Amaurosis Fugax: When One Eye Goes Dark

Every so often, a patient sits in my chair and tells me a story that stops the small talk cold. "Doctor, last Tuesday my right eye went dark — like a shade being pulled down. It lasted maybe two minutes, and then it just… came back." No pain. No injury. Nothing to see by the time they reach me, because the eye looks perfectly normal again.

That little episode has a name — transient monocular vision loss — and when we suspect a tiny embolus caused it, we call it amaurosis fugax, Latin for "fleeting darkness." It is one of the most important stories a patient can tell me, because it is a symptom, not a diagnosis — and sometimes it is the only warning before a stroke.

A blackout in one eye is a TIA of the eye

Here is the idea I need every patient to carry home: if a blood clot briefly blocks the circulation to one retina, that is a transient ischemic attack — a TIA — that happens to announce itself through the eye instead of through speech or a weak arm. The American Heart Association reports that the 90-day risk of stroke after a TIA may run as high as 17.8%, with nearly half of those strokes arriving within the first two days. Two minutes of darkness can be the brain's way of clearing its throat.

The numbers back up the urgency. In one published series of patients with retinal artery blockages or amaurosis fugax, brain MRI showed fresh infarctions in 23% of them — most without a single stroke symptom. The episode in the eye was the visible tip of an iceberg.

Playing detective: what exactly did you see?

Because the examination is usually normal by the time we meet, your description is my best instrument. So I ask a lot of questions, and it helps to know them in advance:

Was it really one eye? People are surprised how often a "left eye" problem turns out to be a left-sided field problem in both eyes — a brain event, not an eye event. If it happens again, cover one eye, then the other. That single detail steers the whole workup.

How did it look? A curtain or shade descending, or the top or bottom half going grey, is the classic embolic pattern. An altitudinal loss — half the visual world gone — is especially telling: studies associate it with roughly 3.5 times the odds of significant internal carotid artery stenosis. Diffuse dimming, a central blur, or a slow constriction each point in other directions.

How long did it last? Ischemic episodes typically run seconds to minutes — most under 15 minutes, rarely beyond 30. Sparkles, zigzags, or colored lights that march and spread over twenty minutes are a different animal, usually migraine or retinal in origin.

Did anything hurt, and what came with it? Pain with eye movement suggests optic neuritis. In patients over 50, I ask pointedly about a new headache, scalp tenderness, pain in the jaw when chewing, aching shoulders and hips, fever, or weight loss — the calling cards of giant cell arteritis, a vessel inflammation that can blind the second eye within days if missed. That is why we check ESR and CRP urgently, and why, when suspicion is high, steroids start immediately while a temporal artery biopsy is arranged. We do not wait for permission from the biopsy to protect the other eye.

The workup, in fast-forward

When the story sounds ischemic, we move the same day, along a stroke pathway:

In my office: vision in each eye, pupils (looking for a relative afferent pupillary defect), color vision, visual fields, eye pressure, and a dilated look at the retina and optic nerve — hunting for embolic plaques, a pale or swollen disc, hemorrhage, or detachment. A normal-looking retina does not end the search; trouble can sit behind the eye.

In the lab: blood count, glucose and metabolic panel, lipids, clotting studies — and ESR and CRP whenever arteritis is on the table.

In the scanner: MRI of the brain with diffusion-weighted imaging, ideally within 24 hours, because it catches the silent infarcts; CT if MRI is not available. Imaging of the neck and head vessels — carotid ultrasound, CT angiography, or MR angiography — to find the stenosis, dissection, or occlusion feeding the problem.

At the heart: an ECG, echocardiography, and rhythm monitoring when indicated, because atrial fibrillation and other cardiac sources send clots to eyes as readily as to brains.

Once the source is found, treatment follows it — antiplatelet therapy and attention to blood pressure, lipids, and diabetes for atherosclerotic disease; stroke-prevention management for a cardiac source; steroids for arteritis; and timely treatment of a tight carotid stenosis, which is one of the most satisfying saves in all of medicine.

If it happens to you

Do not wait for a second performance. A painless blackout in one eye — even one that lasted a minute, even one that happened once — deserves a same-day, emergency evaluation, not a routine appointment three weeks out. Write down which eye, what it looked like, and how long it lasted while the memory is fresh. Cover-one-eye curiosity can wait; the clock cannot.

I have spent my career looking into eyes, and I will tell you the secret of the profession: the eye is the one place where we can watch the brain's circulation at work, live and unfiltered. When one eye goes dark for a minute, it is rarely the eye asking for help. It is the whole circulation, whispering. Our job — yours and mine — is to listen the first time.

This article is educational and is not a substitute for personal medical advice. If you experience sudden vision loss in one eye, seek emergency care immediately.

Author

Paddy Kalish OD, JD and B.Arch Author and Blogger