Electrical stimulation in isolated rabbit retina

Experiments were conducted to assess the effect of stimulating electrode parameters (size, position, and waveform shape) on electrically elicited ganglion cell action potentials from isolated rabbit retina. Thirty-eight isolated rabbit retinas were stimulated with bipolar stimulating electrodes (either 125 or 25 μm in diameter) positioned on either the ganglion or the photoreceptor side. Recording electrodes were placed between the optic disc and the stimulating electrodes. Cathodic-first, biphasic, current waveforms of varying pulse durations (0.1, 0.5, 1 ms) were used. For the four conditions tested (125- electrode and 25-μm electrode, ganglion cell, and photoreceptor positions) threshold currents ranged from 6.7 to 23.6 μA, depending on location and pulse duration. With 1-ms pulse duration, no statistically significant difference was seen between threshold currents when either size electrode was used to stimulate either the ganglion cell side or the photoreceptor side. For all groups, the threshold currents using the 1-ms pulse were lower than those using 0.1 ms, but the 0.1-ms pulses used less charge. These experiments provide a number of valuable insights into the relative effects of several stimulation parameters critical to the development of an implanted electronic retinal prosthesis.