Retinal artery occlusion: In case of central retinal artery occlusion. The arterial phase is particularly delayed. It is often possible to see the slow progression of the dye front. The column of blood is seen to be broken into segments. After the second week the dye begins to flow into the retinal vessels very slowly but may not show full recovery. The fluorescein pattern in branch retinal artery occlusion is again similar to that in central retinal artery except that changes are limited to the affected part of the retina only. Central retinal vein occlusion is often due to both local and systemic causes. Central retinal vein occlusion can be divided into two groups, a nonischaemic and ischaemic type named by Hayreh as venous stasis retinopathy and haemorrhagic retinopathy respectively. Venous stasis retinopathy (VSR) is of a milder form of venous occlusion without significant retinal hypoxia. In the acute stage, the early prearterial phase shows patchy choroidal filling associated with some masking. Late phase shows considerable amount of staining on the wall of the veins, leakage of dye to the surrounding retina, and a typical cystoid macular oedema. Haemorrhagic retinopathy is due to occlusion of central retinal vein associated with significant retinal hypoxia resulting in profound visual loss associated with afferent papillary defect. Fluorescein angiography shows narrowing arteriolar narrowing with extensive capillary closure affecting large parts of the retina. During the resolved stage fluorescein angiography shows gross retinal arteriolar sclerosis, large areas of capillary closures, and neovascularization from the optic disc. Branch retinal vein occlusion shows similar changes limited to the affected sector only.