Chronically Implanted Intraocular Retinal Prosthesis in Three Blind Subjects

Abstract

Abstract: : Purpose: To study the feasibility of implanting an epiretinal prosthesis in humans with bare or no light perception vision from retinitis pigmentosa (RP). Methods:The FDA granted an IDE and USC–IRB approved the study protocol. After obtaining informed consent, the patients were screened using visual psychophysical testing, electrophysiology, ophthalmic photography, and scanning laser ophthalmoscopy. Three patients who met the study criteria were implanted with a Second Sight intraocular epiretinal prosthesis in the eye with worse vision. The implant consisted of an extraocular microelectronic device and an intraocular electrode array, connected by a multiwire cable. The electrode array consisted of a 4x4 grid of platinum electrodes embedded in silicone rubber. The implant was wirelessly activated using an external controller. Electrical stimulus pattern was determined by a custom computer interface or video camera. Results: All the subjects had non–recordable preoperative ERGs and VEPs. As of November 2003 Subject 1 (S1) has been implanted for 21 months, subject 2 (S2) 16 months and subject 3 (S3) for 8 months. All subjects reported the perception of light on all 16 electrodes under proper stimulation. The average stimulus thresholds in S1 was 575uA (at 18months), S2 was 61uA (at 15 months) and S3 was 59uA (at 7 months). During stimulation different colors were reported (white and yellow were the most frequent). Using a head mounted video camera as a source for the stimulus, all the subjects detected room lights on/off with 97% accuracy. Other camera testings: finding objects (3AFC) 84% (p< .001); counting objects (4AFC) 74% (p< .001); objects recognition (3AFC) 63% (p< .001); L position (4AFC) 61% (p< .001). There was a trend in achieving better results with multi–pixel compare to a single–pixel stimulation. In S1 and S2, despite of the small area covered by the array, evoked potentials were recorded in different sessions. No improvement in the VA was noted when the device was electrically inactive despite of frequent electrical stimulation. Conclusions: All the subjects could see visual perceptions that correlate to electrical stimulus from a chronically implanted retinal prosthesis. Patients used a camera driven stimulus to perform simple tasks (i.e. identifying or counting large objects).

Keywords: retina • vitreoretinal surgery • retinal degenerations: hereditary