Flashes of light in your eyes happen when the retina, the thin layer of light-sensing tissue at the back of your eye, gets stimulated by something other than actual light. The most common cause is the gel inside your eye tugging on the retina as it shrinks with age. Less commonly, flashes originate in the brain itself, as with migraines. Most cases are harmless, but a sudden onset of flashing lights can sometimes signal a retinal tear, which needs urgent attention.
How Your Eye Creates False Light
Your retina contains millions of cells that convert light into electrical signals for your brain. These cells can also fire when they’re physically pushed or pulled, and your brain interprets that signal the same way it would interpret real light. The result is a flash, arc, or spark that you see even though no light actually entered your eye. Doctors call these flashes “photopsia,” and they can look like brief lightning streaks, camera flashes, or tiny sparkles at the edge of your vision.
The Most Common Cause: Vitreous Pulling on the Retina
The inside of 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. As you age, it gradually liquefies and shrinks, eventually pulling away from the retina in a process called posterior vitreous detachment, or PVD. That pulling is what triggers the flashes.
PVD typically begins in your 60s or 70s and affects most people by their 80s. If you’re nearsighted, it tends to happen earlier because your eyeball is longer and the vitreous separates sooner. Many people go through PVD without ever noticing symptoms, but when flashes do appear, they’re usually most noticeable in dim lighting or when you move your eyes quickly. You might also see new floaters: small dark spots or squiggly lines drifting across your vision.
The reassuring news is that in most cases, flashes from PVD fade on their own. Symptoms typically become less intense over several weeks, and most people no longer notice flashes or floaters within about three months. There’s no treatment needed for PVD itself. The concern is what can occasionally happen during the process.
When Flashes Signal a Retinal Tear
As the vitreous pulls away, it can sometimes tug hard enough to create a small rip in the retina. About 8% of people with symptomatic PVD turn out to have a retinal tear when examined. A tear left untreated can allow fluid to seep behind the retina, leading to retinal detachment, which is a medical emergency that can cause permanent vision loss.
The flashes from a retinal tear feel similar to those from ordinary PVD, so you can’t distinguish between them on your own. What should raise concern is the combination of symptoms:
- A sudden burst of new floaters, especially many more than you normally see
- Persistent or worsening flashes, particularly in one eye
- A dark shadow or curtain creeping across part of your vision from the side, top, or bottom
If you notice any of these, getting to an eye doctor or emergency room quickly matters. Retinal tears can often be sealed with a brief laser procedure before they progress to a full detachment.
Migraine-Related Flashes Look Different
Not all flashes come from inside the eye. Migraines can cause visual disturbances that originate in the brain, and these look quite different from the brief sparks of PVD. Migraine-related flashes often appear as shimmering, zig-zagging lines or arcs near the center of your vision. Some people describe them as looking like heat ripples rising off hot pavement, or like peering through a kaleidoscope. They can take the shape of jagged fortification patterns (resembling the notched top of a castle wall), rings, crescents, or even checkerboard grids.
These visual episodes typically last between 5 and 60 minutes and often affect both eyes at the same time. They may or may not be followed by a headache. A key difference: migraine flashes tend to shimmer and expand gradually across your visual field, while retinal flashes are quick, like a camera flash or a streak of lightning, and usually appear in one eye only. If your flashes are slow-moving, patterned, and affect both eyes, a migraine is the more likely explanation.
Other Possible Causes
Several other conditions can produce flashing lights in your vision. A blow to the head or eye can mechanically jostle the retina, triggering flashes, which is why people sometimes “see stars” after an impact. High blood pressure and diabetes can both affect the blood vessels that supply the retina, occasionally producing visual disturbances including flashes. Neurological conditions like multiple sclerosis and stroke can also cause photopsia by disrupting the visual pathways between your eyes and brain.
Context matters when figuring out the cause. Flashes that started after a head injury point toward trauma. Flashes accompanied by headache, nausea, or visual shimmer suggest migraine. Flashes that appeared suddenly in one eye alongside new floaters point toward something happening inside the eye itself.
What Happens at the Eye Exam
When you see an eye doctor for flashing lights, the key test is a dilated eye exam. Drops widen your pupils so the doctor can look at the retina, especially its far edges where tears are most likely to form. The standard approach uses a handheld lens and a bright light (indirect ophthalmoscopy), and the doctor may gently press on the outside of your eye to bring the outermost edges of the retina into view. This pressure technique is considered essential for ruling out tears or detachments because the retina curves inward at the front, making those areas hard to see otherwise.
If the view is blocked, for example by a dense cataract or bleeding inside the eye, an ultrasound of the eye can provide an alternative look at the retina. The exam itself is painless aside from light sensitivity while your pupils are dilated, which typically lasts a few hours.
Flashes in One Eye vs. Both Eyes
Paying attention to whether flashes appear in one eye or both gives a useful clue. Retinal issues like PVD and tears almost always affect one eye at a time. If PVD happens in one eye, the other eye often follows within six months to two years, but the episodes are separate. Migraine-related visual disturbances, on the other hand, typically show up in both eyes simultaneously because they’re generated in the brain’s visual processing areas rather than in the eyes themselves.
A simple test: close one eye and see if the flashes disappear. If they only appear with one eye open, the issue is likely in that eye. If they persist no matter which eye you close, the source is more likely neurological.