Retinal vein occlusion is one of the most common causes of sudden painless unilateral loss of vision and second commonest cause of reduced vision due to retinal vascular disease after diabetic retinopathy. The condition is uncommon under the age of 50 but becomes more frequent in later life.

They are of 2 types, either Branch retinal vein occlusion (BRVO), due to blockage of one of the four retinal veins, each of which drains about a quarter of the retina. This happens 2 – 6 times more frequently than central retinal vein occlusion (CRVO), in which there is blockage of the main retinal vein, which drains blood from the whole retina.

The blockage in the vein is usually due to a blood clot, which obstructs the blood flow. The exact cause is unknown, but common conditions that is associated with it are high blood pressure, high cholesterol, diabetes and glaucoma and in young patient's rare blood disorders.

Prevention and treatment

The assessment involves identifying the risk factors as mentioned above in order to minimise the risk of the same thing happening to the other eye and to prevent a further vein occlusion in the affected eye. In a small number of cases, no risk factors can be found, with the cause being unknown.

Initially there are haemorrhages and swelling at the centre of the retina (macular oedema) is the main cause of permanent loss of central vision. The swelling is caused by damaged blood vessels which leak fluid. Intra-vitreal injections are the mainstay of treatment, and anti- vascular endothelial growth factor (anti-VEGF) medicines or steroids in some cases may be helpful in reducing this leakage. These drugs are given by injection into the eye and the injections often need to be repeated as the effect of the medicine wears off. Laser treatment is sometimes helpful in restoring some central vision in branch retinal vein occlusions.

Sometimes, in patients with retinal vein occlusion develop abnormal new blood vessels on the iris at the front of the eye or on the retina. These abnormal blood vessels can bleed or cause a marked pressure rise in the eye leading to further loss of vision. This can normally be prevented by laser treatment to the retina, which is most effective if applied before vision is lost. For this reason, patients with central retinal vein occlusions are normally checked every four to six weeks for six months but branch retinal vein occlusions can be checked less often as the risk is much less.