Migraine aura or retinal flashes?

Not all flashes of light mean the same thing

Seeing flashes of light can be alarming, but not all flashes mean the same thing. The two most common explanations are migraine aura and retinal flashes, and while both involve the same symptom on the surface, they arise from completely different places and carry very different implications.

Understanding which one you are experiencing matters, because the appropriate response is quite different in each case.

A neurological event originating in the brain

Migraine aura is a neurological phenomenon that originates in the brain, not in the eye. It occurs when a wave of electrical activity passes through the visual cortex at the back of the brain. The result is a distinctive visual disturbance that typically begins as a small, shimmering spot near the centre of vision and gradually expands over about twenty to thirty minutes into a curved or zigzag arc of flickering light, often described as kaleidoscope-like or scintillating.

Some people notice missing patches in their vision surrounded by this shimmering arc; others see only the arc of light itself. Crucially, migraine aura affects both eyes simultaneously, because it originates in the brain rather than in one eye. Closing one eye does not make it disappear.

The aura usually resolves completely within an hour, and may or may not be followed by a headache or nausea. Migraine with aura can occur without any headache at all, a pattern that becomes more common with age.

A mechanical stimulus in the eye itself

Retinal flashes, by contrast, originate in the eye itself. They occur when the vitreous gel inside the eye pulls on the retina, stimulating the light-sensitive cells and producing what the brain interprets as a flash of light. These flashes are typically experienced as a brief streak, spark, or arc of light, most often in the peripheral vision.

They are most commonly experienced during a posterior vitreous detachment (PVD), when the gel is separating from the retina. Unlike migraine aura, retinal flashes are usually brief, lasting only a fraction of a second, and they tend to occur repeatedly over hours or days rather than building gradually over twenty to thirty minutes. They are typically seen in one eye only, and are often triggered or worsened by eye movement.

Duration, pattern, and which eye are the key clues

Duration is perhaps the most useful distinguishing feature. Migraine aura builds slowly and typically lasts between twenty minutes and an hour. Retinal flashes are brief, a fraction of a second each, though they may occur repeatedly.

Pattern also differs. Migraine aura produces a distinctive expanding, shimmering zigzag arc. Retinal flashes are usually simpler, brief streaks or sparks without the characteristic expanding arc.

Which eye is affected is another useful guide. Migraine aura affects both eyes simultaneously, because it is generated in the brain. Retinal flashes usually affect one eye only. If you are unsure, closing each eye in turn during an episode can help clarify this.

Accompanying symptoms may also provide clues. Migraine aura is sometimes followed by headache or nausea. Retinal flashes are often accompanied by new or changing floaters.

Retinal flashes warrant urgent assessment; migraine aura usually does not

If you experience flashes that you think may be retinal in origin, particularly if they are brief, in one eye, and accompanied by new or changing floaters, prompt assessment by an eye professional is recommended. A retinal tear can occur when the vitreous pulls on the retina, and if left untreated a tear can progress to a retinal detachment. Not every case of retinal flashes indicates a tear, but examination is needed to determine this.

Migraine aura, while alarming the first time, does not require urgent eye assessment. It is worth discussing with your GP if it is a new symptom or if it occurs without a prior history of migraine, to ensure the diagnosis is correct.