Retinal vein occlusion occurs when one of the tiny veins in the retina becomes blocked by a blood clot.
What is retinal vein occlusion?
This is a serious condition, which can affect your vision, caused by a blood clot in a tiny vein in the retina (the seeing membrane in your eye). The retina is a thin, light-sensitive membrane that lines the back of your eye.
An occlusion is a medical term for blockage so retinal vein occlusion means the retinal vein is blocked. This stops blood draining away from the retina and blood 'backs up' behind the blockage. Fluid and blood will then leak from the blood vessels into the delicate tissue of the retina, forcing its layers apart and affecting its ability to respond to light.
Who gets retinal vein occlusion and why?
Retinal vein occlusion is a fairly common cause of loss of vision in the UK. It is most common in people over the age of 60 years.
It happens because the vein is blocked. This blockage may occur either because of pressure on the outside of the vein (usually from a retinal artery) which squashes or kinks it, or because of sludging of fatty deposits or clotting of blood inside the vein, forming a plug.
Conditions which increase the risk of retinal vein occlusion include:
- High blood pressure.
- High cholesterol/high lipid levels.
- Raised pressure in the eye (glaucoma).
- Conditions which 'thicken' the blood.
What are the symptoms of retinal vein occlusion?
If you have retinal vein occlusion, you will usually notice a decrease in your vision in one eye. Some people describe having a blind spot in one eye. The condition is mostly painless unless there are complications, such as secondary raised pressure in the eye (glaucoma) caused by new blood vessels interfering with the drainage of fluid from inside the eye.
Depending on the severity and also the degree of involvement of the macula, retinal vein occlusions may cause only relatively mild visual loss. Some people who only have a small blockage of a branch retinal vein may not have any symptoms.
Retinal vein occlusion can cause very profound visual loss. This is more commonly seen in central retinal vein occlusion, which affects the whole of the retina, (including the macula where central vision is formed).
How is retinal vein occlusion diagnosed?
Retinal vein occlusion is usually diagnosed after an eye specialist (an ophthalmologist) examines the back of your eye, using an ophthalmoscope. This is a handheld instrument. They may also use a larger special light and magnifier (which you sit at and put your chin on) called a slit lamp. The retina at the back of your eye has a typical appearance in retinal vein occlusion. From the appearance of your retina, the specialist will usually know if you have a central retinal vein occlusion or a branch retinal vein occlusion.
Various other tests may be suggested, including measurement of how well you see (your visual acuity) and your visual fields (to look at how good your edge (peripheral) vision is). Some blood tests may also be suggested - for example, to check your blood sugar and cholesterol levels. Your blood pressure may also be checked.
A number of techniques can provide accurate digital images of the retina and its blood circulation. These images can help see exactly how much damage has occurred to the retina and whether (and how) it might be improved. The tests are usually done after some weeks have passed. They include:
- Retinal photographs. These show the overall image of the retina, allowing the ophthalmologist to see which areas appear to have sustained damage.
- Fluorescein angiography. This allows the ophthalmologist to look in detail at the blood vessels in the eye, and how the blood is flowing through them. A dye is injected (usually into your arm). This dye will then pass to, and move through, the blood vessels at the back of your eye. Then photographs can be taken with a camera to look at the blood flow to your retina. It is particularly helpful for identifying new vessel formation.
- Optical coherence tomography. This gives a very detailed 'cross-sectional' image of the layers of the retina, showing where there is swelling and damage, and how severe it is.
Why is the retina important?
The retina is a thin, light-sensitive membrane that lines the back of your eye. It is delicate, is made of several layers, and needs a good supply of oxygen. Its rich blood supply is drained away by four retinal veins, which feed into one central retinal vein which drains out of the eye.
What happens in retinal vein occlusion?
Retinal vein occlusion occurs when one of the four retinal veins, or the central vein, becomes blocked by a blood clot. This means that blood cannot drain away from the retina as easily. The blood 'backs up' behind the blockage, and fluid and blood leak from the blood vessels into the delicate tissue of the retina, forcing its layers apart and affecting its ability to respond to light.
If this bruising and swelling occur at the centre of the retina (the macula) then central vision can be affected. This is more likely to occur in central retinal vein occlusion, as drainage of blood from the macula is usually shared by all four retinal branch veins. If only one of the four branch veins is blocked, the other three will still drain blood away from the macula.
There are two main types of retinal vein occlusion:
- Branch retinal vein occlusion - the blockage occurs somewhere along the course of one of the four retinal veins. (One retinal vein drains each quarter of the eye.)
- Central retinal vein occlusion - the blockage occurs in the main vein formed by the four retinal veins coming together.
Branch retinal vein occlusion is about three times more common than central retinal vein occlusion.
What causes retinal vein occlusion?
Retinal vein occlusion usually occurs when one of the following occurs:
- A retinal vein is 'pinched off' through the pressure of an artery lying on top of the vein.
- A retinal vein is blocked with a blood clot or fragment of fatty deposit (atherosclerotic plaque) in the wall of the artery.
- More rarely, the vein can be blocked by some inflammatory conditions.
Some things increase your risk of developing retinal vein occlusion. They include:
Risk factors for cardiovascular disease
Cardiovascular diseases are diseases of the heart or blood vessels caused by atheroma. Patches of atheroma are like small fatty lumps that develop within the inside lining of arteries. Atheroma is also known as 'hardening' of the arteries (atherosclerosis). A patch of atheroma makes an artery narrower.
Your risk of developing retinal vein occlusion is increased if you have risk factors for cardiovascular disease. These include:
- High blood pressure: about 7 in every 10 people with retinal vein occlusion have high blood pressure. If high blood pressure is not well controlled, it can also increase your risk of having another episode of retinal vein occlusion (either in the same eye or the other eye). High blood pressure tends to harden the retinal arteries, making them more likely to push against the veins.
- Atherosclerosis: the retinal arteries and veins run very closely together. If the retinal arteries are narrowed due to atherosclerosis, they can become stiff and rigid. It is thought they then press on nearby veins and disturb the blood flow in them. This means that a clot is more likely to form in the vein, leading to retinal vein occlusion.
- High cholesterol/high lipid levels: these increase the fatty deposits inside retinal arteries - these can break off and lodge in the veins.
- Diabetes (this affects the blood vessels in the eye in a variety of ways - see separate leaflet called Diabetic Retinopathy).
- Smoking: this increases the blood's clotting tendency, in addition to worsening the 'hardening' and narrowing of arteries.
Other risk factors
- Having a blood clotting problem such as antiphospholipid antibody syndrome: this can increase your risk of developing retinal vein occlusion.
- Conditions which 'thicken' the blood: these increase the tendency of the blood in the vein to 'sludge' and slow (particularly where there are narrowings).
- Glaucoma: this increases pressure in the eye, which has the effect of slowing the blood flow through the veins.
The combination of high blood pressure, high lipid levels and diabetes is called metabolic syndrome and is a particularly strong risk factor for retinal vein occlusion.
If you are a smoker, giving up smoking is one of the most beneficial things that you can do to reduce your risk.
Retinal vein occlusion treatment
It isn't currently possible to remove the blockage in the tiny retinal vein. Treatment is concentrated on:
- Minimising the damaging effects of the blockage.
- Reducing the risk of a further retinal vein occlusion in the same, or the other, eye.
- Treating any complications.
Minimising the damaging effects
The damage to your retina in retinal vein occlusion is caused by the damaged blood vessels, which then leak fluid. A number of different treatments are used with the aim of reducing the swelling, so that the retina can recover. The earlier this is done, the better the chance of some recovery:
- Anti-vascular endothelial growth factor (anti-VEGF). These medicines, which include ranibizumab, bevacizumab and aflibercept, stop the abnormal blood vessels growing then leaking and bleeding under the retina. They are effective in preventing further central vision loss in 9 times out of 10. Only patients with active leaking of blood and fluid can benefit from these medicines. The medicine is injected into your eye with a fine needle. Local anaesthetic drops are applied to numb your eye and minimise discomfort.
- Steroids. These are also given by injection into the eye. The injections often need to be repeated because their effect wears off as your body 'clears' them from the eye.
- Laser treatment. This is sometimes used in branch retinal vein occlusions and it may be helpful to central vision.
Reducing the risk of a further retinal vein occlusion
It is very important to detect and treat any underlying risk factors for the condition, as you have already 'proved' you are at risk of the condition. The aim is both to reduce the risk of you developing the same condition in the other eye and also to prevent a further vein occlusion in the eye which is already affected. This includes:
- Treatment of high blood pressure. See separate leaflet called High Blood Pressure (Hypertension) for more details.
- Treatment of raised cholesterol levels. See separate leaflet called Cholesterol for more details.
- Good control of diabetes. See separate leaflet called Type 2 Diabetes for more details.
- Giving up smoking if you are a smoker. See separate leaflet called Tips to Help you Stop Smoking for more details.
- Treatment for blood clotting disorders or rare blood problems.
- Diagnosis and treatment of raised pressure in the eye (glaucoma).
Can retinal vein occlusion be prevented?
The same things that can help to reduce your risk of cardiovascular disease may also possibly reduce your risk of retinal vein occlusion. For example:
- Treating high blood pressure if you have high blood pressure.
- Good control of diabetes if you have diabetes.
- Stopping smoking if you are a smoker.
- Reducing high cholesterol levels if they are raised.
- Aiming to be physically active and do regular exercise, if possible.
- Losing weight if you are overweight.
Will my vision return?
Following a retinal vein occlusion you are likely to be left with some visual loss. The extent of the visual loss can vary greatly, depending on the severity of the blockage, the exact site of the vein occlusion, and the degree of complications you experienced. Early diagnosis and treatment may make a difference to the eventual level of visual loss.
Some partial recovery of vision may occur after branch retinal vein occlusion, and visual loss in this condition usually affects only part of the vision of one eye. However, severe central retinal vein occlusions can cause permanent visual loss, even if treated very early.
Retinal vein occlusion will happen again in about 1 in 6 people (either in the same eye or in the other eye) over the five years following on from it.
What are the complications of retinal vein occlusion?
Someone with retinal vein occlusion needs close follow-up so that any complications can be picked up early and treated where possible.
- Macular oedema. This is swelling of the macula at the centre of the retina. It is the main reason why someone with retinal vein occlusion may develop permanent visual problems.
- Neovascularisation. This is abnormal new blood vessel formation at the back of the eye. About one third of people with retinal vein occlusion develop this problem. If abnormal new blood vessels form, this can sometimes lead to increased pressure within the eye and to glaucoma. Also, the new blood vessels are of a poor quality and can sometimes bleed. Another complication is that the new blood vessels can increase the risk that the retina becomes detached. See separate leaflet called Retinal Detachment for more details.
About 1 in 5 patients with retinal vein occlusions develop extra, abnormal blood vessels in the eye. This is neovascularisation. The new blood vessels are stimulated to grow by the shortage of oxygen following the vein blockage. However, they are abnormal in the sense that they are abnormally leaky, and tend to leak fluid and proteins into the eye.
These abnormal blood vessels tend to grow on the iris (the coloured part of the eye), or on the retina itself. They can leak and bleed, and they can also cause a pressure rise in the eye, leading to glaucoma or 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.
How are the complications treated?
- Laser treatment can be used to help treat both macular oedema (swelling of the retina in the macular area, which reduces the oxygen supply) and abnormal blood vessel development. A different kind of laser can be used where the vein occlusion causes neovascularisation leading to glaucoma.
- Surgical options aimed at relieving pressure and improving flow through the retinal veins have been studied for the treatment of retinal vein occlusion, but they have not been found to be effective; also, the complication rates are high.
- Arteriovenous sheathotomy is a surgical treatment which aims to improve flow in the affected vein by detecting the artery which is 'squashing' it and separating them. It is performed at the time as a vitrectomy (removal of the vitreous humour from the eye). It is currently being researched and evaluated.
Further reading and references
Retinal Vein Occlusion (RVO) Guidelines; Royal College of Ophthalmologists (July 2015)
Aflibercept for treating visual impairment caused by macular oedema after branch retinal vein occlusion; NICE Technology Appraisal Guidance, September 2016
Dexamethasone intravitreal implant for the treatment of macular oedema caused by retinal vein occlusion; NICE Technology Appraisal Guidance, July 2011
Anti-VEGF for Retinal Vein Occlusion: Patient Information; Moorfields Eye Hospital
Patel A, Nguyen C, Lu S; Central Retinal Vein Occlusion: A Review of Current Evidence-based Treatment Options. Middle East Afr J Ophthalmol. 2016 Jan-Mar23(1):44-8. doi: 10.4103/0974-9233.173132.
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