Retinal vein occlusions occur when veins carrying blood in the retina are blocked. A blockage in the retina’s main central vein is referred to as a central retinal vein occlusion (CRVO), while a blockage in a smaller vein is called a branch retinal vein occlusion (BRVO).
Vein occlusions cause sudden, painless loss of vision. If the central vision is not involved, often these occlusions go unnoticed by the patient. Most vein occlusions occur where an artery and vein cross. These vessels share a common sheath so when the artery loses its flexibility, the vein can become compressed and can develop a clot which prevents blood from flowing through it. Often when blood cannot flow properly, it leaks into the retina and causes macular edema. The most common risk factors for a vein occlusion are: high blood pressure, obesity, a history of heart disease, glaucoma, diabetes or high cholesterol.
The diagnosis is made with a clinical exam, however retinal imaging tests aid in the diagnosis and evaluation of vein occlusions. The two most common tests to evaluate a vein occlusion are fluorescein angiography (FA) and optical coherence tomography (OCT). These tests allow Dr. Khan to determine the level of venous stasis and ischemia present in the retina as well the degree of edema and where the fluid is leaking from.
Treatment is aimed at treating retinal complications associated with the occluded vein. Macular edema is the main reason for visual loss from vein occlusion and is most often treated with injections of medicine into the eye to stop growth of abnormal blood vessels and to decrease leakage. These drugs have been demonstrated to be quite effective with >50% of patients demonstrating significant visual improvement in studies. Frequent re-treatment is often required and determined on a case-by-case basis. Laser treatment may be used in conjunction with injections in many cases to stabilize the eye.