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Xu zhao, Natalie Pankova, Hai Wang, Teresa Liang, Sepedeh Hariri, Kostadinka Bizheva, Shelley R. Boyd; Patches Of RPE Loss Can Be Detected In Vivo In The Rat Eye Using Confocal Scanning Laser Ophthalmoscopy. Invest. Ophthalmol. Vis. Sci. 2011;52(14):969.
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To visualize RPE loss in vivo using confocal scanning laser ophthalmoscopy (cSLO) in the rat, and to potentially induce patches of hypofluoresence similar to those seen in patients with advanced AMD and geographic atrophy.
The HRAII (Heidelberg Retinal Angiography II) cSLO was used to image the rat fundus in the 488/520 and 790/810nm channels. Adult Brown Norway rats were injected once with 0.35, 2 or 5mg/kg Indocyanine Green (ICG) dye, via tail vein, and no fluorescein was given. cSLO images were taken at baseline (prior to injection), and at 24, 48 and 72 hours. In a second set of experiments, a known RPE toxin, NaIO3 (45mg/kg), was injected via tail vein, and images taken at days 3, 7, 14 and 28. Excised eyes were evaluated by wholemount and posterior eye cup immunohistochemistry and cross-sectional H&E histology. Same-species IgG antibodies were used as negative control.
Unlike the human fundus, the rat RPE layer did not autofluoresce significantly at 488nm. It followed that no patches of RPE loss could be detected. However, after a single injection of ICG dye, the RPE became visible, dose-dependently, within 24 hours and remained labelled for up to 28 days. Following injection of NaIO3, large patches of hypofluorescence became visible 3 days after NaIO3. Histology confirmed RPE and outer retinal loss in areas corresponding with in vivo hypofluorescence. At 28 days after ICG, there was no detectable loss of the RPE in animals that did not receive NaIO3.
ICG dye labels the RPE layer in vivo, and was confirmed by injection of NaIO3, a known RPE toxin. We suggest that labeling of the RPE with ICG dye is a useful tool to visualize the RPE in vivo in rodent models, and could serve as a non-invasive method to follow outer retinal toxicity or loss in the long- or short-term evaluation of ophthalmic drugs, biomaterials and drug delivery devices.
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