Eye Info

Retinal vessel occlusion

Summary: Simple guides designed to help you understand more about your eye condition.

A retinal vessel occlusion is a blockage in the blood vessels of the eye that can cause sight loss. This information describes two different types of vessel occlusion and their affect on vision.

How the eye works

We need light to see what is around us and to see colour. Light bounces off the objects we look at. These reflect different amounts of light which we see as different colours.

Light rays enter the front of our eye through the clear cornea and lens. It is very important that both the cornea and lens are clear as this allows the light to pass directly through the front of the eye to the retina. The cornea and lens bends light so that it can focus on the retina at the back of our eye. This gives us a clear, precise image. The cornea focuses the light towards our retina. The lens fine tunes the focussing of this light

Our tears form a protective layer at the front of the eye and also help to direct the light coming into our eye. The iris, the coloured circle at the front of our eye, changes the size of the pupil and this allows different amounts of light into our eye. The pupil is the dark hole in the middle of the coloured part of our eye. The pupil gets smaller in bright conditions to let less light in and gets bigger in dark conditions to let more light in.

The middle of our eye is filled with a jelly-like substance called the vitreous. The vitreous is clear and allows light to pass directly from the front to the back of our eye.

The retina at the back of the eye is a light-sensitive layer which consists of rod and cone cells. These cells collect the light signals directed onto them and send them as electrical signals to the optic nerve at the back of our eye.

Rod cells are concentrated around the edge of the retina. They help us to see things that aren’t directly in front of us, giving us a rough idea of what is around us. They help us with our mobility and getting around by stopping us from bumping into a things. They also enable us to see things in dim light and to see movement.

Cone cells are concentrated in the centre of our retina where the light is focused by the cornea and lens. This area is called the macula. Cone cells give us our detailed vision which we use when reading, watching TV, sewing and looking at people’s faces. They are also responsible for most of our colour vision.

The optic nerve is made up of thousands of nerve fibres. These fibres pass the electrical signals along to our brain where they are processed into the image we are looking at.

Seeing can be likened to the process of taking pictures on a film with a camera which you then get developed. The retina is like a camera film which stores an image of what we are looking at. The image directed onto the retina is then sent along to the brain where it is processed, like developing a camera film. Therefore we actually 'see' in our brain with the light information sent to it from our eyes. This whole process happens very quickly so that everything we see is in focus.

What are the retinal vessels?

The retina at the back of the eye requires a constant blood supply. This blood supply makes sure that the cells of the retina get all the nutrients they need to continue working. The blood supply also removes any waste material that the cells have finished with. Like the rest of the body there are two types of blood vessels concerned with the blood supply to the retina, arteries and veins,

Arteries carry the fresh blood from the heart and lungs to all the cells in our bodies. Veins take away the blood that has been used by the cells and return it to the lungs and heart to be refreshed with oxygen and other nutrients. This process happens every time our heart beats so there is a constant stream of fresh blood and nutrients reaching all the cells in our bodies.

A blockage in either a retinal vein or artery is medically known as a 'retinal vessel occlusion'. Occlusion means closing or blocking up. They can happen in any of the blood vessels in the body, including the retinal arteries and veins. A retinal vessel occlusion can affect sight.

This information describes the causes of retinal vessel occlusion, the effects they have on vision and any treatment that may be available. Because the occlusion can happen in either a vein or an artery they will be described separately. If you have been diagnosed with a retinal vessel occlusion but are unsure whether it affects a vein or an artery then your GP or ophthalmologist should be able to tell you which type of vessel has been involved.

What causes retinal vessel occlusions?

The main cause of a retinal artery occlusion is atherosclerosis. Atherosclerosis is a problem with the condition of the inside of the blood vessel’s wall. If you imagine a blood vessel like a tube with the blood flowing through it then atherosclerosis is a problem with the inside of the tube. The tube is usually wide and smooth so that the blood flows directly through it. However in some people the inside of this tube becomes thinner or sticky which means it is harder for the blood to flow through it. These patches of sticky blood vessels are called atherosclerotic plaque, sometimes called hardening or thinning of the arteries and veins.

Problems occur because these sticky patches can catch any debris in the blood which in turn makes the plaques bigger. If the plaques become bigger they can cut off part or all of the blood going to or from the retina. Large pieces of debris can also get caught and block off the blood vessel. This can then cause either a vein or an artery occlusion.

Are there any risk factors for retinal vessel occlusions?

There are a number of common risk factors for this thinning of arteries and veins. They are quite familiar since the problem of thinning arteries and veins can cause other problems like heart attacks and strokes. The main risk factors are

  • Age - most retinal vessel occlusions happen in people over 65
  • High blood pressure
  • High cholesterol levels
  • Diabetes
  • Smoking
  • Overweight

Although nothing can be done about our age, all the other risk factors can be controlled. Regular visits to your GP to diagnose any circulation problems like high blood pressure and cholesterol levels, good diabetic control, a healthy diet and stopping smoking can all help to reduce the risk of experiencing a retinal vein occlusion.

What is the difference between an artery occlusion and a vein occlusion?

Retinal artery occlusion

The retinal cells need a constant supply of fresh blood to keep working properly. If the arteries become blocked then this fresh blood cannot reach the cells as it should. When this happens the retinal cells quickly suffer from the lack of fresh oxygen. This stops them working and sight can be affected quite badly. The amount of sight that is affected varies according to the location of the blockage.

Imagine the blood vessels spreading across the retina like a tree. Thinking of them like this can help to understand how much sight is affected by an artery occlusion. The retinal arteries have a large trunk of a blood vessel that splits into smaller branches to feed all parts of the retina. If the trunk of the tree is blocked then a lot of sight will be affected, less sight will be affected if the blockage happens further along in one of the branch arteries.

Retinal vein occlusion

The retinal veins drain away the used blood from the retinal cells. When one of these veins becomes blocked then the used blood cannot drain away properly. This causes the blood to 'back up' in the system. This blocking and pooling of blood can cause the area to swell and may also cause areas of haemorrhage (bleeding). These areas of swelling and backed up blood damage the cells of the retina and therefore damage sight. Again, the extent of the sight loss depends on where the blockage takes place.

What are the symptoms of retinal vessel occlusion?

Both types of retinal vessel occlusion cause a painless loss of vision.

In an artery occlusion this loss of vision usually happens very suddenly with little or no warning. In nearly all cases, one eye is affected. Some people may experience short periods of sight loss (amaurosis fugax) before the sight loss becomes permanent. If you experience short periods of sight loss with sight returning or you suddenly lose vision in one eye, you should attend your local eye accident and emergency department as soon as possible.

In a vein occlusion sight loss may be gradual, you may notice that your sight dims over a period of time. Again in nearly all cases only one eye is affected. If you notice any change in your vision you should have this checked straight away by an eye care professional such as an optometrist (optician).

Is there any treatment for retinal vessel occlusions?

Retinal artery occlusion

Unfortunately there is little treatment available for retinal artery occlusions because the cells on the retina are very sensitive to a lack of blood supply. A disturbance for any length of time in fresh blood to the retinal cells will cause permanent sight loss. In some people the blockage that causes the first sight loss may become dislodged and if the blood supply is started again then some improvement in vision may be seen. Most people however have permanent changes in their vision.

Retinal vein occlusion?

The sight loss caused by this kind of occlusion can sometimes improve on its own. Because the blood 'backing-up' can cause swelling and bleeding, sometimes when this swelling and the blood that has leaked clears up, sight can improve a little. In a few but not all cases, a laser can be used in this type of occlusion to help control bleeding and swelling and this can mean that sight improves a little. Often the laser is also used to stop more damage occurring so although no sight is restored the likelihood of losing more sight is reduced.

Sometimes a retinal vein occlusion can cause new blood vessels to grow around the centre of the retina (macular). If this happens then they can also affect vision quite badly. The ophthalmologist may well recommend that you are seen in the clinic over the following months to check that this isn't happening. If new blood vessels do start to grow then sometimes they can be treated with a laser.

New treatments which include, the use of steroid injections into the eye, injections of drugs which stop new blood vessel growth and surgical techniques are being developed and tested for use in retinal vessel occlusions. At the moment their long-term success in helping vision has not been shown therefore they are not widely available but may be in the future, as more research is completed.

What happens next?

Since retinal vessel occlusions are often connected to other more general circulation problems such as high blood pressure, high cholesterol levels or diabetes then the ophthalmologist may want to check that your heart and blood are healthy. They may want to check your blood and your blood pressure and if they find any problems with this then they will suggest to your GP that they take steps to help with these problems. These may include taking aspirin to help 'thin' the blood, drugs to lower blood pressure if it is high and sometimes drugs to lower the cholesterol levels in your blood. All these steps can improve your circulation and so avoid the chance of having a similar occlusion in your other eye. It is therefore very rare for retinal occlusions to occur in both eyes.

Is there anything that can be done to prevent a retinal vessel occlusion?

Retinal vessel occlusions are fairly common but there are ways of avoiding the chances of having one. Regular checks with the GP can discover whether you may be at risk and if so treatment can be given to improve your chances of not having an occlusion. Drugs to control high blood and cholesterol levels can help along with a good diet, low in fat and saturated fat, stopping smoking and moderate exercise can all help avoid circulation problems that can be the root of the retinal occlusion. You can always ask you GP about steps you can take to make sure you are doing the best to keep your heart and circulation as healthy as possible.

What about my sight?

Retinal vessel occlusions come as a shock to most people. The sudden loss of vision can be upsetting and it is quite normal to feel upset and worried at the time. However because usually the sight loss is in one eye only people can quickly adjust to their new level of vision.

At first you may find that you are constantly aware of the change in your vision and that the sight loss in one eye dominates your vision making it difficult to see using both eyes. However, after a few months you will probably find that this becomes less of a problem. This happens because our brains are able adjust to a new level of vision and are able to make the eye with good sight the dominant one. Usually people find that with time their good eye 'takes over' and that tasks that were difficult become easier.

If a lot of sight in one eye is affected quite badly then, for a period of time, people may feel slightly unbalanced. This is because we are used to having pictures from two eyes to help us make sense of the world. When sight in one eye is affected it can affect our depth perception. You may find that you have trouble judging distances, how high a step is or how far away a table is. With time you should be able to judge these distances better but you should take care in the first couple of months.

You may be concerned about driving following loss of sight in one eye, however it is legal to drive with sight like this. As long as your sight in the other eye is good enough to see a number plate at 20.5 metres wearing any glasses that you may need and you have 120 degrees in your field of vision you will be legally able to drive. Your optician or ophthalmologist will be able to let you know if your sight is good enough for driving. You may be more comfortable waiting until your good eye becomes more dominant but legally, if you have good sight in one eye you are able to drive.

I have a problem with my other eye, what can be done to help?

If you have an eye condition in your other eye that has also affected your vision then your sight loss may be more serious. You may find it useful to contact your local low vision clinic, social services department and organisations for people with poor sight. They will be able to offer you advice and support on coping with poor vision and also to tell you more about the services and benefits for people with sight loss.

What's next?

Our Adapting to sight loss page gives information useful for people with a newly diagnosed sight problem.

If you need more information contact our Helpline on 0845 766 9999 or 020 7388 2525 / helpline@rnib.org.uk - calls are charged at local rates.

RNIB does not comment on every trend or development but, when a treatment becomes established / recognised, we revise our website material to include it.

Unfortunately, RNIB can only answer email enquiries from the UK. But you may find an organisation for people with poor sight in your country through our agencies database.

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Content author: eyehealth@rnib.org.uk

Last updated: 06/03/2008 15:41

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