The central retinal artery is the main blood supply to the inner layers of the eye’s retina. When it is blocked, vision is severely affected and usually results in no light perception.
The condition is typically painless and happens suddenly. The prognosis for recovery of vision is poor, but immediate intervention can significantly improve the chance for restoration.
Causes
A blood clot blocks the flow of blood to the retina, a thin layer of tissue at the back of your eye that helps you see. The clot may form in the small arteries that supply blood to the retina or it can travel from other parts of the body, such as the heart or the carotid artery in the neck. The clot can last for seconds or minutes, or it can be permanent. In the most serious cases, it can lead to vision loss or blindness. Blood clots in the retina are usually a warning sign for clots in other parts of your body, such as in your lungs or brain.
Central retinal artery occlusion (CRAO) occurs when the supply of blood to the macula from the short posterior ciliary artery is cut off. The sudden blockage in the artery causes hypoperfusion of the retina, which leads to rapid cellular damage and visual symptoms. Prompt diagnosis and early treatment to dislodge or lyse the offending embolus or thrombus can reduce the risk of irreversible retinal damage and blindness.
The most common cause of CRAO is atherosclerosis-related thrombosis in the central retinal artery. It is also caused by giant cell arteritis in people older than 55 years, a rare syndrome called sickle-cell hemoglobinopathy, and a variety of other vascular diseases. In general, patients with CRAO are elderly and have a history of cardiovascular disease.
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Symptoms include severe reduced visual acuity, a ring of whitening around the optic disc, macular oedema with the characteristic ‘cherry red’ appearance of the fundus and arterial attenuation on ophthalmoscopy. The optic disc is pale and there are tortuous and dilated blood vessels in the affected area, which are often truncated at the margin. Spectral-domain optical coherence tomography may show a band-like hyperreflective lesion at the level of the inner nuclear layer.
A similar pattern is seen in peripheral branch artery occlusion (PBAO), although it affects a smaller area of the retina. PBAO is sometimes associated with a pigment epithelial defect in the affected eye and with a haemorrhage in the vitreous cavity.
Symptoms
The blood vessels that carry oxygen to the retina at the back of your eye (the optic nerve) can become blocked. When this happens, you may experience severe vision loss. The problem is more likely to happen if you have hardening of the arteries (atherosclerosis) in your heart and carotid artery in your neck. Blood clots may travel from these arteries to your eye. These clots are more likely to occur if you have diabetes or high blood pressure.
When you have CRAO, the area of your vision affected depends on where in your retina the blockage occurs. If it affects the central retinal artery, you will have a sudden and painless vision loss in one eye. Symptoms may last for seconds or minutes. If you have a blockage in a branch retinal artery, you will experience gradual changes in vision, but not a sudden vision loss.
CRAO can also lead to new blood vessels forming in the eye, which is called neovascularization. These abnormal blood vessels are more prone to bleeding and can cause a dangerous increase in the pressure inside your eye (vitreous hemorrhage).
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Another risk factor for CRAO is a history of inflammation of the blood vessels of the eyes or the body in general, such as glaucoma, diabetic retinopathy or systemic lupus erythematosus. Certain medications can also increase your risk, such as steroid drugs and birth control pills.
The symptoms of a retinal artery occlusion can be confused with other health problems, such as migraine headaches or high blood pressure. Only a doctor can determine the cause of your symptoms. Your doctor will ask about your medical history and do a physical exam. He or she will also look at the front of your eye, which includes the outer layer and the inner portion of your eyelid. Your doctor will use a special light and an instrument called an ophthalmoscope to examine your retina. He or she will also look at the blood vessels of your eye to see if they are dilated and normal. He or she will also look for signs of a clot, such as cotton wool spots around your retina and the presence of an embolus.
Diagnosis
The retina is a layer of nerve tissue at the back of your inner eye that senses light and turns it into electrical signals that your optic nerve carries to your brain. A blockage of a blood vessel in your retina can interrupt this flow and cause vision loss. The blockage usually comes from a blood clot or a fat deposit (cholesterol) in your blood vessel.
Your health care provider may diagnose this condition by examining your eye and taking a history of symptoms. He or she will also look for other causes of your health problem. If the clot breaks free and moves to your brain, it could lead to a stroke.
Central retinal artery occlusion occurs when a blood clot (embolus) blocks the central branch of the ophthalmic artery, which supplies the retina. A sudden and painless loss of vision in one eye (ocular emergency) requires prompt medical attention to address the underlying cause and try to restore blood flow to the retina.
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Immediately after a CRAO episode, the patient is usually very anxious and inconsolable. The pupil responds poorly to direct light, but constricts briskly when another eye is illuminated (relative afferent pupillary defect). The fundus often appears pale and bloodless with a cherry-red spot in the center called the macula. In most cases the occlusion is complete and permanent, but in some cases the clot dislodges after 8 to 24 hours and vision returns.
It is important to recognize that the symptoms of a CRAO are very similar to those of an ischaemic stroke and that prompt diagnosis and intervention are essential in order to prevent irreversible vision loss. CRAO should always be treated as an ocular emergency, and it is recommended that the following criteria be used for determining if a patient requires urgent medical attention:
Patients who present with sudden and painful monocular vision loss of more than 24 hours have a good prognosis for recovery of visual acuity, although they may experience a progressive and severe decline in the quality of their remaining vision. The management of CRAO is generally analogous to the treatment of stroke, with emphasis on acute management to restore blood flow and prevention of secondary complications.
Treatment
If the occlusion is treated within an hour of onset, it can be reversed and vision restored. However, if the occlusion continues to last more than an hour, it results in irreversible damage.
Acute CRAO is a medical emergency and prompt referral to an ophthalmologist is essential. The goal of therapy is to dislodge or lyse the offending embolus and restore retinal blood flow. Prompt treatment reduces the risk of secondary ischemic events such as stroke and myocardial infarction.
During a specialized eye exam, your provider will look for signs of a retinal artery blockage, such as floaters or a dark spot in your field of vision (called a macular hole). Your provider will also check the health of your other heart and blood vessels to see if they are affected by the blocked artery.
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The cause of a retinal artery occlusion is usually a blood clot or inflammation in the wall of the retinal vein. The retinal vein connects to the arteries that supply oxygen-rich blood to your retina. In some cases, the inner lining of your retinal vein can grow stiff from a buildup of plaque, which causes blood clots to form in the vein. This can cause the artery to occlude and thereby cut off the blood supply to your retina.
Other signs of a retinal artery occlusion include a reddish or purple color in the center of your field of vision, called an asymptomatic macular hole; and severe vision loss. Your provider will be able to determine the extent of your vision loss by asking you to read letters on a chart.
Blood thinners can help prevent a clot from blocking the artery. These medications can be given orally or by injection into a vein in your arm. The most commonly used blood thinners are aspirin and heparin. Your provider will prescribe a dose that is right for you. You may need to take these medications for a long time. If your occlusion is caused by a problem with your heart or blood vessels, you may need to take these medications longer.
