Abstract
Purpose :
Retinal prosthetic devices strive to restore vision for patients blinded by outer retinal degeneration. Microelectrode arrays of those prostheses apply electric stimuli to activate retinal neurons that survive the degenerative diseases. As a waveform shape of electric pulses, rectangular waveform has been used in most previous studies. However, it remains unknown if the rectangular waveform is the optimal pulse shape that elicits the strongest responses with a given amount of applied charges. Here, we investigated network-mediated responses of ON type retina ganglion cells (RGCs) to evaluate charge-efficiency of three waveform shapes.
Methods :
Cell-attached patch clamp was used to record spikes from RGCs in the isolated retinas of wild-type mice (C57BJ/6J). Alpha RGCs were targeted by their large soma (>20 µm) and classified as ON or OFF types by their light responses. In particular, we focused on the ON type because we previously found the networked-mediated responses are more correlated with their own light-evoked responses in ON than OFF cells, suggesting a possibility of more critical role in artificial visual percept. After classification, we tested three different waveform shapes with identical charge and pulse duration (-400 nC and 10 ms) but differing peak current amplitude: rectangular (-40 uA), linear increase (-80 uA) and linear decrease (-80 uA). A monophasic cathodal stimulus was repeated 7 times for each shape, and we recorded the spiking activities from 5 ON type RGCs.
Results :
The rectangular waveform elicited weaker network-mediated responses (i.e. least charge-efficient) than two other non-rectangular waveform shapes. 1) The peak firing rate of network-mediated responses arising from the rectangular waveform was 74.6±21.4 Hz, while those arising from the linear increase and decrease waveform shapes were 98.8±21.8 Hz (p=0.039) and 117.4±18.8 Hz (p=0.020), respectively. 2) The number of elicited spikes were 14.6±3.3, 19.5±6.2 (p=0.048) and 22.7±6.5 (p=0.029) for the rectangular, linear increase and linear decrease waveform stimuli, respectively.
Conclusions :
At a given amount of charges, linear increase or decrease waveforms were more effective than the rectangular shape to generate stronger network-mediated responses. Our results suggest that the rectangular waveform shape is not optimal for the best charge-efficiency in retinal prosthetic devices.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.