Central Retinal Vein Occlusion
A central retinal vein occlusion (CRVO) is a blood circulation problem. When the blood vessel called the central retinal vein becomes blocked suddenly it causes a rapid reduction in vision. It is like having a small “stroke” in the retina.
WHY IS VISION LOST?
The retina is the light-sensitive nerve tissue lining the back of the eye. Like film in a camera it takes “moving pictures” of everything you see. Your vision depends on a healthy well-nourished retina which require a steady stream of oxygen-rich blood-brought to it by arteries and carried away by veins.
The central retinal vein is the main blood vessel that drains “used” blood from the retina. When that vein gets blocked the entire retinal bloodstream swells and backs up so that fresh blood cannot enter the retina. The backup also causes some retinal hemorrhages (bleeding).
Without the oxygen supplied by a normal blood flow the retina slowly starves and some retinal cells die.
WILL IT GET WORSE?
Vision probably will not improve much. In fact the reduced blood supply sets the stage for the possibility of even more damage to the retina. Months later the starved retina sometimes starts growing new blood vessels. The process is called neovascularization (neo=new; vascular=blood vessels).
Though you might think that new blood vessels are just what the retina needs these vessels are not normal. They are extremely fragile bleed easily and lead to scarring of the clear tissues inside the eye. Any of these complications can further obscure the remaining vision.
WHAT CAUSED THE VEIN OCCLUSION?
The usual cause is a blood clot that forms in the vein. That can happen whenever something slows down the flow of blood; for example pressure on the vein from an overlying or adjacent hardened artery (arteriosclerosis) can slow the flow of blood in the same way a fallen log obstructs a stream. Increased fluid pressure within the eye (glaucoma) or an inflammation in the vein wall (vasculitis) can also slow blood flow. Another cause may be from an increased tendency for blood to clot--this is a rare complication related to oral contraceptives and certain medical conditions.
Most causes of CRVO are related to aging changes in the blood vessels and are more likely to occur if you have atherosclerosis hypertension diabetes or glaucoma.
If the occlusion has existed for only a few hours it may be possible to slow or even reverse some of the retinal damage with eye-drops or other medications. The purpose is to lower the pressure inside the eye and lessen the tendency for further blood clotting. Once you have had the occlusion for more than a day or so there is probably little that can be done to stop the damage or to speed normal healing.
Eventually the blocked vein may re-open or nearby blood vessels (collaterals) may expand and redirect the flow of blood around the blockage site but the vision that has been lost is not likely to return to normal.
If neovascularization develops later a type of laser surgery called pan-retinal photocoagulation (PRP) can help reduce the number and size of the abnormal blood vessels. In this procedure many hundreds of tiny laser burns are made in the retina. The treatment is generally painless and takes less than half an hour; it can be done on an outpatient basis. If the neovascularization does not subside sufficiently within a few weeks additional laser treatments can be given.
PRP is not likely to improve vision directly. It is designed to reduce the risk created by neovascularization. One of these is damage from internal bleeding. Another is development of hemorrhagic glaucoma a much more serious condition than the common type of glaucoma associated with an increased risk of CRVO. Occasionally the laser cannot be used at all especially when there are opacities (dense blood or cataract) within the eye that would block the laser beam from reaching the retina.
Because CRVO can be associated with several medical conditions that affect the rest of the body you may be referred to an internist or family physician for a complete physical check-up.
WHAT TO EXPECT
Routine eye exams are important after a CRVO. What is being watched for are the development of potential late complications especially neovascularization and glaucoma or a pending problem in the other eye. An immediate eye exam is important if you should notice any brief episodes (a minute or so) of vision in your other eye. Permanent loss may be prevented by quick action.
Fortunately complications from retinal vein occlusions are not common and a CRVO is very unlikely to occur in your other eye.