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Hiroyuki Kanda, Takeshi Morimoto, Kentaro Nishida, Yoshiyuki Kitaguchi, Yasuo Terasawa, Kohji Nishida, Takashi Fujikado; Evaluation Of The Safety Of Long-term Suprachoroidal-transretinal Stimulation. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4938.
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Suprachoroidal-Transretinal Stimulation (STS) is one of the electrical stimulation methods for retinal prostheses (Kanda, IOVS 2004). The safety of long-term STS must be evaluated for the clinical application of retinal prostheses using STS. Therefore, we investigated whether retinal damage was induced after chronic STS.
Pigmented rabbits (Kbl: Dutch) were used in this study. A scleral pocket was created at the posterior pole of the eye; a stimulation electrode (single platinum electrode; 0.5 mm in diameter and 0.5 mm in height) was chronically implanted in the scleral pocket. In order to evaluate the retinal damage caused by electrical stimulation, cases of retinal damage due to surgery were excluded from this study. The rabbits were divided into 3 groups and stimulated with currents of different intensities: 700 nC/phase (n = 5), 500 nC/phase (n = 2), and 0 nC/phase (n = 2). The retinas were stimulated with continuous biphasic pulses of 1.0 ms/phase in duration and 20 Hz in frequency for 6 hours. Fundus photography and fluorescein angiography (FA) were performed after the stimulation trial using a scanning laser ophthalmoscope (SLO). The trials were repeated once per week for 3 months. After completion of the trials, the retinal tissue were sectioned, stained with hematoxylin and eosin, and examined by light microscopy.
In all 3 groups of rabbits, no abnormalities were observed by fundus photography and FA, in any of the trials. In addition, retinal damage was not detected by histological examination after chronic STS.
These results demonstrate the safety of long-term STS at intensities less than 700 nC/phase, which is greater than the threshold stimulus required to evoke phosphene (Fujikado, Graefe’s Arch Clin Exp Ophthalmol 2007). Therefore, the clinical application of STS is feasible.
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