Retinal artery occlusion occurs when the retinal artery or one of its branches becomes blocked. This cuts off the blood and nutrient supply to the nerve layer of the retina, leading to permanent damage. It is a common cause of sudden loss of vision in one eye, which occurs over a few seconds. The loss is usually severe. Occasionally both eyes are affected but this is rare.
The condition is an emergency, as very early treatment is needed if there is to be a chance of restoring your sight.
The anatomy of the eye
When you look at an object, light from the object passes through the cornea of your eye, then the lens and then the retina at the back of your eye. Nerve messages pass from the seeing cells (rods and cones) in your retina, down nerve fibres in your optic nerve to your brain. The messages are interpreted by your brain, which enables you to see. If the retina is damaged, a clear picture cannot be produced.
The inner layers of the retina receive their blood supply from retinal arteries which run within the retina itself. The retinal arteries take oxygen and nutrients to the retina. The retinal veins drain blood away from the retina. The outer layer of the retina has a different supply, the ciliary arteries, which comes separately off the ophthalmic artery. When the retinal artery is blocked the ciliary arteries keep working, so that some cells in the retina are saved.
The retinal arteries begin as one single retinal artery that branches off the ophthalmic artery (which itself branches off the carotid artery). Once the retinal artery reaches the retina it divides into four braches which supply blood to the for quarters of the retina. The effect of an artery blockage therefore depends on exactly where the blockage occurs.
Retinal artery occlusion may just as the retinal artery emerges from the optic nerve and hasn't yet branched out - central retinal artery occlusion - or more the block may lodge in one of the four branches - branch retinal artery occlusion.
What is retinal artery occlusion and what causes it?
Retinal artery occlusion occurs when the retinal artery (or one of its branches) becomes blocked. This results in the blood and nutrient supply to the nerve layer of the retina being cut off. This leads to permanent damage and is a common cause of sudden loss of vision in one eye. Rarely, both eyes can be affected by the condition. Retinal artery occlusion is an emergency and requires urgent treatment if there is to be a chance of restoring your sight.
There are a number of ways in which the retinal artery can become blocked. The most common one is by a blood clot or by an embolus, which is a loose piece of material thrown off from elsewhere. This may be a blood clot from elsewhere, a piece of fatty material from a blood vessel wall, or infected material from elsewhere in the body. Alternatively, there may a sudden narrowing of the blood vessel due to small fatty lumps (atheroma) or inflammation.
8 out of every 10 central retinal artery occlusions are due to a combination of narrowed blood vessels due to atheroma, together with local formation of a blood clot. Around 6 in 10 of these patients will have high blood pressure and around 1 in 4 have diabetes.
Inflammatory conditions can make the artery wall swollen and blocked - for example, giant cell arteritis, systemic lupus erythematosus and granulomatosis with polyangiitis (Wegener's granulomatosis).
How common is retinal artery occlusion and who develops it?
Retinal artery occlusion is one of the more common causes of loss of vision in elderly people in the UK. However, it is still quite rare. It affects less than 1 person in every 100,000 per year. It tends to occur in patients over the age of 60 and it seems to affect men slightly more often than women.
What are the risk factors for retinal artery occlusion?
The risk factors can be divided into:
Those which make clots more likely to form
- Clotting disorders, such as sickle cell disease and protein S deficiency.
- Conditions which make clotting more likely, such as pregnancy or after surgery.
- Medications which increase clotting tendency (for example, the oral contraceptive pill).
Those in which clots already exist and are prone to break off
- Carotid artery stenosis. In this condition there is narrowing of the carotid artery by fatty plaques and atherosclerosis. If 'bits' break off from the carotid artery, the next 'bend in the flow' they are likely to encounter is in the ophthalmic or retinal artery.
- Atrial fibrillation. In this condition, a clot is commonly present in the chambers (the atria) at the top of the heart.
- Aortic disease - for example, aortic dissection.
Those in which retinal blood vessels are narrowed and more easily blocked
- Atherosclerosis (see below).
- Inflammation/swelling of artery walls- for example, giant cell arteritis, polyarteritis nodosa and systemic lupus erythematosus.
- Cocaine use causing blood vessel spasm.
- Rarely, retinal migraine causing blood vessel spasm.
- Eye injuries.
- Raised pressure in the eyes (glaucoma).
Those which make other debris more likely to break off into the bloodstream
Debris (such as fatty plaques or infected material) may detach and form loose bits of material (emboli) which can lodge in the retinal artery:
- Atherosclerosis. This accounts for about 8 out of every 10 cases. Small fatty lumps (atheroma) develop within the inside lining of blood vessels (arteries). Atheroma is also known as 'hardening' of the arteries (atherosclerosis). A patch of atheroma makes an artery narrower and can also break off into the bloodstream and form emboli. Atheroma is present in everyone as we age but is likely to be more severe in those who have:
- High blood pressure.
- High cholesterol.
- Increasing age.
- Certain infections. These include infection on the heart valves (endocarditis) and toxoplasmosis.
Around 1 in 10 patients have previously experienced a warning condition called amaurosis fugax. In this condition, all or part of the vision of one eye is temporarily but suddenly lost for periods of seconds or minutes only. This happens when small blockages are occurring temporarily, before the circulation manages to clear them away. It is an urgent warning sign, as it means complete blockage may be imminent.
What are the possible complications of retinal artery occlusion?
The most common complication of retinal artery occlusion is permanent damage to the vision in the affected eye. Damage to the nerves of the retina through lack of a blood supply becomes increasingly irreversible over time. The 'treatment window' during which something can possible be done is probably about 90-100 minutes. However, some form of treatment will usually be attempted within 24-48 hours of onset.
If vision is partially restored a further complication is further visual loss. This may be due to a second clot, or due to neovascularisation. Neovascularisation is abnormal new blood vessel formation at the back of the eye. 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.
What are the symptoms of retinal artery occlusion?
Central retinal artery occlusion
If you have a central retinal artery occlusion, the blockage of your artery occurs just as it enters your eye, before it divides into two, and then into four, branches. The whole of the nerve layer of the retina is affected. You will usually notice a loss of vision in one eye, which comes on quickly and painlessly over a period of seconds. In 19 out of 20 cases the loss of vision is so profound that you can just see fingers to count them, but nothing more. If you can't even count fingers that suggests ophthalmic artery occlusion (see below).
In most cases only one eye is affected - the condition affects both eyes in fewer than 2 in 100 cases.
Branch retinal artery occlusion
When only a branch of the artery is blocked, only the corresponding part of the vision is lost. Sometimes the doctors can pinpoint the site of the blockage by looking at the blood vessel pattern on the back of your eye.
Ophthalmic artery occlusion
If the ophthalmic artery is blocked before the point at which the retinal artery branches off it, the retinal artery will also be blocked. However, the situation is much worse, as in addition to blocking the central retinal artery, this also prevents flow getting to the ciliary arteries (see above). If this happens then the chance of preserving some visual function is much less and the loss of vision is likely to be complete (with no perception of light) from the start.
How is retinal artery occlusion diagnosed?
Retinal artery occlusion is usually diagnosed after an eye specialist (an ophthalmologist) examines the back of your eye, using an ophthalmoscope. This is a hand-held instrument with a light and magnifier. They may also use a larger 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, pale appearance in retinal artery occlusion. The specialist will usually be able to tell if you have a central retinal artery occlusion or a branch retinal artery occlusion.
Various other tests may be suggested, including:
- Taking measurements to check:
- How well you can see (your visual acuity).
- Your pupil reflexes (which are usually impaired).
- Your visual fields (to look at how good your side vision is).
- Blood tests:
- To rule out giant cell arteritis (if untreated this condition will mean that the other eye is also at risk).
- Checks to try to determine the possible original source of artery blockage:
- Your blood pressure will be taken.
- The doctor will listen to your pulse, heartbeat and carotid artery.
Your specialist may advise some other tests to look for possible underlying causes such as diabetes and high blood pressure. Retinal photographs may be taken.
What is the treatment for retinal artery occlusion?
Urgent treatment is needed for retinal artery occlusion if there is to be any chance of preserving useful vision. Depending on the cause, different approaches may be tried: there is no single guaranteed treatment to restore vision.
- If you are seen within 90-100 minutes of start of symptoms, firm eye massage may be tried to try to dislodge the blockage. This is repeated massage of the eyeball over the closed lid for ten seconds with five-second interludes. This only works very occasionally.
- Lowering of the pressure in the eye by draining a little fluid under local anaesthetic. However, this is only occasionally successful. Pressure-lowering drugs may also be tried.
- Injection of 'clot-busting' drugs into the ophthalmic artery (which supplies the retinal artery) has been tried. It has shown some success as long as it is done within six hours of start of symptoms.
- Enhanced external counterpulsation (EECP) is a non-invasive technique. Pneumatic cuffs on the lower extremities are inflated sequentially, aiming to send little pressure waves through the circulation to dislodge the blockage.
- Underlying conditions should be treated. Whilst this does not reverse the blockage in most cases, in the case of giant cell arteritis immediate treatment with steroids may reduce arterial swelling and allow the blood to flow again.
In the longer term doctors will also want to reduce your chance of this ever happening again. This means looking for and treating underlying causes (like high blood pressure and diabetes) and helping you to give up smoking. It also means assessing your carotid arteries to see if they contain other clot tissue which may need to be removed.
What is the outlook (prognosis) for retinal artery occlusion?
This differs a little depending on where the artery has been affected. Treatment must be started very soon after the onset of symptoms for there to be any hope of restoring vision. However, even with early treatment, the chance of useful vision recovery is generally very poor.
- In central retinal artery occlusion, only about one in three patients show any improvement.
- In branch retinal artery occlusion, the outcome is better with most patients achieving 6/12 or better vision in the affected eye. This is because in many cases the other (non-blocked) blood vessels are able to compensate for the damage by routing a supply to the blocked area.
- Occasionally, recanalisation of the artery occurs but this is rare. 1 in 4 eyes have collateral arteries serving the macular retina so that central vision can be retained to some extent.
Patients with retinal emboli are known to be at higher risk of heart disease than people who have never experienced this condition. They should be managed in the same way as patients with a personal history of coronary heart disease.
Can retinal artery occlusion be prevented?
The same things that can help to reduce your risk of cardiovascular disease, atheroma, may also possibly reduce your risk of retinal artery 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.
- Minimising your risk of blood clots through activity and care with medication.
- Managing eye diseases, including raised pressure in the eye (glaucoma).
- Acting on warning signs: seeking medical help IMMEDIATELY if you experience episodes of transient loss of vision.
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