When one of the vessels that carries blood to your eye's retina gets blocked, it can cause painless, but usually sudden, vision loss in one eye. Doctors call this a central retinal artery occlusion (CRAO).
Your retina is the layer of nerves at the back of your inner eye that sense light. Like a tiny video camera, your retina transforms images into electrical signals that your optic nerve carries to your brain. If an occlusion, or blockage of a blood vessel, occurs in your retina, it can be quite serious. The blockage usually stems from a clot or fatty deposit in your blood vessel. This is considered a medical emergency and requires immediate medical attention. If the blood clot breaks free and moves to the brain, it can cause a stroke.
High blood pressure and aging are the main risk factors for CRAO. Glaucoma, diabetes, and conditions in which the blood is thicker and stickier than usual also appear to raise your risk. In women, the condition has been linked to the use of oral contraceptives.
When a CRAO happens, the consequences can be rapid and severe. Usually, some form of vision loss results. Afterward, only 10 to 20 percent of people experience any significant healing.
A disease that is similar to CRAO is branch retinal artery occlusion, or a blockage in one branch of the arteries supplying your retina with oxygen-rich blood. With this form of the disease, you are often able to maintain fair to good vision, and recovery is more likely.
The signs of CRAO are easy to identify:
Sudden blindness in one of your eyes
Sudden, complete blurring of vision in one eye
Gradual loss of vision in one eye over a few weeks
The symptoms may last a few seconds or minutes, or they might be permanent. If you experience only partial blurring or loss of vision, you likely have branch retinal artery occlusion.
If your doctor suspects that you have CRAO, he or she will do a physical examination of the eye after dilation. Your doctor may also do a number of additional eye tests to determine the nature and extent of the damage. One eye test that can make a definite diagnosis is called a fundoscopy, sometimes performed with a biomicroscope and slit lamp.
You'll be tested for high blood pressure, glaucoma, and diabetes. If you are young, your doctor may check whether your blood is thicker than normal with a blood test called a complete blood count.
In addition, your doctor may make other checks of your heart health to see if you have problems with clotting elsewhere. These conditions are often related.
Doctors sometimes use a laser to correct the blockage. Experts say that if you arrive at the hospital with at least 20/40 vision, you will probably have fairly good vision later on. But if your vision in the eye is 20/200 or worse, the prognosis for recovery is not good.
Doctors have had some success using hyperbaric oxygen therapy to treat the problem. According to hyperbaric medicine experts, the retina consumes more oxygen than any other organ in the body. This makes the retina particularly vulnerable to a blood vessel blockage that keeps oxygen-rich blood from reaching it.
In many cases, hyperbaric oxygen therapy, which involves breathing pure oxygen in a pressurized chamber, can provide enough supplemental oxygen to keep the retina viable until normal circulation returns. The increased supply of oxygen in the blood can sometimes cause the retinal arteries to widen, which can lead to improvements in vision.
Success depends partly on the type of blockage and how quickly therapy begins after the blockage forms. Some researchers have found that this therapy works best if started within eight hours of the onset of the blockage.
In other instances, your doctor might try to open up the retinas manually via massage of the affected area, or use clot-busting drugs such as tissue-plasminogen activator, or t-PA. Several other treatments have been attempted with minimal success.
Central retinal artery occlusion is often linked to diabetes or heart problems, although these conditions have not been proved to cause it. A good preventive step is to focus on heart health: Maintain a healthy weight, eat a nutritious diet, exercise regularly, and don't smoke. If you have diabetes, work to keep your blood sugar at a healthy level.