What is retinal vessel occlusion?

DEAR DOCTOR K:

A friend recently lost vision in his right eye because of something called “retinal vessel occlusion.” What is that? Can it be prevented?

DEAR READER:

The retina is the light-sensitive layer at the back of the eye that receives light and then sends a signal to the brain — resulting in vision. Most of the blood circulation to the retina comes through one artery and one vein. If either blood vessel or one of their smaller branches is blocked, this is called an occlusion.

The retinal artery carries oxygen-rich blood to the retina. When a blockage occurs, the retina’s light-sensitive cells begin to suffocate from lack of oxygen. Unless blood flow to the retina can be quickly restored, these cells will die. This can cause permanent and often substantial loss of vision.

Retinal artery occlusion is usually sudden and painless. It almost always involves just one eye, although the second eye may be affected in the future. If a main vessel becomes occluded, a person will likely lose the vision in that eye. He or she may be able to see a hand moving, but probably won’t know it’s a hand, or be able to count fingers.

If a blockage occurs in a smaller vessel, there may be partial vision loss or no symptoms. Sometimes, there is a warning: Trouble seeing in one eye that comes and goes — and then comes and stays.

Most cases of a blocked retinal artery result from a blood clot. The clot may form in the retinal artery, or it may travel there through the bloodstream from elsewhere in the body.

The retinal vein carries blood away from the retina. When the vein is blocked, blood flow backs up. This causes tiny hemorrhages, swelling and other pressure-related damage in the retina.

Retinal artery occlusion is a medical emergency. Loss of vision may be permanent if blood flow is not restored within 24 hours. Treatment aims to increase blood flow to the retina, but treatment options are limited, and none are very effective. They include injecting a clot-busting drug into the retinal artery and using a blood vessel-widening medication to improve blood flow.

There are more options when the vein is blocked. But even these therapies are often unsatisfactory.

Many cases of retinal vessel occlusion are related to atherosclerosis and other conditions, like high blood pressure and diabetes, which damage blood vessels. As a result, you can reduce your risk of this eye problem by not smoking, and controlling your blood pressure, cholesterol and blood sugar. People with diabetes should have a thorough eye exam at least once a year.

Without knowing anything about your health, I can’t say whether you are at risk for the problem your friend has. I hope that he received emergency treatment that restored his vision.