The sudden blockage (occlusion) of the blood vessel called the central retinal vein is a type of small stroke in the retina. (The retina is the light-sensitive nerve tissue lining the back of the eye. It is like film in a camera, taking “moving pictures” of everything you see.) The abrupt disturbance in the retina’s blood circulation usually causes a rapid reduction in vision.
Why Is Vision Lost?
Good vision requires a healthy, well-nourished retina, which depends on a steady stream of oxygen-rich blood – brought to it by arteries and carried away by veins. The central retinal vein (CRV) is the main blood vessel that drains “used” blood from the retina. When this vessel is blocked, the entire retinal bloodstream swells and backs up.
When that happens:
- Fresh blood cannot enter the retina. And without the oxygen that is normally brought by the blood, the retina slowly starves and some retinal cells die.
- Hemorrhages (bleeding) occur in the retina.
- The reduced blood supply sets the stage for the possibility of even more damage to the retina. Months later, the starved retina sometimes starts to grow 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 can 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 most usual cause is a blood clot that forms in the vein. That can happen whenever something slows down the normal flow of blood; for example, pressure on the vein from an overlying hardened artery (arteriosclerosis) can slow the flow of blood in the same way a fallen log tends to obstruct a stream. Increased fluid pressure within the eye (glaucoma) or an inflammation in the vein wall (vasculitis) can also slow blood flow. Or there may simply be an increased tendency for blood to clot (this is a rare complication in some women taking oral contraceptives and in certain medical conditions).
Most causes of CRVO are related to aging changes and are more likely to occur in patients who have atherosclerosis, hypertension, diabetes or glaucoma.
A complete eye examination will be performed, including a test of your vision. The pressure inside your eyes will be checked with a painless test called tonometry. Depending on the type of tonometer used, you may be given anesthetic eye drops.
Your pupils will be dilated (enlarged) with eye drops so the insides of both eyes can be studied. An ophthalmoscope and a slit lamp (clinical microscope) are instruments used for looking inside the eyes, and are especially useful for studying the retina and its blood supply.
Retinal photographs may be taken to determine the extent of the problem. An angiogram (photographs of blood vessels) may be made. For this test, a greenish-orange dye (fluorescent) is injected into a vein in your arm and immediately followed by a series of retinal photographs that track the dye and time its flow as it travels through the eye’s blood vessels. The angiogram also helps identify the site of the vein’s blockage, the extent of damage to the capillaries (the smallest retinal blood vessels), and the presence of neovascularization.
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 after your eye examination.
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.
But if you have had the occlusion for more than a day or so, there is usually little that can be done to stop the damage or to speed normal healing. Eventually, the blocked vein may re-open on its own 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 severity of the abnormal blood vessels. In the procedure, many hundreds of tiny laser burns are made in the retina during a 15- to 30-minute operation. The treatment is generally painless and 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 risks created by neovascularization, such as damage from internal bleeding or the development of hemmmorhagic glaucoma, a much more serious condition than the common type of glaucoma that is sometimes a cause of CRVO. Occasionally the laser cannot be used at all, especially when there are opacities (dense blood or cataract) within the eye that block the laser beam from reaching the retina.
After a CRVO in an older patient, vision will seldom get very much better. Many eyes remain legally blind. Younger patients (under age 50) are more likely to recover some vision, even without treatment; but it may take many months, and even at best their eyesight will not be as good as it was before the occlusion occurred.
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 even 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 loss in your other eye. Permanent loss may be prevented by quick action.
Fortunately, complications of retinal vein occlusions are not common, and a CRVO is very unlikely to occur in your other eye. If you have questions or need assistance with changes to your eyesight, please don't hesitate to call Kirk Eye Center at (970) 744-2566 or complete the form on this page today.