Intraretinal Electrophysiology and Resistivity Profiles of WT and RCS Rat Retina

Retinal prostheses have been utilized in the treatment of blindness resulting from retinal degeneration. However, they have not met patient expectations, leading to market withdrawals. As a result, research continues to focus on improving visual perception, such as by modeling retinal neural activation. The retina's electrical resistivity profile is key, as it influences the current spread during electrical stimulation. To advance efficient stimulation parameters, more data on the electrical properties of the retina in both its healthy and diseased state is needed. While this question has been addressed in mouse models, few data are available from rat models, whose bigger size is advantageous for many applications. To address this knowledge gap, we used flexible penetrating microelectrode arrays to measure intraretinal impedance and electrophysiological activity in retinas from both healthy (WT) and diseased RCS rats, an established model of retinal degeneration. Consequently, we calculated resistivity profiles, consistent with previous mouse retina findings, and correlated them with spontaneous spiking activity. Hence, both impedance and electrophysiological measurements across retinal depths are demonstrated as valuable tools to identify the optimal stimulation depth and simulate the electric field spread during electrical stimulation, which is particularly useful for the development of retinal prostheses. These findings demonstrate that resistivity changes in the degenerated retina significantly impact stimulation protocols and electric field propagation.