blockage of a vein carrying blood from the retina. Small branch veins carry blood from different parts of the retina and drain into the central retinal vein, which leaves the eye at the optic disc. Blockage of the central retinal vein (central retinal vein occlusion) usually results in sudden painless reduction of vision. Distended veins, haemorrhages, and cotton-wool spots are seen in the retina and the optic disc may become swollen. Blockage of a branch of the central retinal vein (branch retinal vein occlusion) results in painless reduction of vision in the affected area, where engorged veins, haemorrhages, and cotton-wool spots may be seen.
Medical dictionary. 2011.