Retinal vein occlusion describes blockage or cessation of blood flow in the vessels taking blood away from the retina.
There are many veins within the retina. If one of the smaller vessels is blocked this is called a "branch retinal vein occlusion" (brvo). When the main vein is blocked it is called a "central retinal vein occlusion" (crvo).
The veins are most commonly blocked because of compression from a neighbouring diseased arteriole (branch of an artery) supplying blood to the retina. The disease of the artery is caused by the same processes that lead to heart attacks (myocardial infarction) and strokes (cerbrovascular accident); these include high blood pressure (hypertension), diabetes, high cholesterol and smoking. These risk factors should be checked for and, if necessary, treated if a vein occlusion is diagnosed.
Occasionally there can be other causes for a vein occlusion, for example, certain blood clotting disorders. This is, however, rare.
Once a vein becomes blocked, fluid leaks out from the vessel and the supply of blood to the affected area of the retina can also become poor. Both these features damage the way the retina works and result in reduced vision. Once a vessel becomes blocked it cannot be unblocked, although there has been research into this area.
If there is leakage of fluid in the retina, this can be treated using injections of a drug (Avastin, Lucentis, or Eylea) into the eye. The drug is known as an "anti-VEGF agent" and is injected directly into the back chamber of the eye. Often there is quite a dramatic improvement in vision. Unfortunately, the treatment is not permanent, and several injections per year may be required.
In order to assess whether treatment may be beneficial, it may be necessary to perform investigations including "fundus fluorescein angiogram" and "optical coherence tomography".
Following a vein occlusion, the patient requires frequent out-patient visits. These examinations are to check for, treat and, if possible, preempt the sequelae of the vein occlusion; these include problems with abnormal blood vessel growth, bleeding inside the eye and increased pressure which can lead to a painful, blind eye. If abnormal blood vessels grow in the eye, a form of laser treatment may be advised.