Figure 1.

Flat (a) and honeycomb (b) configurations of the return electrode for a subretinal prosthesis. (c) Planar pixels with circumferential returns generate locally confined electric fields with shallow vertical penetration. Electric potential (shown in false color scale for 68 nA current) is represented with respect to potential in the middle of IPL, where axon terminals of bipolar cells reside. (d) Return electrodes on top of the insulating walls create a vertical dipole confined to the pixel volume and thereby maximize the vertical potential drop across the target cell layer. Current magnitude (arrow length) is shown in log scale.