Information For Our Patients About Central Retinal Vein Occlusions
Once you have a basic understanding of the eye, you can better understand how your eye problem interferes with vision. In a manner similar to a camera, light enters the front of your eye through the cornea and lens, and is brought to focus on the back of your eye, on the tissue called the retina. In a sense, the retina functions like the film in a camera. From there, the signals are transmitted to the brain, thereby creating sight. The central area of the retina is called the macula. The macula is responsible for sharp, central vision. Good central vision is critical for activities such as reading, driving, and sewing. If the macula is damaged by disease, the "straight ahead" vision is affected. The rest of the retina is responsible for side vision (peripheral vision.)
A central retinal vein occlusion is an obstruction or blockage of the main vein of the retina, in the back of the eye. The blockage usually occurs from a small blood clot, and could be described as a "stroke" in the eye. You may recall that arteries bring fresh nutrients and oxygen rich blood to the tissues, and that veins drain away that oxygen- and nutrient-depleted blood back to the heart. While blood flow into the eye is important, blood flow out is equally important to maintain circulation. When outflow is blocked, as in a retinal vein occlusion, the blood has no place to go and "backs up", damaging the blood vessel walls. Without a way for the blood to flow out of the eye, the blood vessels rupture and bleed into the retina. The damaged veins also leak clear fluid into the retina, making it wet and swollen. This tends to mostly affect the center of the retina (the macula), and is known as macular edema. This back-up of flow is similar to what would occur if a tourniquet were kept in place on an arm for too long. Retinal function is impaired by this bleeding and swelling. The degree of visual loss will depend on how extensive the blockage is. The loss of vision may be significant. Sometimes this is treated by injecting various medications into the eye, including a steroid called Kenalog and a medication known as Avastin.
Depending on the extent of the blockage, your vision may improve, worsen, or remain the same. Vein occlusions can occasionally be complicated by growth of abnormal blood vessels, which can result in bleeding into the vitreous jelly of the eye, or can result in a severe type of glaucoma called neovascular glaucoma. Careful follow up examinations may help allow early detection and treatment of these potential complications.
A special in office test, called a fluorescein angiogram, may be used to help confirm the diagnosis or guide treatment. This test involves injection of a colored vegetable dye into an arm vein to allow us to examine the retinal circulation. Photographs taken with a special camera document the test. The angiogram is valuable because it will demonstrate the extent of diseased retina, and even reveal hidden damage. Thus, critical information is obtained for both treatment and predicting visual recovery (prognosis).
For those more serious cases where abnormal vessel growth occurs, laser treatment may be utilized. In those rare eyes with bleeding into the vitreous (jelly inside the eye) that fail to respond to laser treatment, vitreous surgery may be needed to remove the blood. Retinal specialists specialize in this type of surgery, which is performed in a hospital operating room.
Certain medical conditions increase the risk of developing these blood vessel blockages. The most common include commonly hypertension (high blood pressure), diabetes, or atherosclerosis (hardening of the arteries, and especially carotid artery narrowing). Therefore, referral to your general medical doctor for reevaluation of these conditions is essential. Recognition and control of these medical conditions may prevent these blood vessel blockages from recurring in this eye, the other eye, or elsewhere in the body.
