Temporary blindness, medically termed Transient Visual Loss, is a sudden, temporary reduction or complete loss of sight that can affect one or both eyes. The duration of these episodes is not uniform, ranging widely from mere seconds to several hours, depending entirely on the underlying physiological mechanism. This variability in time is a direct consequence of whether the cause is a fleeting interruption of blood flow, a neurological event, or external irritation. Understanding the difference in duration helps categorize the potential causes and determine the seriousness of the event.
Brief Episodes That Resolve Rapidly
The shortest episodes of temporary vision loss often result from a momentary disturbance in the blood supply to the eye or the brain’s visual centers. These visual obscurations typically last only a few seconds, frequently described as a graying out or a brief blackout of vision. They are commonly triggered by sudden changes in body posture, such as quickly standing up, which causes an immediate, temporary drop in blood pressure and reduced blood flow to the head.
Slightly longer episodes, lasting from one to fifteen minutes, are often associated with a temporary blockage in the retinal artery. This condition is sometimes described as a curtain coming down over one eye. This transient monocular vision loss results from a small clot or debris traveling from the carotid artery in the neck, which briefly obstructs blood flow to the retina. Vision returns quickly when the blockage clears or breaks up, restoring circulation to the eye.
Another cause for these short events is a temporary narrowing of the blood vessels, known as vasospasm. This can restrict the necessary oxygen and nutrient supply to the visual pathways. While these events are brief, often lasting less than a minute, they are distinct from the pressure-related causes and are sometimes triggered by external factors like cold or emotional stress.
Vision Loss That Persists for Minutes or Hours
Vision loss that lasts significantly longer, typically from ten minutes up to an hour, often points toward neurological events rather than circulatory issues. A common example is the visual aura that can precede or accompany a migraine. This temporary vision disturbance is caused by a slow-moving wave of electrical activity across the brain’s visual cortex. This phenomenon usually manifests as shimmering, zigzag lines or a temporary blind spot that gradually expands, generally affecting vision in both eyes for up to sixty minutes before fully resolving.
The duration of this visual aura is distinct because the underlying mechanism is a transient electrical disturbance within the brain tissue, not a physical blockage. The resulting visual symptoms are usually positive, meaning the patient sees something that is not there, like sparkling lights, in contrast to the negative “blackout” symptoms of vascular events. While the visual changes are temporary, the full migraine episode, if it follows, can last for many hours.
Another cause of temporary vision loss lasting several hours or even a day or two is photokeratitis, which is essentially a sunburn of the cornea, the clear front surface of the eye. This condition, often called snow blindness or arc eye, results from excessive exposure to ultraviolet light, such as from welding arcs or reflections off snow. Photokeratitis causes the surface cells of the cornea to become damaged, leading to blurry vision, light sensitivity, and a feeling of grit in the eyes until the corneal cells can naturally regenerate.
When to Get Emergency Medical Help
Any sudden, unexplained loss of vision requires prompt medical evaluation, even if the vision returns quickly, as the underlying cause could indicate a serious health concern. If temporary vision loss occurs and is accompanied by other sudden symptoms, such as slurred speech, confusion, weakness on one side of the body, or a sudden, severe headache, immediate emergency medical attention is necessary. These combinations of symptoms may indicate a stroke or a transient ischemic attack, which demands urgent intervention.
Vision loss that persists for more than one hour should also be treated as a medical emergency, as it exceeds the typical duration for most common temporary causes like migraine auras or the brief circulation-related events.
If the vision loss is sudden and complete in only one eye, or is described as a dark curtain that fails to lift, it could signal an acute event like an impending retinal artery blockage. Recurrent episodes of temporary vision loss, even if they are brief, warrant an immediate and thorough medical investigation to identify and manage any underlying risk factors.
For individuals over the age of fifty, new-onset temporary vision loss accompanied by jaw pain while chewing or a tender scalp also requires urgent care. This is necessary to rule out an inflammatory condition that can cause permanent blindness.