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Hiroyuki Tashiro, Yasuo Terasawa, Kouji Osawa, Motoki Ozawa, Toshihiko Noda, Jun Ohta, Takashi Fujikado; In vivo Characterization of Electrochemically-Treated Platinum Bulk Electrodes for Retinal Prostheses. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5518. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
We have proposed bullet-shaped electrodes with enhanced surface area through electrochemical etching(Terasawa et. al., ARVO 2010). The purpose of this study is to estimate the characteristics of the electrodes in vivo.
The eye of a Japanese white rabbit was used. All procedures conformed to the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research. Two bullet-shaped platinum electrodes, one was with electrochemically etched surface and the other was untreated, were implanted into the sclera of the rabbit. The dimensions of electrodes were 500μm in diameter and 300μm in height respectively. After a recovery period, chronic stimulation was initiated. The stimulation period was 4 weeks. The applied stimulation current pulses consisted of cathodic first (CF) biphasic pulses with amplitudes of 1.2mA, durations of 500μs and rates of 50Hz. Electrical stimulation were applied to the eye for 8 hours per day. The charge delivery capacities (CDCs) and the electrode impedances of the electrodes were evaluated in vivo and also in phosphate-buffered saline (PBS) before and after one-month stimulation.
The CDC of the electrode treated electrochemical etching in vivo was considerably less than the value in PBS. And the reduction of the CDCs and the increase of the electrode impedances were observed afterone-month stimulation in vivo. (see Table 1)
The characteristics of electrodes with porous surface differed in vitro and in vivo. This might be caused by accumulated tissue fluids in fine pores. The electrode performances deteriorated after chronic stimulation in vivo. This should be result of a number of factors that could occur during implantation of electrodes: 1) mechanical damage caused by the insertion trauma; 2) bacterial infection; and 3) an inflammatory response to the presence of a foreign body resulting in fibrosis. We are considering local treatment of the sclera after electrode insertion trauma with dexamethasone.
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