Development of an Intraocular Retinal Prosthesis to Benefit the Visually Impaired

Abstract

Neural prostheses have been used as treatment for a variety of neurological disorders, motivating engineers and scientists to pursue prostheses for presently incurable human diseases related to the nervous system. A retinal prosthesis is based on the principle of activating nerve cells using a device implanted on the retina. In an intraocular retinal prosthesis, the stimulation device is placed internal to the eye. Retinal prosthesis potentially targets the restoration of vision in persons affected by outer retinal degenerative diseases. The most common diseases are age-related macular degeneration (AMD) and retinitis pigmentosa (RP) (1). RP is a collective name for a number of genetic defects that result in photoreceptor loss. RP affects the rods (used in night vision) first and then the cones (used in ambient daylight levels). AMD results from abnormal aging of the retinal pigment epithelium and retina. Persons with AMD will start to have distorted vision and eventually, lose most of the vision in the central 30°. In both the diseases, the vision is impaired because of the damage to the photoreceptors that convert photons to neural signals. Postmortem evaluations of retina with RP or AMD have shown that a large number of cells remain healthy in the inner retina compared with the outer retina (2,3). The inner retina is made up of horizontal, bipolar, amacrine, and ganglion cells. Further, electrical stimulation of humans with RP and AMD results in the perception of light; so the neural cells can be activated, providing the hope of restoring lost vision in blind persons (4). A chronic implant with 16 electrode sites on the retina in three blind patients has yielded promising results (5). After being implanted with the prosthetic device, the patients were able to detect motion of a white bar (up, down, left, or right), detect a rectangular object, count objects, discriminate the orientation of two white bars in an “L” configuration regarding where the corner of the L was positioned, and discriminate between a dessert plate, a coffee cup, and a plastic knife.