A blood vessel in the retina may become blocked, causing sudden, painless loss of vision.
Blockage may occur in the main artery or vein in the retina (arteries supply blood, and veins drain blood away) or in their branches.
The central retinal artery, the main vessel that supplies blood to the retina, can become completely blocked by a particle (such as a piece of atherosclerotic plaque—see see Atherosclerosis—or a blood clot) that floats in the bloodstream (becoming an embolus) until it gets stuck in and blocks a vessel. Giant cell arteritis, an inflammation of the blood vessels, is also a possible cause of retinal artery blockage.
Retinal veins may become blocked in people with glaucoma, diabetes, or high blood pressure. Such blockage occurs mainly in older people.
If the central retinal artery is blocked, the affected eye has a sudden but painless loss of vision over the entire field of vision or sometimes only a part of it. Vision loss ranges from mild to severe.
Blockage of the central retinal vein causes similar symptoms except that vision loss sometimes is gradual, occurring over days or weeks. Recurrences are common.
Blockage of the central retinal artery or vein may also cause growth of abnormal blood vessels on the retina or iris. Sometimes these abnormal blood vessels bleed or cause glaucoma.
Using an ophthalmoscope, doctors can see changes in blood vessels and the retina. If the central retinal artery is blocked, the retina may be pale. If the central retinal vein is blocked, the veins may be engorged or enlarged, and the front of the optic nerve may be swollen.
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 and then photographs the retina. Doppler ultrasonography may sometimes be used to observe blood flow in the vessels.
If the artery has been blocked by an embolus, doctors need to search for a source. They often do tests such as echocardiography or carotid artery ultrasonography.
Treatments for blockage of the main artery or vein or their branches tend not to be very effective. Preventing such blockages by controlling risk factors (for example, high blood pressure, diabetes, and other risk factors for atherosclerosis) is more effective.
Blockage of an Artery:
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 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 other embolus and allow it to enter a smaller branch of the vessel, thereby reducing the area of damage to the retina.
Blockage of a Vein:
Laser treatment of the leaking blood vessels can help improve vision for people with a blockage in a branch of the retinal vein. Injections of drugs into the eye are being investigated as treatments for vein blockage.
Abnormal Blood Vessel Growth:
Laser treatment may be used to destroy abnormal blood vessels if they develop on the iris or angle.
Last full review/revision November 2008 by Sunir J. Garg, MD, FACS