Prosthetic Vision with a Photovoltaic Substitute for the Lost Photoreceptors

Retinal degenerative diseases lead to blindness due to loss of photoreceptors, while neurons in the inner retinal layers are still preserved. We developed a system substituting the lost photoreceptors with photovoltaic arrays. Visual information captured by a camera is projected onto the subretinal implant from augmented-reality glasses using pulsed near-infrared (880nm) light. Photovoltaic pixels convert this light into electric current, stimulating the second-order retinal neurons, which then pass visual information through the retinal neural network to the brain. This approach preserves many features of natural vision, simplifies surgery by avoiding bulky electronics and wiring, allows scaling the number of electrodes to thousands and retains normal association of eye movements with visual perception. Photovoltaic arrays implanted in patients blinded by age-related macular degeneration provided monochromatic form vision perceived simultaneously with the remaining peripheral natural vision. Clinical trials with 43 patients across 17 centers in 5 European countries demonstrated letter acuity matching their 100mm pixel size (20/420). Electronic zoom enables patients to read and write smaller fonts, improving visual acuity, on average, by 5 lines of the vision chart - up to 20/63. Decreasing the pixel size for higher resolution is challenging due to reduced penetration depth of electric field in tissue. We developed various strategies for shaping the electric field, including current steering and 3-dimensional electrodes. With this new design, grating acuity with 40mm pixels in rats matched the pixel pitch, while with 20mm, it reached their natural resolution limit of 28mm. If successful in clinical trials, implants with 20mm pixels have the potential to increase acuity up to 20/80 without zoom, and reach 20/20 with zoom, providing highly functional restoration of sight to millions of patients blinded by retinal degeneration.

Speaker: Daniel Palanker, Stanford University