Central Retinal Artery Occlusion
The retina is supplied by one major artery. When this artery becomes blocked by a blood clot or plaque, little or no blood reaches the retina. This causes complete and sudden vision loss, usually in one eye. The sustained loss of vision is often preceded by short periods of vision loss which resolves. This condition, although painless, is similar to what happens in the brain during a stroke. Within 90 minutes of the loss of blood flow to the retina, the retina suffers irreversible damage. Because of this, the great majority of patients will suffer severe and permanent visual loss.
Branch Retinal Artery Occlusion
There is a main artery supplying blood flow to the retina. After entering the back of the eye, this main artery branches into many small blood vessels much like the branches of a tree. A branch retinal artery occlusion is a blockage of one of these branches. Following a branch retinal artery occlusion, a patient will describe either a defect in the side vision area or a sudden loss of central vision if the branch artery involves the macula. The macula is the portion of the retina that is the central vision area used for fine detailed reading vision. There are many arteries around the macula that are necessary for proper function. If one of the central arteries is involved in the occlusion, significant reading vision may be lost. Vision following a branch artery occlusion can range from normal 20/20 vision to hand motion. In one study over 75 percent of patients had initial vision of 20/40 or better. Investigation for associated general medical conditions is necessary following onset of an arterial occlusion. Branch retinal artery occlusion may be associated with small arterial embolism, hypertension, and other systemic abnormalities that affect blood vessels. BRAO may also be due to general medical or ocular inflammatory conditions. There is no specific direct treatment for a branch retinal artery obstruction.
Central Retinal Vein Occlusion
Like a central retinal artery occulsion, a central retinal vein occlusion occurs when the blood vessels that feed the retina are blocked by a blood clot or plaque. In this case, the main vein that leaves the retina is blocked which causes a backup of fluid and blood. The backup causes the central retinal artery to stop pumping blood to the retina which leads to the loss of circulation in the retina and subsequent retinal injury which leads to vision loss. In addition, the lack of oxygenated blood in the retina causes new blood vessels to form (neovascularization). These new blood vessels leak blood and fluid onto the retina which can lead to other problems.
Branch Retinal Vein Occlusion
A branch retinal vein occlusion happens when a branch of the central retinal vein, which drains blood and fluid from the retina, becomes clogged with a blood clot or plaque. The blockage of the vein causes pressure buildup in the capillaries which causes them to burst and spill blood on the retina. The size and location of the vein that is blocked determines the amount of damage done. For example, if the vein that is blocked is a larger vein closer to the central retinal vein, the damage will be larger because more blood vessels behind it are blocked.
