Retinal vein occlusion: sudden painless vision loss, causes and treatment

Guy’s and St Thomas’ NHS Foundation Trust explains that retinal vein occlusion happens when an artery presses on and blocks a vein in the retina. Cambridge University Hospitals and Moorfields Eye Hospital describe it as a blockage that forms in a retinal vein, usually a blood clot, which obstructs blood flow. The retina is the thin lining at the back of the eye, comparable to the film in a camera.

When a vein is blocked, blood and other fluids leak into the retina, causing bruising and swelling as well as starving the retina of oxygen. This interferes with the light-sensitive cells and reduces vision. Guy’s and St Thomas’ notes that retinal vein occlusions can be permanent and that some people respond well to treatment but can still have some reduction in vision afterwards.

There are two types. A branch retinal vein occlusion (BRVO) is due to blockage of one of the four retinal veins, each draining about a quarter of the retina. A central retinal vein occlusion (CRVO) is due to obstruction of the main retinal vein, which is formed by the four branches. The trusts say that loss of vision is generally more severe if the central vein is affected.

The symptom Moorfields lists is blurred vision without pain. Because retinal vein occlusion can come on suddenly, any sudden change in vision should be assessed urgently.

The exact cause is generally unknown, but there are common conditions that increase the risk. The NHS sources list high blood pressure, high cholesterol, glaucoma, diabetes, smoking and some rare blood disorders. Moorfields adds that in a small number of cases no risk factors are found.

Looking for and treating these conditions is a central part of care. Cambridge says that treating the risk factors dramatically reduces the risk of a further occlusion in both eyes, and that without treatment there is a high risk of recurrence causing further damage to the affected eye and damage to the other eye.

• High blood pressure: Cambridge says that if your blood pressure is higher than 140/80 on several occasions, treatment is normally advisable.

• High cholesterol: diet changes may be discussed with a GP, and tablets such as statins may be suggested.

• Glaucoma: treatment with drops to lower eye pressure is highly effective at preserving sight and reducing the risk of further occlusions.

• Diabetes: detection and good control is essential to preserve vision.

• Smoking: the more you smoke, the greater the risk of another vein occlusion.

• Rare blood disorders: usually identified by simple blood tests and supervised by a blood specialist if treatment is needed.

Cambridge describes three procedures frequently recommended: retinal photography to document the degree of retinal damage and detect improvement or deterioration, fluorescein angiography to determine whether laser treatment is needed to reduce macular oedema and to prevent loss of vision from bleeding or raised pressure, and optical coherence tomography (OCT), which measures the amount of bruising and swelling at the macula and assesses the need for and response to treatment.

Because the underlying risk factors matter, checks of blood pressure, cholesterol and blood sugar are a sensible part of the assessment, and your eye doctor or GP will advise which are needed.

Persistent swelling at the centre of the retina is the main cause of lasting central vision loss. Cambridge says a course of anti-VEGF injections into the eye or steroids may sometimes be helpful in restoring some central vision, normally recommended about three months after the occlusion. Guy’s and St Thomas’ says an eye doctor might suggest a corticosteroid implant, dexamethasone intravitreal implant (Ozurdex), which eases the swelling, and that other medicines injected directly into the eye, aflibercept and ranibizumab, might be helpful if it is not suitable.

Guy’s and St Thomas’ also says laser treatment can sometimes help restore some central vision and, if suggested, is generally done about 3 months after the occlusion. Which option is right depends on the type of occlusion, the degree of swelling and your general health, and your eye doctor will explain the choice.

Cambridge says about 30% of patients develop abnormal blood vessels on the iris or retinal surface, which can bleed or cause a marked pressure rise in the eye, and that this can normally be prevented by laser treatment to the retina if required. Guy’s and St Thomas’ similarly notes that when the central vein is blocked the blood supply can be permanently affected, and abnormal vessels might need further treatment.

Guy’s and St Thomas’ says that if you have a BRVO, follow-up appointments take place every 4 to 6 months for about 18 months, after which symptoms are less likely to worsen. With a CRVO, appointments are every 6 to 8 weeks for the first 6 months and then may be less frequent, with most patients discharged after 2 years. Cambridge gives a similar pattern, with most patients discharged after about one year.

Outlook varies. Some people keep good vision, and others have lasting loss. The trusts stress that the aim is to treat swelling and complications and to prevent a further occlusion by managing risk factors.

Sudden loss or blurring of vision, even without pain, needs same-day assessment through an eye casualty, A&E or NHS 111. Cambridge advises contacting the emergency eye clinic or on-call ophthalmologist if your sight deteriorates dramatically or your eye becomes painful. Make sure your blood pressure, cholesterol and diabetes are being reviewed, since treating risk factors is central to preventing a further occlusion.