Retinal vein occlusion is a blockage in the blood supply from the retina -- the light-sensitive tissue in the back of the eye.

Veins of the retina can become blocked by a blood clot. Retinal vein occlusion also can occur when the retinal arteries put pressure on the retinal vein. This is usually caused by a condition such as:

• Blood clot
• Diabetes
• Glaucoma
• Hardening of the arteries (atherosclerosis)
• High blood pressure

Retinal vein occlusion most often affects older people. Risk factors are related to the disorders that cause the blockage.

• Sudden blurring or vision loss in all or part of one eye

Tests to evaluate the retina include:

• Color vision
• Examination of the retina after dilating the pupil
• Fluorescein angiography
• Intraocular pressure
• Pupil reflex response
• Refraction test
• Retinal photography
• Slit lamp examination
• Testing of side vision (visual field examination)
• Visual acuity

Other tests may include:

• Blood tests for diabetes, high cholesterol, and triglyceride levels
• Blood tests to look for a clotting problem (in patients under age 40)

The health care provider should closely monitor any blockage for several months, because many harmful effects, such as glaucoma, take 3 or more months to develop.

Treatment can include aspirin and laser therapy.

Clinical trials are now underway to determine whether drugs that stop the growth of abnormal blood vessels (anti-VEGF drugs) might help treat retinal vein occlusion.

The outcome varies. Patients with retinal vein occlusions often regain excellent sight.

• Glaucoma
• Partial or complete vision loss in the affected eye

Call your health care provider if you have sudden blurring or vision loss.

The measures used to prevent other blood vessel diseases, such as coronary artery disease, may decrease the risk of retinal vein occlusion. These measures include:

• Eating a low-fat diet
• Exercising
• Losing weight if you're overweight

Aspirin is commonly used to prevent additional blockages in the vein.

Controlling diabetes is also helpful for preventing retinal vein occlusion.

Wu L, Arevalo JF, Roca JA, Maia M, Berrocal MH, Rodriguez FJ, et al. Pan-American Collaborative Retina Study Group (PACORES). Comparison of two doses of intravitreal bevacizumab (Avastin) for treatment of macular edema secondary to branch retinal vein occlusion: results from the Pan-American Collaborative Retina Study Group at 6 months of follow-up. Retina. 2008;28:212-219.

Kreutzer TC, Alge CS, Wolf AH, Kook D, Burger J, Strauss R, et al. Intravitreal bevacizumab for the treatment of macular oedema secondary to branch retinal vein occlusion. Br J Ophthalmol. 2008;92:351-355.