There are two main types of vascular occlusions in the retina; those that affect the venous system and those that affect the retinal arteries. Each is further broken into “branch” (aka hemi) or central; depending upon the extent of involvement of the vascular tree, i.e., central connotes involvement of the entire retina, whereas branch is usually half the retina or less.
In general, vein occlusions may occur in healthy individuals and is thought to be related to hypertension. Arterial occlusions may occur in patients with systemic vascular disease and occur when an “embolus” gets lodged in a retinal artery.
In both situations, involvement of the macula directly correlates with loss of vision. Branch retinal vein occlusions probably have the best visual prognosis. Central venous and artery occlusions have a worse visual prognosis and also have a greater chance of complications such as neovascular glaucoma.