Chronic Electrical Stimulation of the Retina in RCD1 and Normal Dog

Abstract

Abstract: : Purpose: To study the effects of chronic stimulation on the retina of normal and RCD1 dog. Methods: A Second Sight Model 1 retinal stimulator was implanted. The implant consisted of an extraocular microelectronic device and an intraocular electrode array, connected by a multiwire cable. The electronics were packaged in a hermetic ceramic case approximately 25x25x5 mm. This case was fixed to the skull using standard plastic surgery materials and the skin was closed over the implant. The wire was tunneled subcutaneously to the orbit, wrapped once around the eye, and entered the eye via a pars plana sclerotomy. The array was secured to the retina with a single retinal tack. After a 2-4 week recovery period, an electronic test system was worn by the dog to provide the power and data to the implanted device. The implant was monitored with indirect ophthalmscopy, fluorescein angiography, and electroretinography. Results: Electrical stimulation was performed for 60 days (1 normal dog) and 120 days (2 RCD1 dogs). Stimulation was performed with 180 uA and 90 uA of current on 8 electrodes at each level (all electrodes 1 ms, cathodic first biphasic pulses). Minimal retinal damage was noted due to mechanical interaction in 1 implant. Electrical evoked potentials were obtained in 2/2 dogs using a subdural recording electrode array. Electroretinograms in the normal dog were of similar amplitude and latency (A-Wave latency preop – 17, postop- 19 ms; A-Wave magnitude preop – 37 uV, postop- 52 uV; B-wave latency preop – 33 msec, postop- 39 ms; B-Wave amplitude preop- 87 uV; postop- 124 uV). Electroretinograms could not be obtained from the blind dogs either preoperatively or post-operatively. Histological analysis of tissue showed no damage specific to electrical stimulation in either the normal or RCD1 dogs. Conclusions: Electrical stimulation did not damage the retina in either normal or RCD1 dog. Electrical stimulation could produce a cortical response in blind dogs. Electrical stimulation with an epiretinal array continues to show promise as a means of restoring vision to the totally blind.

Keywords: retina • retinal degenerations: hereditary • vitreoretinal surgery