Flashes of light in your eye are usually caused by something tugging on your retina, the light-sensitive layer at the back of your eye. The most common reason is an age-related change called posterior vitreous detachment, which happens to most people eventually and is typically harmless. But flashes can also signal a retinal tear or detachment, which is a medical emergency. The pattern of the flashes, whether they affect one eye or both, and what other symptoms come with them all help determine what’s going on.
The Most Common Cause: Vitreous Detachment
Your eyeball is filled with a gel-like substance called vitreous humor. In your early 20s, this gel is thick and firmly attached to your retina. As you age, the gel gradually turns to liquid, loses its structure, and eventually collapses on itself and peels away from the retina. This process is called posterior vitreous detachment (PVD), and it’s extremely common.
As the gel separates, it can pull on the retina. Your retina interprets that mechanical tug as light, so you see brief flashes, usually at the edges of your vision. These flashes tend to be more noticeable in dim lighting or when you move your eyes quickly. They can come and go over weeks or even months as the gel fully detaches. Many people also notice new floaters during this time: tiny specks or squiggly lines drifting across their field of view.
PVD itself doesn’t damage your vision and doesn’t require treatment. The flashes eventually stop once the vitreous has fully separated. The concern is that in a small percentage of cases, the gel pulls hard enough to tear the retina on its way off, and that tear needs immediate attention.
When Flashes Signal a Retinal Tear or Detachment
A retinal tear happens when the vitreous pulls forcefully enough to rip the retina. Left untreated, fluid can seep through the tear and lift the retina away from the wall of the eye. That’s a retinal detachment, and it can cause permanent vision loss.
The warning signs that set a tear or detachment apart from a simple vitreous detachment include:
- A sudden shower of new floaters, not just one or two, but many dark specks or lines appearing all at once
- Flashes of light that are persistent or increasing rather than occasional
- A shadow or curtain creeping across part of your vision, often starting at the side
- Blurred vision that comes on suddenly
- Worsening peripheral vision
Any combination of these symptoms is a medical emergency. A retinal tear can often be sealed with laser treatment or a freezing procedure if caught quickly, preventing it from progressing to a full detachment. Once the retina detaches, surgery is required, and the visual outcome depends heavily on how much of the retina was affected and how quickly you were treated. There is no safe window to “wait and see.” Contact an eye care provider the same day, or go to the emergency room.
Migraine-Related Flashes Look Different
Not all flashes come from something pulling on the retina. Migraines can produce visual disturbances that include shimmering or zigzag lines, blind spots, or a wave-like aura that moves across your field of view, alternating between light and dark. These visual episodes typically last 20 to 60 minutes, affect both eyes at the same time, and may or may not be followed by a headache. Nausea, sensitivity to light, and sensitivity to sound are other clues pointing toward migraine.
The key distinction: retinal flashes tend to be brief, arc-like, and confined to one eye. Migraine auras affect both eyes simultaneously, last longer, and have a more complex visual pattern. Because the symptoms can overlap, it’s worth getting checked if you’re not sure which one you’re experiencing, especially if it’s your first time.
Causes Outside the Eye
A useful rule of thumb from clinical practice: if the flashes happen in only one eye, the cause is likely inside that eye. If both eyes see flashes at the same time, the problem may be neurological or systemic.
Bilateral flashes can result from a drop in blood pressure (such as standing up too quickly), blood sugar abnormalities, or reduced blood flow to the brain. Certain medications, including some heart drugs and antipsychotics, can also trigger flashes as a side effect. More rarely, flashes in both eyes can indicate a transient ischemic attack (a brief interruption of blood flow to the brain) or increased pressure inside the skull. If you experience flashes along with weakness or numbness in your face or limbs, difficulty swallowing, confusion, or altered consciousness, that points toward a neurological cause and warrants emergency evaluation.
What Happens at the Eye Exam
When you go in for flashes, an ophthalmologist will dilate your pupils with eye drops and examine the inside of your eye with specialized instruments. Dilation takes about 20 to 30 minutes to kick in and makes your vision blurry and light-sensitive for a few hours afterward, so plan to have someone else drive you home.
The exam focuses on the peripheral retina, which is where most tears occur. A standard eye check with a basic scope isn’t sufficient for this because it only shows the central retina. The ophthalmologist needs to look at the full interior surface of your eye, which is why a referral to a specialist matters. If they find a tear, treatment can often happen the same day. If the retina looks intact, you’ll likely be asked to come back for a follow-up in a few weeks, since new tears can develop as the vitreous continues separating.
Who Is Most at Risk
Posterior vitreous detachment becomes increasingly common after age 50, and most people will experience it by their 70s or 80s. You’re at higher risk for complications like retinal tears if you are very nearsighted (which makes your retina thinner and more stretched), have had eye surgery such as cataract removal, have a history of eye injury, or have a family history of retinal detachment. If you’ve already had a retinal tear or detachment in one eye, the other eye carries a higher risk as well.
Even without these risk factors, any new onset of flashes deserves an eye exam. Most of the time the news will be reassuring, but the cases that aren’t reassuring are time-sensitive enough that getting checked promptly is worth the inconvenience.