Retinal Vein Occlusion (RVO) happens when one or more of the veins that drain blood from the retina becomes blocked. It may lead to mild to severe vision loss, depending on the severity and location of the blockage. It affects about 1 to 2% of people over 40, although most cases occur in people over 60. Although the amount of vision loss can be significant, especially if it affects the central part of the retina (macula), this disease will not cause total or black blindness. It usually only occurs in one eye, although about 10% of people with RVO will eventually develop the problem in the other eye. Steps can be taken to reduce the risk of it recurring in the same eye or affecting the other eye.
Blood clots can form in blood vessels anywhere in the body. Sometimes, this happens when blood vessel walls are damaged which causes them to become sticky. However, in the retinal veins, clots form most commonly when blood flow is slowed by compression of the vein by a thick walled artery next to it. This causes cells in the blood to stick to each other, forming a clot. As blood slows further, more cells stick to the clot making the obstruction bigger. This leads to a RVO.
Why do people get RVO?
The likelihood of a clot forming may be increased in some people who have damaged blood vessel walls as a result of risk factors (or conditions that make the chance of a RVO higher). These risk factors include:
high blood pressure
high cholesterol and lipid levels
some other disorders that affect blood clotting.
Although many of these issues are more likely to occur as we get older, RVOs can occur in younger healthy individuals too.
How does RVO cause vision loss?
The retinal veins normally drain the stale blood from the eye back to the heart and lungs. When RVO occurs the used blood cannot drain away properly. This causes the blood to ‘back up’ in the system. The blockage and pooling of blood can cause the retina, especially the central retina or macula, to swell and may also cause areas of haemorrhage (bleeding). These areas of swelling and backed up blood can damage the cells of the retina and therefore damage sight. The extent of the sight loss depends on where the blockage takes place.
Although nothing can be done about our age, all the other risk factors can be controlled. Regular visits to the GP (to diagnose and manage any circulation problems like high blood pressure and high blood lipid levels), good diabetic control, a healthy diet, exercise and stopping smoking can all help to reduce the risk of experiencing a retinal vein occlusion. In people who have already had a retinal vein occlusion, it is important to get these risk factors under control to reduce the risk of another occlusion in the same or the other eye.
What are the symptoms of RVO?
Most people with a retinal vein occlusion notice a gradual, painless loss of vision, although if the blockage is well to the side of the retina (away from the central macula), there may be little or no vision loss noticed. In nearly all cases, only one eye is affected. Any change in vision should be checked immediately by an eye care professional such as an ophthalmologist or optometrist. Even if there are no vision problems, a comprehensive eye exam should be performed every two years as obvious symptoms are not always present. The eye care professional may also be able to pick up other eye problems such as macular degeneration, glaucoma or diabetic retinopathy at an early stage before they cause any problems.
How is it diagnosed?
RVO can be diagnosed on a clinical examination by an Optometrist or Ophthalmologist. All patients with RVO should be referred to an Ophthalmologist. RVO can be partial, where only a part of the retinal circulation is involved (Branch RVO or BRVO) or total where the main vein draining the retina is blocked (Central RVO or CRVO).
Are any tests required?
Sometimes, tests are required to determine the severity and extent of RVO and to detect any disease that may lead to it. These include:
Fluorescein angiography - in our practice, Ultra Wide Field fluorescein angiography is used as it more easily captures the widest view of the retina to determine how wide an area of retina the RVO involves, as well as providing information about how badly it affects the peripheral retinal circulation
Blood tests - sometimes it is necessary to exclude an underlying physical cause of the RVO, for example, diabetes, an auto-immune disorder or blot clotting disease can be a factor resulting in RVO. A diagnosis of such a disease leads to treatment aimed at preventing a recurrence of RVO in the same or other eye, as well reducing the risk of blood clots elsewhere, particularly in the brain where a stroke can occur.
Visual Field examination - because RVO can affect peripheral vision, tests to measure visual field can be used to measure the severity of disease and to follow up progress of the disease and its response to treatment
Treatment of general health and reducing risk factors Eyes suffering from RVO may be monitored without treatment if the occlusion is mild, does not cause vision loss and/or is not associated with macular swelling. At the same time, all people with RVOs should have their general health and risk factors treated. For example, better control of diabetes, high blood pressure and abnormal blood lipids can reduce the chance of a recurrence of RVO in the same or other eye.
Eye injections Where there is macular swelling (or macula oedema) and especially if there is also significant reduction in vision, medical eye injections (of antiVEGF - a drug that reverses swelling of the macular and can also reduce diseased blood vessels that grow as a response to a lack of oxygen) are used to reduce macular swelling, improve and maintain vision. Where macular oedema is not responsive to antiVEGF treatment, steroids can be used to good effect.
Laser treatment In cases or RVO where there is established lack of blood flow to the area of obstruction (known as ischaemic RVO) and there is growth of diseased new blood vessels (a process known as neovascularization) that may ultimately bleed, laser can be used to reduce the risk of bleeding into the vitreous gel of the eye to prevent severe loss of vision.
In situations of central RVO or CRVO, where there appears to be an imminent lack of blood supply to the retina, laser treatment can also be applied tocreate a bypass within the eye to re-establish adequate blood flow. This treatment is know as Laser Retino-choroidal Anastomosis.
Any surgical or invasive procedure carries risks. Before proceeding, you should seek a second opinion from an appropriately qualified health practitioner