Restoration of Sight with Photovoltaic Subretinal Prosthesis

Retinal degeneration leads to blindness due to gradual loss of photoreceptors. Information can be reintroduced into the visual system by patterned electrical stimulation of the remaining retinal neurons. Photovoltaic subretinal prosthesis directly converts light into pulsed electric current in each pixel, stimulating the nearby inner retinal neurons. Visual information is projected onto the retina by video goggles using pulsed near-infrared (~900nm) light. This design avoids the use of bulky implants with power supplies, decoding electronics and wiring, thereby greatly reducing the surgical complexity. Optical activation of the photovoltaic pixels allows scaling the implants to thousands of electrodes, and multiple modules can be tiled under the retina to expand the visual field.

Subretinal arrays with 70μm photovoltaic pixels provide highly localized stimulation:  retinal ganglion cells respond to alternating gratings with the stripe width of a single pixel, which is half of the native resolution in rat retina (~30μm). Similarly to normal vision, retinal response to prosthetic stimulation exhibits flicker fusion at high frequencies (>20 Hz), adaptation to static images, and non-linear summation of subunits in the receptive fields. In rats with retinal degeneration, the photovoltaic subretinal arrays restore visual acuity up to half of its normal level, as measured by the cortical response to alternating gratings. If these results translate to human retina, such implants could restore visual acuity up to 20/250. With eye scanning and perceptual learning, human patients might even cross the 20/200 threshold of legal blindness. Ease of implantation and tiling of these wireless modules to cover a large visual field, combined with high resolution opens the door to highly functional restoration of sight.