Seeing flashes of light in the dark is usually caused by physical tugging on the retina, the light-sensitive layer at the back of your eye. The most common reason is age-related changes to the gel-like substance that fills your eyeball. These flashes are more noticeable in darkness because there’s no competing light to wash them out, and they often increase with head or eye movement.
Most of the time, occasional flashes are harmless. But a sudden increase in flashes, especially alongside other visual changes, can signal something that needs prompt attention.
How the Gel Inside Your Eye Creates Flashes
Your eye is filled with a clear, jelly-like substance called the vitreous. When you’re young, it holds its shape firmly and stays attached to the retina. As you age, this gel starts to break down. It becomes more liquid, and the remaining solid fibers clump together and pull away from the retina. That pulling is the key: when anything tugs on the retina, the retina interprets the mechanical force as light, producing a brief flash even though no actual light entered your eye.
This process accelerates in middle age and beyond. About 24% of people between ages 50 and 59 have some degree of vitreous separation from the retina, and that number climbs to 87% by ages 80 to 89. The flashes tend to be quick, often appearing in your peripheral vision, and are most noticeable in dim environments or first thing in the morning.
The same mechanism explains why rubbing your eyes or pressing on them can produce spots of light. Any mechanical stimulation of retinal cells generates a light signal, regardless of whether actual photons are involved. Doctors call these “phosphenes,” and they’re a normal quirk of how the retina works.
Posterior Vitreous Detachment
The most common clinical cause of new flashes in people over 45 is posterior vitreous detachment, or PVD. This happens when the shrinking vitreous gel finally separates from the retina entirely. During the separation process, you may notice flashes of light (usually in one eye), new floaters that look like dark spots or squiggly lines, or both.
PVD itself is not dangerous. It’s a normal part of aging, and for most people the flashes gradually fade over weeks to months as the vitreous finishes pulling away. However, in roughly 14.5% of people who develop PVD symptoms, the separating gel tears the retina on its way off. A retinal tear can lead to retinal detachment if left untreated, which is why new-onset flashes deserve an eye exam even though the odds favor a benign explanation.
Risk factors that make PVD happen earlier or with more complications include significant nearsightedness, prior eye surgery, eye inflammation, and diabetes.
Migraine Aura
Flashes linked to migraines look and behave differently from retinal flashes. A migraine aura typically affects both eyes at once and lasts 10 to 30 minutes. Instead of a quick spark in your side vision, you might see bright geometric lines, zigzag patterns, or a shimmering C-shaped arc that expands across your visual field. The classic pattern resembles the walls of a medieval fortress, which is why it’s sometimes called a “fortification spectrum.”
Some people experience aura without ever getting a headache afterward. If your flashes come with these expanding, structured patterns and resolve within half an hour, migraine aura is the likely explanation. Retinal flashes, by contrast, are brief (a fraction of a second), appear in one eye only, and don’t form organized shapes.
Other Causes Worth Knowing
Low blood pressure when you stand up quickly (orthostatic hypotension) can produce brief visual disturbances, though these tend to look more like tunnel vision or a general dimming rather than distinct flashes. They happen because your brain temporarily gets less blood flow, and they resolve within seconds of your circulation catching up.
Diabetes and macular degeneration can also cause flashes, though these conditions usually come with other visual symptoms like blurriness or distorted straight lines. People who’ve had cataract surgery sometimes notice flashes afterward as well.
Visual snow syndrome is a separate condition that’s sometimes confused with photopsia. Instead of brief, distinct flashes, visual snow looks like continuous tiny flickering dots across your entire visual field, similar to TV static. It’s persistent rather than momentary, which makes it a different experience altogether.
When Flashes Are an Emergency
A few specific warning signs distinguish a routine flash from a potential retinal tear or detachment:
- A sudden flood of new floaters. Seeing a few floaters is normal. Suddenly seeing many more than usual is not.
- A shadow or curtain across part of your vision. This can appear from the side, top, or center of your visual field and suggests the retina may be pulling away.
- Blurred or reduced vision alongside flashes. In studies of PVD patients, visual impairment was a significant predictor of a retinal tear, while flashes alone were not.
- Symptoms lasting less than 24 hours with rapid onset. A very sudden, short-duration burst of symptoms was also associated with a higher chance of retinal tears in clinical data.
If you experience any of these combinations, same-day evaluation by an eye specialist is important. Retinal tears caught early can be treated with a quick outpatient laser procedure that effectively prevents progression to full detachment.
What an Eye Exam Looks Like
To evaluate flashes, an eye doctor will dilate your pupils with drops and examine the retina directly. This allows them to see whether the vitreous has separated cleanly or whether there’s a tear. They’ll also check your visual acuity with an eye chart, test your peripheral vision by having you count fingers in different quadrants, and check how your pupils respond to light.
If something concerning is found, additional imaging like optical coherence tomography (a detailed cross-sectional scan of the retina) can provide more information. The whole process is straightforward and painless, though your vision will be blurry for a few hours from the dilation drops.
For isolated, occasional flashes in the dark with no floaters, no vision changes, and no curtain effect, a routine appointment within a few weeks is reasonable. Many people over 50 discover during these visits that they simply have a normal vitreous separation in progress.