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Yongsook Goo, Kun No Ahn, Seol A Jae, Joo Yun Kim; Comparison of Electrically Evoked Retinal Ganglion Cell (RGC) Responses by Square Pulse and Triangle Pulse in rd1 mice. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1026. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Retinal prosthesis has been developed for the patients with retinitis pigmentosa (RP) and age related macular degeneration (AMD), and is regarded as the most feasible method to restore vision. Extracting optimal electrical stimulation parameters for the prosthesis is one of the most important elements for the success of retinal prosthesis. Here, we used charge balanced biphasic current pulse and we compared efficiency of three different pulse shapes evoking RGC responses in rd1 mice.
The well-known animal model for RP, rd1 (Pde6brd1) mice at postnatal 8 weeks were used (n=9). From the ex-vivo retinal preparation, retinal waveforms were recorded with 8 × 8 MEA. Biphasic current pulses in the form of cathodic phase-1st and anodic phase-2nd were applied once per second (1 Hz, x50). We tested 3 different pulse shapes with same charge; 1) biphasic square pulse (I: intensity, D: duration), 2) biphasic triangle pulse with intensity doubled (2xI, D) to satisfy same charge requirement with square pulse, 3) biphasic triangle pulse with duration doubled (I, 2xD) to satisfy same charge requirement with square pulse. For intensity modulation, duration of the pulse was fixed to 500 μs and the intensities of the pulse were modulated from 5 to 40 μA. For duration modulation, intensity of the pulse was fixed to 30 μA and the durations of the pulse were modulated from 60 to 500 μs. The electrically-evoked RGC spikes was defined as positive when the number of RGC spikes for 400 ms after stimulus was 1.3 times higher than that for 400 ms before stimulus in post-stimulus time histogram.
RGC responses were well modulated both with square pulse and triangle pulse by varying the intensity and duration of the pulse. Amplitude modulation shows that RGC response is preferentially activated by biphasic triangle pulse with duration doubled especially with 5 μA (p<0.001) and 10 μA (p<0.01). Duration modulation shows that RGC response is preferentially activated by biphasic triangle pulse with duration doubled especially with 60 and 100 μs (p<0.001) and 200 μs (p<0.05).
Biphasic triangle pulse with duration doubled is always efficient than square pulse and biphasic triangle pulse with intensity doubled both in amplitude modulation and duration modulation.
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