Visual Perception in Blind Subjects with Microelectronic Retinal Prosthesis

Abstract

Abstract: : Purpose:To report the dynamic testing of human epiretinal implant in two blind subjects (S1 and S2) with Retinitis Pigmentosa. Methods:The FDA and USC-IRB approved the study protocol. Once the informed consent was obtained and the subjects met the qualifications in electrophysiological and psychophysical tests, a Second Sight Model 1 prosthesis was implanted in the worse eye. The intraocular component consists of 16 electrodes in a 4x4 distribution. After the recovery period the retinal electrical stimulation was started. The stimulus patterns was controled either by a computer interface or by the images captured by a head mounted video camera.Using the computer interface two electrodes were activated in sequence and the subject was trained to describe the direction as up, down, left, or right (four alternative, forced choice). Camera testing was done using white objects either moving or stationary over a black background. Results:Sequential activation tests conducted with the computer – 75% (12 in 16 for S1) and 90% (9 in 10 for S2) correct answers to describe the direction (up, down, left or right). The subjects are able to count and localize up to two objects: 60% (12 in 20 for S1) and 90% (9 in 10 for S2). S2 recognized object movement directions with 70% accuracy (7 in 10). Conclusions:The subjects can reliably report the stimulus produced by activation of the electrodes and its spatial location. The use of electrodes in different arrangements and settings can be used to obtain more complex images. These encouraging results further demonstrate the feasibility of a retinal prosthesis. Improvement in the resolution (number of electrodes and pixels) and a better understanding of the interaction between electrical stimulation and the retina will make such a device even more useful.

Keywords: retina • image processing • retinitis