Current distribution during parallel stimulation: implications for an epiretinal neuroprosthesis.

A simplified mathematical model has been developed in order to better understand local current spread when multiple simultaneous current sources are used in an epiretinal neuroprosthesis. To test the model, pairs of platinum electrodes of 430 μm diameter and an intra-pair spacing of 1 mm between centers, were arranged either in-line or in parallel, in a bath of physiological saline. Each pair was separated by distances from 1 mm to 6 mm. The currents in each electrode in the bath were measured and compared with the computational model of the same arrangement. This approach allowed us to quantify return current interaction between parallel sources. As predicted, with parallel electrodes and matching currents in each electrode pair, there is no current cross-talk. However with imbalanced current sources, significant cross-talk is evident. The cross-talk decreases as a function of electrode pair separation. The implication of this work in the design of an epiretinal neuroprosthesis is discussed.