Shimmering lights in your vision, sometimes called photopsia, can come from dozens of different sources, but the most common by far is migraine aura, a neurological event that produces flickering, zigzag, or scintillating patterns even without a headache. Other causes range from perfectly harmless phenomena like seeing your own white blood cells move through retinal capillaries to serious conditions like retinal tears or vascular disease. The specific pattern, duration, and whether one or both eyes are affected usually tell clinicians which category a visual disturbance falls into.
Migraine Aura and the Brain’s Electrical Storm
The classic shimmering arc that migraine sufferers describe, often a C-shaped or zigzag band of flickering light that slowly expands across the visual field over five to sixty minutes, originates not in the eye but in the visual cortex at the back of the brain. A wave of abnormal electrical activity called cortical spreading depression rolls across neurons in that region, briefly exciting them and then suppressing them. Mathematical models of this wave match the visual patterns people report remarkably well, linking the geometry of the hallucination to the anatomy of the cortex itself.1PubMed Central. Migraine Visual Aura and Cortical Spreading Depression-Linking Mathematical Models to Empirical Evidence
A systematic review comparing two forms of migraine-related visual disturbance found that the more common type, migraine with aura, typically produces “positive” symptoms in both eyes simultaneously: scintillating scotomas (sparkling blind spots) in about three-quarters of cases and zigzag lines in roughly half. These symptoms almost always last between five and sixty minutes, then resolve. The rarer retinal migraine, by contrast, affects only one eye and tends to produce “negative” symptoms like partial or total vision loss rather than shimmering patterns.2PubMed Central. Differentiating Visual Symptoms in Retinal Migraine and Migraine With Aura: A Systematic Review of Shared Features, Distinctions, and Clinical Implications
This distinction matters practically. If shimmering lights appear in both eyes at the same time, migraine aura is highly likely and the cause is cortical. If you close one eye and the lights disappear completely, the problem is in the open eye, and you are dealing with a retinal or vascular issue rather than a brain-based one. That simple cover-one-eye test is one of the most useful things you can do in the moment.
When the Vitreous Gel Pulls on the Retina
After migraine, the second most common reason people see shimmering or flashing lights is mechanical tugging on the retina by the vitreous, the clear gel filling the inside of your eye. As you age, this gel gradually liquefies and shrinks, and at some point it can peel away from the retina in what is called a posterior vitreous detachment (PVD). The retina has no pain receptors, but it does respond to mechanical stimulation by firing off light signals. The result is brief flashes or sparkles, often in your peripheral vision and most noticeable in dim lighting.
A large study of symptomatic eyes found that posterior vitreous detachment was present in about 89 percent of eyes presenting with flashes alone, compared to only 20 percent in asymptomatic eyes. The concern is that the vitreous sometimes pulls hard enough to tear the retina. In that study, retinal breaks were found in roughly 13 percent of eyes that had flashes, significantly higher than the 4 percent rate in asymptomatic eyes with PVD.3American Journal of Ophthalmology. Relationship between floaters, light flashes, or both, and complications of posterior vitreous detachment A retinal tear left untreated can progress to a retinal detachment, which is a surgical emergency. This is why eye doctors take new-onset flashes seriously, especially when they come with a sudden increase in floaters or a curtain-like shadow creeping across your visual field.
Vitreomacular traction, where the vitreous gel remains abnormally attached to the macula (the central part of your retina), can also cause photopsia alongside blurred or distorted vision.4PubMed Central. Idiopathic vitreomacular traction and macular hole: a comprehensive review of pathophysiology, diagnosis, and treatment Unlike PVD flashes, which often settle down over weeks as the gel finishes separating, traction-related symptoms persist until the adhesion resolves or is treated surgically.
Harmless Light Shows You Can See Every Day
Not every visual shimmer points to a problem. Your eyes generate a few light phenomena all on their own that are entirely normal.
If you have ever looked at a bright blue sky and noticed tiny bright dots zipping around in squiggly paths, you were watching your own white blood cells travel through the capillaries on the surface of your retina. Known as the blue field entoptic phenomenon, this occurs because white blood cells are more transparent to the short-wavelength blue light illuminating the retina than the surrounding red blood cells. Each white cell creates a tiny gap in the light absorbed by the blood column, and your brain perceives that gap as a bright moving speck. Under optimal conditions, with uniform blue light at around 430 nanometers, many of these corpuscles are visible, tracing curved paths that follow the retinal capillary loops.5Noninvasive Assessment of the Visual System. Optimal Strategy in Using the Blue Field Simulation Technique for the Measurement of Macular Blood Flow Studies of retinal microvascular tissue confirmed that the phenomenon is produced by leukocytes flowing specifically within the macular capillaries.6Investigative Ophthalmology and Visual Science. Investigation of the source of the blue field entoptic phenomenon Researchers have even used the effect clinically to estimate macular blood flow, since the speed and number of visible dots correlate with how much blood is reaching your central retina.7PubMed. Blue field entoptic phenomenon in amblyopia
Pressure phosphenes are another harmless variety. If you rub your closed eyes and see swirling patterns of light, that is your retina responding to mechanical pressure rather than actual photons. The effect intensifies when the body is warm; research has shown that heating the hands and body above about 42°C in a humid environment enhances the phosphene response, and the mechanism involves redistribution of electrical charges within the retinal layers.
Medications That Make Your Eyes See Things
Several prescription drugs are known to produce shimmering or flickering in your vision as a side effect, and the mechanisms are surprisingly well understood.
Ivabradine, a heart-rate-lowering drug used for angina and heart failure, causes phosphenes in some patients. The drug works by blocking a specific electrical current in the heart’s pacemaker cells, but a very similar current exists in retinal neurons. In the retina, this current normally dampens the visual system’s response to slow, noisy electrical signals, tuning your perception toward faster, more meaningful visual inputs. When ivabradine inhibits that current in retinal cells, the filtering breaks down, and random fluctuations in the retina, including signals generated by thermal breakdown of the light-sensing pigment rhodopsin, become more likely to register as perceived flashes of light.8PubMed Central. Cellular mechanisms underlying the pharmacological induction of phosphenes The effect is dose-dependent and typically fades as you adjust to the medication.
Digoxin, a much older heart drug derived from foxglove, can produce an even wider range of visual disturbances at toxic levels. Patients have reported snowy vision, colored halos, photopsia, and the famous xanthopsia, a yellow-tinting of the visual world that some art historians have speculated influenced paintings by artists who may have been treated with digitalis preparations. The mechanism involves digoxin inhibiting a sodium-potassium pump in multiple cell types of the retina, including photoreceptors and Müller cells, which disrupts the electrical properties of these cells.9PubMed Central. Xanthopsia Due to Digoxin Toxicity as a Cause of Traffic Accidents: A Case Report10PubMed Central. Colored floaters as a manifestation of digoxin toxicity In one documented case, a patient developed not just blurry and snowy vision but also photopsia, color perception changes, and worsening of pre-existing visual hallucinations, all traceable to digoxin toxicity. Electroretinography confirmed diffuse dysfunction in both rod and cone photoreceptors.11PubMed Central. Spectrum of digoxin-induced ocular toxicity: a case report and literature review
Beyond these two well-studied examples, other drugs can produce visual shimmer. Sildenafil (Viagra) at high doses can cause a bluish tint and light sensitivity because it inhibits an enzyme found in retinal cells. Some anti-seizure medications, certain antibiotics, and even overuse of quinine have been reported to cause photopsia, though the evidence for many of these is scattered across case reports rather than large studies.
Blood Flow Problems and the Eye
When blood supply to the eye or the visual areas of the brain drops temporarily, shimmering or flashing lights can appear as the deprived tissue misfires. The causes range from something as mundane as standing up too fast to something as dangerous as carotid artery disease.
Orthostatic hypotension, the brief drop in blood pressure when you rise quickly from sitting or lying down, is probably the most common vascular trigger. You see a graying or sparkling of your visual field for a few seconds as cerebral blood flow dips, and then everything returns to normal. In healthy people, especially younger adults, this is rarely a concern. In older adults, particularly those taking blood pressure medication, it can be more frequent and more pronounced.
At the serious end of the spectrum is amaurosis fugax, a transient loss of vision in one eye caused by temporary interruption of blood flow, typically from a clot or plaque in the carotid artery. While the classic description is of a curtain descending over vision, some patients present with atypical symptoms. One documented case involved a 73-year-old man with hypertension and diabetes who experienced repeated episodes of lightning bolt-shaped glittering filling the entire visual field of one eye. Imaging revealed severe carotid artery narrowing on the same side and small strokes in the corresponding brain hemisphere, indicating that the visual disturbances were caused by a precarious blood flow situation in the artery feeding his eye.12PubMed. Unique visual symptom of amaurosis fugax: a case report Cases like this illustrate why new-onset flashing lights in one eye in someone with vascular risk factors should be evaluated urgently.
Inflammatory Conditions of the Retina
A less common but important cause of photopsia is inflammation at the back of the eye. Multiple evanescent white dot syndrome (MEWDS) is a striking example. It typically affects young, nearsighted women between the ages of 20 and 40 and often follows a viral illness. The hallmark presentation includes sudden decreased vision, photopsias (flashes or shimmer), and visual field defects in one eye. An eye exam reveals tiny yellow-white dots scattered across the deep retina and sometimes mild inflammation of the optic disc.13PubMed Central. Multiple evanescent white dot syndrome (MEWDS): update on practical appraisal, diagnosis and clinicopathology; a review and an alternative comprehensive perspective
The reassuring feature of MEWDS is that it is almost always self-limiting: the dots disappear and vision recovers over weeks to months without treatment. But other inflammatory conditions affecting the retina and choroid, such as birdshot chorioretinopathy or acute posterior multifocal placoid pigment epitheliopathy, can also produce photopsia and may require immunosuppressive treatment. Any time shimmering lights are accompanied by eye pain, redness, or progressive blurring, inflammatory causes climb the list of suspects.
Visual Hallucinations After Sight Loss
People who have lost a significant portion of their vision, whether from macular degeneration, glaucoma, or other conditions, sometimes begin to experience visual phenomena ranging from simple flashes and geometric patterns to complex images of people or landscapes. This is Charles Bonnet syndrome, and understanding why it happens helps explain something fundamental about how the visual brain works.
The prevailing explanation is the deafferentation hypothesis: when the eyes stop sending normal visual input to the brain, the visual cortex does not simply go quiet. Instead, it becomes spontaneously hyperexcitable, generating its own activity in the absence of real signals. Research using neuroimaging has provided converging evidence supporting this idea, demonstrating increased visual cortical excitability in people with sight loss who experience hallucinations.14PubMed Central. Visual cortical activity in Charles Bonnet syndrome: testing the deafferentation hypothesis The hallucinations can include simple phenomena like flashes and geometric shapes as well as complex formed images. People with Charles Bonnet syndrome are cognitively normal and typically recognize that the hallucinations are not real, which distinguishes the condition from psychiatric disorders.
An estimated 10 to 40 percent of people with significant vision loss experience some form of Charles Bonnet hallucination, though many never mention it to their doctors, often out of fear of being thought mentally unwell. If you or someone you know has vision loss and begins seeing flashes, patterns, or images that are not there, it is worth knowing that this is a recognized neurological response to reduced visual input, not a sign of cognitive decline.
Persistent Aura Without Infarction
For most migraine sufferers, the visual aura resolves within an hour. In rare cases, however, the aura symptoms persist for more than a week, or even months or years, without any evidence of stroke on brain imaging. This condition, known as persistent aura without infarction, has been reported in only a small number of patients in the medical literature. One early report described a 43-year-old woman with a three-decade history of migraine with aura whose visual symptoms simply failed to resolve after an episode, leaving her with ongoing visual disturbance in one half of her visual field.15PubMed. Persistent aura without infarction: decription of the first case studied with both brain SPECT and perfusion MRI
Research suggests that the visual cortex in these patients remains in a state of sustained hyperexcitability, as though the cortical spreading depression that normally passes in minutes has left behind a lasting alteration in neural activity.16PubMed. Sustained visual cortex hyperexcitability in migraine with persistent visual aura The condition is poorly understood and difficult to treat. Some patients respond partially to migraine preventive medications, but for others the visual disturbance becomes a chronic daily reality. If you have migraine aura symptoms that have lasted longer than a week, imaging is warranted to rule out stroke, and the diagnosis of persistent aura without infarction can only be made after that exclusion.
Light Flashes in Space and During Radiation Therapy
Astronauts have reported seeing flashes of light with their eyes closed since the Apollo missions, and the phenomenon puzzled researchers until it was demonstrated that high-energy charged particles in cosmic radiation can trigger visual signals as they pass through the eye and possibly through visual areas of the brain.17PubMed Central. Light flashes and other sensory illusions perceived in space travel and on ground, including proton and heavy ion therapies The same effect occurs on the ground during proton and heavy ion therapy for cancer, particularly when treatment beams are directed near the eyes or head. Patients undergoing these therapies sometimes report brief flashes during treatment sessions.
The mechanism is direct physical stimulation of the retina by ionizing radiation, not unlike the way pressure phosphenes work except the energy source is a subatomic particle instead of your finger. The flashes are typically described as streaks, dots, or brief bright spots. For astronauts on long-duration missions, the phenomenon raises questions about cumulative retinal and neural exposure, but the flashes themselves are not considered harmful in isolation.
After Cataract Surgery
If you have had cataract surgery and notice an arc or crescent of light at the edge of your vision, especially in dim lighting or when light enters from the side, you are experiencing a well-characterized phenomenon related to the artificial lens implanted during the procedure. The edge design of intraocular lenses can create internal reflections that project light onto the peripheral retina in a way the natural lens never did. Researchers have simulated these photic effects using optical modeling software to understand how the shape, thickness, and edge geometry of different lens designs produce different patterns of unwanted light on the retina.18PubMed Central. Simulation of photic effects after cataract surgery for off-axis light sources
These post-surgical light arcs are annoying but not dangerous, and the brain gradually learns to ignore them through a process called neuroadaptation. Most patients find the phenomenon much less noticeable after several months. Newer lens designs with modified edge profiles have reduced the problem, but it has not been eliminated entirely. If the flashes are sudden, come with floaters, or involve the central visual field rather than the far periphery, they may indicate a different problem, such as a retinal tear, and warrant a prompt exam even in someone who has recently had cataract surgery.
How to Tell Which Type You Are Experiencing
With so many possible causes, a few practical features help narrow down what is going on:
- Duration: Migraine aura builds slowly over five to sixty minutes and then fades. Retinal flashes from vitreous traction are brief, lasting a fraction of a second each. Vascular events like amaurosis fugax typically last seconds to minutes. Anything persisting for days or weeks suggests inflammation, persistent aura, or Charles Bonnet syndrome.
- One eye or both: Close one eye at a time. If the shimmer is visible with either eye alone, the problem is in the brain (migraine, cortical event, or occipital seizure). If it disappears when you cover one specific eye, the cause is in that eye or its blood supply.
- Pattern: A slowly expanding arc of zigzag or shimmering lines is the classic cortical aura. Brief pinpoint flashes in the periphery, especially triggered by eye movement, suggest vitreous traction. Tiny bright dots moving in squiggly paths against a blue sky are leukocytes and perfectly normal.
- Accompanying symptoms: Floaters arriving alongside flashes raise suspicion for a retinal tear. Headache following the visual disturbance by 20 to 60 minutes points toward migraine. Nausea and color vision changes suggest drug toxicity. Pain and redness suggest inflammation.
None of these rules are absolute, and overlapping presentations are common. A person can have both vitreous detachment and migraine, for instance, making it hard to know which is causing a given flash. When in doubt, new-onset flashing lights, particularly if sudden and persistent, warrant an eye exam. The stakes of missing a retinal tear or a vascular warning sign far outweigh the inconvenience of a visit that turns out to be reassurance.