Retinal degenerative diseases lead to blindness due to loss of the "image capturing" photoreceptors, while neurons in the "image-processing" inner retinal layers are relatively well preserved. Information can be reintroduced into the visual system using electrical stimulation of the surviving inner retinal neurons. Some electronic retinal prosthetic systems have been already approved for clinical use, but they provide low resolution and involve very difficult implantation procedures.
We developed a photovoltaic subretinal prosthesis which converts light into pulsed electric current, stimulating the nearby inner retinal neurons. Visual information is projected onto the retina from video goggles using pulsed nearinfrared (~880nm) light. This design avoids the use of bulky electronics and wiring, thereby greatly reducing the surgical complexity. Optical activation of the photovoltaic pixels allows scaling the implants to thousands of electrodes. In preclinical studies, we found that prosthetic vision with subretinal implants preserves many features of natural vision, including flicker fusion at high frequencies (>20 Hz), adaptation to static images, center-surround organization and non-linear summation of subunits in receptive fields, providing high spatial resolution. Results of the clinical trial with our implants (PRIMA, Pixium Vision) having 100µm pixels, as well as preclinical measurements with 75 and 55µm pixels, confirm that spatial resolution of prosthetic vision can reach the sampling density limit.
For a broad acceptance of this technology by patients who lost central vision due to age-related macular degeneration, visual acuity should exceed 20/100, which requires pixels smaller than 25µm. I will describe the fundamental limitations in electro-neural interfaces and 3-dimensional configurations which should enable such a high spatial resolution. Ease of implantation of these wireless arrays, combined with high resolution opens the door to highly functional restoration of sight.
Daniel Palanker is a Professor in the Department of Ophthalmology and Director of the Hansen Experimental Physics Laboratory at Stanford University. He received MSc in Physics in 1984 from the Yerevan State University in Armenia, and PhD in Applied Physics in 1994 from the Hebrew University of Jerusalem, Israel. Dr. Palanker studies interactions of electric field with biological cells and tissues, and develops optical and electronic technologies for diagnostic, therapeutic, surgical and prosthetic applications, primarily in ophthalmology. In the range of optical frequencies, these studies include laser-tissue interactions with applications to ocular therapy and surgery, and interferometric imaging of neural signals. In the field of electro-neural interfaces, he is developing high-resolution retinal prosthesis for restoration of sight, and implants for electronic control of secretory glands and blood vessels.
Several of his developments are in clinical practice world-wide: Pulsed Electron Avalanche Knife ( PEAK PlasmaBlade , Medtronic), Patterned Scanning Laser Photocoagulator ( PASCAL , Topcon), Femtosecond Laser-assisted Cataract Surgery ( Catalys , Johnson & Johnson), and Neural Stimulator for enhancement of tear secretion ( TrueTear , Allergan Inc.). Photovoltaic retinal prosthesis for restoration of central vision in AMD ( PRIMA , Pixium Vision) is in a clinical trial.