Retinal artery occlusion is a blockage of the blood supply in the arteries to the retina -- the light-sensitive tissue in the back of the eye.

Retinal arteries may become blocked by a blood clot or substances (such as fat or plaque) that get stuck in the arteries. These blockages may occur due to hardening of the arteries in the eye.

Also, clots may travel from other parts of the body and block an artery in the retina. A common source of a clot would be from the carotid artery in the neck or from the heart lining.

Most clots are caused by conditions such as:

• Diabetes
• Disease of the two large blood vessels in the neck (carotid artery disease)
• Disorder of high blood fats (hyperlipidemia)
• Heart rhythm problem (atrial fibrillation)
• High blood pressure

If a branch of the retinal artery is blocked, part of the artery will not have enough blood and oxygen. If this happens, you may lose part of your vision.

Retinal artery blockage or occlusions may last from only a few seconds to a few minutes. They also may cause permanent vision loss. The amount of vision loss is partly related to the location of the blockage.

People with retinal arterial occlusion, whether it is temporary or permanent, have a risk of stroke because clots may also move to the brain.

Retinal vessel occlusion more often affects older people. Risk factors are related to the disorders that cause the blockage.