Retinal Vein Occlusion
What is a retinal vein occlusion?
Normally, the retina is nourished by oxygen-rich blood that is brought to it by arteries and drained away by veins. Retinal vein occlusion occurs when a vein (a drainage channel) is blocked.
What are the causes of retinal vein occlusion?
Typically retinal vein occlusion occurs when blood flow is slowed down and forms a clot which blocks the vein. The most common reason for slowed venous blood flow is direct pressure from a hardened artery. A stiff retinal artery with arteriosclerosis lies across a retinal vein and compresses it, resulting in blood turbulence. The turbulent blood flow creates a clot which stops the circulation, and the blood cells and fluid in the vein become back logged and extrude into the retina.
High blood pressure is the most common cause of arteriosclerosis and consequently is the major risk-factor for retinal vein occlusions. Other conditions that may lead to a retinal vein occlusion are glaucoma, diabetes mellitus, lupus, and some blood clotting disorders. Certain medications such as oral contraceptives have been associated with vein occlusions due to hyper-coagulation.
Why is vision lost as consequence of retinal vein occlusion?
Impaired blood drainage causes bleeding as well as accumulation of fluid in the retina (edema). The affected retina looses some of its normal function.
The extent of damage and the visual symptoms produced depend on the size of the blocked vein and its exact location. Central retinal vein occlusion (CRVO) will affect a larger portion of the retina compared to branch retinal vein occlusion (BRVO). If a BRVO occurs toward the peripheral part of the retina, one may hardly notice it. But if it occurs in or near the central zone of the retina that is critical for sharp vision - vision is likely to be affected.
What are serious complications of retinal vein occlusion?
A serious threat to vision can develop following the occlusion of a large retinal vein by growth of new blood vessels – neovascularization. These are not normal blood vessels, and they grow in response to decreased retinal oxygen supply. They are dangerous to the eye because they can bleed and lead to other complications. Early diagnosis and prompt treatment of new vessels will generally prevent major problems.
What tests are performed after a retinal vein occlusion?
The vision, pupil response, intra-ocular pressure, anterior segment, and the retina need to be examined.
A fluorescein angiogram (FA) is performed to classify the extent and location of the vein occlusion, to identify damage to capillaries (the smallest retinal blood vessels), and to detect whether or not neovascularization has developed. Optical coherence tomography (OCT) study will measure the degree of the retinal edema in the macula.
Since retinal vein occlusion is associated with medical conditions that possibly affect the rest of the body (i.e. high blood pressure, which also increases the risk of a heart attack and stroke), you will be referred to an internist or family physician for a complete check-up following your eye examination.
How is retinal vein occlusion treated?
Once a retinal vein occlusion has occurred, there is no conservative way to renew the blood flow. During the natural healing process, the blocked vein may reopen on its own, or some nearby blood vessels (called collaterals) may develop to reroute the blood flow around the site of blockage.
Medical and/or laser treatment is recommended based on the condition of the eye and the results of the FA and OCT studies. The goal of treatment is to reduce retinal edema, prevent complications of neovascularization, and aid in the natural recovery process of the eye.
The vast majority of treated eyes will avoid complications and have improved vision. Prompt and appropriate treatment is important for obtaining good long-term visual results.