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Chuan-Chin Chiao, Yueh-Chun Tsai, Chung-Yu Wu; Temporal integration of repeated electrical stimuli in the pulse number modulation of retinal prosthesis. Invest. Ophthalmol. Vis. Sci. 2018;59(9):4564.
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There are still many challenges remained in the retinal prosthesis development. One issue is when increasing the duration or amplitude of stimulating pulse for activating retinal cells, it is has a tendency to exceed the limitation of the electrochemical window (or “water window”). To overcome this challenge, we investigated the potential of the pulse number modulation in the retinal prosthesis design. Electrical stimulation in the pulse number modulation, which fixes the total amount of charge injection and varies the strength of the stimulus only by the number of pulses, can significantly prevent the redox reaction from exceeding the water window by reducing the charge accumulation with shorter and smaller bi-phasic pulses.
The present study was to systematically characterize the performance of temporal integration in the pulse number modulation with electrophysiological recording of the retinal ganglion cells (RGCs). Multi-electrode array (MEA) was used to stimulate and record the retina from rd1 mice.
The results showed that the charges of repeated bi-phasic pluses in the pulse number modulation were integrated over time and evoked RGC responses successfully, even though the pulse number modulation was not as efficient as the amplitude and pulse width modulations. Moreover, it was found that longer inter-pulse intervals did not affect the temporal integration of electrical stimulation of multiple repeated pulses in driving RGC responses. Finally, the effect of temporal integration of multi-pulse electrical stimulation on RGC responses was likely originated from the upstream retinal neurons, not from stimulating RGCs directly.
Electrical stimulation with the pulse number modulation has great potentials in the retinal prosthesis design. These findings not only demonstrate the effect of temporal integration on visual prosthesis, but also provide an insight into the optimization of the photovoltaic retinal prosthesis. This strategy could be developed into an improved prosthesis device able to restore vision in the future.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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