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Hyung Jung Yoo, Kyo-in Koo, Sangmin Lee, Seok-jun Hong, Jae-hyun Ahn, Jang Hee Ye, Sang Baek Ryu, Kyung Hwan Kim, Yongsook Goo, Dongil D. Cho; A Model of Subretinal Neural Pathways for Retinal Prosthesis Using in vitro Experiments. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4937.
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In this paper, a model of subretinal neural pathways for retinal prosthesis is presented. In order to investigate the neural pathways of subretinal stimulation, the response of evoked spikes from ganglion cell is recorded and the threshold current is measured with respect to current stimulation to photoreceptor cell. The experiment is performed using an in vitro setup instead of in vivo setup, to control the number of valid variables.
Isolated rabbit retina is attached on conventional recoding microelectrode array (MEA) (MEA 200/30, Multi-Channel Systems MCS GmbH, Germany) which has 60 channels. The stimulating MEA developed using Microelectromechanical Systems (MEMS) technology is fixed on the attached retina with customized jig. The biphasic current pulse stimulation which has 5 ~ 200 µA amplitude with 1 ms duration is allowed to the stimulating MEA. The electrical responses are measured from the recording MEA with a sampling rate of 25 kHz/channel. The experiment is performed using three different types of stimulation, which are monopolar, bipolar, and dual monopolar. The evoked responses are recorded, and the measured outputs are averaged after 50 times of repetitions.
The evoked responses by the current stimulation occur at the stimulation site or near the stimulation site. This indicates that the photoreceptor cell is not directly connected to the ganglion cell. The monopolar stimulation excites the same number of neurons with less amplitude than the bipolar stimulation. The threshold charge of monopolar and bipolar stimulation is around 10 ~ 20 nC.
In order to investigate the neural pathways of subretinal stimulation, the response of the single and dual stimulation were measured, using the in vitro experiment setup. The monopolar stimulation excites more number of neurons than the bipolar stimulation at the same current amplitude. Both stimulations show the threshold charge of 10 ~ 20 nC. The geometrical relation between the stimulation and the response seems relatively low.
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