Implanted Intraocular Retinal Prosthesis in Six Blind Subjects

Abstract

Abstract: : Purpose: To evaluate an epiretinal prosthesis implanted in subjects with bare or no light perception due to retinitis pigmentosa. Methods: The FDA granted an IDE and USC–IRB approved the study protocol. After obtaining informed consent, subjects were screened using visual psychophysics, electrophysiology, ophthalmic photography, and scanning laser ophthalmoscopy. Six subjects who met study criteria were implanted with a Second Sight intraocular epiretinal prosthesis in the eye with worse vision. Implants consist of an extraocular microelectronic device and an intraocular electrode array, connected by a multiwire cable. The electrode array is a 4x4 grid of platinum electrodes embedded in silicone rubber. Electrodes are wirelessly activated using an external controller. Electrical stimulation was begun between 7 and 15 days post–operative. We report here data examining threshold and impedances for each electrode, and perceptual performance with electrical stimulation mediated by a head mounted video camera. Results: As of November 2004 6 subjects have been implanted for 5–33 months. Thresholds varied both within and across subjects. S1: 35–1121 uA; S2: 16 – 777 uA; S3: 18 – 412 uA; S4: 20 – 385 uA; S5: 10 – 31 uA; S6: 6 – 41 uA. Performance using the head mounted video camera suggests that patients are capable of interpreting patterned electrical stimulation. Subjects can localize the position of, or count the number of, high contrast objects with 74–99% accuracy (3 or 4 Alternative Forced Choice (AltFC)), and can discriminate simple shapes such as the orientation of a bar or an "L" (2 or 4AltFC) with 61–80% accuracy. There was a trend towards subjects performing better when stimulated using meaningful patterns of electrical stimulation, rather than all electrodes being stimulated identically. There was no improvement in perceptual acuity when the device was electrically inactive, suggesting that electrical stimulation did not improve the health or function of the retina Conclusions: Epiretinal prostheses can produce percepts with stimulus current as low as 6 uA. Subjects can use a camera to detect and identify objects in their environment.

Keywords: retina • retinal degenerations: hereditary • vitreoretinal surgery