Seeing flashes when no light is there means something other than light is setting off part of your visual system, such as pressure, pulling, or a signal in the brain. So the same sensation can come from something as harmless as rubbing your eyes or from something that threatens your sight. What usually separates the two is not the flash itself but what comes with it and how suddenly it started.
The Most Common Cause Is the Eye’s Gel Pulling on the Retina
The inside of your eye is filled with a clear gel called the vitreous, which sits against the retina, the light-sensing layer at the back of the eye. With age the gel becomes more liquid and shrinks, and eventually it separates from the retina. As the gel pulls on the retina, the retina fires as if it had seen light, producing quick flashes.1PubMed Central. Spontaneous posterior vitreous detachment: A glance at the current literature This separation is very common after about age 50, and it is more common in people who are nearsighted or have had eye surgery.
These flashes tend to look like a thin arc or streak of light at the edge of your vision, most noticeable in a dim room or when you move your eyes. New floaters, such as specks, cobwebs, or a ring, often show up at the same time, and usually only one eye is affected at first.
The gel is firmly attached in a few places, such as around the edges of the retina, and the tugging is strongest at those points. If it stays stuck in one spot, the flashes can continue until it either releases or tears the retina.
In some people the pulling tears the retina, and most retinal tears start from this same aging of the gel.2PubMed Central. Rhegmatogenous Retinal Detachment—an Ophthalmologic Emergency That is why a first episode of new flashes deserves an eye exam even though most turn out to be a simple separation of the gel.
You can’t tell a clean separation from a tear by how the flashes feel. Only a dilated eye exam shows whether the retina is intact.
Warning Signs That Mean See a Doctor Today
- A sudden burst of new floaters along with flashes
- A dark curtain or shadow spreading across part of your vision a common type of tear, prompt treatment cuts detachment risk from at least half to under 5%.3PubMed Central. Rhegmatogenous Retinal Detachment—an Ophthalmologic Emergency
- Any drop or blurring in vision alongside flashes
- Flashes that suddenly become more frequent
A retinal detachment, where the retina lifts away from the back of the eye, typically announces itself with flashes, floaters, or a dark curtain.4PubMed Central. Rhegmatogenous Retinal Detachment—an Ophthalmologic Emergency Eye doctors treat it as an emergency because a detached retina stops working.5PubMed Central. Rhegmatogenous Retinal Detachment—an Ophthalmologic Emergency A tear caught before it becomes a detachment has an extremely good outlook.6American Society of Retina Specialists. Retinal Tears
A curtain or shadow is a fixed dark area that tends to grow. A shadow that starts at the edge and moves inward, from the side, top, or bottom, suggests that part of the retina has lifted and stopped working. Because it can enlarge over hours, the lost area can reach the center of your vision if care is delayed, so don’t wait it out overnight.
Call your eye doctor right away and say “new flashes and floaters” so you’re seen urgently. If no eye doctor is reachable, go to an emergency department. Don’t drive yourself if your vision is affected. Note which eye is involved and when it started.
To sort causes, cover one eye, then the other. Flashes from the eye usually show up in only one eye, while brain-related flashes usually appear in the view of both eyes, but this is one clue among several, not a reliable test on its own.
What Happens at the Eye Exam and How Tears Are Fixed
The key test is a dilated exam, where drops widen your pupil so the doctor can see the edges of the retina. Dilation isn’t always done routinely for flashes, though; one survey found it used in only about half of such visits.7PubMed. Optometrists’ examination and referral practices for patients presenting with flashes and floaters So if you have new flashes, ask whether your pupils will be dilated.8PubMed. The content of optometric eye examinations for a presbyopic patient presenting with symptoms of flashing lights
The doctor looks for a horseshoe-shaped tear, a small hole, or any area where the retina has started to lift. They also check for bleeding into the gel, which can suggest a tear. The doctor may gently press on the outside of your eye to bring the far edges into view, which can cause brief pressure or mild discomfort.
The drops take about 20 to 30 minutes to work. Bright light may sting briefly as the doctor looks. Your vision stays blurry and light-sensitive for hours, so bring sunglasses and someone to drive you.
A retinal tear is usually treated with a laser or a freezing probe that creates spot-welds around the tear.9American Society of Retina Specialists. Retinal Tears For10American Society of Retina Specialists. Retinal Tears11Netra Eye Institute. Can PVD Be Reversed? Posterior Vitreous Detachment Explained Treatment doesn’t remove every risk, since new tears can form later.12Netra Eye Institute. Can PVD Be Reversed? Posterior Vitreous Detachment Explained
If no tear is found, you may still be asked to return in a few weeks. Come back at once if any of the danger signs appear.
Zigzags and Shimmering Shapes From Migraine
Migraine aura, the visual disturbance that can come before a migraine, often shows shimmering zigzag lines that slowly spread outward across your vision.13PubMed. Exploring the visual hallucinations of migraine aura: the tacit contribution of illustration It comes from a wave of activity moving across the visual part of the brain, not from the eye.14PubMed. Exploring the visual hallucinations of migraine aura: the tacit contribution of illustration An aura usually lasts about 5 to 60 minutes and may be followed by a headache, or not. It often begins as a small bright spot or shimmer near the center of vision, then grows over several minutes into a C-shaped arc with a zigzag edge, often leaving a blind or blurry patch behind.
To tell aura from retinal flashes: aura is a pattern that grows and moves, while retinal flashes are brief streaks. Aura still shows with your eyes closed and in the view of both eyes.
A mini-stroke can also cause flashing lights, zigzags, or sparkles.15Cognitive FX. TIA Vision Symptoms: Treating Blurry Vision, Double Vision & More So a first-ever aura, especially after age 50 or with weakness, numbness, or trouble speaking, needs emergency care.
Harmless Everyday Flashes
Rubbing or pressing your eyes can make you see lights and colors.16All About Vision. Phosphenes (Seeing Stars) Pressing on a closed eyelid produces glowing patches, rings, or colored spots that last as long as you press and fade soon after. They appear in the eye you pressed, and they don’t form a growing zigzag the way a migraine aura does.
Standing up fast can briefly drop your blood pressure and bring on flashes or zigzags.17HealthTap. What Does It Mean If You See Flashes of Light? Sneezing, hard coughing, laughing, nose blowing, or a blow to the head can do the same.18Biology Stack Exchange. Why does strenous exercise cause vision of lights Occasional flashes with these triggers that vanish in seconds are usually not a worry.
Frequent lightheadedness on standing is worth mentioning to a doctor. Flashes after a head injury, especially with vision changes, need a check. And if flashes continue without any trigger, treat them as new flashes.
Medicines and Eye Surgery That Cause Light Effects
One of the most common side effects of ivabradine is temporary brightness in part of your vision, often set off by sudden light changes.19DailyMed. IVABRADINE The drug slows the heart rate in certain heart failure and angina patients, and its light effects come from how it acts on cells in the retina. Episodes usually last seconds to minutes rather than flashing constantly. They are usually mild, don’t interfere with daily life, and can fade on their own within days.20PubMed Central. Ivabradine for the Prevention of Anthracycline-Induced Cardiotoxicity in Female Patients with Primarily Breast Cancer: A Prospective, Randomized, Open-Label Clinical Trial
Because the drug treats a heart condition, stopping it yourself can leave that condition untreated, so tell your prescriber instead. Say when it happens, what it looks like, and whether it follows light changes. Even if you know the drug causes light effects, flashes that look different from your usual pattern should still be checked.
After cataract surgery, some people see arcs, streaks, or glare, mainly from light reflecting off the edge of the new lens.21PubMed. Pseudophakic Dysphotopsia: Review of Incidence, Cause, and Treatment of Positive and Negative Dysphotopsia These come from outside light, unlike flashes from gel pulling, which need to be checked separately.22PubMed Central. Dysphotopsias or Unwanted Visual Phenomena after Cataract Surgery Lasting light effects are a common source of dissatisfaction after surgery and can often be managed.23PubMed. Pseudophakic Dysphotopsia: Review of Incidence, Cause, and Treatment of Positive and Negative Dysphotopsia Flashes in the dark or with new floaters still need a retina check, and cataract surgery raises the chance of the gel pulling away later.
Less Common Eye and Nerve Conditions
In people with the wet form of macular degeneration, many report flickering or flashing lights in the affected eye.24JAMA Ophthalmology. Visual Symptoms Associated With Choroidal Neovascularization: Photopsias and the Charles Bonnet Syndrome Fragile new blood vessels grow under the macula, the central retina used for reading and faces, and can leak fluid that disturbs the cells. Along with flickering, people often notice straight lines looking wavy or a gray or blank spot in the center of vision. This form can damage central sight quickly, so new distortion or a central blank spot calls for prompt evaluation, which can include injections that slow the leaking.
Some people with vision loss see more complex images, from grids to people or faces, called Charles Bonnet syndrome.25Macular Society. Charles Bonnet syndrome and visual hallucinations These images result from vision loss, not mental illness, and the person usually knows they are not real. Telling an eye doctor is useful, since the condition is common and a diagnosis can be reassuring.
Some inflammatory retina conditions cause shimmering flashes with blurred vision or blind spots.26PubMed Central. A Review of the Inflammatory Chorioretinopathies: The White Dot Syndromes They can also cause sudden vision loss with flashes off to the side.27BMJ Case Reports. Persistent photopsia: multiple evanescent white dot syndrome in a sexagenarian In optic nerve inflammation, often linked to multiple sclerosis, eye movements can trigger flashes.28PubMed. Movement phosphenes in optic neuritis: a new clinical sign Pain on moving the eye is one clue that points toward the optic nerve.
Preeclampsia, a dangerous rise in blood pressure in pregnancy, can damage the retina and disturb vision.29Medical hypothesis, discovery & innovation in optometry. Retinal changes in preeclampsia Flashes or blurred vision while pregnant need same-day medical care, especially with headache, swelling, or high readings. Most of these changes clear after delivery, though about a third of people have lasting effects.30Medical hypothesis, discovery & innovation in optometry. Retinal changes in preeclampsia
How Long Flashes Last
Flashes from rubbing your eyes or standing up last seconds. Mini-stroke flashes can last moments to several hours.31Cognitive FX. TIA Vision Symptoms: Treating Blurry Vision, Double Vision & More Flashes from the gel pulling away usually fade over weeks to a few months as the gel settles. They tend to come in short bursts that grow less frequent over time rather than staying steady. Floaters from the same event usually last longer than the flashes and may only fade in part.
Keep follow-up appointments even if symptoms fade. A change in pattern, not just duration, is the reason to call again.