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Michael H. Davies, Steven Yeh, Andrew J. Stempel, Kathleen Mohs, John F. Payne, Hassan T. Rahman, Michael R. Powers, Justine R. Smith, Joao M. Furtado; Topical Endoscopic Fundus Imaging in Murine Oxygen-Induced Retinopathy. Invest. Ophthalmol. Vis. Sci. 2012;53(14):2530.
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Murine oxygen-induced retinopathy (OIR) is widely used to investigate retinal ischemic vasculopathy. However, this model relies on the study of post-mortem tissue. We aimed to visualize OIR in vivo using topical endoscopy fundus imaging (TEFI), and correlate the findings with results of standard histopathological evaluations.
OIR was generated by exposing 7-day old (P7) pups to 75% oxygen for 5 days, followed by room air recovery. Controls were exposed to room air only. TEFI was performed on P12, P15, P17, P21 and P25 mice (n=3-6 mice/group) under general anesthesia with dilated pupils using a tripod-mounted Nikon D90 camera, a 60 mm F/2.8 D lens, a 58-52 step down ring, a Storz 481C halogen light and a Storz 1218 tele-otoscope. Retinal images of posterior pole, and where possible, peripheries, were formatted with Nikon ViewNX2 software, and vascular tortuosity was graded 0-4 against standard photographs by two masked examiners. Mice were euthanized immediately following image acquisition. Right retinas were fixed in 4% PFA, stained with fluorescently tagged isolectin to identify vessels, and visualized by confocal microscopy. Percentage of retinal vaso-obliteration was measured by a masked examiner. Left eyes were formalin-fixed, and 5μm paraffin sections stained with H&E and retinal neovascularization (NV) was quantified.
In agreement with the literature, compared to control mice, hyperoxia-exposed mice suffered retinal vaso-obliteration, peaking at P12 (32.4% vs. 1.5%, p = 0.0011) and retinal NV, maximal at P17 (23.7 ± 2.6 nuclei/section vs. 0.09 ± 0.03 nuclei/section, p <0.0001). By TEFI, retinal vascular tortuosity was observed in hyperoxia-exposed mice as early as P15 (p = 0.011). Tortuosity peaked at P17 (Grade 2.75 ± 0.08 vs. Grade 0.06 ± 0.06, p < 0.0001), correlating with retinal NV observed in H&E histology. In addition, tortuosity was reduced, but still significantly higher than controls, at P21 and P25 (p<0.005), in concordance with histological evidence of reduced retinal NV.
We report the clinical observation of retinal vascular tortuosity in mice, as visualized by TEFI. These data appear to correlate with histological and whole mount results, demonstrating the validity of this technique. One advantage of this technique is the potential to image a single animal over the time course of the disease.
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