Temporary peripheral vision loss, known medically as a scotoma or visual field defect, describes a transient blind spot or area of impaired sight within the normal visual field. This loss can manifest as a shimmering, zigzag pattern or a simple dark patch that appears and then resolves completely. The symptom is defined by its temporary nature, differentiating it from permanent vision loss. It often signals a disturbance in the visual pathways, which include the eyes, optic nerves, and the visual processing centers in the brain. Understanding the underlying cause is important because while some are benign, others signal a medical emergency.
Visual Disturbances Triggered by Migraines
The most frequent non-threatening cause of temporary vision loss is a migraine aura, specifically a visual aura. This event often precedes the headache phase of a migraine, though it can occur without a headache, a condition known as an acephalgic migraine. The classic manifestation is a scintillating scotoma, which starts as a small, shimmering or flickering spot near the center of vision and slowly expands outward toward the periphery.
This visual disturbance is not a problem with the eye itself but a temporary neurological phenomenon in the brain’s visual cortex, located in the occipital lobe. The underlying mechanism is believed to be cortical spreading depression (CSD). This is a slow-moving wave of intense electrical activity followed by a period of suppression. This wave travels across the visual cortex at a rate of approximately 3 to 6 millimeters per minute, accounting for the gradual expansion of the visual symptoms. The visual aura typically lasts between five and sixty minutes before the visual field returns to normal.
Reduced Blood Flow and Circulatory Issues
A more serious cause of temporary vision loss relates to a brief failure of blood flow to the visual system. A Transient Ischemic Attack (TIA), often referred to as a “mini-stroke,” occurs when a small blood clot or plaque temporarily blocks an artery supplying the brain or the eye. When this blockage affects the retinal artery, it causes temporary monocular vision loss, or vision loss in one eye, known as Amaurosis Fugax.
This vision loss is frequently described as a curtain or shade descending over the eye. It usually lasts only a few seconds to several minutes before vision is fully restored. While the temporary nature of the blockage means no permanent damage occurs, a TIA is a warning sign of a high risk for a future, more severe stroke. The source of the clot is often an atherosclerotic plaque in the carotid artery in the neck.
Another circulatory cause is orthostatic hypotension, a sudden drop in blood pressure when moving from a sitting or lying position to standing. Gravity causes blood to pool in the lower extremities, momentarily reducing the blood flow to the brain and eyes. This temporary lack of oxygenation can lead to visual symptoms such as blurred vision, dimming, or “tunnel vision.” The visual change is transient and resolves quickly once blood pressure stabilizes or the person sits down.
Other Ocular and Neurological Conditions
Beyond migraines and major circulatory issues, other specific conditions can cause temporary visual field changes. Episodes of severe anxiety or panic attacks can also induce temporary visual symptoms, including tunnel vision or blurred sight. This is often a result of the body’s “fight-or-flight” response, which includes hyperventilation. Rapid breathing alters the balance of oxygen and carbon dioxide in the blood, causing blood vessels to constrict, leading to lightheadedness and transient visual disturbances. Certain types of focal seizures can also briefly affect the visual cortex, causing temporary flashes of light or visual field loss.
Recognizing Serious Symptoms
While a temporary visual disturbance may be a harmless migraine aura, it is important to recognize signs that indicate a potentially life-threatening event like a TIA or stroke. Any sudden vision loss should be considered a medical emergency until proven otherwise. The most concerning signs are vision loss that is sudden and accompanied by other neurological symptoms.
These associated “red flag” symptoms include sudden weakness or numbness on one side of the body, difficulty speaking or slurred speech, or a sudden, severe headache. Vision loss confined to one eye strongly suggests an issue with the blood supply to the eye, necessitating immediate medical evaluation due to the high risk of subsequent stroke. Recognizing these concurrent symptoms and seeking urgent attention can significantly reduce the risk of permanent disability.