Central retinal vein occlusion: occurs when a thrombus forms in the retinal veins and blocks the drainage of blood from the retina
Branch retinal vein occlusion: venous occlusion at any branch of the central retinal vein resulting in visual problems in the area drained by that branch
Blockage of a retinal vein causes pooling of blood in the retina, resulting in leakage of fluid and blood causing macular oedema and retinal haemorrhages
This results in damage to the tissue in the retina and loss of vision
It also leads to the release of VEGF, which stimulates the development of new blood vessels (neovascularisation)
Clinical features
Sudden painless loss of vision
Branch retinal vein occlusion may result in visual field defects corresponding to affected branch