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Example of a scintillating scotoma, as may be caused by cortical spreading depression
Scintillating scotoma is the most common visual aura preceding migraine and was first described by 19th-century physician Hubert Airy (1838–1903). It is often confused with ocular migraine, which originates in the eyeball or socket.
Although many variations occur, scintillating scotoma usually begins as a spot of flickering light near or in the center of the visual field, which prevents vision within the scotoma area. The affected area flickers but is not dark. It then gradually expands outward from the initial spot. Vision beyond the borders of the expanding scotoma(s) remains normal with objects melting into the scotoma area background similarly to the physiological blind spot, which means that in the early stages when the spot is in or near the center, objects may be seen better by not looking directly at them. The scotoma area may expand to completely occupy one half of the visual area, or it may also be bilateral. It may occur as an isolated symptom without headache in acephalgic migraine.
As the scotoma area expands, some people perceive only a bright flickering area that obstructs normal vision, while others describe seeing various patterns. Some describe seeing one or more shimmering arcs of white or colored flashing lights. An arc of light may gradually enlarge, become more obvious, and may take the form of a definite zigzag pattern, sometimes called a fortification spectrum (i.e. teichopsia, from Greek τεῖχος, town wall), because of its resemblance to the fortifications of a castle or fort seen from above. It also can resemble the "dazzle" camouflage patterns used on ships in WWII. Others describe patterns within the arc as resembling Widmanstätten patterns.
The visual anomaly results from abnormal functioning of portions of the occipital cortex, at the back of the brain, not in the eyes nor any component thereof, such as the retinas. This is a different disease from retinal migraine, which is monocular (only one eye).
It may be difficult to read and dangerous to drive a vehicle while the scotoma is present. Normal central vision may return several minutes before the scotoma disappears from peripheral vision.
Sufferers can keep a diary of dates on which the episodes occur to show to their physician, plus a small sketch of the anomaly, which may vary between episodes.
Scintillating scotomas are most commonly caused by cortical spreading depression, a pattern of changes in the behavior of nerves in the brain during a migraine. Migraines, in turn, may be caused by genetic influences and hormones. People with migraines often self-report triggers for migraines involving stress and a wide variety of foods. While monosodium glutamate (MSG) is frequently reported as a dietary trigger, some scientific studies do not support this claim.
Scintillating scotoma may also be caused by other serious neurological or cardiovascular conditions, especially when the onset occurs later in life.
Symptoms typically appear gradually over 5 to 20 minutes and generally last fewer than 60 minutes, leading to the headache in classic migraine with aura, or resolving without consequence in acephalgic migraine. Many migraine sufferers evolve from scintillating scotoma as a prodrome to migraine to scintillating scotoma without migraine. The scotoma typically spontaneously resolves within the stated time frame, leaving few or no subsequent symptoms, though some report fatigue, nausea and dizziness as sequelae.
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