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Yukari Nakano, Yasuo Terasawa, Hiroyuki Tashiro, Koji Osawa, Motoki Ozawa, Takashi Fujikado; Safety assessment of chronic electrical stimulation to rabbit retina for six months by Femtosecond Laser-induced Porous electrode of visual prosthesis. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):778. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
We have been developing a visual prosthesis based on Suprachoroidal-Transretinal Stimulation (STS). In this study, we applied electrical stimulation to the retinae of seven rabbits with our system for six months in order to clarify the effect of long-term electrical stimulation to their eyes.
Platinum stimulation electrodes (diameter: 0.5 mm, height: 0.3 mm) with Femtosecond Laser-induced Porous surface [Terasawa et al., ARVO E-abstracts 5538, 2012] were used for electrical stimulation. The electrode array was implanted into a scleral pocket on the eye of a rabbit. Current pulses were applied between the stimulation electrode and the return electrode (Cathodic-First, 1.5mA, 0.5ms, 50Hz, 8h/day). We performed ophthalmological examination with fundus photography and optical coherence tomography (OCT) before electrical stimulation and every four weeks during electrical stimulation. The presence of retinal damage was assessed histologically in the tissue samples of the enucleated eyes. All procedures conformed to the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research.
Chronic electrical stimulation for six months did not cause any damages of retinae in six of seven cases. However, decrease of cell density in the outer layer of the retina was observed in one case. In this one case, the thickness of the sclera between the choroid and the electrode tip was 78 μm, which was about 30% of the average thickness of the other six cases (259 μm). It is inferred that proximity of the electrode to the retina was one of the factors that caused the cell decrease in the outer layer of the retina. Given the different of the thickness of sclera between rabbit and human, this proximity is unlikely occur in human case. There was no significant difference in the thickness of the sclera on the electrode between before and after the electrical stimulation in all the seven cases.
In six of seven cases, electrical stimulation did not cause damage to the retinae and surrounding tissues, therefore electrical stimulation of retinae was shown to be safe. However, the cell decrease in the outer layer of the retina was observed in one case. We are going to investigate the relationship between the thickness of the sclera on the electrode and occurrence of cell decrease in the future.
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