Inventing a new outlook

Age-related macular degeneration (AMD) is one of the leading causes of vision loss for older Americans, and for patients suffering from atrophic AMD, vision loss is permanent. That’s why 15 years ago, in an effort to restore sight in advanced dry AMD patients, Daniel Palanker, PhD, professor of ophthalmology, invented and developed a photovoltaic retinal prosthesis, now called PRIMA.

By restoring the flow of visual information into the retina, we were able to provide prosthetic central vision for AMD patients, perceived simultaneously with their residual peripheral vision.

PRIMA is a prosthetic system comprised of a photovoltaic implant that is placed under the central retina and activated by light projected from transparent augmented-reality glasses. The inner retinal neurons are then stimulated electrically, allowing the patient to see.

Since its initial design, Palanker and his collaborators in the Departments of Ophthalmology and Electrical Engineering at Stanford have set out to continually advance the quality and efficacy of PRIMA. In a recent feasibility trial, five patients have been implanted with the first generation PRIMA retinal prosthesis, which has 100 micrometer pixels. These patients were able to identify numbers, letters and symbols with acuity up to 20/440, closely matching the limit of the current pixel density: 20/420. Of the 20 research programs around the world working on similar devices, none have resulted in higher visual acuity than PRIMA.

“By restoring the flow of visual information into the retina, we were able to provide prosthetic central vision for AMD patients, perceived simultaneously with their residual peripheral vision,” Palanker said. “These results gave us confidence to pursue the development of higher resolution implants.”

Palanker’s latest design has a 3D electro-neural interface, which enables much smaller pixels and lower stimulation thresholds. Using this approach, his team recently made the first demonstration of prosthetic vision in rats with acuity that in human patients may provide 20/80 vision, and with electronic magnification, could even reach 20/20.

“These latest preclinical results are very exciting and encouraging,” Palanker said, “paving the way to very functional restoration of sight to millions of patients suffering from advanced AMD and other retinal degenerative diseases.”

By KATHRYN SILL

Kathryn Sill is a web and communications specialist for the Byers Eye Institute in the Department of Ophthalmology, at Stanford University School of Medicine. Email her at ksill@stanford.edu.