Photovoltaic retinal prosthesis
Photovoltaic retinal prosthesis is a technology for restoring sight to patients blinded by degenerative retinal diseases, such as retinitis pigmentosa and age-related macular degeneration (AMD), when patients lose the 'image capturing' photoreceptors, but neurons in the 'image-processing' inner retinal layers are relatively well-preserved. This subretinal prosthesis is designed to restore a patients' sight by electrically stimulating the surviving inner retinal neurons, primarily the bipolar cells. Photovoltaic retinal implants are completely wireless and powered by near-infrared illumination (880nm) projected from the video goggles. Therefore, they do not require such complex surgical methods as  needed for other retinal implants, which are powered via extraocular electronics connected to the retinal array by a trans-scleral cable. Optical activation of the photovoltaic pixels allows scaling the implants to thousands of electrodes. Studies in rats with retinal degeneration demonstrated that prosthetic vision with such 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. Grating visual acuity measured with 70μm pixels matches the sampling density limit (pixel pitch). Clinical trial  with these implants (PRIMA, Pixium Vision) having 100μm pixels started in 2018, and the initial results already confirmed that patients indeed perceive projected patterns with spatial resolution limited by the pixel size. Implants with pixels of 50μm and smaller are being developed by Palanker group at Stanford University.