Abstract
Purpose: :
To develop a preparation to examine how epiretinal stimulation of the retina by long pulse trains affects normal retinal ganglion cell function.
Methods: :
The action potentials of retinal ganglion cells were recorded extracellularly with tungsten electrodes using an in-vitro eyecup preparation of the rabbit retina. Epiretinal electrical stimulation was delivered using a saline-filled optically transparent tube (0.5 mm diam.) over the retinal surface forming the receptive field center. Trains of biphasic (cathodic/anodic) 1msec pulses were delivered to the retina at 50Hz for periods of 1 minute. To assess retinal ganglion cell function, the receptive field center was presented periodically with spot stimuli during the course of the experiment. Pulse train charge densities were tested between 4.4 - 884uC/cm2/phase.
Results: :
Low charge density (4.4 -44uC/cm2/phase) pulse trains had little effect on the light-evoked firing of most ganglion cells and there was little impairment of the light-evoked response after train stimulation (6% impaired, n=18 cells; 6% impaired, n=16). However as the charge density of the trains reached 133 uC/cm2/phase, there was often a transient loss of the light-evoked firing in 53% of the cells after train stimulation (n=15 cells). Of those affected, the time to recover the light response averaged 0.54 min. Similar results were seen at 442 uC/cm2/phase; 54% cells impaired (n=13 cells), time of recovery averaged 1.6 minutes. The spontaneous firing rate of the ganglion cell was often reduced for several minutes after pulse train stimulation at 133 or 442uC/cm2/phase. No significant threshold differences were observed for ON- vs OFF-center ganglion cells to epiretinal train stimulation.
Conclusions: :
Epiretinal stimulation by high charge density pulse trains for one minute appears to impair local retinal ganglion cell function for short periods which could cause a transient refractory period to phosphene perception in the retinal region below the electrodes. The threshold charge density for observing visual impairment in many cells with long train stimulation was 133uC/cm2/phase.
Keywords: electrophysiology: non-clinical • ganglion cells • pathology: experimental