Eye Occlusions,
Blockages or Eye Strokes

By Chris A. Knobbe, MD

Eye strokes occur when blockages (occlusions) within veins and arteries cause decreased or distorted vision. Severity of vision loss depends on the extent and location of the problem.

Just as strokes occur in other parts of the body because blood flow is blocked, your eye also may suffer damage when vital structures such as the retina and optic nerve are cut off from nutrients and oxygen flowing through your blood.

Besides having an eye exam to detect signs of an eye occlusion, you'll also need your family doctor or internal medicine physician to evaluate you for high blood pressure, artery disease or heart problems that may be responsible for the blockage.

If a blockage is found, the type of eye occlusion you have is categorized by its location.

Branch Retinal Artery Occlusion (BRAO)

A branch retinal artery occlusion usually occurs suddenly. While typically painless, a BRAO can cause an abrupt loss of peripheral vision. In some cases, you may also lose central vision.

Usually the cause is a clot or plaque (embolus) that breaks loose from the main artery in the neck (carotid) or from one of the valves or chambers in the heart.

No ocular therapy has been proven to help. However, some ophthalmologists may try ocular massage or a fluid tap from the eye (anterior chamber paracentesis) in the case of an acute or sudden arterial occlusion. Your ophthalmologist also may prescribe a glaucoma medication to dislodge the embolus, if the condition has been present for fewer than 12 to 24 hours.

Loss of visual acuity with a BRAO will depend mostly on whether arterial blood flow has been disrupted and/or if swelling is present in the macula, where fine focusing occurs.

You also will be evaluated for cardiovascular risk factors and treated accordingly, often in conjunction with your regular doctor.

Most people with BRAO have narrowing of the carotid or neck artery, high blood pressure, cholesterol disorders, cardiac disease or combinations of these disorders.

Your eye doctor will evaluate you every one to two months until your vision is stable. Vision recovery depends on whether the central macula is involved initially.

More than 80 percent of people who have BRAO will recover visual acuity of 20/40 or better*, although most people will have noticeable and permanent vision problems such as blind spots or distortions.

Rarely, you may develop other complications from BRAO, such as neovascularization of the retina or iris. Neovascular glaucoma also is possible.

Branch Retinal Vein Occlusion (BRVO)

People who have a branch retinal vein occlusion near the retina may have decreased vision, peripheral vision loss, distorted vision or blind spots. A BRVO involves only one eye and usually develops in a person with high blood pressure or diabetes.

The cause of BRVO is a localized clot (thrombus) development in a branch retinal vein due to hardening of the arteries (arteriosclerosis) in an adjacent, small branch retinal artery.

Your ophthalmologist will see retinal bleeding along the involved retinal vein in a clear pattern that nearly always leads to the correct diagnosis. Many ophthalmologists will do a fluorescein angiogram during the recovery period if neovascularization is suspected.

A fluorescein angiogram is a safe, in-office diagnostic procedure in which fluorescein dye is administered through the vein (IV) or sometimes orally for retinal photography.

BRVO patients are typically re-evaluated every one to two months to determine if chronic macular swelling (edema) and/or neovascularization are present. If macular edema persists beyond three to six months and visual acuity is reduced below 20/40, you may receive laser treatment.

If you meet guidelines for treatment, laser photocoagulation has been shown to improve vision and increase your chances that final visual acuity will be 20/40 or better. If neovascularization develops or if the BRVO involves a significantly large area of retina leading to neovascularization, you may undergo pan-retinal laser photocoagulation to repair damaged areas.

For many people, retinal hemorrhage and macular swelling will end in a few months, with retention of good vision. If you need laser treatment, your ophthalmologist will use strict criteria to determine whether you will benefit. These criteria result largely from the Branch Retinal Vein Occlusion Study, in which patients with BRVO who had laser treatment were compared with those who didn't have it.

In July 2009, the FDA approved Ozurdex as a biodegradable, injectable steroid implant for treating macular edema following branch retinal vein occlusion or central retinal vein occlusion.

Laser treatment appears to be a safer and equally effective treatment for BRVO when compared with steroid injections, according to a major study known as Standard Care vs. Corticosteroid for Retinal Vein Occlusion (SCORE). Results were announced in September 2009 by the study's sponsoring agency, the National Eye Institute.

Central Retinal Artery Occlusion (CRAO)

Central retinal artery occlusion usually occurs with sudden, profound, but painless vision loss in one eye. Most people with CRAO can barely count fingers in front of their face or see light from the affected eye.

The condition may be preceded by episodes of vision loss known as amaurosis fugax. The cause of CRAO is most commonly a clot or embolus from the neck (carotid) artery or the heart. This clot blocks blood flow to the retina.

CRAO is considered a "stroke" of the eye. Studies show that about two-thirds of patients have underlying high blood pressure and one-fourth of patients will have significant carotid artery disease (plaque with narrowing of the artery lining), cardiac valvular disease or diabetes.

Naturally, some people will have combinations of these and other underlying disorders. You may need an extensive medical evaluation by an internal medicine physician, including imaging techniques of carotid artery doppler ultrasound and echocardiography.

Your ophthalmologist may diagnose CRAO after an examination of the eye, including a dilated pupil exam. With CRAO the retina will be pale and the vessels narrowed. If you are seen within the first few hours of onset, the retinal signs may not yet be present, and a fluorescein angiogram may be required to confirm the diagnosis. This procedure, which is very safe, entails injection of fluorescein intravenously with retinal photography afterward.

No treatment method has been shown conclusively to benefit CRAO. But if you are seen within 24 hours after acute vision loss begins, many ophthalmologists may attempt to dislodge the embolus through methods such as:

• Using glaucoma medications to decrease internal eye pressure.
• Having you inhale 5 percent carbon dioxide gas, then using ocular massage.
• Performing a minor surgical procedure known as anterior chamber paracentesis, in which numbing drops are used and a small amount of fluid is withdrawn from the front of the eye.

If the embolus can be dislodged, blood flow to the retina may be restored partially. Vision loss is less likely if the occlusion has been present only a very short time. However, studies have shown that the retina suffers irreversible injury after only 90 minutes of blood flow loss (ischemia). Despite all attempts to preserve vision, even when you are seen immediately, most patients suffer severe and permanent visual loss.

Some people with CRAO will have temporal arteritis (giant cell arteritis), an inflammatory condition of the arteries, which calls for treatment with systemic steroids to prevent loss of vision in both eyes.

Central Retinal Vein Occlusion (CRVO)

Central retinal vein occlusion causes sudden, painless vision loss that can be mild to severe. Most people will have high blood pressure, chronic open-angle glaucoma and/or significant hardening of the arteries.

When CRVO occurs, the final outcome may involve a thrombus or clot of the central retinal vein just where it enters the eye. Your eye doctor may find mild to severe hemorrhages and cotton-wool spots in the retina (which can indicate poor or absent blood flow).

Initial vision loss when you first are diagnosed with CRVO is a good indicator of the final visual outcome. That is, the worse the vision initially, the worse the final visual acuity. In fact, in half of people with CRVO, final visual acuity remains within three lines on the eye chart of the first visual acuity measurements taken.

Two basic classes of CRVO are:

• Ischemic: poor blood flow and accompanying poor vision.
• Non-ischemic: much better vision when you are first seen and fewer clinical findings.

The prognosis for non-ischemic CRVO is good. But the ischemic type almost always has vision of 20/100 or worse at first, with a much higher risk of developing complications. People with ischemic CRVO must see the eye doctor often, perhaps every few weeks, so they can be evaluated for signs of neovascularization or abnormal vessel growth in the retina and on the iris.

Neovascularization of the retina or optic nerve may cause bleeding (vitreous hemorrhage), and neovascularization of the iris may result in intractable glaucoma, which means high internal eye pressure that fails to respond to conventional therapy.

Both CRVO conditions, if they develop, typically are treated with laser to the retina (pan-retinal photocoagulation) in attempts to cause regression of the neovascularization.

Results of a recent major study (SCORE) also indicate that corticosteroid injections may help reduce vision loss in people with CRVO.

The International Eye Disease Consortium (IEDC) estimates that about 16.4 million adults worldwide are now affected by retinal vein occlusions, as reported in the February 2010 issue of the Ophthalmology journal.

"We need to understand how hypertension and other cardiovascular risk factors impact BRVO and CRVO, and how glaucoma[[article link]] impacts CRVO, in various ethnic groups and populations so that appropriate preventive and treatment strategies can be designed," said the study's lead investigator, Tien Y. Wong, MD, PhD.

Above all, if you have sudden vision loss or any other symptoms of eye stroke, visit your doctor immediately.

*According to the reference book Ophthalmology, 2nd ed.

[Page updated February 2010]