Abnormal vessel patterns in phototoxic rat retinopathy studied by vascular replicas

Permeability abnormalities of vessels in rat phototoxic retinopathy have been described for sodium fluorescein and the fluoresceinated dextrans. Since fenestrated vessels within the pigment epithelium (RPE-vessels) had connections to retinal capillaries but not to choroidal vessels, it was presumed that the continuous retinal vessels became fenestrated when located in the abnormal environment of the pigment epithelial cell. It was necessary to rule out a choroidal origin of these unusual RPE-vessels, since they may be a model for other vasculopathies. Vascular cast replicas of whole retinal and choroidal vessel beds from rats with advanced phototoxic retinopathy were studied by scanning electron microscopy. No connection between the retinal and choroidal vasculature was found. Retinal vessels entering the pigment epithelium formed medusa-like coils in local areas. Marked capillary dropout and vessel tortuosity were characteristic. The choroidal capillary bed was normal. This model is appropriate for study of the plasticity of retinal capillaries as seen in diabetic retinopathy and senile macular degeneration.