– How your eye works
– What causes an occlusion?
– What are the risk factors?
– Retinal artery occlusion (RAO)
– Retinal vein occlusion (RVO)
– How will I manage with the change in my sight?
– Can I still drive?
– What if both of my eyes are affected by sight loss?
How your eye works
Your retina is a delicate tissue that lines the back of your eye and is sensitive to light. It converts the light into electrical signals that travel along the optic nerve to your brain. The brain interprets these signals to “see” the world around you.
The retina is supplied with blood by a delicate network of blood vessels. These blood vessels can be damaged by diabetes, hypertension (high blood pressure) and other conditions.
Most light entering your eye is focused onto a tiny area of your central retina called the macula. This highly specialised area of your retina measures approximately 5mm in diameter. The macula is vital because it lets you recognise colours and see the fine detail needed to carry out activities such as reading and writing. The rest of your retina, called the peripheral retina, gives you peripheral vision (also known as side vision).
The retina receives all the nutrients it needs to continue working via blood in the arteries and removes any waste that is produced through veins. Arteries carry blood from the heart around the body, and veins carry it back to the heart. Blood travels around your whole body keeping every part nourished and working. The arteries and veins in your eye are smaller than in other parts of the body, but they do a similar job.
Unfortunately arteries and veins can become blocked. These blockages can happen anywhere in the body. When it occurs in the retina it’s called a retinal artery occlusion or a retinal vein occlusion.
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What causes an occlusion?
The main cause of retinal artery or vein occlusion is atherosclerosis. Atherosclerosis is a problem with the condition of the inside wall of blood vessels. Blood vessels are like tubes. They are usually wide and smooth so that the blood flows easily through them. In some people, the inside of the blood vessels become narrow and sticky. This can make it difficult for the blood to easily flow through them. These narrow patches are called atherosclerotic plaques (or an atheroma) and are often described as hardening or thinning of the vessels. These sticky patches can catch debris in your blood, which in turn makes the plaque bigger. Blood clots can also form on these plaques, again making them bigger, and reducing blood flow. As these plaques grow, they can cut off some, and potentially all of the blood flowing through the vessel.
Sometimes, part of a vessel wall plaque which forms in a larger vessel may break off. This piece (an embolus) will then flow with the blood, potentially blocking a smaller vessel downstream – this is called an embolism. An embolism can block an artery and if this happens in your retina, it’s called a retinal artery occlusion.
Veins and arteries run very closely together at the back of the eye and cross over each other. If someone has narrowing of their retinal arteries due to atherosclerosis, this can cause the hardened arteries to press onto the nearby veins. This in turn can cause the vein to narrow, potentially causing a blockage. When a vein in the retina is blocked, it is called a retinal vein occlusion.
What are the risk factors?
Factors which increase your risk of retinal vessel occlusion include:
- age – most retinal vessel occlusions happen in people over 65
- hypertension (high blood pressure)
- high cholesterol levels
- blood clotting disorders
- glaucoma or raised intraocular (eye) pressure
Your GP can diagnose circulation problems like hypertension and prescribe medication to help control them and limit the chance of related complications. If you are diabetic, then good diabetic control can help reduce the risk of blood vessel problems.
Lifestyle changes can also help to reduce your risk of atherosclerosis, which can also go some way to reverse the development of atherosclerotic plaques. These steps are also likely to improve your general health as a whole, reducing your risk of developing conditions like diabetes, stroke, and cardiovascular disease as well as keeping your eyes healthy.
- Stopping smoking. Smoking reduces the amount of oxygen your blood can carry, as well as damaging the lining of blood vessels and making arthrosclerosis more likely. Talk to your doctor or pharmacist for help with giving up.
- Eating a healthy diet. This includes consuming different fruits and vegetables, whole grains, lean meats, poultry without skin, and seafood. A healthy diet is low in salt, added sugar, saturated fats, and refined grains.
- Drinking less alcohol. While there is some evidence that alcohol can have a protective effect on coronary heart disease in small quantities, this is still dependent on many other factors including age, and lifestyle. Discuss your individual circumstances with your doctor to get help and advice on this.
- Keeping active. It is thought that even a modest increase in physical activity reduces your risk of atherosclerosis as well as coronary heart disease.
- Maintaining a healthy weight. People who are overweight are more likely to have poor diets and lead sedentary lifestyles. Their lipid (fats like cholesterol) levels in their blood are also likely to be high.
People with a high eye pressure are more likely to have a vessel occlusion. Your optician can tell if you have high eye pressure and refer you to an ophthalmologist if needed. Glaucoma is where your eye pressure causes damage to the optic nerve at the back of your eye. If you have glaucoma, keeping your eye pressure under control can prevent damage to your optic nerve as well as lowering your risk of a retinal vessel occlusion.
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Retinal artery occlusion (RAO)
If you have an artery occlusion, you may lose your sight with little or no warning. If you suddenly lose vision in one or both eyes, you should attend your local hospital Accident and Emergency (A&E) department straight away.
Some people may experience warning symptoms of brief periods of sight loss every now and again, before they have permanent loss of vision. If you experience this, you should have your eyes examined as soon as possible by an optometrist or at an A&E department. Not every temporary loss of vision is due to artery occlusion, but these symptoms need investigating to work out the reason.
Your retinal arteries deliver blood which is rich in oxygen to the cells of your retina. If retinal arteries become blocked, then blood and the essential oxygen cannot reach the retinal cells. Without a constant supply of fresh blood and oxygen, the cells of the retina are quickly damaged and this means that the cells stop working and sight can be permanently lost. The amount of sight lost depends on where the blockage has occurred.
The main artery supplying your retina enters your eye with your optic nerve; this is called the central retinal artery. At the point it enters the eye it splits in half, one branch for the upper retina, and another branch for the lower retina. In turn each branch splits again, to a left and a right side. In total, there are four branch arteries supplying blood to all areas of your retina.
If the central artery becomes blocked, then little to no blood will enter your eye, and it will affect all of your vision in that eye. This type of occlusion is a central retinal artery occlusion (CRAO). If the blockage happens in one of the branch arteries, then only some of your sight in that eye will be affected. This type of blockage is a branch retinal artery occlusion (BRAO).
Is there any treatment for a retinal artery occlusion?
Unfortunately there is little treatment that can help to bring back sight following a retinal artery occlusion. The cells on the retina are very sensitive to a lack of blood supply, which can result in permanent sight loss. Although the chances of restoring any vision are low, if you are seen at the hospital within four hours of having a retinal artery occlusion, then your doctor may try some treatment to dislodge the blockage and get the blood flowing again.
Your ophthalmologist may lower your eye pressure in an attempt to dislodge the blockage and restart the blood supply. By lowering the pressure inside your eye, the vessel can expand and the blood may flow more easily. The pressure is lowered by using medications (tablets and eye drops) or using a small needle (under anaesthetic) to take some fluid out of the eye.
You may also be instructed to massage your eye. This causes a raising and lowering of the eye pressure, which may dislodge the blockage and allow the blood to flow again.
If the blockage moves, then an improvement in your vision may be seen. How much improvement you see will depend on how long it has been before the blockage started to move, and how far it moves. Most people however still have permanent changes in their vision, as unfortunately there’s no treatment available to reverse the damage to cells caused by the lack of blood supply.
As a retinal artery occlusion is commonly only in one eye, most people manage with the sight from their other eye; though you will require a period of adjustment to your new vision.
After a retinal artery occlusion, it is crucial to have further tests, usually by your GP, to try and find out if there is an underlying risk factor that may have caused this. Sometimes the blood tests (and possibly other investigations) do not find anything wrong. If a cause is suspected then it can be treated or managed to reduce the risk of another occlusion occurring in the other eye.
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Retinal vein occlusion (RVO)
If you have a retinal vein occlusion, you may notice your sight in one eye dimming or blurring over a period of days, leaving you with poor vision. If you experience any change in your vision you should have your eyes examined as soon as possible. Your optometrist is best placed to examine your eyes for milder vision changes, though if you feel your sight has deteriorated a lot or very quickly, you should visit your local A&E department.
The retinal veins drain away used blood from the retinal cells. When one of these veins becomes blocked, then the used blood cannot drain away. This causes the blood to collect in the veins, which causes swelling and haemorrhages (bleeding). These areas of swelling and bleeding damage the cells of the retina, which can affect your sight. How much sight is affected depends on where the blockage takes place.
The veins are spread out all over the retina, but join together to form larger veins. Similar to the arteries, there are four branch veins that join together to form the central retinal vein that leaves the eye through the optic nerve at the back of your eye. If the blockage is in the central retinal vein (known as a central retinal vein occlusion or CRVO) it can affect all your vision in that eye. If it is in one of the branch retinal veins (known as a branch retinal vein occlusion or BRVO), then it will usually affect a smaller area of your sight in that eye.
What is the treatment for a retinal vein occlusion?
The sight loss caused by branch retinal vein occlusion may cause no or little visual loss, and can get better without any treatment. If you have a central retinal vein occlusion, more of your vision will be affected. Some of the changes to your vision may be caused by the swelling and bleeding the occlusion causes. If this swelling improves and the blood is reabsorbed, your sight may get better. Because of this, your ophthalmologist may choose to wait for a few months before starting any treatment.
Your ophthalmologist will discuss with you whether you need treatment depending on whether you have developed any complications from the vein occlusion. If treatment is recommended they will explore which type of treatment you need and the timing of the treatment. Treatment is not always needed when you first have a vein occlusion, but you will still be monitored by the eye clinic. It is likely that you will continue to be monitored for around two years, whether you have treatment or not.
Your ophthalmologist will also recommend that you see your GP. Your GP will try to find out if there is an underlying risk factor that may have caused this. Sometimes the blood tests (and possibly other investigations) do not find anything wrong. If a cause is suspected, then it can be treated or managed to reduce the risk of another occlusion occurring in the other eye.
If you have a retinal vein occlusion, one or more of the following complications may mean you need treatment:
- macula oedema (swelling of your central retina)
- neovascularisation (new blood vessel growth)
- high eye pressure (glaucoma).
The most common need for treatment is if you have macular oedema – this is when your central macular area of your retina is swollen with fluid. It is caused by a damaged vein, which leaks fluid and collects at your macula. Macula oedema can cause problems with your central vision, leading to difficulties recognising faces, reading or watching television with that eye.
If you have macular oedema you will be monitored by the eye clinic at regular intervals.
There are two main treatments for macular oedema, anti-VEGF injections and steroid injections.
Anti-VEGF stands for anti-vascular endothelial growth factor. Vascular endothelial growth factor is a protein produced by cells when there is not enough oxygen or blood flow to an area. It promotes leakiness of blood vessels and can stimulate the growth of new blood vessels in that area. Anti-VEGF drugs work by blocking these chemical signals helping to reduce swelling in the macula.
Anti-VEGF medication is given as injections into the eye. Normally, a course of three injections, one a month for three months, is given to start with. After this your eye will be checked at the hospital every four to eight weeks. You may be given further injections if your ophthalmologist thinks they are needed. It’s quite common for people to have more injections after the first three.
Anti-VEGF medicines are injected into the vitreous, which is the jelly that fills the inside of your eye. This is called an intravitreal injection. The injection needs to be given in a clean sterile room or an operating theatre to reduce the risk of infection.
Before the injection, you’ll be given anaesthetic eye drops to make your eye numb, antiseptic drops to clean the eye and if necessary an antibiotic drop to help prevent you from getting an infection. The injection is not usually painful, but your eye may be a little sore after the anaesthetic wears off.
We have more information about anti-VEGF treatment here.
Steroids are used to control swelling and this is usually given in the form of an implant about the size of a grain of rice. This implant is injected into your eye in a similar way to an anti-VEGF injection. It slowly releases a steroid for up to six months, though more than one implant might be required after the previous one has worn off.
Possible complications of anti-VEGF injections and steroid implants
All medicines and treatments can have side effects. It’s not always possible to predict whether you will experience any side effects but most people do not have any complications. When deciding on a treatment, your doctor will consider your individual circumstances before recommending a specific one. If you are concerned by any possible side effects or complications, it is best to discuss this with your ophthalmologist.
Intravitreal injections come with the risk of infection (approximately 1 in 1,000). This is minimised with the use of sterile equipment, and using a clean room. There is also a risk of a retinal detachment from an injection (approximately 1 in 7,000). The most common side effects reported are: redness and haemorrhage (bleeding) at the site of the injection, eye pain from the injection, and headache.
Steroids can cause side effects in the eye, but the risks of using steroids are considered smaller than the risk to your vision if no treatment was given.
Steroids are known to cause cataracts (clouding of the lens in your eye). They can also increase the pressure within your eye, which can lead to glaucoma. These side effects do not happen to everyone, and they can be managed if they occur.
Cataracts can be treated using surgery to remove the cloudy lens and replacing it with an artificial one. Raised eye pressure and glaucoma can be managed with eye drops to help lower your eye pressure.
Neovascularisation (new vessel growth)
If a large part of your retina is affected by the retinal vein occlusion, like in a central retinal vein occlusion, areas of the retina become starved of oxygen. This is called ischaemia. The eye responds to ischaemia by attempting to grow new blood vessels, a process called neovascularisation. This is nature’s way of trying to repair the damage by growing a new blood supply to the oxygen-starved area of your retina.
Unfortunately, these new blood vessels have weak walls, and grow in the wrong places. They can grow on the surface of the retina or on the iris at the front of the eye. These blood vessels bleed very easily. New blood vessels on the retina can result in more haemorrhages and damage to the retina, or bleeding into the jelly of the eye. At the iris, new blood vessels can cause your eye pressure to rise and lead to glaucoma.
Most people do not get neovascularisation after a vein occlusion, though if you do it can be treated with a laser.
High eye pressure (glaucoma)
New blood vessel growth at the iris can cause your eye pressure to rise and this can lead to glaucoma.
Your eye produces a fluid called aqueous humour, which is always being drained from your eye. The fluid is drained at the angle between your iris and cornea. If you have growth of new blood vessels in this area, it can cause the drainage angle to become blocked and cause the pressure in your eye to rise. If the pressure in your eye is too high, it can cause damage to your optic nerve – this is called glaucoma.
This is rare, but on average happens around 100 days after the initial vein occlusion, hence is often called 100-day glaucoma. It may also be called new vessel glaucoma (NVG), or rubeotic glaucoma.
If your ophthalmologist sees growth of new vessels in this area, then they will offer you laser treatment. You may also need eye drops and more rarely, surgery, to control your eye pressure.
Managing your general health after a vessel occlusion
Since the main cause of a vessel occlusion is atherosclerosis, and this is affected by a range of general health issues, your GP will have a key role after you have had a vessel occlusion. It is likely that they will want to monitor risk factors such as your blood pressure, blood sugar and cholesterol levels more closely, and you may be prescribed new or more medications to help control these. Your GP can also provide advice and help with stopping smoking and with managing your weight, as well as advice on exercise. Taking steps to manage these things can improve your general blood circulation and reduce your chance of having a similar occlusion in your other eye.
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How will I manage with the change in my sight?
How much a vessel occlusion will affect your sight varies from person to person. Some people do not notice much difference unless they cover the unaffected eye, and others are very aware of the change all the time. Because you use both eyes together to see in three dimensions (3D), when one eye is affected you may have difficulty judging distances. You may feel clumsy, misjudge steps, pavements and the position of objects, for example cups. However after a few months you will probably find that this becomes less of a problem. This is because our brains are able to 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 previously difficult become easier.
Can I still drive?
You may be able to continue driving a car or motorcycle if the vision in your other eye is unaffected by other eye conditions, and can meet the visual requirements for driving. You’re required by law to tell the Driver and Vehicle Licensing Authority (DVLA) if you have any eye conditions which may affect your vision in both eyes. Ask your optometrist or your ophthalmologist for advice about whether your sight meets DVLA standards and whether you can continue driving. Even if you’re told that your sight does meet DVLA standards, you may be advised to wait until you have adapted to having poorer vision in one eye before you resume driving.
What if both of my eyes are affected by sight loss?
If the affected eye was your good eye and you have a sight problem in your other eye, then you may need to make changes or use aids to make the most of your remaining sight. This may mean making things bigger, using brighter lighting or using colour to make things easier to see.
A low vision assessment can explore these things with you. Your GP, optometrist (also known as an optician) or ophthalmologist (also known as a hospital eye doctor) can refer you to your local low vision service for an assessment.
You can also find out tips for making the most of your sight by downloading our guide:
You should also ask your ophthalmologist whether you’re eligible to be registered as sight impaired (partially sighted) or severely sight impaired (blind). Registration can act as your passport to expert help and sometimes to financial concessions. Even if you aren’t registered, a lot of this support is still available to you.
Local social services should be able to give you information on staying safe in your home and getting out and about safely. They should also be able to offer you some practical mobility training to give you more confidence when you are out.
It’s completely natural to be upset when you’ve been diagnosed with a vessel occlusion, and it’s normal to find yourself worrying about the future and how you will manage with a change in your vision. We’re here to support you every step of the way, and to answer any questions you may have – just get in touch with our Sight Loss Advice Service.
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