Avoidance of axonal activation in epiretinal implants using short biphasic pulses

Retinal implants allow patients suffering from degenerative retinal diseases to regain visual percepts. Despite considerable effort in developing and improving retinal neuroprostheses in the last decades, the restored vision in patients does not achieve sufficient quality. The elicited percepts do not accurately match the stimulating pixels and therefore the formation of high acuity vision is hindered. One of the main obstacles in epiretinal implants is the concurrent activation of cells close to a stimulating electrode and cells that have their axons traversing the electrode. In this study, we use computational modeling to examine the effect of pulse duration on the selectivity of focal versus non-focal activation. Our results suggest that biphasic pulses in the range of 10-20 microseconds can prevent axonal activation while still reliably activating target neurons.