CRV retinal occlusion. Ophthalmoscopy view of the retina of the eye, showing occlusion of the central retinal vein (CRV). Retinal occlusion is the blockage of one or more blood vessels of the retina, in this case branches of the central vein. Blockage has caused subsequent bursting and haemo- rrhage (bleeding), appearing as diffuse red patches. Cotton wool (yellow) spots also repre- sent blood vessel damage. The central retinal vein passes from the surface of the retina through the optic disc (at lower left) & out of the eyeball. Veins appear darker red than arteries. Occlusion may be due to atherosclerosis: fatty deposits on vein walls due to high levels of cholesterol.