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E. D. Cohen; A Novel Method for Examining the Effects of Electrical Stimulation on the Light Response of Retinal Ganglion Cells. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5872. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To develop a preparation to examine how epiretinal stimulation of the retina by long pulse trains affects normal retinal ganglion cell function.
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.
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.
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.
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