Blockage of Central Retinal Arteries and Branch Retinal Arteries
(Central Artery Occlusion, Branch Artery Occlusion)
An artery in the retina (the transparent, light-sensitive structure at the back of the eye) may become blocked, causing sudden, painless loss of vision.
Blockage may occur in the main artery that supplies blood to the retina or in its branches
The central retinal artery, the main vessel that supplies blood to the retina, can become completely blocked by an embolism or thrombosis (formation of a blood clot in the artery).
An embolism is a collection of solid material that floats in the bloodstream until it gets stuck in and blocks a blood vessel. The material that forms an embolus can come from a piece of atherosclerotic plaque (see Atherosclerosis), fat, infected material from an infected heart valve (endocarditis), or a noncancerous (benign) tumor in a heart chamber (atrial myxoma).
Giant cell arteritis, an inflammation of the blood vessels, is also a possible cause of retinal artery blockage.
Sometimes the cause of the blockage is unknown.
The affected eye has a sudden and severe but painless loss of vision over the entire field of vision. Sometimes only a part of the field of vision is affected.
Blockage of the central retinal artery may also cause growth of abnormal blood vessels on the retina or iris. Sometimes these abnormal blood vessels bleed or cause a painful type of glaucoma (called neovascular glaucoma).
Using an ophthalmoscope, doctors can see changes in blood vessels and the retina. If the central retinal artery is blocked, the retina may appear pale.
Fluorescein angiography helps determine the extent of damage to the retina and helps the doctor plan treatment. In this procedure, a doctor injects dye into a vein in the arm and then photographs the retina. Optical coherence tomography (an imaging study) can help show that the retina is swollen, which is common.
Once retinal artery occlusion has been diagnosed, doctors need to search for a source of an embolus. They do tests such as echocardiography and carotid Doppler ultrasonography. They may also do blood tests to diagnose giant cell arteritis.
If the blockage occurred in a branch of the central retinal artery, people may maintain good to fair vision. If the blockage occurred in the central retinal artery itself, vision loss is often profound, even with treatment. Once the retinal tissue becomes permanently damaged, which can happen as quickly as 90 minutes after the blockage, vision loss is usually permanent. If giant cell arteritis is the cause of the retinal artery blockage, prompt diagnosis and treatment may allow people to regain some lost vision and be protected from damage to the other eye.
Because treatments tend not to be effective, preventing such blockages by controlling risk factors (for example, high blood pressure, diabetes, and other risk factors for atherosclerosis) is desirable.
Immediate treatment is often given in an attempt to unblock the retinal artery. However, treatments are rarely effective. Pressure inside the eye sometimes can be lowered by giving drugs that lower blood pressure (such as timolol eye drops or acetazolamide taken by mouth) or intermittently massaging the closed eyelids with the fingers.
Alternatively, a procedure called anterior chamber paracentesis may help lower pressure inside the eye. In this procedure, drops are placed in the eye to numb the eye, and then a needle is inserted into the anterior chamber to withdraw a small amount of fluid, thereby rapidly lowering the pressure in the eye.
Lowering the pressure inside the eye by massage or by anterior chamber paracentesis may dislodge a blood clot or embolus and allow it to enter a smaller branch of the vessel, thereby reducing the area of damage to the retina.
People with suspected giant cell arteritis are given high-dose corticosteroids either by mouth or by vein as soon as possible.
Laser treatment may be used to destroy abnormal blood vessels to treat or prevent neovascular glaucoma, prevent further vision loss from bleeding within the eye, or both. However, treatment of neovascular glaucoma is difficult.