Sudden loss of vision: a case-based approach

The presentation

Picture an older adult who suddenly cannot see out of one eye. There is no pain, the eye looks normal from the outside, and it happened over seconds to minutes. That painless, sudden, one-eyed loss is a classic emergency pattern that points towards a problem with the blood supply to the eye or the retina. Now picture someone whose vision has become blurred and patchy over a day or two, with flashing lights and a shower of new floaters, as if a curtain is coming across their view. That is a different but equally urgent story. How fast the loss came on, whether one or both eyes are affected, and whether there is pain shape everything the clinician does next.

The questions that matter

A few questions do most of the work. Is the loss in one eye or both? One-eyed loss usually means a problem in front of where the two eyes' nerves join, such as the retina or its blood supply; loss on the same side of both eyes suggests a problem further back in the brain. Was it sudden or gradual, and did any vision come back? A brief loss that fully recovers within an hour may be a warning of stroke. Is there pain, especially with a red eye, headache or scalp tenderness? Are there flashing lights, floaters or a shadow spreading across the vision? Each answer narrows down the cause and the urgency.

The sight and life-threatening causes

Several causes must not be missed. A blockage of the retinal artery causes sudden, painless, severe loss in one eye and behaves like a stroke of the eye — every minute counts. A retinal vein blockage also causes sudden painless loss. Retinal detachment brings flashing lights, a surge of floaters and a spreading curtain across the vision. Giant cell arteritis, seen in older people, can cause sudden loss with headache, scalp tenderness and jaw ache, and can blind the other eye within days if not treated. A brief total loss in one eye that recovers (amaurosis fugax) or loss affecting both eyes on one side can signal a stroke or mini-stroke and needs emergency assessment.

Other important causes

Not every sudden change is a blocked artery. Acute angle-closure glaucoma causes a painful red eye with blurred vision, haloes around lights, headache and sometimes vomiting, and is itself an emergency. Bleeding into the jelly of the eye (vitreous haemorrhage), common in people with diabetic eye disease, causes sudden floaters and haze. Wet macular degeneration can cause fairly rapid central blurring and distortion, where straight lines look bent. Optic neuritis, inflammation of the eye's nerve, causes loss over hours to days with pain on eye movement, often in younger adults. Even a migraine can cause a temporary visual disturbance, though this should never be assumed until serious causes are ruled out by a clinician.

The safe pathway

The rule for sudden vision loss is simple: treat it as an emergency until proven otherwise. Sudden loss of vision in one or both eyes, a curtain or shadow across the sight, new flashing lights with a shower of floaters, or vision loss with headache and scalp tenderness all need urgent, same-day eye care — usually eye casualty or a hospital eye service. Loss affecting one side of the vision in both eyes, or a brief loss that recovers, should be treated as a possible stroke: in the UK that means calling 999. A chemical splash needs the eye rinsing with water straight away while getting emergency help. When sight fails suddenly, fast action protects it — waiting rarely does.