3-D finite element modeling analysis of epiretinal electrical stimulation — Effects of electrode size and electrode shape

Epiretinal electrical stimulation provides a promising approach to restore functional vision for patients suffering from retinal degenerative diseases. The electrodes of epiretinal prosthesis stimulate the surviving ganglion cells and cause visual percepts. To further improve the performance of epiretinal electrodes, an optimized solution in electrode design has to be found based on modeling analysis. In this study, different three-dimensional (3-D) electrode models were built to investigate the effects of electrode size and electrode shape on epiretinal electrical stimulation. The retina was presented by a multi-layered computational model using finite element method. Results indicate that small-sized electrodes required lower threshold current but higher threshold charge density. Non-planar electrodes had higher threshold currents than disk electrode. Concave electrodes needed less threshold charge densities than disk and convex ones. Under the stimulation of the same-multiple threshold current, the activation areas of disk and concave electrodes were more convergent than that of convex electrodes. To conclude, small-sized electrode is recommended if the charge density could be within the safe limit. In consideration of superior electrode safety and stimulation selectivity, concave electrodes are more preferable choices among the electrodes with different geometric shapes. The modeling simulation result of disk electrodes showed a desirable concordance with the animal electrophysiological experiments. This modeling analysis of different 3-D electrodes on epiretinal electrical stimulation may provide meaningful guidance for the optimization of future electrode design.