Model Based Investigation of Virtual Electrodes of the Multi-Electrode Array for Epiretinal Prostheses

Abstract

<p>Visual prostheses are an emerging technology to restore vision in blind </p><p>individuals. The level of vision currently attainable with these prostheses is crude and </p><p>far from the level of normal vision though. Epiretinal prostheses work by using a multi- </p><p>electrode array implanted within the eye on the inner layer of the retina to electrically </p><p>stimulate the neural elements beneath the electrodes and produce punctate visual </p><p>percepts of light called phosphenes. Stimulation by serially delivering a cathodic </p><p>monopolar pulse of current with each electrode in the array would require the least </p><p>power to construct pixilated images of the visual scene. There is the possibility of </p><p>complex stimulation schemes that may be able to preferentially stimulate the neural </p><p>elements between the electrodes of the multi-electrode array by utilizing multiple </p><p>electrodes of the array at once though. Although this would require more power, this </p><p>would effectively increase the resolution capabilities of the epiretinal prosthesis without </p><p>the need to increase the number of electrodes on the multi-electrode array. To </p><p>investigate the possibility of such a stimulation scheme, a computational model of the </p><p>inner layers of the human retina including the nerve fiber layer and ganglion cells was </p><p>constructed. The model response was validated against studies of biological ganglion </p><p>cells, and under comparable conditions reproduced features of epiretinal stimulation </p><p>seen clinically. The response of the computational model of the inner retinal layers to </p><p>stimulation by up to two electrodes at once in the multi-electrode array was then </p><p>determined to evaluate the possibility of producing phosphenes between the electrodes. </p><p>The investigation found that disk electrodes using rectangular pulses of equal </p><p>magnitude could not produce a distinct phosphene between the electrodes of the model.</p>