33.5 Closed-Loop 100-Channel Highly-Scalable Retinal Implant with 1.02μW Analog ED-Based Adaptive-Threshold Spike Detection and Poisson-Coded Temporally Distributed Optogenetic Stimulation

Intraocular stimulators have demonstrated promise in treating patients with retinal degeneration (e.g., age-related macular degeneration) by restoring visual input to the compromised retina. This is done by capturing images with an electronic photosensor and subsequently stimulating remaining retinal cells, (e.g., bipolar, ganglion), thus bypassing the dysfunctional photoreceptors. Figure 33.5.1 (top, left) shows sub-and epi-retinal electrical stimulators, with the former potentially offering more natural vision restoration and the latter being less invasive. Regardless, a common issue with reported electrical retinal stimulators is their lack of cell-type specificity, which results in stimulating both ON and OFF pathways in the retinal network, as illustrated by the simulation results shown in Fig. 33.5.1 (left). This leads to contradictory messages to the brain, resulting in constrained visual perception, regardless of spatial resolution. This, and the introduction of various promoter opsins that allow for specifically activating ON pathway cells, make optogenetic stimulators a more promising alternative as shown in Fig. 33.5.1 (left). Additionally, optical stimulators can be epi-retinally implanted (i.e., less invasive) while stimulating bipolar cells for more natural vision restoration, thanks to the retinal neural network’s light transparency.