INSTITUTE OF PHYSICS PUBLISHING JOURNAL OF NEURAL ENGINEERING J. Neural Eng. 2 (2005) S105–S120 doi:10.1088/1741-2560/2/1/012 Design of a high-resolution optoelectronic retinal prosthesis Daniel Palanker 1 , Alexander Vankov 1 , Phil Huie 1 and Stephen Baccus 2 1 Department of Ophthalmology and Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305-4085, USA 2 Department of Neurobiology, Stanford University, Stanford, CA 94305-4085, USA E-mail: palanker@stanford.edu Received 11 November 2004 Accepted for publication 14 December 2004 Published 22 February 2005 Online at stacks.iop.org/JNE/2/S105 Abstract It has been demonstrated that electrical stimulation of the retina can produce visual percepts in blind patients suffering from macular degeneration and retinitis pigmentosa. However, current retinal implants provide very low resolution (just a few electrodes), whereas at least several thousand pixels would be required for functional restoration of sight. This paper presents the design of an optoelectronic retinal prosthetic system with a stimulating pixel density of up to 2500 pix mm −2 (corresponding geometrically to a maximum visual acuity of 20/80). Requirements on proximity of neural cells to the stimulation electrodes are described as a function of the desired resolution. Two basic geometries of sub-retinal implants providing required proximity are presented: perforated membranes and protruding electrode arrays. To provide for natural eye scanning of the scene, rather than scanning with a head-mounted camera, the system operates similar to ‘virtual reality’ devices. An image from a video camera is projected by a goggle-mounted collimated infrared LED-LCD display onto the retina, activating an array of powered photodiodes in the retinal implant. The goggles are transparent to visible light, thus allowing for the simultaneous use of remaining natural vision along with prosthetic stimulation. Optical delivery of visual information to the implant allows for real-time image processing adjustable to retinal architecture, as well as flexible control of image processing algorithms and stimulation parameters. (Some figures in this article are in colour only in the electronic version) 1. Introduction As the population ages, age-related vision loss from retinal diseases is becoming a critical issue. Two retinal diseases are the current focus of retinal prosthetic work: retinitis pigmentosa (RP) and age-related macular degeneration (AMD). In these diseases, the ‘imaging’ photoreceptor layer of the retina degenerates, yet the ‘processing circuitry’ and ‘wiring’ subsequent to photoreceptors are at least to some degree preserved. Retinitis pigmentosa occurs in about 1 out of 4000 live births, corresponding to 1.5 million people worldwide. This disease is the leading cause of inherited blindness. Age-related macular degeneration is the major cause of vision loss in people over 65 in the Western world. Each year 700 000 people are diagnosed with AMD, and 10% of these people become legally blind. Currently, there is no effective treatment for most patients with AMD and RP. However, if one could bypass the photoreceptors and directly stimulate the inner retina with visual signals, one might be able to restore some degree of sight. One important factor affecting this strategy is that the absence of normal signaling from photoreceptors can lead to some progressive degeneration and mis-wiring of retinal circuitry [1, 2]. This type of degeneration is a general property of neural circuits. Thus, for an electronic implant to properly transmit visual signals to the inner retina, any degeneration of circuitry must not drastically change how these signals are interpreted by the higher brain. This is true in the case of cochlear implants, which bypass degenerated primary auditory sensory neurons; both the nerve and the downstream neural 1741-2560/05/010105+16$30.00 © 2005 IOP Publishing Ltd Printed in the UK S105