Initiation and stability of pursuit eye movements in simulated retinal prosthesis at different implant locations.

PURPOSE To assess the possible effects of retinal prosthesis implant location on the initiation and stability of pursuit eye movements. METHODS Six normally sighted subjects visually tracked a horizontally moving target in natural vision and in simulated prosthetic vision. Subjects were instructed to press a key when the target jumped. Prosthetic vision was simulated with a 10 x 10 array of 1 degrees diameter phosphenes. Three implant locations in the retina were simulated: macular, 8 degrees superior, and 8 degrees nasal. Target motion had two speeds: 4 degrees /s and 8 degrees /s. Eye movement latency, horizontal stability, and vertical stability were assessed. Key-press behaviors responding to target jump were analyzed to evaluate functional eye movements. RESULTS Compared with natural vision, horizontal eye position with respect to target position was less stable in simulated prosthetic vision at macular, superior, and nasal implant locations, in ascending order of the degree of instability. Vertical eye position with respect to target position in simulated prosthetic vision with the superior implant location was less stable in tracking slow target motion than fast. Eye movement latency in simulated prosthetic vision was longer than in natural vision. Key-press performance was impaired in simulated prosthetic vision. CONCLUSIONS Pursuit eye movements in prosthetic vision, compared to natural vision, are significantly slower in initiation and less smooth in motion. They seem, however, still functional, even if the prosthesis is implanted in the peripheral retina. A superior implant locus may help the prosthesis wearer better control horizontal eye movements, which are more frequently used in the activities of daily living.