A flash of light in your eye usually happens when something physically tugs on your retina, the light-sensitive layer at the back of your eye. Your retina can only send one type of signal to your brain, so whether it’s stimulated by actual light or by physical pulling, you perceive a flash. The most common cause is the gel inside your eye shrinking with age and pulling on the retina as it separates. Less commonly, flashes signal a retinal tear or accompany a migraine aura.
How the Flash Happens Inside Your Eye
Your eye is filled with a clear, jelly-like substance called the vitreous. When you’re young, this gel is firmly attached to the retina. Over time, it liquefies and begins to pull away. Each time it tugs on the retina, the retina’s nerve cells fire as though they’ve been hit by light, and your brain interprets that signal as a brief flash or streak. This is purely mechanical: physical tension on the retina creates an electrical impulse that looks like light, even though no light entered the eye.
These flashes often appear in your peripheral vision and last only a fraction of a second. Some people describe them as a lightning bolt or a camera flash off to the side. They tend to be more noticeable in dim lighting or darkness, when there’s less visual input competing for your attention.
Posterior Vitreous Detachment: The Most Common Cause
The most likely explanation for a new flash of light in your eye is posterior vitreous detachment, or PVD. This is when the vitreous gel fully separates from the retina. It’s extremely common: an estimated 66% of people between ages 66 and 86 develop it. But it can happen earlier, especially if you’re nearsighted, have had eye surgery, or have experienced an eye injury.
PVD itself is not dangerous. The flashes and any accompanying floaters (small dark spots or squiggly lines drifting across your vision) typically become less noticeable within a few months as your brain learns to filter them out. The concern with PVD is what it can trigger. As the vitreous peels away, it sometimes pulls hard enough to tear the retina. That’s why new flashes warrant an eye exam even though the underlying process is usually harmless.
Retinal Tears and Detachment
A retinal tear is a small rip in the retina caused by vitreous traction. Fluid can seep through that tear and lift the retina off the back wall of the eye, causing a retinal detachment. This is a genuine emergency because a detached retina, if left untreated, leads to permanent vision loss in the affected area.
The warning signs of a tear progressing to a detachment include a sudden increase in floaters (sometimes described as a shower of tiny dark spots), persistent flashes of light, and a shadow or “curtain” creeping across part of your visual field. If only a small portion of the retina has detached, you may not notice much change in your vision at all, which is why the flashes and floaters are such important early clues.
Flashes from a retinal problem and flashes from a harmless PVD can look identical, so you can’t tell the difference on your own. The American Academy of Ophthalmology’s triage guidelines recommend being seen within 24 hours if you experience a sudden onset of flashes or new floaters.
Migraine Aura: A Different Kind of Flash
Not all flashes come from inside the eye. Migraine auras produce visual disturbances that originate in the brain, not the retina. The experience is quite different from the split-second flash of a vitreous tug. Migraine auras typically last between 5 and 60 minutes and involve expanding patterns: zigzag lines, shimmering arcs, twinkling lights, or floating geometric shapes. A headache often follows, though not always.
One useful distinction: a standard migraine with aura affects both eyes, because the disturbance is in the brain’s visual processing area. A retinal migraine, which is rarer, affects only one eye. You can test this by covering one eye at a time. If the flashing pattern is visible regardless of which eye is open, it’s coming from the brain. If it disappears when you cover one eye, the problem is in that eye specifically.
Migraine auras are generally not harmful, but a first-time episode can feel alarming and is worth mentioning to your doctor, particularly if you experience vision loss or blind spots along with it.
Other Possible Causes
Rubbing your eyes hard can mechanically stimulate the retina and produce flashes or colorful spots. A blow to the head can do the same, which is the origin of the phrase “seeing stars.” These flashes are brief and stop once the pressure is removed.
A sudden drop in blood pressure, such as standing up too quickly, can briefly reduce blood flow to the brain and cause sparkles or flashing in your vision. This is more of a circulation issue than an eye problem, and the visual effects resolve within seconds as blood flow normalizes.
What Happens at the Eye Exam
If you go in for new flashes, expect a dilated eye exam. Drops will widen your pupils so the doctor can see your retina clearly. The main tool is an indirect ophthalmoscope, a head-mounted light and magnifying lens that gives a wide view of the retina’s interior. The doctor may also use scleral depression, gently pressing on the outside of your eye with a small instrument to bring the far edges of the retina into view. This is the area where tears are most likely to form, and seeing it requires some manipulation.
If the view inside the eye is blocked by bleeding or other debris, an ultrasound (B-scan) can image the retina through the obstruction. The entire exam is painless aside from mild pressure during scleral depression, and the dilation drops blur your near vision for a few hours afterward, so bring sunglasses and plan on not driving yourself.
If a tear is found, it can usually be sealed with laser treatment or a freezing procedure in the office, preventing it from progressing to a detachment. If no tear is found, you’ll likely be asked to come back for a follow-up in a few weeks, since tears can develop in the days after the vitreous first separates.
Which Flashes Need Urgent Attention
A single, brief flash that happened once and hasn’t returned is less concerning than a pattern of repeated flashes, but any new flash deserves attention. The situations that call for a prompt exam within 24 hours include:
- New, repeated flashes in one eye, especially if they started within the last few days
- A sudden burst of new floaters alongside the flashes
- A shadow or dark curtain appearing in any part of your visual field
- Any noticeable change in vision that accompanied the flashes
If you’re experiencing a curtain-like shadow spreading across your vision, this suggests a retinal detachment may already be underway, and same-day evaluation is appropriate. The earlier a detachment is caught, the better the visual outcome after treatment.