Central retinal artery occlusion: sudden sight loss, causes and emergency care

The retina is the light-sensitive layer at the back of the eye. RNIB explains that its arteries deliver oxygen-rich blood, and that if they become blocked the retinal cells are quickly damaged, stop working and sight can be permanently lost. The main artery supplying the retina enters the eye with the optic nerve and is called the central retinal artery. At the point it enters the eye it splits into branches for the upper and lower retina.

When the central artery is blocked, almost no blood reaches the retina and vision in that eye is affected as a whole. This is a central retinal artery occlusion, or CRAO. A blockage in a branch is a branch retinal artery occlusion (BRAO) and affects a particular area of vision. RNIB notes that retinal artery occlusion usually happens in only one eye.

RNIB describes sudden loss of sight, usually over seconds, with no pain. You should attend A&E straight away if you suddenly lose all or part of your vision in one or both eyes. The speed matters because the retinal cells are very sensitive to lack of blood supply.

Some people have a warning episode first. RNIB describes amaurosis fugax as sudden, temporary loss of all or part of the vision in one eye for seconds or minutes before it returns, which happens when small blockages occur momentarily before the circulation clears them. It is an urgent warning sign and should be examined as soon as possible by an optometrist or at A&E. Not every temporary loss of vision is due to artery occlusion, but it needs investigating immediately to find the cause.

• Sudden loss of vision in one eye, painless.

• Loss of all vision or of part of the visual field.

• Brief episodes of vision loss that recover (amaurosis fugax) before the permanent event.

The same processes that block an artery in the eye can block arteries elsewhere. RNIB says the risk factors for retinal vessel occlusion are similar to those for cardiovascular disease, and that treating risk factors may help to reduce the chances of other vessels becoming blocked, such as those leading to stroke or heart attack.

The NHS says that a TIA, or mini stroke, is caused by a temporary disruption in blood supply to part of the brain, with symptoms including visual disturbance and face, arm and speech problems, and that it is a warning sign that you may be at risk of a full stroke. If you also have any face drooping, arm weakness or speech difficulty, call 999 immediately. After a CRAO, RNIB says further tests are crucial to find an underlying cause and that your GP may be involved.

RNIB says artery occlusions are commonly caused by atherosclerosis or an embolus. Atherosclerosis is a build-up of fatty plaques inside artery walls, which can narrow vessels or cause clots. An embolus is a piece, for example of plaque from a larger artery, that breaks off and blocks a smaller vessel downstream. Less common causes include vasculitis (inflammation of the artery wall), trauma, sickle cell disease and clotting disorders.

Risk factors include age (most retinal vessel occlusions happen in people over 60), high blood pressure, high cholesterol, diabetes, blood clotting disorders, glaucoma or raised eye pressure, smoking and obesity. In a small number of cases no risk factor is found.

RNIB is candid that there is little treatment that can help to bring back sight following a retinal artery occlusion. The chances of restoring any vision are low, but if you are seen at hospital within a few hours, your ophthalmologist may try treatment aiming to dislodge the blockage and restore blood flow. Options described include lowering eye pressure with medicines or by removing a little fluid from the eye using a fine needle under anaesthetic, and massaging the eye to alter pressure. If the blockage moves further downstream, less of the retina is affected.

RNIB adds that even if a blockage moves, retinal cells may already have been permanently affected, so there is no guaranteed treatment. Most people manage with the sight from their other eye, although it may take time to adjust to the new level of vision.

RNIB says it is crucial to have further tests after a retinal artery occlusion to find any underlying risk factor. You may be referred to your GP, who looks for and treats problems such as high blood pressure, high cholesterol or diabetes. You may have blood tests to check for clotting disorders, and an assessment of the carotid arteries in the neck to see whether they contain plaques, which may sometimes need surgical removal. These steps cannot reverse sight loss that has already happened, but they aim to protect the other eye and to reduce the chance of stroke or heart attack.

RNIB lists lifestyle steps that reduce risk: stopping smoking, eating a healthy diet, drinking less alcohol, being active (it suggests aiming for at least 150 minutes of moderate activity a week) and maintaining a healthy weight. It also notes that you are required by law to tell the DVLA about eye conditions that may affect vision in both eyes, and that you should ask your optometrist or ophthalmologist whether your sight meets driving standards.

Sudden loss of vision is an emergency and is assessed through NHS A&E, where an ophthalmologist assesses the eye. Follow-up for blood pressure, cholesterol, diabetes and the carotid arteries is usually through a GP and hospital clinics on the NHS. Private eye clinics may be able to see you for non-emergency review, but an acute event should not be delayed by seeking a private appointment.