Retinal Vein Occlusion

Overview

Retinal vein occlusions occur when one of the veins that drain blood from the retina is blocked. These blockages typically occur where a retinal artery and retinal vein cross over each other. If the artery develops arteriosclerosis (hardening of the arteries), it can press down on the vein and cause it to become occluded. When this occurs, blood can no longer flow through the vein, pressure builds up behind the blockage and causes the rupture of the small blood vessels within the retina. These damaged blood vessels then allow blood and fluid to leak out into the retina.

Most retinal vein occlusions occur in the elderly. Risk factors include high blood pressure, diabetes, arteriosclerosis, glaucoma, and smoking. Less common conditions that may lead to a vein occlusion include diseases that cause the blood to become abnormally thick, and blood clotting abnormalities. These latter conditions are uncommon, and an extensive medical evaluation is not usually required unless the patient is particularly young or has a history of other blood clots.

Retinal veins occlusions can be divided into two main categories depending on which vein is blocked: branch retinal vein occlusions and central retinal vein occlusions.

Branch Retinal Vein Occlusion

Branch retinal vein occlusion (BRVO) refers to a blockage in any of the branches leading to the main vein of the eye. If the vein that is blocked is close to the center of the retina, i.e. the macula, then the resulting blood and fluid which may leak out of the damaged blood vessels may cause blurry and/or distorted vision. This is called macular edema and is the most frequent cause of loss of vision with a BRVO. Another possible cause of loss of vision is termed macular ischemia. This refers to a condition when the blood vessels that supply oxygen to the macula are so severely damaged that they can no longer function and close off, thereby depriving the macula of the oxygen and nutrients it requires. To help determine whether visual loss is a result of macular edema or macular ischemia, a fluorescein angiogram may be performed. This is a test in which a dye is injected into a vein in the arm, and photographs are taken as the dye travels through the retinal blood vessels. If the damage to blood vessels is so severe as to cause widespread ischemia, then a third complication may occur termed neovascularization. This refers to the growth of new but fragile blood vessels which may bleed into the cavity of the eye (vitreous hemorrhage), or pull on the retina and cause a retinal detachment.

Central Retinal Vein Occlusion

A central retinal vein occlusion (CRVO) refers to a blockage of the main vein that drains all of the blood from the eye. A CRVO is usually more severe than a BRVO, although milder cases do occur. In addition to causing loss of vision from macular edema or macular ischemia, a CRVO may predispose to the growth of abnormal blood vessels on the iris of the eye. These vessels can then grow into and close off the area that drains fluid from the eye. This condition is termed neovascular glaucoma, and can cause severe pain, loss of vision, and eventually lead to the loss of the eyeball itself.

Signs and Symptoms

• sudden onset
• blurred or missing area of vision (BRVO)
• severe loss of vision (CRVO)

Treatment and Prognosis

In the initial months following the development of a BRVO, it may be difficult to predict the ultimate visual outcome. For many patients, the hemorrhage and macular edema will gradually resolve over several months, with improvement in vision. If vision does not improve over time due to macular edema, laser photocoagulation may be performed to seal off the leaking blood vessels, allow fluid to resorb, and hopefully improve vision.

Macular edema occurring as a result of a CRVO is not amenable to laser photocoagulation.

Neovascularization that may develop in patients with either a BRVO or CRVO is also treated with laser photocoagulation. While not resulting in visual improvement, it is successful in preventing further loss of vision from either vitreous hemorrhage or neovascular glaucoma.

Patients with retinal vein occlusions must be followed very closely for the first 6-12 months, to both monitor the condition and detect immediately any further complications. The risk for a vein occlusion to develop in the fellow eye is probably less than 10%.