Abstract
Purpose :
An important factor in the success of electrical stimulation in retinal prosthetics that remains poorly understood is the influence of disease state on electrical stimulation thresholds. We examined the influence of disease progression on it by measuring ganglion cell spiking from ex vivo retina in the RD10 mouse model of retinal degeneration.
Methods :
RD10 mice (ages 60-110) were enucleated. The isolated retina was perfused with oxygenated Ames medium at physiological temperature. Retina was mounted with ganglion cell side up over a custom-made multi-electrode array in a specialized recording chamber. The array consisted of 30 µm diameter sputtered iridium oxide film (SIROF) spaced at 50 µm. Charge-balanced biphasic current pulses were delivered in 1 or 5 ms duration pulses per phase. We varied the current amplitude to deliver between 1 to 25 nC to determine the current/charge versus spiking activity relationship. Recordings were made in the "loose-patch" configuration using a whole-cell patch clamp amplifier to record action potentials in response to electrical stimulation.
Results :
We recorded from 62 ganglion cells and quantified efficiency of electrical stimulation by calculating the threshold (10% max response), half-maximal, saturation (90% maximal response), and dynamic range (90% - 10%) of the stimulation current. Although we report “maximal” responses, we do not believe this is a property of the cell response but our current injection limit. Current injection magnitude was limited to stimuli delivering 25nC of charge based on the current injection capacity of the electrodes, and responses typically did not saturate before reaching this value by examining the relationship between threshold, half-max or dynamic range and age. We observed a week negative correlation between any of these pairs with the strongest and steepest relationship being between half max stimulating current and age (slope = -85.8 ± 38.7 nA/day, R2=0.075566; threshold: slope = -29.7 ± 39.9 nA/day, R2=0.00915627; maximum: slope = -68.8 ± 43.6 nA/day, R2=0.0398822; dynamic range: slope = -39.1 ± 64.4 nA/day, R2=0.00610941).
Conclusions :
Despite RD10 disease progression, little effect on spiking responses to prosthetic current stimulation may occur, with the biggest effect being a slight reduction in the amount of current needed to achieve half-maximal stimulation. This may be due to a reduction in the maximal stimulation, however more work is required to test this idea.
This is a 2020 ARVO Annual Meeting abstract.