Basic studies of three dimensionally stacked retinal prosthesis toward for clinical trials

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We have already decided appropriate material for stimulus electrode and parameters such as current and patterns to stimulate a retina. We reported the differences of behavioral activities in between normal rabbits and photoreceptor degenerated rabbits with experiments using a maze. The purpose in this year is to clarify the visual acuity in animals which was implanted our developed retinal prosthesis. For this purpose, we chose cynomorgus monkeys as experimental animals because we can apply the same method as evaluating the visual acuity for human. However there is no report to degenerate photoreceptors in monkeys. To degenerate photoreceptors in a monkey, we tested three chemical compounds, sodium iodate, N-methyl-nitrosourea (NMU), and sodium nitropruside (SNP) which have been reported to degenerate photoreceptors in rabbits and rats. When we injected sodium iodate intravenously or NMU intraperitonealy amplitude of visually evoked potential was decreased. But we could not induce the degeneration of photoreceptors completely. By using rabbits, we tried to investigate effects of stimulus current on the visual acuity. We implanted electrode array which has various size of each electrode onto a retina, and recorded evoked potentials from 64 points in primary visual cortex. The responses induced by high current stimulation as 500 uA were observed in a wide area in the primary visual cortex. These results may indicate that lower current is suitable for giving higher resolution.