A comprehensive study of neural retina stimulation towards better visual prosthesis resolution

A major obstacle to make retinal prostheses a realistic technology to restore a functional form of vision allowing normal mobility is the low resolution achieved by current devices. Aims. Using photovoltaic pixels based on organic materials, we aimed at building a wireless high-density epiretinal prosthesis able to restore a theoretical visual acuity of 20/600. Our high-resolution stimulation device also makes it possible to dissect the retinal circuitry activation under spatially confined stimulus to further investigate the mechanisms of neural response clustering. Methods. Extracellular recordings of photovoltaic prosthetic-evoked spiking activity were conducted on explanted Rd10 mice retinas upon increasing exposure conditions. A quantitative analysis of RGCs’ direct and indirect activation thresholds was performed using a custom-made MEA. Both square pulses and continuous photovoltage profiles, measured on top of photovoltaic pixels, were used as stimulation waveforms. Results. Direct and network-mediated light-evoked responses were both detected in retinas explanted on the photovoltaic pixels. Moreover, significant differences in the activation thresholds were observed between photovoltage pulses and square pulses injection. Conclusions. Both photovoltaic stimulation and electrical injection of light-triggered voltage profiles elicited a reproducible activity in explanted dystrophic retinas. Besides, the use of capacitive voltage profiles generated by the photovoltaic device enabled to lower the threshold for INL-mediated RGCs activation. Our results provide interesting insights for the use of non-diraquien pulses in neural tissues stimulation. They also suggest that the promotion of epiretinal indirect RGCs’ excitation could have a beneficial effect on the spatial confinement of the neural retina’s response to prosthetic stimulation.