The retina—the layer of light-sensitive cells at the back of the eye—is nourished by the flow of blood, which provides nutrients and oxygen that nerve cells need. When there is a blockage in the veins into the retina, retinal vein occlusion may occur.
Branch retinal vein occlusion (BRVO) is a blockage of the small veins in the retina. (When there is blockage of the main vein in the retina, it is called Central Retinal Vein Occlusion.)
BRVO often occurs when retinal arteries that have been thickened by atherosclerosis (hardening of the arteries) cross over and place pressure on a retinal vein. When the vein is blocked, nerve cells within the eye may die.