Corrosion cast demonstration of retinal vasculature of normal Wistar-Kyoto rats.

Plastic corrosion casts of the rat retinal vasculature were studied by scanning electron microscopy. This technique demonstrated the entire retinal vasculature of the rat. The retinal blood vessels supplying the rat's retina have a definite and fairly constant pattern. At the disk there are usually six main artery and vein branches that run symmetrically towards the periphery. Veins are wider and more tortuous. The characteristic arrangement of endothelial cell nuclear indentations clearly differentiates arteries from veins. Retinal arteries have side-arm and dichotomous branchings. The number of vessel branches is greater on the nasal side than on the temporal side of the retina. The vein-over-artery crossing phenomenon is more frequent than the artery-over-vein. Retinal capillaries appear tortuous and are arranged cylindrically in two layers. The superficial network of capillaries comes essentially from arterioles, while deep layer capillary networks are more regularly and densely arranged and are mainly connected with venules. The inner and the outer capillary networks have interconnections, vertical runs and short vascular bridges. Within the retina there are regional variations in capillary pattern and distribution. More regular, dense and rich capillary networks are observed in the peripheral area than at the posterior pole area. No arteriovenous shunts were seen. The study of such plastic casts makes possible a more accurate assessment of some aspects of vascular abnormalities. These findings will be helpful in further investigations of retinal vascular abnormalities.