Arteries bring blood to the eye and veins bring blood back to the heart. Sudden vision loss occurs when a retinal artery is blocked. This is like a very small stroke. Most retinal artery occlusions are embolic. That means that a piece of calcium or cholesterol travels through the blood vessels leading to the eye and lodges in one of the retinal arteries and blocks it. This blocks circulation to the retina causing sudden painless vision loss. If a branch retinal artery is occluded, a portion of vision is lost. This usually looks like a shadow in the vision, either on the top half or bottom half of the vision. When the central retinal artery, the main artery to the retina, is blocked, total vision loss occurs. Usually patients can see light and some movement, but not much more. Sometimes a partial retinal artery occlusion will allow for some vision. Unfortunately, it only takes about 45 minutes of blockage for the retina to experience permanent damage, leading to permanent vision loss.
A branch retinal artery occlusion occurs when one of the branches of the central retinal artery is blocked. Most patients with a branch retinal artery occlusion lose side vision, usually above or below central vision. They can usually see pretty well straight ahead. Whlie looking at the words on this page, if you had a branch retinal artery occlusion, you might not see the top of the computer screen (or the bottom). Most retinal artery occlusions are cause by an embolis which forms in the heart or the carotid artery. The embolis travels to the eye and blocks either the central retinal artery or the branch retinal artery. Retinal artery occlusions are rarely caused by inflammation closing a retinal vessel. Diseases like giant cell arteritis in the elderly or toxoplasmosis and behcets disease in the young can rarely occlude a retinal artery. There is no effective treatment of branch retinal artery occlusion. Some physicians will try lowering the intraocular pressure by removing a small amount of fluid from the eye, prescribing pressure lowering eye drops or even having the patients rebreath into a paper bag. Since branch retinal artery occlusions usually do not adversely affect central vision, and since there is no proven treatment for them, most patients with branch retinal artery occlusion are not offered experimental therapy.
The circulation to the retina enters the eye through the central retinal artery. When a patient develops a sudden occlusion of the central retinal artery, the vision suddenly and severely declines. Research has shown that retinal cells become irreversibly damaged after the vessel is occluded for more then 45 minutes. Patients with a central retinal artery occlusion can usually only see shapes and movevment. Over time, 5% to 10% of patients recover some useful vision. The majority of patients recover some side vision, but do not regain central vision.