Sudden vision loss — warning signs

When to treat it like an emergency

Sudden vision loss or change in one eye is a reason to act fast — some causes can be reversed if treated within hours. Treat a sudden blackout, a shadow or curtain, a burst of new floaters, or sudden distortion of straight lines as an emergency: contact an eye doctor or emergency services right away. These simulations show what some of those warning signs can look like.

Overview

Central retinal artery occlusion (CRAO) happens when the main artery supplying blood to the retina becomes blocked, usually by a clot or plaque that has traveled from elsewhere in the body. Because the retina needs a constant blood supply to function, the blockage causes sudden, painless, severe vision loss in that eye — for many people, the vision drops to counting fingers or worse within seconds to minutes. Eye doctors and stroke specialists treat CRAO as the eye's equivalent of a stroke, because the retina is really an extension of the brain and central nervous system, and because a CRAO can be an early warning sign of a broader risk of stroke. This simulator shows one severe presentation: a profound, near-total darkening and blurring across the whole field of the affected eye.

Symptoms of CRAO

• Sudden, painless, severe loss of vision in one eye, developing over seconds to a few minutes
• Vision loss is usually profound — often described as going almost completely dark or dim in that eye
• No pain, redness, or discomfort in most cases, which can make people delay seeking care
• Occasionally preceded by brief, repeated episodes of vision loss lasting seconds to minutes (amaurosis fugax) in the hours or days before
• Loss is confined to one eye at onset, since the blockage affects that eye's own blood supply

What causes CRAO

• A blood clot or piece of plaque (embolus) that travels from the heart or the carotid arteries in the neck and lodges in the retinal artery — the most common mechanism
• Hardening and narrowing of the arteries (atherosclerosis) affecting the vessels that supply the eye
• Giant cell arteritis, an inflammation of blood vessels that occurs mainly in older adults and can cause CRAO — a distinct emergency requiring urgent treatment to protect the other eye
• Blood clotting disorders, which are a more common cause in younger people without typical vascular risk factors
• Other rare causes, including inflammation of blood vessels, trauma, or a clot related to eye or heart procedures

Central Retinal Artery Occlusion (CRAO) risk factors

• High blood pressure
• High cholesterol and atherosclerosis
• Diabetes
• Heart disease, including irregular heart rhythms such as atrial fibrillation, and prior heart valve disease
• Narrowing of the carotid arteries in the neck
• Smoking
• Older age
• Symptoms suggesting giant cell arteritis, such as new headaches, scalp tenderness, jaw pain when chewing, or unexplained weight loss and fatigue in someone over 50

Prevention & early detection

• Managing blood pressure, cholesterol, diabetes, and heart rhythm problems lowers the risk of the vascular causes
• Stop smoking
• If you have symptoms of giant cell arteritis, seek prompt medical evaluation — early treatment can prevent CRAO in the other eye
• Follow up on any brief, unexplained episodes of vision loss (amaurosis fugax) right away rather than waiting to see if they recur
• Regular checkups for cardiovascular risk factors, since CRAO shares many of the same underlying causes as stroke and heart attack

Treatment

CRAO is treated as a true emergency, and management is time-sensitive because retinal tissue can be damaged within a short window after blood flow stops. There is no single treatment proven to reliably restore vision once the artery has been blocked for long, so much of the urgent work focuses on the immediate emergency-room evaluation: checking for giant cell arteritis (which needs urgent steroids if suspected, to protect the other eye), and evaluating for the same underlying causes as a stroke, including imaging of the heart and the carotid arteries in the neck. Because CRAO and stroke share so many risk factors and mechanisms, a same-day medical work-up (often in an emergency department, alongside neurology) is standard, and finding and treating the underlying cause helps prevent a future stroke or a second eye event. Low-vision rehabilitation can help with daily tasks if vision loss is permanent. The exact plan is decided together with your eye doctor and physician.