Comparison of Electrical Stimulation Thresholds in Normal and Retinal Degenerated Mouse Retina

PurposeTo compare the threshold for electrically elicited action potentials of retinal ganglion cells in normal mouse retina and photoreceptor degenerated (rd) mouse retina.MethodsMicroelectrode recordings were made from retinal ganglion cells of normal and rd mice. Mice with a genetically based retinal degeneration (rd mice) were grown to the age of 16 weeks, when light-evoked responses could no longer be recorded. A bare wire was placed in the vitreous to stimulate the retina with charge-balanced current pulses. The following pulse shapes were investigated: single, square biphasic pulse, single sine wave, and biphasic pulse trains.ResultsNormal mice had significantly lower stimulus thresholds than rd mice for all pulse shapes. In normal and rd mice, short pulses were more efficient with respect to total charge used, but required a higher current. In normal mice, sine wave stimulation was significantly more efficient than a biphasic pulse of the same duration. No difference was noted between sine wave and square wave stimulation in rd mice. Pulse trains offered little benefit over single pulses.ConclusionThe amount of electrical charge required to elicit an action potential is dependent on the condition of the retina and the shape of the stimulus pulse used to deliver the charge.