Flashing Lights in Vision: Causes and When to Worry

What flashes look like

People describe:

• brief lightning streaks or arcs, often in the outer (peripheral) vision
• sparks or camera-flash bursts, more noticeable in the dark or when moving the eyes
• shimmering, flickering zigzag lines that spread slowly (migraine aura)
• flickering or sparkles in a blurred patch of vision

Where and how long the flashes appear helps distinguish the cause. Retinal flashes are in one eye and last a second or less. Migraine flashes affect the same side of vision in both eyes (still there with either eye closed) and evolve over 5 to 60 minutes.

Causes of flashing lights in vision

Posterior vitreous detachment (PVD)

The inside of the eye is filled with a clear gel, the vitreous, attached to the retina. With age, the gel shrinks and becomes more liquid. Eventually it peels away from the retina. As it tugs on the retina, it triggers brief flashes, usually at the side of vision, and often a new floater shaped like a ring, cobweb or fly.

Posterior vitreous detachment is very common after 50 and happens earlier in nearsighted people and after cataract surgery or eye injury. It is not harmful in itself, but in roughly 1 in 10 people with symptoms the pull causes a retinal tear.

Retinal tear and retinal detachment

A retinal tear allows fluid to pass under the retina and lift it off, causing retinal detachment. Warning signs:

• a sudden burst of many new floaters or a "shower of soot"
• flashes that persist or increase
• a shadow or curtain spreading from the edge of vision
• blurred or lost central vision if the macula detaches

Tears found early can be sealed with a laser or freezing treatment in the clinic. A detachment needs surgery, ideally within days or sooner if central vision is still intact.

Migraine aura

Migraine with aura often starts with a small flickering spot that expands into a shimmering, zigzag crescent (a "fortification spectrum") over 5 to 20 minutes, then fades within an hour. A headache often follows, but some people, especially over 50, get aura without headache (sometimes called ocular migraine). Because the cause is in the brain, the image is in both eyes.

Other causes

• Pressure on the eye or rapid eye movements: brief stars or sparks.
• Standing up quickly: a short dip in blood pressure can cause a gray-out with sparkles.
• Head injury: "seeing stars."
• Stroke or transient ischemic attack (TIA): affecting the back of the brain, may cause flashes or lost vision with other neurological signs. See stroke.
• Optic neuritis: flashes with eye movement, eye pain and blurred vision, sometimes in multiple sclerosis.
• Inflammation of the retina or choroid and some retinal diseases.
• Medicines: some drugs (such as ivabradine) cause light phenomena; digoxin toxicity can cause yellow-tinged vision.
• Occipital seizures: brief colored circles or flashes, usually in one side of vision.

Comparing the main causes

What happens at the eye exam

An optometrist or ophthalmologist will check your vision and put in dilating drops to widen the pupils. They then examine the whole retina, including its edges, with a bright light and lens. They may press gently on the eye to see the far edges, and use an ultrasound if the view is blocked by blood. The exam takes about an hour while the drops work, and you should not drive afterward.

If no tear is found, you may be asked to return in 4 to 6 weeks, because tears can still develop as the gel separates. Return sooner if symptoms change.

Treatment

• PVD without a tear: no treatment. Flashes usually fade over weeks to a few months, and floaters become less noticeable as the brain adapts.
• Retinal tear: laser (photocoagulation) or freezing (cryopexy) to seal around the tear, done in the clinic.
• Retinal detachment: surgery such as pneumatic retinopexy, scleral buckle or vitrectomy.
• Migraine aura: migraine treatment and prevention; identify triggers such as poor sleep, missed meals and stress.
• Stroke or TIA: emergency assessment and treatment.

Frequently asked questions

When should I worry about flashing lights in my eye?

Seek a same-day eye exam for any new flashes in one eye, especially with new floaters. Go to the ER for a shadow or curtain over your vision, sudden vision loss, or flashes with weakness, numbness or speech problems. These can signal retinal detachment or stroke.

What causes flashing lights in the corner of my eye?

Most often, the vitreous gel pulling on the retina as it separates with age (posterior vitreous detachment). The flashes are brief, lightning-like and more visible in dim light. Because the same process can tear the retina, new flashes always need a dilated eye exam.

Are flashing lights a sign of a stroke?

Rarely. A stroke affecting the vision areas of the brain more often causes loss of part of the visual field than flashes. Flashes with sudden weakness, numbness, facial droop, confusion or speech problems are an emergency. Call 911.

Can anxiety or stress cause flashing lights?

Stress can trigger migraines, which cause visual aura with flashing zigzags. Stress itself does not damage the retina. Any new flashes in one eye should be checked for a retinal tear rather than assumed to be from stress.

How long do flashes last after a vitreous detachment?

Flashes from posterior vitreous detachment usually settle over several weeks, though they can come and go for a few months. Floaters fade more slowly. If flashes increase, many new floaters appear, or a shadow develops, get examined again urgently.