Retinal Vein Occlusions


What is a Retinal Vein Occlusion?
Retinal vein occlusions are blockages of the blood flow through the veins that take blood away from the retina. There are two main types of vein occlusion, branch retinal vein occlusion (BRVO) and central retinal vein occlusion (CRVO). In CRVO’s the entire retina is affected, while in a BRVO only a portion of the retina is affected.


What are the Signs and Symptoms of Retinal Vein Occlusions?
Blurry vision involving either the entire visual-field, or a portion of the visual-field are often noted. The symptoms can be the result of decreased blood flow to the retina as well as the development of macular edema.


What causes Retinal Vein Occlusions?
It is theorized that vein occlusions occur when there is compression of a retinal vein by a neighboring retinal artery. Over time it is believed that artery walls can become thicker and stiffer. In areas where veins and arteries travel together, they are surrounded by a sheath of tissue, so the vein becomes compressed by the thickened artery. This in turn leads to turbulence in the vein that eventually results in the formation of a clot which blocks blood flow. Risk factors for the development of vein occlusions include hypertension, smoking, diabetes and glaucoma.


What are the effects of Retinal Vein Occlusions?
The most common effect of vein occlusions is macular edema. Macular edema develops because of a leakage of fluid from the damaged vessels. If the damage to the vessels is severe enough and the blood supply, and therefore the oxygen supply to the retina, is completely blocked, then ischemia develops. Ischemia in turn can lead to the formation of abnormal vessels either on the retina, or in the front of the eye on the iris. These vessels can break leading to bleeding, or hemorrhage. They can also block the outflow of fluid from the eye causing a severe form of glaucoma called neovascular glaucoma (NVG).


How are Retinal Vein Occlusions treated?
The treatment for vein occlusions revolves around the treatment of the macular edema that can develop. In BRVO’s, laser is often the first-line therapy and is usually effective. Laser however has been shown to be ineffective for patients with CRVO. In these patients, or in patients with BRVO in which laser didn’t work, injections of medications into the eye can often be effective. The injections are either a steroid (Kenalog), or a medication that reduces the leakiness and formation of abnormal vessels (Avastin). In some cases of BRVO and CRVO, surgery may be an option to “decompress” the affected vein.


In patients with hemorrhage or with glaucoma, laser is performed to the peripheral retina in an effort to cause the abnormal vessels to regress. Hemorrhages will often clear without intervention; however it is occasionally necessary to undergo surgery to remove the blood. For patients with NVG, injections of a medication that can cause abnormal vessels to regress may also be offered (Avastin).


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Branch Retinal Vein Occlusion


Central Retinal Vein Occlusion