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Hiroyuki Kanda, Takeshi Morimoto, Yasuo Terasawa, Yukari Nakano, Kohji Nishida, Takashi Fujikado; Evaluation of long-term implantation of an inactive 49-channel electrode array for STS retinal prosthesis. Invest. Ophthalmol. Vis. Sci. 2014;55(13):1814.
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We developed a second-generation device for STS (Suprachoroidal-Transretinal Stimulation) retinal prostheses. The electrode array of this device comprises 49 stimulating electrodes and a multiplexer IC-chip. To verify its safety, we investigated its effects following chronic implantation for 6 months.
Inactive devices were used to assess chronic implantation (Fig. 1). These implants include a multiplexer and an electrode array of 49-channel porous electrodes (diameter, 0.5 mm; height, 0.3 mm). Three eyes of 3 pigmented rabbits were used. We created a scleral pocket at the posterior pole of the eye and inserted the electrode array. Implants were implanted for 6 months without electrical stimulation. Fundus photography, fluorescein angiography (FA), indocyanine green angiography (IA), optical coherence tomography (OCT), and slit-lamp examination were performed at 1 week, 1 month, 3 months, and 6 months after implantation. After the experiment was concluded, the eyes were enucleated, and the retinas were stained with hematoxylin and eosin and examined by light microscopy.
OCT (Fig. 2), FA, IA, and histological examination at 6 months after implantation revealed no significant changes in the retinal areas (49 × 3 = 147 areas) where the electrodes were located. No retinal damage, including retinal edema, retinal detachment, ischemia in choroidal circulation, or FA leakage, was identified. Furthermore, no conjunctival dehiscence or erosion was observed at the location of the multiplexer. At the center of the array, the thickness of the residual sclera on the electrodes significantly decreased from 103 ± 28 μm to 74 ± 29 μm (mean ± SD) (p < 0.01, n = 3, paired t-test) during 6 months of implantation.
These results indicate that the electrode array of a second-generation device for STS retinal prosthesis is safe for chronic implantation. Moreover, during chronic implantation, the distance between the electrode and the retina decreased with the thinning of the sclera, thereby suggesting that phosphene threshold might be decreased by chronic implantation.
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