Permeability of blood-retinal barriers in urethane-induced rat retinopathy: a fluorescein angiographic, vitreous fluorophotometric, and fluorescence microscopic study.

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Abstract
Urethane-induced rat retinopathy, characterised by permeability abnormalities of the blood-retinal barriers (BRB), was studied during the developmental phases by fluorescein fundus angiography (FFA), vitreous fluorophotometry (VF), and fluorescence microscopy (FM). A distinction based on VF values could be made at the p less than 0.02 confidence level between the retinopathic rats as a group and the control rats. Fluorescence microscopy provided a basis, however, for subdividing the test group into those rats with evidence of intraretinal leakage of NaFl and those without. Statistical analysis of the VF values of the control (A), nonleaky retinopathic (B), and leaky retinopathic (C) rats showed no significance between groups A and B, but highly significant differences between groups A and C (p less than 0.001) and between groups B and C (p less than 0.01). Fluorescence microscopy also showed that leakage of NaFl from retinal vessels occurred only after the retinopathy has progressed to the point where retinal vessels had become incorporated into the pigment epithelium. We conclude from this fluorescent marker clinicopathological study that breakdown of the blood-retinal barriers is a result of an interaction between the retinal pigment epithelium (RPE) and the retinal vessels after the vessels become incorporated into the RPE.