Focal stimulation of retinal ganglion cells using subretinal 3D microelectrodes with peripheral electrodes of opposite current

Subretinal prostheses have been developed to stimulate survived retinal ganglion cells (RGCs), indirectly following the physiological visual pathways. However, current spreading from the prosthesis electrode causes the activation of unintended RGCs, thereby limiting the spatial resolution of artificial vision. This study proposes a strategy for focal stimulation of RGCs using a subretinal electrode array, in which six hexagonally arranged peripheral electrodes surround a stimulating electrode. RGCs in an in-vitro condition were subretinally stimulated using a fabricated electrode array coated with iridium oxide, following the three different stimulation configurations (with no peripheral, six electrodes of opposite current, and six ground). In-vitro experiments showed that the stimulation with six electrodes of opposite current was most effective in controlling RGC responses with a high spatial resolution. The results suggest that the effective utilization of return electrodes, such as by applying an opposite current to them, could help reduce current spreading beyond the local area targeted for stimulation and elicit RGC responses only in the vicinity of the stimulating electrode.