The retina is the light-sensitive layer at the back of the eye that is responsible for vision. Blood circulation to most of the retina's surface is through only one artery and only one vein. If either blood vessel or one of their smaller branches is blocked, blood circulation to the retina can be significantly disrupted. The blockage is called an occlusion. When this happens, the eye typically loses vision, often suddenly. The condition is painless.

Retinal Artery Occlusion
The retinal artery carries oxygen-rich blood to the retina. When a blockage occurs in the retina's main artery, or in one of its small branches, the retina's light-sensitive cells gradually begin to suffocate from lack of oxygen. Unless normal circulation to the retina can be restored promptly, these cells will die within a few minutes or hours depending on how completely the blood flow is obstructed. This can cause permanent and often substantial loss of vision.

In adults, there are two main reasons that the retina's artery would become blocked: a thrombus or an embolus.

• A thrombus (blood clot) � Inside the retinal artery, a blood clot typically develops at a site where the artery's lining has already been damaged by a chronic illness, such as high blood pressure (hypertension), diabetes or atherosclerosis. Atherosclerosis is a common cardiovascular problem that produces cholesterol deposits called plaques along the walls of arteries, decreasing blood flow.



• An embolus (floating blood clot or debris in the bloodstream) � In the retinal artery, an embolus is usually a tiny blood clot or a piece of atherosclerotic plaque that has been carried through the bloodstream from a damaged area of the heart, aorta or carotid artery (in the neck). For this reason, the embolus is often interpreted as a warning sign of cardiovascular disease elsewhere, especially in the carotid artery. Rarely, pieces of a tumor from elsewhere in the body can embolize.

Less often, a retinal artery occlusion may be caused by vasculitis (inflammation of the artery's wall), trauma, sickle cell disease, clotting disorders, oral contraceptives or damage from radiation treatments. Overall, retinal artery occlusion is a rare illness that is responsible for only one out of every 10,000 visits to ophthalmologists (physicians who specialize in eye problems) in the United States. The average person with the illness is between 50 and 70 years old and has a history of heart disease, high blood pressure or diabetes. In almost all cases, only one eye is affected.

Retinal Vein Occlusion
The retinal vein carries blood away from the retina. When the vein is blocked, blood flow backs up and causes tiny hemorrhages, areas of swelling, and other pressure-related damage in portions of the retina that are located near the blocked blood vessels. This can cause minimal or substantial loss of vision, depending on the extent of this retinal damage. Some common risk factors for this form of retinal vessel occlusion include high blood pressure, diabetes, open-angle glaucoma, lymphoma, leukemia, multiple myeloma, syphilis and use of oral contraceptives.

The primary symptom of retinal artery occlusion is a sudden, painless, persistent, substantial loss of vision in one eye. In about 10% of those affected, this loss of vision is preceded by one or more episodes of a condition called amaurosis fugax. Amaurosis fugax is a temporary episode of decreased vision, usually lasting no more than 10 to 15 minutes, that is sometimes described as "closing a curtain" on one eye.

Although retinal vein occlusion also causes painless loss of vision, this vision loss sometimes develops gradually over several days or weeks rather than suddenly. Also, depending on the extent of retinal damage, some people have only minimal blurring of vision, while others have more substantial vision loss.

After reviewing your symptoms, the doctor will ask questions about your medical history, especially any history of high blood pressure, heart disease, diabetes, glaucoma, eye trauma or amaurosis fugax. Next, your doctor will do a thorough eye examination, including tests of your visual acuity (how well you can see) and peripheral vision. Finally, the doctor will use special eyedrops to dilate (open wide) your pupils to examine the inside of your eye, including the retina. During this examination, the doctor will use an instrument called an ophthalmoscope to see whether your retina's blood supply appears to be normal, or whether there are areas of whiteness (a sign of arterial occlusion), hemorrhage, a visible embolus lodged in a retinal vessel, or other problems. In some cases, the doctor also may order fluorescein angiography, a test that uses an injected dye to analyze blood flow in the eye.

In some people, especially those who are elderly, retinal artery occlusion may be caused by temporal arteritis, a form of blood vessel inflammation, rather than to a thrombus or embolus. A special blood test called an erythrocyte sedimentation rate may help to confirm this diagnosis.

In addition, if the doctor suspects that your eye problem is being caused by emboli from undiagnosed cardiovascular illness, you may need diagnostic tests to evaluate the blood flow in your heart and carotid arteries. Also, blood tests may be necessary to determine your cholesterol levels or to check for blood clotting disorders, especially in very young people.

Whenever the retina's circulation is blocked, loss of vision may be permanent if the blockage is not removed within 24 hours. Ideally, the problem should be treated within two hours or less.

Since many cases of retinal vessel occlusion are related to high blood pressure, atherosclerosis or diabetes, it may be possible to prevent this eye problem by controlling your blood pressure, cholesterol level and blood sugar. Also, all diabetics should have a thorough eye examination through dilated pupils at least once a year.

To help prevent retinal artery occlusion related to traumatic eye injuries, always wear appropriate protective eye gear (goggles, face shield, face mask) at work and while playing sports. Also, remember to use a seat belt whenever you ride in a car to prevent your face and eyes from hitting the dashboard during a collision.

Oral contraceptives have been linked to some cases of retinal vessel occlusion. Ask your doctor about your risk of this rare side effect before you begin taking birth control pills.

Treatment depends on the type of occlusion.

Retinal Artery Occlusion
Treatment focuses on increasing blood flow to the retina, while trying to dislodge the thrombus or embolus from the blocked artery. Options include:

• Ocular massage � The doctor uses his or her finger to apply pressure to your eye through your closed eyelid.



• Breathing carbogen � By breathing this mixture of 95% oxygen and 5% carbon dioxide, you may be able to increase the flow of blood and oxygen to your retina.



• Rebreathing carbon dioxide � If carbogen is not available, the doctor may ask you to breathe into a paper bag to increase the amount of carbon dioxide in your blood. The increased level of carbon dioxide should dilate (widen) the arteries in your retina, increasing blood flow.



• Anterior chamber paracentesis � An eye specialist uses a needle to remove a few drops of fluid from inside your eye. This decreases the pressure within your eye, making it easier for blood to flow through your retinal artery.



• Experimental therapies � These include injection of a clot-dissolving medication directly into the eye's circulation, administration of vasodilators (medications that widen blood vessels), exposure to hyperbaric oxygen and destruction of retinal emboli with lasers.

In rare cases, when retinal artery occlusion is caused by temporal arteritis rather than a thrombus or embolus, treatment involves long-term treatment with high-dose corticosteroid medications.

Retinal Vein Occlusion
Treatment depends on the extent of blockage:

• Partial blockage � When only a small branch of the central retinal vein is blocked, sealing around the damaged area with a laser (laser photocoagulation) may improve vision.



• Total blockage � When the entire central retinal vein is blocked, there is no effective treatment. However, laser photocoagulation may be used to prevent complications, such as glaucoma.

If you experience a sudden loss of vision, seek emergency medical help immediately. Prompt treatment provides the best chance at restoring vision, particularly when the retina's artery is blocked.

If the entire retinal artery has been blocked, the outlook for restoring vision is usually poor, especially if symptoms have lasted longer than a few hours. If only a small branch of the artery is blocked, however, the prognosis is often very good; about 80% of affected eyes eventually improve.

The situation is similar for retinal vein occlusions. Blockage of the entire vein has a much poorer prognosis than blockage of only one small branch. Laser treatments sometimes produce dramatic improvements in vision in people with small branch occlusions.

National Eye Institute
2020 Vision Place
Bethesda, MD 20892-3655
Phone: 301-496-5248
http://www.nei.nih.gov/

American Academy of Ophthalmology
P.O. Box 7424
San Francisco, CA 94120-7424
Phone: 415-561-8500
Fax: 415-561-8533
http://www.aao.org/news/eyenet/