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J. G. Eng, R. N. Agrawal, F. N. Ross-Cisneros, G. Dagnelie, R. J. Greenberg, J. D. Weiland, A. A. Sadun, M. S. Humayun; Morphometric Analysis of Optic Nerves From an End-Stage Retinitis Pigmentosa Patient Implanted With an Active Epiretinal Array. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1777. doi: https://doi.org/.
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To morphometrically characterize optic nerve changes in a patient with end-stage retinitis pigmentosa implanted with a chronic active epiretinal array.
A 74-year-old male with end-stage autosomal dominant retinitis pigmentosa in both eyes was implanted with a 16-electrode epiretinal array in the right eye. At the time of implantation, visual acuity had remained at no light perception and light perception in the right and left eyes, respectively, for the preceding 6 years. At 8 months post-implantation, silicone oil was injected in the right eye. Intraocular pressure remained well-controlled throughout. The array remained fixed over the macula until patient’s death from unrelated causes approximately 5 years and 3 months after array implantation. Both eyes were enucleated post-mortem and at the time of dissection, optic nerves were nicked peripherally for orientation, fixed in half-strength Karnovsky’s, and then processed and embedded. Sections were cut at 1 µm and stained with p-phenylenediamine (PPD). Total optic nerve axons and axons in each optic nerve quadrant were quantified by sampling approximately 64 regions across the entire optic nerve cross-section.
Total optic nerve axon count was 45,726 ± 3004 in the right eye vs. 140,393 ± 4740 in the left eye (p < 0.05). Given the loose retinotopic order within the optic nerve immediately posterior to the globe, the temporal quadrant of the right optic nerve corresponded roughly to the site of epiretinal array implantation and stimulation. In the right optic nerve, the axon density in the temporal quadrant was not significantly different from that in the superior quadrant but was significantly increased compared to the inferior and nasal quadrants (p < 0.05). Axon densities in the right optic nerve quadrants were as follows: temporal - 12,718 ± 1005 axons/mm2; superior - 13,663 ± 1377 axons/mm2; inferior - 5,358 ± 1049 axons/mm2; nasal - 9,462 ± 786 axons/mm2. There was no evidence of silicone oil infiltration.
Chronic implantation and electrical stimulation with an epiretinal array did not result in damage that could be appreciated when comparing axon densities within the right optic nerve. The difference in axon count between the right and left eyes could be a result of advanced disease or multiple other surgeries performed on the right eye.
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