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What are
Retinal Vascular Occlusions? The retina is the light-sensitive membrane lining the inside of the eye that allows us to see. Arteries are the small blood vessels that carry blood into the eye to bring oxygen and nutrition to the retina; veins are the blood vessels that carry blood from the retina, out of the eye, and back to the heart. A blockage in any of the blood vessels in the retina can affect vision and is known as a retinal vascular occlusion. Retinal Artery Occlusions Retinal artery occlusions can be divided into two major types: central retinal artery occlusions (CRAOs), and branch retinal artery occlusions (BRAOs). The central retinal artery is the major artery supplying blood to the retina. All of the arteries within the retina are branches off of the central retinal artery. When the central retinal artery becomes obstructed (a CRAO), the blood supply to the entire retina is compromised. When a smaller branch artery is blocked (BRAO), only the retina supplied by that branch is affected and vision is not as severely affected. When a retinal arterial occlusion develops, the affected individual usually notices an abrupt decline in vision either affecting the entire field of vision (CRAO), or only a portion (BRAO). Vision in the affected area is usually severely blurred, and lights are much dimmer. Some people feel there is a shade or curtain covering part of their vision. On examination, the affected retina loses its transparency and becomes somewhat grey or white in appearance. The majority of retinal artery occlusions are caused by emboli. Emboli are small particles that have been carried along in the bloodstream and then lodge in a small blood vessel like those found in the retina. Atherosclerotic plaques in the carotid arteries in the neck are the most frequent source of embolic particles. Emboli can also originate from clots in the heart. Individuals who have had a retinal artery occlusion should have a workup to look for possible embolic sources. An individual who has had a retinal artery occlusion is at increased risk for a stroke or heart attack. The treatment for retinal artery occlusions has been disappointing. In most cases, the affected retina has already suffered permanent damage at the time the individual seeks treatment. A number of treatments have been tried including lowering the pressure in the eye both with drops and by surgically removing fluid, breathing into a paper bag in an attempt to dilate the blocked artery, and ocular massage in an attempt to dislodge the embolus. Unfortunately, these treatments usually prove unsuccessful and vision rarely returns to normal. Retinal Vein Occlusions When a retinal vein becomes obstructed, a pressure build-up develops in the vessels that drain into that vein. This increased pressure can lead to small blood vessels breaking with hemorrhage into the retina. The pressure may also lead to the leakage of fluid into the retina making the retina swollen. If the central retina is affected, vision may suffer. Like their arterial counterparts, retinal vein occlusions can be divided into central retinal vein occlusions (CRVOs) when the major retinal vein is obstructed, and branch retinal vein occlusions (BRVOs) when a branch vein is blocked. Individuals with retinal vein occlusions usually note the abrupt onset of blurred vision in the affected area. On examination, hemorrhages and/or swelling are seen in the affected area. The cause of retinal vein occlusions is not completely understood. There is fairly good evidence that high blood pressure (hypertension) is a major risk factor for retinal vein occlusion. The site of obstruction is almost always located where a retinal artery crosses over a retinal vein. In individuals with high blood pressure, the wall of the artery may become thickened and hardened causing it to compress the relatively thin-walled vein and predisposing to obstruction. However, vein occlusions can occur in individuals without hypertension. In many such cases, no specific cause for the occlusion is ever found. With time (usually many months to years), the blood in the retina will slowly be absorbed and collateral vessels will form. Collateral vessels are small vessels that develop which allow blood to bypass the obstructed vein. Despite these efforts at healing, the retina may have suffered permanent damage which can limit visual recovery. In some cases, laser treatment may be helpful in the treatment of retinal vein occlusions. In cases of branch vein occlusion when retinal swelling is present, laser treatment can help reduce the swelling and improve vision. If abnormal blood vessels grow (neovascularization), laser treatment may be indicated to reduce the chance of bleeding inside the eye. An experimental technique, laser-induced chorioretinal anastomosis, is also under investigation as a treatment for select cases of retinal vein occlusion. Dr. Goldman has extensive experience in the diagnosis and treatment of retinal vascular occlusions. If you or a someone you know has retinal vascular occlusion or other retinal problem, please call us to arrange a comprehensive evaluation at either of our convenient locations. |
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