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Hiroyuki Kanda, Takeshi Morimoto, Yasuo Terasawa, Yukari Nakano, Kohji Nishida, Takashi Fujikado; Evaluation of safety of porous surface electrodes for STS Retinal prosthesis. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1046. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
We have reported that our originally developed retinal prostheses with suprachoroidal-transretinal stimulation (STS) effectively elicited phosphene with current less than 1.0 mA in patients with advanced retinitis pigmentosa (Fujikado, IOVS 2010). Now we have developed a novel porous stimulating electrode (porous electrode) for retinal prostheses for STS system (Terasawa, ARVO 2012). The porous electrode has a large surface area introducing porous surface of the platinum bulk electrode with a femtosecond laser irradiation. To verify their safety, we investigated the threshold current for retinal damage by a 48-h continuous-stimulation test.
Ten eyes of 10 pigmented rabbits were used in this study. We created a scleral pocket at the posterior pole of the eye and implanted the stimulating electrode. The stimulating electrode comprised a single-channel porous electrode (diameter, 0.5 mm; height, 0.3 mm). The rabbits were divided into four groups and stimulated with electrical currents of different intensities: 1.0 mA (n = 2), 1.5 mA (n = 3), 2.0 mA (n = 3), and 3.0 mA (n = 2). Continuous biphasic pulses of 0.5 ms/phase were applied at a frequency of 20 Hz for 48 h under general anesthesia. Fundus photography, fluorescein angiography (FA), and optical coherence tomography (OCT) were performed before and after applying the electrical currents. After the experiment was concluded, the eyes were enucleated and the retinas were stained with hematoxylin and eosin, and examined by light microscopy.
In the 1.0 mA and 1.5 mA groups, changes were not observed on fundus photography, FA, OCT, or histological examination. Leakage of fluorescent dye was observed in one of three cases in the 2.0 mA group and in all cases in the 3.0 mA group. Probit analysis of the relationship between retinal pigment epithelium (RPE) damage and stimulus intensity suggested that 2.1 mA led to an RPE damage incidence rate of 50%.
These results indicate that the threshold current to induce retinal damage is greater than the current to elicit phosphene in STS. Therefore, the porous electrodes are feasible as stimulating electrodes for STS retinal prostheses.
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