A visual aura is a transient neurological event, a temporary disturbance in the visual cortex that processes vision. It typically precedes or accompanies a migraine, though it can occur without a subsequent headache. This phenomenon is characterized by fully reversible visual impairments. While not harmful, the experience can be unsettling, especially when it occurs for the first time.
The Classic Scintillating Scotoma
The most common form of visual aura is the scintillating scotoma, which combines “scotoma” (a blind spot) with “scintillating” (flickering or shimmering). This disturbance often begins as a small, flickering spot or shimmering patch near the center of the visual field. It quickly develops into a distinct pattern of bright, geometric, zigzag lines.
This intricate pattern is often described as a “fortification spectrum” or teichopsia because its angular, jagged edges resemble the battlements of a medieval fort. The lines may appear black and white or brightly colored, constantly flickering. As the aura progresses, this shimmering, zigzagged arc gradually expands outward, often forming a C-shape or crescent.
The area enclosed by the expanding geometric pattern often becomes a temporary blind spot where vision is obscured. This combination of a flickering border and a central blind area defines a scintillating scotoma. The pattern expands in a slow, steady march across the visual field, distinguishing it from other visual phenomena. This progression reflects a wave of altered electrical activity, known as cortical spreading depression, moving across the visual cortex.
Other Common Visual Phenomena
While the scintillating scotoma is the typical visual aura, the experience can manifest in other ways involving less structured changes. A simpler positive symptom is photopsia, characterized by unformed flashes of light, stars, or shimmering spots added to the visual field. These flashes are usually brief and may appear spontaneously.
Some individuals experience non-geometric visual distortions, such as blurring or a shimmering effect that makes objects look as if they are viewed through heat waves. Another variation is temporary vision loss, sometimes described as a curtain descending over the eye, termed amaurosis fugax when monocular. Unlike the classic aura, which affects both eyes (originating in the brain), visual changes in only one eye may signal a different, more serious condition.
Less common are visual hallucinations involving complex, patterned images or a kaleidoscope effect. These varied experiences highlight that a visual aura is a spectrum of neurological events, not limited to a single pattern, though they all stem from the same temporary neural disruption.
Duration, Progression, and When to Seek Help
A visual aura is defined by its temporary nature, with symptoms typically lasting between five and sixty minutes. Symptoms usually build gradually over about five minutes, which differentiates a migraine aura from other sudden neurological events. The expanding visual pattern will typically grow and move toward the edge of the field of vision before completely fading away.
The visual aura may occur before or during the headache phase, or entirely without a subsequent headache, which is known as acephalgic migraine. Since the symptoms are temporary, vision returns to normal after the aura has passed, and the event does not cause lasting damage to the eyes or brain.
While visual auras are generally benign, any new visual disturbance requires medical evaluation to rule out more serious conditions. Seek immediate medical attention if a visual change is sudden, lasts longer than an hour, or is accompanied by symptoms like weakness, difficulty speaking, or numbness on one side of the body. These symptoms can overlap with signs of a stroke or other serious neurological issues requiring prompt diagnosis.