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

我们已经决定了用于刺激电极的适当材料以及诸如电流和图案的参数以刺激视网膜。采用迷宫实验研究了正常兔和光感受器退化兔的行为活动差异。本年度的目的是阐明植入我们开发的视网膜假体的动物的视力。为此，我们选择食蟹猴作为实验动物，因为我们可以使用与人类视力评估相同的方法。然而，还没有关于猴子光感受器退化的报道。为了使猴子的光感受器退化，我们测试了三种化合物，碘酸钠，N-甲基-亚硝基脲（NMU）和硝普钠（SNP），这些化合物已被报道会使兔子和大鼠的光感受器退化。当静脉注射碘酸钾或腹腔注射NMU时，视觉诱发电位的幅值降低。但我们无法完全诱导光感受器变性。本实验用家兔观察刺激电流对视敏度的影响。在视网膜上植入不同大小的电极阵列，记录初级视皮层64个点的诱发电位。500 μ A大电流刺激引起的反应在初级视皮层的广泛区域内观察到。这些结果可以表明，较低的电流适合于给出较高的分辨率。

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.