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Ryan J. Dashek, Charlene B. Y. Kim, Carol A. Rasmussen, Elizabeth A. Hennes-Beean, James N. Ver Hoeve, T. Michael Nork; Retinal Ganglion Cell (RGC) Axotomy by Endodiathermy in Non-Human Primates. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2460.
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To develop a reliable method for isolating the outer retina in non-human primates.
Contiguous endodiathermy spots were placed along the inferior 180o adjacent to the optic nerve margin in the right eyes of 4 cynomolgus monkeys. Two 25 ga cannulae were inserted through the conjunctiva/sclera using trocars. A fiberoptic light was passed through one 25 ga cannula and a sharp-tipped endodiathermy was passed through the other. A flat contact lens was used to visualize the retina. The individual diathermy spots were placed at or near the inferior margin of the optic nerve using enough energy to cause retinal whitening. Care was taken to avoid the large retinal vessels. Fundus photographs were obtained on the day of diathermy placement and again at 3 months. Fluorescein angiography and spectral domain optical coherence tomography (sdOCT) measurements were also done at 3 months. Multifocal electroretinography (mfERG) testing was done at various intervals. Two of the animals were sacrificed at 3 months and the eyes immersion fixed in paraformaldehyde. Segments of retina were embedded in Durcupan. Immunohistochemistry (IHC) for glial fibrillary acidic protein (GFAP), rhodopsin, S-cone opsin and M/L-cone opsin was performed. Optic nerve segments were post-fixed in osmium tetroxide and stained with paraphenylene diamine.
One of the 4 animals experienced moderate post-operative inflammation that cleared with subconjunctival steroid. At 3 months, there was marked thinning of the inferior nerve fiber layer evident on both fundus photography and by sdOCT. Fluorescein angiography showed no indication of retinal vascular disturbance distal to the diathermy spots. mfERG first order kernel N1 and P1 waveforms at 3 months were present in the inferior retinae (distal to the optic nerve) and qualitatively similar to those in the non-diathermized superior retinae. Sections of optic nerves showed loss of >95% of axons in the inferior nerves. Radial retinal sections showed marked reduction in cells in the ganglion cell layer and thinning of the nerve fiber layer. The photoreceptor morphology and IHC opsin staining were similar in the diathermized and non-diathermized retinae. GFAP staining of the outer retina was normal in the both regions, as well.
RGC axotomy by endodiathermy was well-tolerated and may have advantages over laser photocoagulation despite its being an invasive procedure.
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