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Y. Goo, J. Ye; Comparison of Electrical Stimulation Parameters for Normal and Degenerate Mouse Retina. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3040. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Retinal prosthesis is regarded as the most feasible method for the blind caused by retinal diseases such as RP or AMD. One of the prerequisites for the success of retinal prosthesis is the optimization of the electrical stimuli applied through the prosthesis. Since electrical characteristics of degenerated retina are expected to differ from those of normal retina, we compared the differences in current and voltage stimulation parameters between the normal and degenerate retina to provide a guideline for the optimization of electrical stimulation for the upcoming prosthesis.
C57BL/6J and C3H/HeJ (rd/rd mice) strain mice were used as the normal and the degenerate retina respectively at the age of postnatal 4 weeks (n=3/strain). After isolation of retina, the retinal patch was attached with the ganglion cell side facing the surface of MEA. 8 × 8 grid layout MEA (electrode diameter: 30 µm, electrode spacing: 200 µm, and impedance: 50 kΩ at 1 kHz) was used to record in vitro retinal ganglion cell activity. Monopolar electrical stimulation was applied through one of the 60 MEA channel, and the remaining channels were used for recording. Current and voltage stimulation was applied on the same retinal patch and the response was compared. The electrical stimulus was a constant current (or voltage), charge-balanced biphasic, anodic-first square wave pulse without interphase delay, and 35 trains of pulse was applied at a rate of 0.5 Hz. Different electrical stimuli were applied. First, phase width was varied (60 ~ 1000 µs). Second, stimulus intensity was varied (current: 2 ~ 60 µA, voltage: 0.1 ~ 3.0 V). Evoked responses were analyzed from averaged data with 35 trains of pulse. Charge density was calculated with Ohm’s and Coulomb’s law.
The calculated threshold of charge density ranged from 85 to 283 µC/cm2 in normal retina. In degenerate retina, the threshold of charge density was 142 ~ 354 µC/cm2 on current stimulation, while that was 142 ~ 708 µC/cm2 on voltage stimulation. Both retina showed 0.5 ~ 1 ms of latency and there was no statistical difference between the two.
The result showed that degenerate retina needed higher charge density to evoke the ganglion cell responses compared to the normal retina. In degenerate retina, the charge density needed with voltage stimulation was almost two-fold higher than that with current stimulation, which might be induced by substantial impedance level of tissue.
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