Retina artery occlusion

Retinal artery occlusion refers to the blockage of the artery that carries oxygen to the nerve cells in the retina at the back of the eye. Lack of oxygen supply to the retina can lead to serious vision loss.

Symptoms

Retinal artery occlusion is usually associated with sudden, painless loss of vision in one eye. The area of ​​the retina affected by the blocked vessels determines the area and extent of vision loss.

Occlusion of the main retinal artery (CRAO) often results in severe vision loss. However, about 25% of people who develop CRAO have an additional artery called the cilioretinal artery in the retina. 

A blockage in a smaller artery is called a branch retinal artery occlusion (BRAO). This can cause the loss of part of your visual field. If the affected area is not in the center of the eye or is relatively small, a BRAO may go unnoticed without symptoms.

Causes

Retinal artery occlusion occurs due to blockage, often by an embolus (a small piece of cholesterol that blocks blood flow) or a clot. Retinal artery occlusion can be temporary, lasting only a few seconds or minutes, if the blockage is relieved and blood flow to the retina is restored, or it can be permanent.

Common risk factors include:

• Carotid artery disease
• Atherosclerosis 
• Artificial heart valves 
• Heart tumors
• Arrhythmia
• Diabetes
• High blood pressure
• Intravenous drug use
• Giant-cell arteriitis
• Clotting disease such as sickle cell anaemia
• Oral contraceptive use
• Homocystinuria (an inherited disorder that prevents your body from processing the amino acid methionine. This leads to an excessive buildup of homocysteine ​​in the blood and urine)
• Pregnancy
• Platelet disorders

Most patients with retinal artery occlusion are over 60 years old and are more often men than women. Only 1% to 2% of cases involve both eyes.

Diagnosis

CRAO is usually diagnosed by examining the retina, which shows a "corneal patch," where the center of the macula appears red, with the surrounding retina pale due to lack of blood flow. BRAO appears as an area of ​​superficial retinal whitening along the occluded vessel

Retinal bleaching generally lasts 4 to 6 weeks before resolving. Fluorescein angiography (FA) shows delayed filling of the retinal arteries. Optical coherence tomography (OCT) provides detailed images of the central retina and shows swelling of the inner layers of the retina in the affected area, which over time atrophies, becoming much thinner than normal.

Treatment and outcome

Unfortunately, there is no clinically proven cure for CRAO. Several treatments can be used, including:

• Anterior chamber puncture (removal of fluid from the front of the eye with a small-gauge needle) to reduce intraocular pressure and remove the piston
• Reducing intraocular pressure with medication
• Eye massage with the thumb to remove the clot

However, for any treatment to be potentially effective in CRAO, it must be applied within a short period of time, probably within 4 to 6 hours of symptom onset. Unfortunately, none of these treatments have been shown to improve the natural history of the disease.

Thrombolytic therapy, administered either intravenously or directly through the ophthalmic artery, has also been tried, but clinical trials have not shown this treatment to be effective.

An important aspect of managing retinal artery occlusion is for your doctor to identify and manage risk factors that may lead to other vascular diseases. The risk factors for CRAO are the same atherosclerosis risk factors as for stroke and heart disease. Tests are important to try to identify the source of the clot from another part of the body. These tests include:

• Carotid ultrasound to determine if there are carotid plaques
• Cardiac ultrasound to look for heart valve disease
• The doctor may also order a measurement of your blood sedimentation rate and a temporal artery biopsy, which may be useful if giant cell arteritis is suspected.

Vision loss in CRAO is usually severe. Visual field loss in BRAO is usually permanent, but central visual acuity may be as good as 20/40 or better in 80% of eyes.

The formation of new blood vessels in the retina or iris that are prone to bleeding is a rare complication seen after CRAO or BRAO. The growth of these vessels can further reduce vision by causing vitreous hemorrhage and glaucoma. If this occurs, laser photocoagulation therapy is used to create burns in the area of ​​the blocked artery to try to reduce the oxygen demand of the retina and thus stop the growth of the abnormal blood vessels.

In this case, intravenous injections of anti-VEGF drugs such as Avastin® (bevacizumab), Lucentis® (ranibizumab) or Eylea® (aflibercept) can also be used.