Flashes of Light in Your Vision

Why the eye sees light that is not there

The retina responds to any stimulation by sending a signal the brain interprets as light. Mechanical traction (the vitreous pulling on the retina as it separates or moves) is the most common stimulus and produces brief flashes, typically at the edge of vision and most noticeable in the dark or when the eye moves. The same traction can tear the retina at a point of firm attachment, which is why flashes and floaters are treated as a warning until the retina has been examined.

Retinal flashes versus migraine aura

• Retinal flashes: brief, like a camera flash or lightning, usually in one eye, at the edge of vision, in the dark or with eye movement, and often accompanied by new floaters
• Migraine aura: a shimmering, zigzag or crescent pattern that starts small and expands across the vision over about twenty minutes, affects both eyes, and may be followed by a headache or occur alone; it originates in the brain, not the eye

If you are unsure which you have, be examined. Retinal causes are excluded by examination, and migraine aura is then diagnosed by its pattern.

Other causes

A blow to the eye or head, which stimulates the retina directly; rubbing the eyes; low blood pressure on standing; and, rarely, inflammation or other retinal disease. Persistent flashes without a vitreous cause are investigated further.

What the examination involves

The pupils are dilated and the whole peripheral retina is examined with a bright light and a wide-field lens, sometimes with gentle pressure on the eyelid to bring the far periphery into view. Any tear found is referred promptly to a retina specialist for laser sealing. If the examination is clear, it is usually repeated after a few weeks, because tears can appear as the vitreous continues to separate, and you are told to return at once if symptoms change.