Flashes of light in the corner of your eye usually come from the vitreous gel inside the eyeball tugging on the retina, a process that becomes increasingly common as you age. The single most frequent cause is posterior vitreous detachment (PVD), which accounts for roughly 40% of all cases of these visual flashes. While most episodes are harmless, about one in seven people who show up at an eye clinic with new flashes or floaters turns out to have a retinal tear, so the symptom deserves attention even when it seems minor.
What Is Happening Inside Your Eye
Your eye is filled with a clear, jelly-like substance called the vitreous. In youth, this gel is firmly attached to the retina, the thin layer of tissue lining the back of the eye that captures light and sends signals to the brain. Over the decades, the gel gradually liquefies. Collagen fibers inside the vitreous thicken, clump together, and the overall volume of the gel shrinks.1PubMed. Aging and age-related changes of the vitreous body Eventually, the vitreous pulls away from the retina entirely, a process called posterior vitreous detachment.
When the gel tugs on the retina as it separates, retinal cells get stimulated mechanically rather than by actual light. Your brain interprets that stimulation as a flash. Because the vitreous tends to separate first at the periphery, you typically notice these flashes in the corner or edge of your vision rather than dead center. They are often described as quick, lightning-like streaks that are white in color, more noticeable in the dark, and sometimes triggered by moving your head or eyes.2Ophthalmology. Photopsias: A Key to Diagnosis
PVD is extremely common. Most people over 60 will experience it at some point, and many notice the flashes for a few weeks before they taper off as the gel completes its separation. In a study of patients presenting with both floaters and flashes, nearly 90% had a confirmed PVD.3Elsevier. Relationship between floaters, light flashes, or both, and complications of posterior vitreous detachment The process itself is not dangerous, but the traction it places on the retina can sometimes cause complications.
When Flashes Mean a Retinal Tear or Detachment
The concern with PVD is that as the vitreous peels away, it can pull hard enough to rip a small hole in the retina. A retinal tear is considered the main precursor to retinal detachment, a condition where the retina lifts away from the tissue underneath it and can cause permanent vision loss if untreated.4PubMed Central. Rhegmatogenous retinal detachment–an ophthalmologic emergency The classic warning triad is flashes, a sudden burst of new floaters, and a shadow or curtain creeping across your visual field.
Among people who go to an ophthalmologist with new-onset flashes or floaters, about 14% have a retinal tear.5JAMA. Acute-Onset Floaters and Flashes: Is This Patient at Risk for Retinal Detachment? That means the majority do not, but the stakes are high enough that the symptom gets treated as a potential emergency. Even among patients initially told they have an uncomplicated PVD with no tear, about 3.4% develop a tear within the following six weeks, which is why ophthalmologists typically schedule a follow-up exam a few weeks later.5JAMA. Acute-Onset Floaters and Flashes: Is This Patient at Risk for Retinal Detachment?
Horseshoe-shaped tears are especially worrying because they remain attached to the vitreous at one end, meaning ongoing traction keeps pulling the flap and can extend the damage. These tears are directly linked to the evolution of PVD, with vitreoretinal traction considered the driving mechanism even before the detachment of the vitreous is clinically obvious.6PubMed Central. Longitudinal Progression of Horseshoe Retinal Tear-Associated Rhegmatogenous Retinal Detachment Without Clinically Evident Complete Posterior Vitreous Detachment: A Case Report In other words, the tear can happen before you or your doctor can confirm that the vitreous has fully separated.
Migraine Flashes Look Different
Not every flash in your peripheral vision comes from something happening inside the eye. Migraine aura, which affects a significant minority of migraine sufferers, produces visual disturbances that originate in the brain rather than the retina. In the large review of photopsia causes, migraine accounted for about 6.5% of cases.2Ophthalmology. Photopsias: A Key to Diagnosis
Migraine aura typically looks quite different from vitreous-related flashes. Instead of a brief lightning-bolt in one eye, you tend to see shimmering zigzag lines, expanding arcs of flickering light, or a sparkling crescent that drifts across your visual field over 20 to 60 minutes. These visual phenomena are thought to result from a wave of electrical activity spreading slowly across the visual cortex.7PubMed Central. Migraine Visual Aura and Cortical Spreading Depression-Linking Mathematical Models to Empirical Evidence A headache usually follows, though some people get the aura without any pain at all.
The practical way to distinguish the two: vitreous flashes tend to be instantaneous, like a camera flash or a bolt of lightning, and they happen in one eye. Migraine aura tends to build and evolve over minutes and is present in both eyes because the source is in the brain, not the retina. If you close one eye and the flash disappears, the cause is likely in the eye you just covered. If the flash persists regardless of which eye is open, it is probably neurological. That said, anyone experiencing a brand-new visual disturbance for the first time should get checked rather than self-diagnosing.
Who Is Most Likely to Experience These Flashes
Age is the dominant risk factor. The vitreous degenerates gradually over decades, with liquefaction and fiber clumping accelerating after middle age.1PubMed. Aging and age-related changes of the vitreous body Most people first notice flashes and floaters in their 50s or 60s, though the process can start earlier.
Nearsightedness substantially raises the risk. In one study of symptomatic PVD, about 59% of eyes with no subsequent retinal tear were myopic, but among eyes that did develop a tear afterward, the figure jumped to over 86%.8BMC Ophthalmology. Myopia as a risk factor for subsequent retinal tears in the course of a symptomatic posterior vitreous detachment Longer eyeballs stretch the retina thinner, making it more vulnerable to tearing when the vitreous pulls on it. If you are significantly nearsighted and start seeing new flashes, that context makes prompt evaluation more important.
Cataract surgery is another well-established trigger. One study found that PVD progressed roughly seven times faster in eyes that had undergone cataract surgery compared to eyes that had not, within the first year after the procedure.9PubMed Central. Progression of posterior vitreous detachment after cataract surgery The risk is influenced by factors like the length of the eyeball, the patient’s age, how much ultrasound energy was used during the procedure, and whether the vitreous was already partially liquefied beforehand.10PubMed Central. Construction and evaluation of an individualized nomogram prediction model for posterior vitreous detachment in patients with cataract surgery Younger patients and those with longer eyes are also at higher risk for retinal detachment following cataract surgery, especially if there was a complication during the operation itself.11PubMed. Risk factors for retinal detachment following cataract surgery: the impact of posterior capsular rupture
Red Flags That Need Same-Day Attention
Peripheral flashes on their own, especially if they have been coming and going for weeks in the same pattern, are less alarming than a sudden change. The symptoms that push an eye complaint into true emergency territory have been studied in triage settings, and the findings match what ophthalmologists have long warned about.
A large triage study found that certain features strongly predicted the need for same-day emergency eye examination. Vision loss carried nearly a five-fold increase in the odds of needing immediate care. A dark shadow or curtain in the vision of one eye more than doubled the odds.12Nature. Enhancing Ophthalmic Triage: identification of new clinical features to support healthcare professionals in triage Subjective visual reduction, meaning you feel your vision has gotten worse, is also the single most important symptom associated with an underlying retinal tear.5JAMA. Acute-Onset Floaters and Flashes: Is This Patient at Risk for Retinal Detachment?
In practical terms, you should seek urgent evaluation if you experience any of the following alongside new flashes:
- Sudden floater shower: A burst of many new floaters at once, often described as spots, cobwebs, or a swarm of gnats, suggests the vitreous has freshly separated and may have torn the retina in the process.
- Shadow or curtain: A dark area encroaching on your peripheral or central vision from any direction is a hallmark of retinal detachment in progress.
- Reduced vision: Any noticeable drop in how clearly you can see, even if the flashes seem mild.
- Recent eye surgery: If you have had cataract surgery or another intraocular procedure within the past several weeks, new flashes deserve prompt attention given the accelerated PVD risk.
Flashes that have been stable for months, occur only briefly when you rub your eyes, or appear as shimmering patterns that resolve on their own within an hour are less urgent, though still worth mentioning at your next routine eye appointment.
What Happens During the Eye Exam
When you go in for new flashes or floaters, the ophthalmologist will dilate your pupils to get a wide view of the retina. The examination typically involves a slit-lamp microscope and an indirect ophthalmoscope with a bright headlamp. One prospective study of community referrals found that slit-lamp examination alone caught 85% of retinal tears, but adding indirect ophthalmoscopy with scleral depression (gently pressing on the outside of the eye to bring the far periphery of the retina into view) brought detection up to 97%.13Eye. Posterior vitreous detachment and retinal tear – a prospective study of community referrals
The doctor will also look for vitreous hemorrhage, which is blood leaking into the gel from a torn retinal blood vessel. Finding blood in the vitreous dramatically raises the likelihood that a tear is present.5JAMA. Acute-Onset Floaters and Flashes: Is This Patient at Risk for Retinal Detachment? Conversely, the absence of vitreous pigment (tiny cells shed from the retinal pigment layer) is a reassuring sign that a tear has not occurred.
If no tear or detachment is found on the first visit, expect a follow-up within about six weeks. That window matters because the vitreous can still be in the process of separating, and a tear can develop days or weeks after the initial tug. You will likely be told to come back immediately if symptoms change, particularly if new floaters appear or a shadow develops.
How Retinal Tears Are Treated
Finding a retinal tear before it progresses to a full detachment is the ideal scenario, because a tear can usually be sealed with a quick outpatient procedure. The standard approaches are laser photocoagulation and cryotherapy (freezing). Both work by creating a ring of scar tissue around the tear that bonds the retina to the tissue beneath it, preventing fluid from seeping through and lifting the retina off.14Cochrane Database of Systematic Reviews. Interventions for asymptomatic retinal breaks and lattice degeneration Laser treatment takes only a few minutes and is done right in the clinic with topical anesthesia.
Once a tear has progressed to a full detachment, repair becomes more involved, typically requiring surgery under anesthesia with techniques like a vitrectomy (removing the vitreous gel) or a scleral buckle (placing a silicone band around the eye to push the wall inward against the detached retina). Recovery times are longer, and visual outcomes depend heavily on whether the detachment has reached the central macula. This is why the emphasis falls so heavily on catching tears early, while they are still small and treatable in a few minutes.
Less Common Causes Worth Knowing About
PVD and migraine together account for roughly half of all photopsia cases, but the list of possible causes is surprisingly long. One comprehensive review identified 32 distinct causes.2Ophthalmology. Photopsias: A Key to Diagnosis Some of the less familiar ones are worth knowing about because they require entirely different management.
Transient retinal ischemia, where blood flow to the retina is briefly interrupted, can cause fleeting visual disturbances in one eye. This is sometimes called amaurosis fugax, and it can be a warning sign of vascular disease or an impending stroke rather than an eye problem per se.15PubMed Central. Transient monocular visual loss These episodes tend to cause a brief dimming or blackout of vision rather than a bright flash, but some people describe light phenomena. The critical distinction is that vascular episodes call for cardiovascular workup, not just a retinal exam.
Low blood sugar (hypoglycemia) appeared in about 3% of photopsia cases in the same review, and conditions as varied as retinitis pigmentosa, medication side effects from drugs like digitalis, and even severe coughing were documented as triggers.2Ophthalmology. Photopsias: A Key to Diagnosis People who have had intraocular lens implants after cataract surgery occasionally see flashes from light reflecting off the edge of the lens, a phenomenon called dysphotopsia. Charles Bonnet syndrome, where people with significant vision loss experience vivid visual hallucinations, also made the list, though this condition is well understood to be benign and not a sign of psychiatric illness.
The variety of potential causes underscores why a proper exam matters. A flash from vitreous traction and a flash from reduced blood flow to the retina can feel similar to the person experiencing them, but they lead to completely different clinical pathways.
Why Mechanical Pressure on the Eye Creates Light
You have probably noticed that pressing on your closed eyelids produces blobs of light. These are called phosphenes, and they happen because retinal cells are sensitive to pressure as well as light. Any mechanical stimulation of the retina, whether from your finger, a bump to the head, or the vitreous gel pulling during a PVD, generates electrical signals that the brain reads as light.
Research on phosphenes has explored this phenomenon in practical contexts, including studying how phosphene positions shift when people move their eyes, which has implications for visual prosthetics designed to help blind individuals navigate.16PubMed Central. Evaluation of Phosphene Shifts During Eye Movements to Enhance Safe Visual Assistance for Visually Impaired Individuals The key insight for understanding your peripheral flashes is that the retina does not distinguish between “real” light from the outside world and mechanical stimulation. It fires either way. This is why vitreous traction produces flashes that look indistinguishable from actual light, and why they tend to appear in the part of your visual field that corresponds to where the vitreous is actively pulling.
The temporal (outer) side of the visual field is where PVD flashes show up most frequently, with about 86% of PVD-related flashes localized there.2Ophthalmology. Photopsias: A Key to Diagnosis This makes anatomical sense because the vitreous is more firmly attached at certain peripheral zones of the retina, and the nasal retina (which maps to the temporal visual field) is one of those attachment points. So “corner of the eye” flashes, particularly on the outer side, are entirely consistent with the vitreous separating exactly where it tends to separate.