Retinal Vein Occlusion

What is a retinal vein occlusion?

Retinal veins are blood vessels in the retina which carry blood away from the eye. The retinal veins and arteries enter and leave the eye with the optic nerve at the back of the eye.

When a retinal vein becomes blocked the circulation of the eye is affected and this leads to a characteristic pattern of retinal bruising (haemorrhage) and some loss of vision.

It is possible to block a single branch of the retinal vein (branch retinal vein occlusion – BRVO) or to block the central retinal vein (central retinal vein occlusion – CRVO). Depending on the size of the blocked vessel, the vision may be affected in one part of the visual field or the entire visual field. Some retinal vein occlusions are partial - meaning that there is still some flow of blood in the vessel, while others are total. A total blockage is known as an “ischaemic” retinal vein occlusion and may cause more complications later (see below).

Symptoms

Most patients with retinal vein occlusion experience a sudden blurring vision. It is possible to have a small retinal vein occlusion that goes unnoticed until the patient has a routine eye test. If the retinal vein occlusion affects the central area of the retina (the macula) then there will be a dramatic loss of vision.

What is an ‘ischaemic’ retinal vein occlusion?

When a vein is completely blocked the blood supply to the retina is reduced severely. The term ‘ishaemic’ refers to the subsequent lack of oxygen suffered by the retina. If a large area of the retina is ischaemic, chemicals may be released by the retina to encourage new blood vessels to grow within the eye. This can be considered as the body’s attempt to heal or bypass the oxygen shortage. Unfortunately, these new blood vessels can cause complications. (see below)

Complications of ischaemia

New blood vessel growth: at first the new blood vessels do not cause problems. However they are often very fragile and may rupture causing bleeding into the inside of the eye. This can affect the vision still further. The new vessels may also shrink and lead to pulling forces on the retina that can result in a retinal detachment.

Glaucoma: new blood vessels can also appear on the iris in the front of the eye. These vessels can block the normal channels used to drain fluid from the eye causing the pressure in the eye to rise. This is called neovascular or secondary glaucoma. Rising pressure may be the source of considerable discomfort and further loss of vision.

What are the causes of vein occlusion?

Many retinal vein occlusions occur in otherwise healthy patients and an underlying cause might not be found. However, there are some associations with other medical problems and your doctor will check for these:

• High blood pressure
• High cholesterol
• Diabetes
• Rare blood disorders
• Glaucoma
• Smoking

What tests might I have?

Many patients undergo a retinal fluorescein angiogram - to assess the severity of the blockage and see if treatment is needed. (see A-Z for fluorescein angiography). Your consultant will decide if this test is needed.

What treatment is available?

Treatment of retinal vein occlusion is complex. Many patients will be monitored for up to two years after the onset to allow detection and treatment of problems that might be associated with the blockage. Fortunately, many retinal vein occlusions get better on their own – perhaps one in five patients will return to normal.

Your doctor will treat any underlying medical condition eg high blood pressure or high cholesterol.

Treatments exist to limit the long term damage from retinal vein occlusion. Argon laser treatment can help to reduce blood vessel leakage in the central retina (macular oedema) and can also be used to eliminate new vessels on the retinal surface or on the iris. In a few cases, a vitrectomy operation is required to treat a vitreous haemorrhage or retinal detachment.

Over the last few years there have been a number of new treatments using lasers or surgery, to try to encourage recovery of vision – either by bypassing the blockage (generating a ‘shunt’ vessel), or to unblock the original retinal vein. While there have been reports of improvement in vision, these techniques have often not been subjected to clinical trials and they are not widely used. You may wish to discuss these treatments with your consultant.

Injection of steroid drugs (triamcinolone) into the eye (intravitreal injection) may be used to improve vision where there is macular oedema unresponsive to laser treatment. This can improve vision in many cases but the effect usually wears off after 6 months. Occasionally this injection technique might lead to high pressure (another type of glaucoma) or cataract formation and you should discuss the merits of steroid injection with your consultant.

Glaucoma can be an urgent complication in patients who have an ischaemic central retinal vein occlusion. Argon laser treatment to the retina is often successful in reducing this but other glaucoma treatments may be required such as the use of eye drops, surgery or cyclodiode laser treatment. Control of glaucoma is important not only to avoid a painful eye condition but also to prevent further long term vision loss from optic nerve damage.

The future prognosis?

The outlook often depends on the severity and extent of the original vessel blockage as well as the age and general health of the patient. For patients with central retinal vein occlusion there is a risk that the circulation deteriorates to the point of ischaemia in about 1/3 cases and these patients have the greatest risk of severe vision loss. Approximately 20-30% of patients show improvement and some patients may return to normal vision.

What can I do?

Often venous occlusion is associated with high blood pressure and generalised vascular disease (atherosclerosis). Lifestyle changes aimed at reducing the risk may include stopping smoking, a healthy diet, and regular exercise. The benefit of these activities extends beyond that of the venous occlusion and will also reduce death rates from heart attack and stroke. Your GP will help reduce your cardiovascular risk by prescribing medications for high blood pressure, raised cholesterol and diabetes if indicated. Aspirin may also be prescribed to help reduce the risk of vessel blockage and stopping the oestrogen pill in women may be advisable.