Performance of visual tasks using an epiretinal prosthesis

Abstract

Abstract: : Purpose: To measure the accuracy with which test subjects implanted with an epiretinal prosthesis can perform simple visual tasks. Methods: The FDA and USC–IRB approved the study protocol. Informed consent was obtained. Once the subjects met the qualifications in electrophysiological and psychophysical tests, a Second Sight epiretinal prosthesis was implanted in the worse eye. The intraocular component consists of 16 electrodes in a 4x4 distribution. Electrical stimulation was started between 7 and 15 days post–operative. The tests were divided in two categories: controlled tests (stimulus/patterns generated by computer) and camera tests (stimulus generated by a head mounted video camera). Using the computer interface different situations were simulated as: movements and position of the perceptions and orientation lines of electrodes (horizontal or vertical). Using the head mounted camera, tests were divided in camera still and camera scanning. Camera scanning results were also analyzed in two different situations: using single pixel (s–p) and using multi–pixel (m–p) resolution. Results: The results were significantly better than by chance. Computer controlled tests: sequential activation (4 alternative forced choice (AFC)) 70% (p< .001); orientation of lines of electrodes (2 AFC) 78% (p< .01); spatial location left/right (2 AFC) 75% (p< .01); spatial location up/down (2 AFC) 85% (p< .01). The patients also could recognize the direction of movements of a white bar in 59% (p< .01) in camera controlled tests. Comparing one vs. multi–pixel resolution, subjects required less time to provide a correct answer when multiple pixels were used (counting objects 27s, p< .0001; L position 80s, p< .0003) and a trend towards better performance when using multiple pixels (the number of pixels varied between subjects). One vs. multi–pixel: finding objects s–p=77%, m–p = 89% (p= .12); counting objects s–p=70%, m–p=80% (p= .12); objects recognition s–p=56%, m–p=68% (p= .13); L position s–p=59%, m–p=66% (p= .35). Conclusions: Test subjects with no better than light perception vision can perform simple visual tasks using an epiretinal prosthesis. An increased number of pixels and electrodes may produce better results and greater functionality.

Keywords: retina • retinitis • vitreoretinal surgery