The retina receives its blood supply from tiny, delicate vessels called arteries. Veins drain blood away from the eye. Smaller veins (branches) drain into a larger vein (central retinal vein). Occasionally, an artery will press up against a vein and cause it to close off. Closure can occur in a branch retinal vein (BRVO) or the central retinal vein (CRVO). This process blocks the circulation out of the eye, and causes retinal hemorrhages, swelling (edema), and permanent changes to the retinal circulation.
Vein occlusions typically happen to people over the age of 50. Risk factors include diabetes, high blood pressure, high cholesterol, and history of smoking. Younger patients who develop an occlusion may have a blood or inflammatory disorder (lupus or sarcoidosis, for example). A CRVO, in some cases, can be caused by uncontrolled eye pressure.
Symptoms of a BRVO include a sudden, painless loss of a portion of the visual field. Rarely, the first symptoms of a chronic BRVO would be a sudden increase in floaters. A CRVO causes a sudden, painless loss of central vision. Typically, the vision loss is much more severe in a CRVO than a BRVO.
A retinal vein occlusion can only be properly diagnosed during a dilated eye exam. The outside of the eye will look completely normal.
A BRVO will cause hemorrhages and decreased circulation in one section of the retina. These hemorrhages may take months or even years to resolve. Swelling in the central portion of the retina (macular edema) is found in 60% of cases. If the circulation is damaged significantly, the eye will compensate for this by creating new blood vessels (neovascularization) to nourish the retina. These abnormal vessels never work properly, and often leak. This may cause the back cavity of the eye to fill up with blood (vitreous hemorrhage).
A CRVO will cause retinal hemorrhages and decreased circulation throughout the entire retina. CRVO almost always causes macular swelling (edema). If the circulation is poor enough, abnormal blood vessels will develop in the front of the eye. This process can lead to a blinding disease called neovascular glaucoma, which is extremely painful and may even lead to total loss of the eye.
There is no way to completely prevent a vein occlusion. Controlling risk factors such as high blood pressure, cholesterol, and diabetes is important. A blood thinner such as an aspirin may be recommended for some patients. In patients who have developed a vein occlusion, the lifetime risk for developing an occlusion in the other eye is about 10%.
Many treatments are currently being investigated to treat macular edema associated with retinal vein occlusion.