Retinal vessel occlusion

What is it?

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 primarily through one artery and 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.

If a main vessel becomes occluded, the eye typically loses vision, often suddenly. If blockage occurs in a smaller branch vessel, there may be partial vision loss or no symptoms. The condition is often 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 condition, 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 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 an uncommon problem. People more likely to be affected are older and have a history of heart disease, high blood pressure or diabetes. In almost all cases, only one eye is affected. Diabetic retinopathy (which is a common condition) can be thought of as an occlusive condition of the retinal blood vessels. In diabetic retinopathy, the blood vessels affected are much smaller than the arteries involved in classic retinal artery occlusion.

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. Risk factors for this form of retinal vessel occlusion include older age, high blood pressure, diabetes, smoking, glaucoma, and hypercoagulable states. Hypercoagulable states are conditions that cause people to have a higher than average risk of forming blood clots. Hypercoagulability can be inherited. Or it can develop as part of another disease, such as systemic lupus and some cancers.

Symptoms

The usual 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.

Diagnosis

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. Your 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 or a slit lamp 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. Doctors order blood tests such as erythrocyte sedimentation rate and C reactive protein to help make this diagnosis but an ultrasound or biopsy may be recommended to confirm the 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 young people.

Expected duration

Whenever the retina's arterial circulation is blocked, loss of vision may be permanent if the blockage is not resolved within 24 hours. Treatments for retinal arterial blockage are limited. There are more available options when the vein is blocked but even these therapies are often unsatisfactory.

Prevention

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 not smoking and controlling your blood pressure, cholesterol level and blood sugar. Also, people with diabetes 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.

Treatment

Treatment depends on the type of occlusion.

Retinal artery occlusion

Retinal artery occlusion is a medical emergency. Treatment focuses on increasing blood flow to the retina as soon as possible. However, none of the therapies have proven to be best and results are frequently disappointing. Options include:

• Injecting a clot buster – The doctor injects a drug called a thrombolytic directly into the retinal artery near the site of occlusion.
• 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.
• Medications to lower eye pressure – These include eye drops, acetazolamide, or mannitol.
• Ocular massage – The doctor uses his or her finger to apply pressure to your eye through your closed eyelid. The hope is that this can dislodge an embolus or thrombus.
• Vasodilator medication – Drugs such as nitroglycerin, isosorbide and pentoxifylline may be given to help improve blood flow.
• 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 might dilate (widen) the arteries in your retina, increasing blood flow.

When retinal artery occlusion is caused by temporal arteritis, doctors prescribe high dose corticosteroids with or without other immunosuppressant medications (such as tocilizumab). The corticosteroid dose is gradually tapered over many months.

Retinal vein occlusion

In many cases, no urgent treatment is needed and the condition can be monitored carefully. Treatment is focused on stopping both macular edema and over growth of small blood vessels in the retina called neovascularization. The usual treatment is a series of injections of an anti-VEGF (anti-vascular endothelial growth factor), such as ranibizumab or aflibercept, into the eye. Corticosteroids (by injection into the eye or as a drug-containing implant) can be effective as well. Blood thinners are occasionally recommended, such as when a condition causing excessive clotting is discovered. Surgery, including removal of the fluid within the eye, may be recommended for complications of retinal vein occlusion, such as persistent bleeding.

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.

When to call a professional

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.

Prognosis

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.

The situation is similar for retinal vein occlusions. Blockage of the entire vein has a poorer prognosis than blockage of only one small branch. However, the outlook has become a bit more favorable with the use of anti-VEGF injections. Laser treatments sometimes produce dramatic improvements in vision in people with small branch vein occlusions.

Additional info

National Eye Institute
https://www.nei.nih.gov/

American Academy of Ophthalmology
https://www.aao.org/