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J. Phillips, B. Hanzlicek, H. Yin, A.Y. Chow, M. Pardue, S.L. Ball; Superior versus Inferior Implantation of the Subretinal Artificial Silicon Retina (ASR) chip in RCS Rats . Invest. Ophthalmol. Vis. Sci. 2004;45(13):4176.
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Purpose: Subretinal implantation of an ASR chip into the superior retina of the RCS rat has been shown to result in the preservation of photoreceptors (Pardue et al., 2003). However, the RCS rat is known to have delayed photoreceptor degeneration in the superior region of the retina as to compared to other retinal areas (Lavail and Battelle, 1975). To determine whether the superior retina is a "privileged" site in the RCS rat, artificial silicon retina (ASR) devices were subretinally implanted in the superior and inferior retina. Methods: Three week old RCS rats were implanted with an active ASR superiorly in one eye and inferiorly in the other eye. Littermates served as unoperated controls. Preservation of retinal function after implantation was measured biweekly with ERGs after implantation. At 8 weeks post implantation the eyes were enucleated and fixed in mixed aldehydes. Posterior eye cups were processed into plastic resin and sectioned vertically at 0.5µm. The number of photoreceptor nuclei was counted in individual retinal sections in 0.5mm segments. Results: The rate of retinal function loss, as determined by ERG recordings, was slower in eyes implanted with an ASR device compared to unoperated eyes regardless of placement within the eye. The ERG b–wave responses in implanted eyes were 2 to 3 times larger in amplitude than unoperated eyes from 4 to 8 weeks post–implantation. Retinal function was similar in eyes implanted superiorly and inferiorly. Anatomical analysis showed a 4 to 5 fold greater number of photoreceptors directly overlying the implant in both the superiorly and inferiorly implanted eyes compared to unoperated eyes. Increased photoreceptor preservation also extended to approximately 1mm adjacent to the implant. Conclusions: Superior and inferior implanted eyes showed similar patterns of photoreceptor preservation, both functionally and anatomically. These results suggest that both the superior and inferior regions of the RCS rat retina benefit from ASR chip implantation and that the naturally occurring delay in degeneration in the superior retina does not extend neuropreservation by the ASR chip. Superior and inferior retina both make good candidates for implantation.
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