What Causes Sudden Loss of Peripheral Vision in One Eye?

Sudden loss of peripheral vision in one eye is almost always a sign that something has gone wrong with the retina, the optic nerve, or the blood supply feeding them. The most common culprits include retinal detachment, blocked retinal blood vessels, optic nerve inflammation or ischemia, and acute glaucoma. Some of these are true emergencies where hours matter, while others resolve on their own but signal a deeper problem worth investigating.

Retinal Detachment and the “Dark Curtain”

Retinal detachment is one of the most recognizable causes of sudden peripheral vision loss in one eye, and it is the diagnosis many people fear when they notice a shadow creeping in from the side. The most common type, called rhegmatogenous retinal detachment, happens when the gel-like vitreous inside the eye degenerates and pulls away from the retina, creating a tear. Fluid seeps through the tear and lifts the retina away from the tissue underneath it. People typically notice light flashes, a burst of new floaters, and then a dark curtain or shadow encroaching on their side vision.¹

The curtain usually starts at the edge of your visual field and moves inward as more retina peels away. Where the shadow appears depends on which part of the retina is detaching: a detachment at the top of the retina causes a shadow rising from below, and vice versa. If the detachment reaches the macula, the central part of the retina responsible for sharp straight-ahead vision, the damage becomes much harder to reverse. This is why eye doctors treat retinal detachment as an emergency. Surgical repair within the first day or two, before the macula lifts off, gives the best chance of preserving good vision.

Risk factors include aging (the vitreous naturally shrinks and pulls away from the retina over time), high myopia, previous eye surgery, and a family history of detachment. If you notice a sudden increase in floaters accompanied by flashing lights and any kind of shadow in your peripheral vision, get to an eye clinic the same day.

Blocked Blood Vessels in the Retina

The retina has its own network of arteries and veins, and when one of them gets blocked, the area it supplies stops working. Two types of blockage commonly affect peripheral vision in one eye: branch retinal artery occlusion and branch retinal vein occlusion.

A branch retinal artery occlusion (BRAO) happens when a clot or piece of plaque lodges in one of the smaller arteries branching off the central retinal artery. Because only a segment of the retina loses its blood supply, the vision loss is restricted to a portion of the visual field rather than the whole eye.² The loss is painless and typically happens within seconds. People often describe it as a wedge-shaped blind spot that appeared out of nowhere. This matters beyond the eye itself because the clot frequently comes from the same place: fatty plaques in the carotid artery or the heart. A BRAO is essentially a mini-stroke of the eye, and it raises the risk that a full stroke could follow. Your doctor will almost certainly want to evaluate your carotid arteries and heart once a BRAO is diagnosed.

Branch retinal vein occlusion (BRVO) is more common and works differently. Instead of an artery getting blocked, a vein gets compressed, usually at the point where an artery and vein cross over each other. Degenerative changes in the vessel walls and abnormal blood-clotting factors contribute to the blockage.³ The backed-up blood causes swelling and hemorrhages in the affected part of the retina, producing a blurred or dark patch in that part of the visual field. BRVO tends to develop over hours rather than seconds and is strongly linked to high blood pressure. While some cases improve on their own over weeks to months, complications like chronic swelling of the macula can develop, sometimes requiring injections to preserve vision.

Optic Nerve Problems

The optic nerve carries visual information from the retina to the brain, and damage to it in one eye can wipe out a section of peripheral vision or central vision or both, depending on which nerve fibers are affected.

Ischemic Optic Neuropathy

Non-arteritic anterior ischemic optic neuropathy (NAION) is the most common acute optic nerve problem in adults over 50. It happens when blood flow to the front of the optic nerve drops below what the tissue needs to survive. The small arteries supplying the optic nerve head become insufficient, the nerve fibers swell, and because the optic disc is a tight space, the swelling compresses the fibers further in a vicious cycle.⁴ The result is sudden, painless vision loss that usually affects the lower half or one side of the visual field in one eye. People often wake up with it, noticing that the bottom or side of their vision in one eye is missing.

NAION tends to strike people with small, crowded optic discs (sometimes called “disc at risk”), and it is strongly associated with diabetes, high blood pressure, and sleep apnea. Unfortunately, there is no proven treatment that restores the lost vision. The focus after a NAION episode shifts to managing cardiovascular risk factors to protect the other eye, because roughly 15 to 20 percent of people eventually develop the same problem in their fellow eye.

Optic Neuritis

Optic neuritis, inflammation of the optic nerve, tends to hit a younger population, typically adults in their 20s to 40s. Unlike the painless onset of NAION, optic neuritis usually comes with pain behind or around the eye that gets worse when you move it.⁵ Vision loss develops over hours to days and can affect any part of the visual field, including peripheral zones. Colors often look washed out in the affected eye.

The most common underlying cause of optic neuritis is a demyelinating process, where the immune system attacks the insulating sheath around the nerve fibers. Multiple sclerosis is the condition most frequently linked to this type of optic neuritis.⁶ That does not mean everyone who gets optic neuritis has MS, but it does mean doctors will typically order brain imaging to look for other signs of demyelination. Most episodes improve substantially over weeks, though some residual loss can remain.

Giant Cell Arteritis

Giant cell arteritis (GCA) deserves its own discussion because missing it can cost you vision in both eyes. GCA is an inflammatory condition of medium and large arteries that almost exclusively affects people over 50, with the average age of onset closer to 70.⁷ The inflammation can choke off blood flow to the optic nerve, causing a form of ischemic optic neuropathy that is more severe and more urgent than the non-arteritic type discussed above.

What makes GCA especially dangerous is that it can rapidly progress to the second eye if untreated. Vision loss from GCA is often preceded by warning symptoms: new-onset headaches, tenderness in the temple area, jaw pain while chewing, scalp tenderness, fatigue, and sometimes fever or unexplained weight loss. If anyone over 50 presents with sudden vision loss in one eye plus any of these symptoms, doctors treat it as a medical emergency and start high-dose corticosteroids immediately, sometimes before blood tests confirm the diagnosis. The goal is to save the other eye.

Acute Angle-Closure Glaucoma

Most people associate glaucoma with slow, gradual peripheral vision loss, but acute angle-closure glaucoma is a different beast. It happens when the drainage pathway inside the eye gets physically blocked, causing intraocular pressure to spike rapidly. The symptoms are dramatic: severe eye pain, redness, blurred or hazy vision, headache, nausea, and sometimes vomiting.⁸ The headache and nausea sometimes lead people to an emergency room thinking they have a migraine or even a stomach bug rather than an eye problem.

While the hallmark symptom is pain and blurred vision rather than a clean peripheral-field loss, the dangerously high pressure can damage the optic nerve within hours, producing lasting visual field deficits that begin at the periphery. People with anatomically narrow drainage angles, which is more common in farsighted eyes and in people of East Asian descent, are at higher risk. Treatment involves rapidly lowering the eye pressure with medications and then performing a laser procedure to create a new drainage pathway.

Transient Peripheral Vision Loss

Not every episode of sudden peripheral vision loss is permanent. Two conditions cause brief episodes that resolve on their own but have very different implications.

Amaurosis fugax is a temporary loss of vision in one eye, lasting seconds to minutes, caused by a transient reduction in blood flow to the retina. It often feels like a curtain descending over the eye and then lifting. The cause is usually the same as BRAO: a small embolus from the carotid artery or heart that temporarily blocks a retinal vessel before breaking up or passing through. Amaurosis fugax is a warning sign for stroke, and anyone who experiences it needs urgent vascular workup.

Retinal migraine looks superficially similar but has a completely different cause. It is a rare, diagnosis-of-exclusion condition typically seen in younger patients with a history of migraines, and it is thought to involve reversible vasospasm of retinal blood vessels rather than an actual clot.⁹ The vision disturbance is temporary and may be followed by a headache. The practical distinction is critical: a 25-year-old migraine sufferer with brief monocular vision loss has a very different risk profile than a 65-year-old with carotid artery disease, but both need evaluation to sort out which category they fall into.

Less Common Causes Worth Knowing About

Several other conditions can produce sudden or subacute loss of peripheral vision in one eye. They are less frequent but important to recognize because treatment options and urgency vary widely.

Infections of the retina, particularly acute retinal necrosis (ARN), can destroy peripheral retinal tissue rapidly. ARN is caused by herpes-family viruses, most often varicella-zoster virus or herpes simplex virus. Inflammation, bleeding, and actual death of retinal tissue spread from the periphery toward the center.¹⁰ Retinal detachment is a frequent complication, occurring in a substantial proportion of affected eyes. ARN requires aggressive antiviral treatment, and even with treatment, visual outcomes can be poor.

Tumors pressing on the optic nerve or the visual pathways inside the skull can also erode peripheral vision, though this tends to happen gradually rather than in a single sudden event. Meningiomas compressing the optic nerve, for example, typically cause vision loss that worsens over months, and the severity of the loss correlates with how long the compression has been present.¹¹ That said, a person may not notice slow peripheral loss until it crosses a threshold that feels sudden. Head trauma is another recognized cause, with injuries to the optic nerve, the orbit, or the intracranial visual pathways all capable of producing visual field deficits.¹²

Certain medications can also damage the optic nerve fibers that serve peripheral vision. Ethambutol, a drug used to treat tuberculosis, is the best-known offender. It typically affects central vision first, but peripheral fibers can also be involved, leading to constricted visual fields.¹³ Anyone taking ethambutol is usually monitored with regular visual field tests for this reason.

When It Is Not Structural at All

A proportion of people presenting with visual field loss have no identifiable structural problem with their eye, optic nerve, or brain. This is sometimes called functional visual loss. It is real in the sense that the person genuinely experiences it, but there is no damage to the visual system that explains it. The condition appears to involve the brain’s processing of visual signals rather than the hardware itself.

Functional visual field deficits tend to produce distinctive patterns on testing. Concentric field constriction, where the visual field appears to be narrowed into a tunnel from all directions, is the most common pattern. In a study of patients with functional visual loss, field abnormalities were predominantly concentric, and most patients with this pattern showed variable results on repeated testing, meaning the size of the tunnel changed from test to test in a way that structural disease would not produce.¹⁴ This variability is actually one of the key clues that tips off the clinician. Functional visual loss does not mean someone is faking. It is a recognized neurological phenomenon, and it often occurs alongside other functional neurological symptoms or significant psychological stress.

Why Timing and Symptoms Matter for Triage

One of the most important things to understand about sudden peripheral vision loss in one eye is that the appropriate level of urgency depends heavily on the accompanying symptoms and the speed of onset. Neuro-ophthalmic emergencies, if not identified and treated quickly, can lead to permanent vision loss or even life-threatening complications like stroke.¹⁵

A few rules of thumb help sort things out:

• Painless and instantaneous: Think vascular. A retinal artery or vein blockage, or amaurosis fugax. Get evaluated the same day, both for the eye and for stroke risk.
• Painless with flashes and floaters: Think retinal detachment. Same-day evaluation.
• Painful with eye redness: Think acute angle-closure glaucoma or sometimes infection. Emergency evaluation.
• Painful with eye movement: Think optic neuritis. Urgent but not emergency-room-level; see an eye doctor within a day or two.
• Vision loss with headache, jaw pain, or scalp tenderness in someone over 50: Think giant cell arteritis. This is a true emergency where same-day treatment with steroids can save the other eye.

None of these rules replaces professional evaluation, but they give you a sense of how doctors think about triage when a patient walks in with sudden visual field loss. The common thread is that almost every cause on this list benefits from prompt attention, so the safest default is to treat any sudden peripheral vision loss in one eye as urgent until proven otherwise.

How Peripheral Vision Loss Affects Everyday Life

Even when the acute emergency has been managed, living with a permanent peripheral visual field defect presents practical challenges that go beyond what many people expect. The biggest concern for most people is driving. A systematic review of studies examining driving performance in people with visual field loss found that deficits included problems with lane positioning, spatial judgment, steering consistency, and an increased risk of collisions. However, the picture is more nuanced than a blanket “you can’t drive” verdict. Across several prospective on-road assessment studies, roughly 87 to 88 percent of subjects with visual field loss were judged to be safe drivers.¹⁶

The extent and location of the field loss matter enormously. A small peripheral deficit in one eye may be partially compensated by the overlapping field of the other eye, since the two eyes’ visual fields overlap through most of the central region. Larger deficits, especially those affecting the temporal (outer) field of the affected eye, are harder to compensate for because that region has less overlap with the other eye’s field. Many jurisdictions have specific visual field requirements for driver licensing, and these vary widely. If you have been diagnosed with a lasting peripheral field defect, it is worth checking local regulations and, if possible, getting a formal driving assessment rather than guessing whether your vision is adequate behind the wheel.

Beyond driving, people with peripheral vision loss in one eye often report difficulty in crowded environments, bumping into objects on the affected side, and feeling less confident walking in unfamiliar places. Compensatory strategies include training yourself to make more frequent head turns toward the blind side, using wider mirrors in the car, and positioning yourself in rooms so the intact side of your vision faces the area with the most activity. Occupational therapists and low-vision specialists can help develop these habits systematically.