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H. Kanda, H. Sawai, T. Morimoto, T. Fujikado, Y. Tano, Y. Fukuda; Suprachoroidal-Transretinal Stimulation (STS) Can Elicit Localized Evoked Responses From the Superior Colliculus in Normal and RCS Rats . Invest. Ophthalmol. Vis. Sci. 2003;44(13):5053.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: In order to minimize insult to the retina while implanting stimulating electrodes, we developed a new stimulation method for the retinal prosthesis, named suprachoroidal-transretinal stimulation (STS). To evaluate whether the STS is appropriate to evoke artificial vision, we measured threshold intensity of the evoked potentials (EPs) from the superior colliculus (SC) and their localization in normal and Royal College of Surgeons (RCS) rats. Methods: Female hooded rats (Long Evans, n=17) with ages 8-14 weeks and RCS rats (n=6) with ages 25-30 weeks were used. The animals were anesthetized and maintained with urethane (1.75g/kg, i.p.). Every procedure conformed to the Guideline of ARVO. A small fenestration (diameter: about 0.5mm) was made in upper temporal part of the sclera. For electrical stimulation, a silver ball electrode (diameter: 0.2-0.3 mm) was placed on the fenestration. Another electrode of epoxy coating stainless wire (diameter: 0.5mm), with an exposed tip of about 0.2mm, was inserted into the vitreous. Between the two electrodes electrical pulses of 5-100 µA in amplitude and 0.05-0.5ms in duration were applied. The EPs were recorded from the SC with another silver ball electrode (diameter: 0.2 mm) which was systematically moved with a micromanipulator to cover an area of 0.5×0.5mm – 1.0×1.0mm on the SC surface. Results: In response to STSs triphasic EPs appeared having similar wave forms to those evoked by stimulation of the optic nerve. The threshold intensity of the STS was about 5-10nC in both normal and RCS rats. The EPs to suprathreshold STSs were localized in a collicular surface area of 0.12+/-0.07mm2. In all cases the EP with a maximum amplitude was obtained from the SC area that represents the locus of retina that was stimulated with the STS. Conclusions: The STS can focally activate retinal ganglion cells with reasonable currents in normal rats as well as in RCS rats. The STS is less invasive to the retina than other methods of retinal stimulation such as epiretinal and subretinal implants. Therefore, we conclude that the STS method is suitable for designing a new type of retinal prosthesis.
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