrors in a non-planar arrangement, is presented. The non-planar folding of the telescopes is used to simultaneously reduce pupil and image plane astigmatism. The former improves the adaptive optics performance by reducing the root-mean-square (RMS) of the wavefront and the beam wandering due to optical scanning. The latter provides diffraction limited performance over a 3 diopter (D) vergence range. This vergence range allows for the use of any broadband light source(s) in the 450-850 nm wavelength range to simultaneously image any combination of retinal layers. Imaging modalities that could benefit from such a large vergence range are optical coherence tomography (OCT), multi- and hyper-spectral imaging, single- and multi-photon fluorescence. The benefits of the non-planar telescopes in the BAOSO are illustrated by resolving the human foveal photoreceptor mosaic in reflectance using two different superluminescent diodes with 680 and 796 nm peak wavelengths, reaching the eye with a vergence of 0.76 D relative to each other.

    View details for DOI 10.1364/BOE.2.001757

    View details for Web of Science ID 000299878800032

    View details for PubMedID 21698035

    View details for PubMedCentralID PMC3114240

  • Variability in parafoveal cone mosaic in normal trichromatic individuals BIOMEDICAL OPTICS EXPRESS Dees, E. W., Dubra, A., Baraas, R. C. 2011; 2 (5): 1351?58
  • Optical properties of the mouse eye BIOMEDICAL OPTICS EXPRESS Geng, Y., Schery, L., Sharma, R., Dubra, A., Ahmad, K., Libby, R. T., Williams, D. R. 2011; 2 (4): 717?38


    The Shack-Hartmann wavefront sensor (SHWS) spots upon which ocular aberration measurements depend have poor quality in mice due to light reflected from multiple retinal layers. We have designed and implemented a SHWS that can favor light from a specific retinal layer and measured monochromatic aberrations in 20 eyes from 10 anesthetized C57BL/6J mice. Using this instrument, we show that mice are myopic, not hyperopic as is frequently reported. We have also measured longitudinal chromatic aberration (LCA) of the mouse eye and found that it follows predictions of the water-filled schematic mouse eye. Results indicate that the optical quality of the mouse eye assessed by measurement of its aberrations is remarkably good, better for retinal imaging than the human eye. The dilated mouse eye has a much larger numerical aperture (NA) than that of the dilated human eye (0.5 NA vs. 0.2 NA), but it has a similar amount of root mean square (RMS) higher order aberrations compared to the dilated human eye. These measurements predict that adaptive optics based on this method of wavefront sensing will provide improvements in retinal image quality and potentially two times higher lateral resolution than that in the human eye.

    View details for DOI 10.1364/BOE.2.000717

    View details for Web of Science ID 000299876900001

    View details for PubMedID 21483598

    View details for PubMedCentralID PMC3072116

  • Race- and Sex-Related Differences in Retinal Thickness and Foveal Pit Morphology Wagner-Schuman, M., Dubis, A. M., Nordgren, R. N., Lei, Y., Odell, D., Chiao, H., Weh, E., Fischer, W., Sulai, Y., Dubra, A., Carroll, J. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2011: 625?34


    To examine sex- and race-associated differences in macular thickness and foveal pit morphology by using spectral-domain optical coherence tomography (SD-OCT).One hundred eighty eyes of 90 healthy patients (43 women, 47 men) underwent retinal imaging with spectral-domain OCT. The lateral scale of each macular volume scan was corrected for individual differences in axial length by ocular biometry. From these corrected volumes, Early Treatment Diabetic Retinopathy Study (ETDRS) grids of retinal thickness were generated and compared between the groups. Foveal morphology was measured with previously described algorithms.Compared with the Caucasians, the Africans and African Americans had reduced central subfield thickness. Central subfield thickness was also reduced in the women compared with the men, although the women also showed significant thinning in parafoveal regions. There was no difference between the sexes in foveal pit morphology; however, the Africans/African Americans had significantly deeper and broader foveal pits than the Caucasians.Previous studies have reported race- and sex-associated differences in macular thickness, and the inference has been that these differences represent similar anatomic features. However, the data on pit morphology collected in the present study reveal an important and significant variation. Between the sexes, the differences are due to global variability in retinal thickness, whereas the variation in thickness observed between the races appears to be driven by differences in foveal pit morphology. These differences have important implications for the use of SD-OCT in detecting and diagnosing retinal disease.

    View details for DOI 10.1167/iovs.10-5886

    View details for Web of Science ID 000287097400037

    View details for PubMedID 20861480

    View details for PubMedCentralID PMC3053303

  • Images of photoreceptors in living primate eyes using adaptive optics two-photon ophthalmoscopy BIOMEDICAL OPTICS EXPRESS Hunter, J. J., Masella, B., Dubra, A., Sharma, R., Yin, L., Merigan, W. H., Palczewska, G., Palczewski, K., Williams, D. R. 2011; 2 (1): 139?48


    In vivo two-photon imaging through the pupil of the primate eye has the potential to become a useful tool for functional imaging of the retina. Two-photon excited fluorescence images of the macaque cone mosaic were obtained using a fluorescence adaptive optics scanning laser ophthalmoscope, overcoming the challenges of a low numerical aperture, imperfect optics of the eye, high required light levels, and eye motion. Although the specific fluorophores are as yet unknown, strong in vivo intrinsic fluorescence allowed images of the cone mosaic. Imaging intact ex vivo retina revealed that the strongest two-photon excited fluorescence signal comes from the cone inner segments. The fluorescence response increased following light stimulation, which could provide a functional measure of the effects of light on photoreceptors.

    View details for DOI 10.1364/BOE.2.000139

    View details for Web of Science ID 000299872300014

    View details for PubMedID 21326644

    View details for PubMedCentralID PMC3028489

  • Registration of 2D Images from Fast Scanning Ophthalmic Instruments Dubra, A., Harvey, Z., Fischer, B., Dawant, B. M., Lorenz, C. SPRINGER-VERLAG BERLIN. 2010: 60?71
  • In Vivo Imaging of Microscopic Structures in the Rat Retina INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE Geng, Y., Greenberg, K. P., Wolfe, R., Gray, D. C., Hunter, J. J., Dubra, A., Flannery, J. G., Williams, D. R., Porter, J. 2009; 50 (12): 5872?79


    The ability to resolve single retinal cells in rodents in vivo has applications in rodent models of the visual system and retinal disease. The authors have characterized the performance of a fluorescence adaptive optics scanning laser ophthalmoscope (fAOSLO) that provides cellular and subcellular imaging of rat retina in vivo.Enhanced green fluorescent protein (eGFP) was expressed in retinal ganglion cells of normal Sprague-Dawley rats via intravitreal injections of adeno-associated viral vectors. Simultaneous reflectance and fluorescence retinal images were acquired using the fAOSLO. fAOSLO resolution was characterized by comparing in vivo images with subsequent imaging of retinal sections from the same eyes using confocal microscopy.Retinal capillaries and eGFP-labeled ganglion cell bodies, dendrites, and axons were clearly resolved in vivo with adaptive optics. Adaptive optics correction reduced the total root mean square wavefront error, on average, from 0.30 microm to 0.05 microm (measured at 904 nm, 1.7-mm pupil). The full width at half maximum (FWHM) of the average in vivo line-spread function (LSF) was approximately 1.84 microm, approximately 82% greater than the FWHM of the diffraction-limited LSF.With perfect aberration compensation, the in vivo resolution in the rat eye could be approximately 2x greater than that in the human eye because of its large numerical aperture (approximately 0.43). Although the fAOSLO corrects a substantial fraction of the rat eye's aberrations, direct measurements of retinal image quality reveal some blur beyond that expected from diffraction. Nonetheless, subcellular features can be resolved, offering promise for using adaptive optics to investigate the rodent eye in vivo with high resolution.

    View details for DOI 10.1167/iovs.09-3675

    View details for Web of Science ID 000272355900050

    View details for PubMedID 19578019

    View details for PubMedCentralID PMC2873188

  • First-order design of off-axis reflective ophthalmic adaptive optics systems using afocal telescopes OPTICS EXPRESS Gomez-Vieyra, A., Dubra, A., Malacara-Hernandez, D., Williams, D. R. 2009; 17 (21): 18906?19


    Expressions for minimal astigmatism in image and pupil planes in off-axis afocal reflective telescopes formed by pairs of spherical mirrors are presented. These formulae which are derived from the marginal ray fan equation can be used for designing laser cavities, spectrographs and adaptive optics retinal imaging systems. The use, range and validity of these formulae are limited by spherical aberration and coma for small and large angles respectively. This is discussed using examples from adaptive optics retinal imaging systems. The performance of the resulting optical designs are evaluated and compared against the configurations with minimal wavefront RMS, using the defocus-corrected wavefront RMS as a metric.

    View details for DOI 10.1364/OE.17.018906

    View details for Web of Science ID 000270766800057

    View details for PubMedID 20372626

  • In Vivo Autofluorescence Imaging of the Human and Macaque Retinal Pigment Epithelial Cell Mosaic INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE Morgan, J. W., Dubra, A., Wolfe, R., Merigan, W. H., Williams, D. R. 2009; 50 (3): 1350?59


    Retinal pigment epithelial (RPE) cells are critical for the health of the retina, especially the photoreceptors. A recent study demonstrated that individual RPE cells could be imaged in macaque in vivo by detecting autofluorescence with an adaptive optics scanning laser ophthalmoscope (AOSLO). The current study extended this method to image RPE cells in fixating humans in vivo and to quantify the RPE mosaic characteristics in the central retina of normal humans and macaques.The retina was imaged simultaneously with two light channels in a fluorescence AOSLO; one channel was used for reflectance imaging of the cones while the other detected RPE autofluorescence. The excitation light was 568 nm, and emission was detected over a 40-nm range centered at 624 nm. Reflectance frames were registered to determine interframe eye motion, the motion was corrected in the simultaneously recorded autofluorescence frames, and the autofluorescence frames were averaged to give the final RPE mosaic image.In vivo imaging demonstrated that with increasing eccentricity, RPE cell density, and mosaic regularity decreased, whereas RPE cell size and spacing increased. Repeat measurements of the same retinal location 42 days apart showed the same RPE cells and distribution.The RPE cell mosaic has been resolved for the first time in alert fixating human subjects in vivo using AOSLO. Mosaic analysis provides a quantitative database for studying normal and diseased RPE in vivo. This technique will allow longitudinal studies to track disease progression and assess treatment efficacy in patients and animal models of retinal disease.

    View details for DOI 10.1167/iovs.08-2618

    View details for Web of Science ID 000263665000049

    View details for PubMedID 18952914

    View details for PubMedCentralID PMC2790524

  • In vivo imaging of the fine structure of rhodamine-labeled macaque retinal ganglion cells Gray, D. C., Wolfe, R., Gee, B. P., Scoles, D., Geng, Y., Masella, B. D., Dubra, A., Luque, S., Williams, D. R., Merigan, W. H. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2008: 467?73


    The extent to which the fine structure of single ganglion cells, such as dendrites and axons, can be resolved in retinal images obtained from the living primate eye was investigated.Macaque retinal ganglion cells were labeled with retrograde transport of rhodamine dextran injected into the lateral geniculate nucleus. Fluorescence images of the ganglion cells were obtained in vivo with an adaptive optics scanning laser ophthalmoscope.Axons and dendritic arborization could be resolved in primate retinal ganglion cells in vivo, comparing favorably in detail with ex vivo confocal images of the same cells. The full width at half maximum of the transverse line spread function (LSF) was 1.6 microm, and that of the axial point spread function (PSF) was 115 microm. The axial positional accuracy of fluorescence-labeled objects was approximately 4 microm.This in vivo method applied to ganglion cells demonstrates that structures smaller than the somas of typical retinal cells can be accessible in living eyes. Similar approaches may be applied to image other relatively transparent retinal structures, providing a potentially valuable tool for microscopic examination of the normal and diseased living retina.

    View details for DOI 10.1167/iovs.07-0605

    View details for Web of Science ID 000252747000061

    View details for PubMedID 18172127

  • Wavefront sensor and wavefront corrector matching in adaptive optics OPTICS EXPRESS Dubra, A. 2007; 15 (6): 2762?69


    Matching wavefront correctors and wavefront sensors by minimizing the condition number and mean wavefront variance is proposed. The particular cases of two continuous-sheet deformable mirrors and a Shack-Hartmann wavefront sensor with square packing geometry are studied in the presence of photon noise, background noise and electronics noise. Optimal number of lenslets across each actuator are obtained for both deformable mirrors, and a simple experimental procedure for optimal alignment is described. The results show that high-performance adaptive optics can be achieved even with low cost off-the-shelf Shack-Hartmann arrays with lenslet spacing that do not necessarily match those of the wavefront correcting elements.

    View details for DOI 10.1364/OE.15.002762

    View details for Web of Science ID 000245076200001

    View details for PubMedID 19532513

    View details for PubMedCentralID PMC4793900

  • In vivo fluorescence imaging of primate retinal ganglion cells and retinal pigment epithelial cells OPTICS EXPRESS Gray, D. C., Merigan, W., Wolfing, J. I., Gee, B. P., Porter, J., Dubra, A., Twietmeyer, T. H., Ahmad, K., Tumbar, R., Reinholz, F., Williams, D. R. 2006; 14 (16): 7144?58


    The ability to resolve single cells noninvasively in the living retina has important applications for the study of normal retina, diseased retina, and the efficacy of therapies for retinal disease. We describe a new instrument for high-resolution, in vivo imaging of the mammalian retina that combines the benefits of confocal detection, adaptive optics, multispectral, and fluorescence imaging. The instrument is capable of imaging single ganglion cells and their axons through retrograde transport in ganglion cells of fluorescent dyes injected into the monkey lateral geniculate nucleus (LGN). In addition, we demonstrate a method involving simultaneous imaging in two spectral bands that allows the integration of very weak signals across many frames despite inter-frame movement of the eye. With this method, we are also able to resolve the smallest retinal capillaries in fluorescein angiography and the mosaic of retinal pigment epithelium (RPE) cells with lipofuscin autofluorescence.

    View details for DOI 10.1364/OE.14.007144

    View details for Web of Science ID 000239861100018

    View details for PubMedID 19529085

  • Preisach classical and nonlinear modeling of hysteresis in piezoceramic deformable mirrors OPTICS EXPRESS Dubra, A., Massa, J. S., Paterson, C. 2005; 13 (22): 9062?70


    In this work the Preisach classical and nonlinear models are used to model the hysteretic response of a piezoceramic deformable mirror for use in adaptive optics. Experimental results show that both models predict the mirror behavior to within 5% root-mean-squared (rms) error. An inversion algorithm of the Preisach classical model for linearization of the mirror response was implemented and tested in an open-loop adaptive optics system using a Shack-Hartmann (SH) sensor. Measured errors were reduced from 20% rms to around 3%.

    View details for DOI 10.1364/OPEX.13.009062

    View details for Web of Science ID 000232977500043

    View details for PubMedID 19498942

  • Double lateral shearing interferometer for the quantitative measurement of tear film topography APPLIED OPTICS Dubra, A., Paterson, C., Dainty, C. 2005; 44 (7): 1191?99


    A lateral shearing interferometer designed and built for the study of the precorneal tear film topography dynamics and its effect on visual performance is presented. Simple data processing algorithms are discussed and tested on data illustrating different tear topography features: postblink tear undulation, tear breakup, eyelid-produced bumps and ridges, bubbles, and rough precontact lens tear surfaces.

    View details for DOI 10.1364/AO.44.001191

    View details for Web of Science ID 000227459600011

    View details for PubMedID 15765699

  • Study of the tear topography dynamics using a lateral shearing interferometer OPTICS EXPRESS Dubra, A., Paterson, C., Dainty, C. 2004; 12 (25): 6278?88


    The dynamics of the pre-corneal tear film topography are studied on 21 subjects with a purpose-built lateral shearing interferometer. Interesting tear topography features such as post-blink undulation, break-up, eyelid-produced bumps/ridges, bubbles and rough pre-contact lens tear surfaces were recorded. Using the calculated tear topography maps, the effects of the tear dynamics in visual performance, refractive surgery and ophthalmic adaptive optics are discussed in terms of wavefront RMS. The potential of lateral shearing interferometry for clinical applications such as dry eye diagnosis and contact lens performance studies is illustrated by the recorded topography features such as post-blink undulation, break-up, eyelid-produced bumps/ridges, bubbles and rough tear surfaces in front of contact lenses.

    View details for DOI 10.1364/OPEX.12.006278

    View details for Web of Science ID 000225708300025

    View details for PubMedID 19488274

  • Wave-front reconstruction from shear phase maps by use of the discrete Fourier transform APPLIED OPTICS Dubra, A., Paterson, C., Dainty, C. 2004; 43 (5): 1108?13


    Fast wave-front reconstruction methods are becoming increasingly important, for example, in large astronomical adaptive optics systems and high spatial resolution shear interferometry, where pseudoinverse matrix methods scale poorly with problem size. Wave-front reconstruction from difference measurements can be achieved by use of fast implementations of the discrete Fourier transform (DFT), obtaining performance comparable with that of the pseudoinverse in terms of the noise propagation coefficient. Existing methods that are based on the use of the DFT give exact results (in the absence of noise) only for the particular case in which the shear is a divisor of the number of samples to be reconstructed. We present two alternate solutions for the more general case when the shear is any integer. In the first solution the dimensions of the problem are enlarged, and in the second the problem is subdivided into a set of smaller problems with shear amplitude equal to one. We also show that the retrieved solutions have minimum norm and calculate the noise propagation coefficient for both methods. The proposed algorithms are implemented and timed against pseudoinverse multiplication. The results show a speed increase by a factor of 50 over the pseudoinverse multiplication for a grid with N = 3 x 10(3) samples.

    View details for DOI 10.1364/AO.43.001108

    View details for Web of Science ID 000188878900012

    View details for PubMedID 15008490

  • Axial irradiance distribution throughout the whole space behind an annular aperture: comments APPLIED OPTICS Ferrari, J. A., Dubra, A. 2003; 42 (19): 3754?55


    We comment on the recent paper by Harvey and Krywonos [Appl. Opt. 41, 3790-3795 (2002)], in which approximate irradiance calculations along the axis of a circular aperture illuminated by a plane wave are performed. As the starting point of their calculations, an approximated version (valid for z > lambda) of the Rayleigh-Sommerfeld diffraction integral is used. They based their numerical conclusions on a misleading "near field criterion," which guides the readers to the wrong idea that their calculations are valid even for the very near field behind the aperture. Their ideas are not original; the exact calculations of diffracted fields behind a circular aperture have been known for 40 years.

    View details for DOI 10.1364/AO.42.003754

    View details for Web of Science ID 000183901700007

    View details for PubMedID 12868810

  • Visualization of phase objects using incoherent illumination OPTICS COMMUNICATIONS Perciante, C. D., Ferrari, J. A., Dubra, A. 2000; 183 (1-4): 15?18
  • Precision synchronous polarimeter with linear response for the measurement of small rotation angles APPLIED OPTICS Arnaud, A., Silveira, F., Frins, E. M., Dubra, A., Perciante, C. D., Ferrari, J. A. 2000; 39 (16): 2601?4


    A synchronous polarimeter was set up for the measurement of small rotation angles of the polarization plane of light. The polarimeter is based on a polarizer-Faraday modulator-analyzer structure with a synchronous detection scheme, which produces a linear system response. The theoretical background is studied, and the system performance is investigated experimentally. We achieved an accuracy of the order of 10(-4) deg, or 5 mg/dl of glucose in a 1-cm light path.

    View details for DOI 10.1364/AO.39.002601

    View details for Web of Science ID 000087311100011

    View details for PubMedID 18345177

  • Conversion of bright nondiffracting beams into dark nondiffracting beams by use of the topological properties of polarized light OPTICS LETTERS Frins, E. M., Ferrari, J. A., Dubra, A., Perciante, D. 2000; 25 (5): 284?86


    We present a method for the generation of an axial phase dislocation on a wave front, which is induced by topological properties of polarized light. This effect is shown to be useful for conversion of bright nondiffracting beams into dark nondiffracting beams. Experiments showing the generation of dark nondiffracting beams have been performed.

    View details for DOI 10.1364/OL.25.000284

    View details for Web of Science ID 000085650500002

    View details for PubMedID 18059855

  • Fast Hankel transform of nth order JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION Ferrari, J. A., Perciante, D., Dubra, A. 1999; 16 (10): 2581?82
  • Robust one-beam interferometer with phase-delay control OPTICS LETTERS Ferrari, J. A., Frins, E. M., Perciante, D., Dubra, A. 1999; 24 (18): 1272?74


    A robust one-beam interferometer with external phase-delay control is described. The device resembles a Mach-Zehnder interferometer in which the two arms are together in one collimated beam. However, the proposed device is not an amplitude-division interferometer but a wave-front division one. The phase-delay control occurs at the interferometer output with the help of two polarizing beam splitters, a quarter-wave plate, a Faraday rotator, and a polarizer. An additional phase delay is introduced by application of an electrical current to the Faraday rotator or by rotation of the polarizer (the latter is of topological origin), which permits the use of techniques of phase-stepping interferometry.

    View details for DOI 10.1364/OL.24.001272

    View details for Web of Science ID 000082832000006

    View details for PubMedID 18079777

  • Space integrating joint transform correlator using a moving grating OPTICAL ENGINEERING Ferrari, J. A., Dubra, A., Perciante, D., Rodriguez, B. 1999; 38 (7): 1211?15

    View details for DOI 10.1117/1.602270

    View details for Web of Science ID 000081432100018

  • Current sensor using heterodyne detection APPLIED OPTICS Ferrari, J. A., Dubra, A., Arnaud, A., Perciante, D. 1999; 38 (13): 2808?11


    Based on the Faraday effect for measuring ac current, we describe a fiber-optic sensor that uses laser-diode intensity modulation to perform heterodyne signal detection. The sensor output at the carrier frequency is used as a reference signal to normalize the results. The sensing element consists of a few coils low-birefringence fibers between polarizers. We built the current sensor described above and tested its performance--sensitivity and noise--as functions of the angle between polarizers.

    View details for DOI 10.1364/AO.38.002808

    View details for Web of Science ID 000080091000012

    View details for PubMedID 18319858

  • Diffracted field by an arbitrary aperture AMERICAN JOURNAL OF PHYSICS Dubra, A., Ferrari, J. A. 1999; 67 (1): 87?92

    View details for DOI 10.1119/1.19195

    View details for Web of Science ID 000077708100011

  • Precise polarization measurements using polarizing sheets APPLIED OPTICS Dubra, A., Ferrari, J. A. 1998; 37 (34): 8156?58
  • Nonlinear joint transform correlator using one-dimensional Fourier transformation OPTICAL ENGINEERING Rodriguez, B., Dubra, A., Martinez, C., Escuder, G., Ferrari, J. A. 1998; 37 (10): 2742?47

    View details for DOI 10.1117/1.601809

    View details for Web of Science ID 000076398600011

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