High Resolution Photovoltaic Subretinal Prosthesis for Restoration of Sight
In photovoltaic subretinal prostheses, each pixel converts light into electric current to stimulate the nearby inner retinal neurons. Visual information is projected onto the implant by video goggles using pulsed near-infrared (~880 nm) light. This design
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High Resolution Photovoltaic Subretinal Prosthesis for Restoration of Sight Henri Lorach and Daniel Palanker
Abstract In photovoltaic subretinal prostheses, each pixel converts light into electric current to stimulate the nearby inner retinal neurons. Visual information is projected onto the implant by video goggles using pulsed near-infrared (~880 nm) light. This design avoids the use of bulky electronics and trans-scleral 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. 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. Photovoltaic arrays with 70 μm pixels restored visual acuity up to a pixel pitch in rats blinded by retinal degeneration, which is only twice lower than natural acuity in these animals. 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. Keywords Photovoltaic prosthesis • Retina • Electrical stimulation • Retinal surgery • Blindness • Visual acuity • Safety • Restoration of sight Key Points • Prosthetic visual acuity with subretinal photovoltaic arrays matches the pixel pitch of 65 μm, suggesting that smaller pixels may further increase spatial resolution. • Implants with 65 μm pixel pitch restore half of the normal acuity in blind rats. Such spatial resolution would correspond to 20/250 acuity in a human eye.
H. Lorach (*) Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, USA e-mail: [email protected] D. Palanker Department of Ophthalmology and Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, USA © Springer International Publishing Switzerland 2017 V.P. Gabel (ed.), Artificial Vision, DOI 10.1007/978-3-319-41876-6_9
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H. Lorach and D. Palanker
• Wireless nature of photovoltaic implants allows implantation of multiple modules via small retinotomy to cover large visual field, and to follow the eye curvature. • Intensity of NIR light required to activate the subretinal implants is safe.
Introduction Retinal degenerative diseases, such as age-related macular degeneration and retinitis pigmentosa, lead to blindness due to gradual loss of photoreceptors, while the inner retinal neurons survive to a large extent [10, 26], albeit with some rewiring [12, 22]. Retinal prostheses aim at restoring sight by electrical stimulation of these surviving neurons. In the epiretinal approach, the primary target of stimulation are the retinal ganglion cells (RGCs) [1,
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