The State of Visual Prosthetics-Hype or Promise?By Dagnelie, Gislin, PhD; Schuchard, Ronald A., PhD; Journal of Rehabilitation Research and Development, Vol. 44, No. 3, pp. xi-xiv
Department of Veterans Affairs
Publication Date: 2007
Article examines the potential of electronic or neurochemical prostheses for restoring some functional vision to people who are blind by reviewing the proposed approaches and assessing their promise. Early cortical implants used electrodes placed between the meninges. A mapping procedure is used to determine the location of each electrode’s phosphene in the visual field, and real-time image processing and stimulation software then extracts and projects contours onto the best-matching electrodes. These phosphenes do not convey real-form vision, yet they do provide the wearer crude localization of outlines in the scene. Newer penetrating probes under development may provide smaller phosphenes, and thus better resolution, at much lower and safer injection levels. Introperative stimulation in patients with late-stage retinitis pigmentosa (RP) has shown that phosphenes could be elicited from blind retinal areas long after photoreceptor degeneration. Researchers are now working on various implants in which a matrix of electrodes stimulates the surviving retinal cells with imagery collected by an external camera and reduced to match the resolution of the electrode ray. Trials conducted with prototype implants in patients with late-stage RP indicate that these patients can detect phosphenes at individual electrodes, discriminate crude shapes upon multiple electrode stimulation, and recognize simple stimuli presented via a head-mounted camera. Other retinal prosthesis groups are exploring integrated concepts in which the eye’s optics become part of a prosthetic imaging device, which in turn generates the signals to drive the secondary neurons. The simplest implementation of such a device, an array of small photodiodes under the retina, appears to have beneficial effects in RP patients with some residual vision. Factors that limit the potential for functional visual prostheses at the present time are discussed.
Department of Veterans Affairs (Website:http://www.vard.org)
VA Rehabilitation Research & Development Service (Web Site: http://www.rehab.research.va.gov )
This publication is included in the library of the National Rehabilitation Information Center (NARIC), accession number J52923