Halos in vision are bright, glowing rings that appear around light sources, and they result from light scattering or bending as it passes through the eye’s optical structures. The cornea, the crystalline lens, and even the tear film can all redirect light before it reaches the retina, and when any of those layers becomes irregular or cloudy, incoming light rays spread rather than focusing to a sharp point. Cataracts, glaucoma, corneal disease, and refractive surgery are among the most frequent culprits, though the list extends to contact lens wear, certain medications, and even neurological conditions.
How the Eye Normally Handles Light and Why That Goes Wrong
In a healthy eye, the cornea and lens work together to focus incoming light onto the retina in a tight, orderly way. Halos appear when something disrupts that precision. Light hitting an irregular or opaque surface scatters in many directions instead of converging at a single focal point. Some of those scattered rays land on the retina outside the intended spot, creating a diffuse glow around the light source you are looking at. A classic study of glaucoma-related halos found that these rings originate from diffraction within the cornea and must be distinguished from halos caused by the crystalline lens or by particles floating on the corneal surface, because the mechanism and clinical significance differ for each.1American Journal of Ophthalmology. The Mists and Halos of Glaucoma
This scattering is sometimes called “forward light scatter” or straylight, and it also explains the related complaint of glare, where bright lights feel painfully intense. Research has shown a direct relationship between how much straylight reaches the retina and how large the halo appears around a given light source.2PubMed. Relationship between halo size and forward light scatter In short, more scatter equals bigger, brighter halos.
Cataracts
Cataracts are the single most common reason people develop halos, especially with age. As proteins in the crystalline lens clump together and become opaque, they scatter light in every direction. The fundamental effect of cataract on the eye’s optics is forward light scattering, which is responsible for reduced contrast sensitivity, glare, and lower visual acuity.3Eye. The morphology of cataract and visual performance You might first notice halos when driving at night, because oncoming headlights provide a bright point source against a dark background, which is the perfect setup for scattered light to become visible.
Not all cataracts produce halos equally. The type and location of the opacity within the lens matter. A cataract concentrated at the back of the lens (posterior subcapsular) tends to cause more glare and halo symptoms than one developing at the periphery, because it sits right in the path of focused light. The progression is usually gradual, so many people adapt to mild halos for years before the symptoms become bothersome enough to warrant surgery.
Glaucoma and Rising Eye Pressure
Glaucoma can produce halos through a different route: elevated intraocular pressure causes the cornea to swell. When fluid pressure inside the eye climbs, the cornea absorbs extra water and its normally transparent layers become slightly hazy. That edema scatters light in much the same way a fogged-up window does. In acute angle-closure glaucoma, the pressure spike can be dramatic, and the sudden onset of rainbow-colored halos around lights is considered a hallmark warning sign. If you see colored rings around lights along with eye pain, nausea, or a sudden drop in vision, that combination warrants emergency medical attention because the optic nerve can be permanently damaged within hours.
A less well-known variant involves pigment dispersion syndrome, where pigment granules shed from the iris and float into the front chamber of the eye. A case report documented a young man who experienced blurred vision and halos after strenuous exercise, linked to a release of pigment into the anterior chamber and a corresponding rise in eye pressure.4PubMed. Exercise-induced increase of intraocular pressure in the pigmentary dispersion syndrome The floating particles scatter light in the same way a dusty room scatters a flashlight beam. For people with this condition, halos can come and go with physical activity rather than being constant.
Corneal Conditions
Because the cornea is the eye’s outermost lens and handles about two-thirds of total focusing power, even subtle changes to its transparency or shape can produce halos. Fuchs’ endothelial corneal dystrophy is one such condition. In Fuchs’, the cells that pump fluid out of the cornea gradually fail, so the cornea swells overnight when the eyelids are closed and fluid has nowhere to evaporate. A study of advanced Fuchs’ eyes found that corneal thickness increased by roughly 41 micrometers from afternoon to morning, compared to only about 6 micrometers in healthy eyes, and that this swelling was accompanied by a significant increase in glare and a myopic shift that impaired morning vision.5PubMed. Morning Myopic Shift and Glare in Advanced Fuchs Endothelial Corneal Dystrophy People with Fuchs’ often describe halos and foggy vision that are worst upon waking and improve as the day goes on and the cornea dries out.
Corneal edema from other causes, including post-surgical swelling, viral infections, or chemical injury, can produce the same halo effect. The common thread is always disrupted transparency: whenever the corneal tissue takes on excess water, its normally uniform structure becomes irregular enough to scatter light.
After LASIK, PRK, or Lens Implant Surgery
Halos are one of the most frequently discussed side effects of refractive eye surgery. LASIK reshapes the cornea with a laser, and the transition zone between the treated area and untreated cornea can scatter light, particularly when the pupil dilates in dim conditions and expands beyond the treated zone. Research on patients who had successful LASIK found that the severity of halos correlated with specific types of optical irregularities on the corneal surface, particularly spherical aberration and coma.6PubMed Central. Night vision disturbances after successful LASIK surgery Other minor surface imperfections did not contribute significantly to halos when analyzed individually.
An earlier study of PRK, the predecessor to LASIK, distinguished between two separate nighttime visual disturbances. Starburst effects, where streaks radiate outward from a light, were linked to reduced corneal transparency and tended to be temporary. Halos, by contrast, behaved more like blur circles caused by a residual focusing error, and in a small number of patients they persisted long term, especially those with larger pupil diameters.7Eye. Disturbances in night vision after excimer laser photorefractive keratectomy The distinction matters practically: if your halos after surgery seem to be fading month by month, they are likely related to corneal healing. If they remain stable, especially in very dark settings, the issue is more likely optical.
Cataract surgery introduces a similar dynamic when a multifocal intraocular lens is implanted. Multifocal lenses split incoming light to provide focus at multiple distances, but that design inherently sends some light to places the retina is not “expecting,” which can register as halos. A comparison study found that about a third of patients receiving multifocal lenses noticed new halos after surgery, compared to roughly one in nine with standard single-focus lenses, and that patients with corneal irregularities or astigmatism above one diopter experienced significantly larger halos with the multifocal design.8PubMed. Objective and subjective evaluation of photic phenomena after monofocal and multifocal intraocular lens implantation The majority of patients in that study were not bothered by the halos, which speaks to the brain’s ability to adapt over time, a process called neuroadaptation. Still, the trade-off is worth discussing with your surgeon before choosing a lens type.
Contact Lens Wear and Corneal Hypoxia
If you wear contact lenses and occasionally notice halos or a hazy veil over your vision, the culprit may be oxygen deprivation. A contact lens resting on the cornea reduces the amount of oxygen reaching the corneal surface from the air. When oxygen levels drop enough, the outermost corneal cells redistribute their internal water content, creating local changes in refractive index that scatter light. This phenomenon is called Sattler’s veil, and it produces a corneal haze in which halos appear around lights, even though the cornea has not actually thickened or absorbed extra water.9Eye & Contact Lens. Physiologic Changes of the Cornea with Contact Lens Wear
Sattler’s veil is more common with older hydrogel lens materials than with modern silicone hydrogel lenses, which let substantially more oxygen through. Overwearing any lens, sleeping in lenses not designed for overnight use, or wearing lenses in dry environments can bring it on. The fix is usually simple: remove the lenses for a few hours and the cornea recovers. But repeated episodes of hypoxia can cause longer-term changes to the corneal epithelium, so chronic halos from lens wear are worth bringing up with your eye care provider rather than just powering through them.
Medications That Affect the Eyes
Several systemic medications can cause halos as a side effect, sometimes through corneal deposits and sometimes through changes in the lens or pupil. Amiodarone, a drug widely used for heart rhythm disorders, is one of the better-documented examples. Nearly all patients taking amiodarone develop microscopic deposits in the cornea over time, and these deposits scatter light in a way that produces colored halos around lights.10Medical Hypothesis, Discovery & Innovation in Optometry. Ocular side effects of systemic medications The deposits are generally harmless and usually resolve after the drug is stopped, but regular eye exams are recommended for anyone on long-term amiodarone therapy.
Other medications associated with halos include certain antihistamines and anticholinergic drugs, which dilate the pupil and allow more peripheral light to enter the eye, and corticosteroids, which can accelerate cataract formation with prolonged use. Topiramate, an anti-seizure medication sometimes used for migraines, has been linked to acute angle-closure episodes that produce sudden halos, eye pain, and blurred vision. If you notice new halos shortly after starting a medication, that timing is worth mentioning to your prescriber.
Neurological Origins
Not every visual disturbance originates in the eye itself. Visual snow syndrome is a neurological condition in which people see persistent static across their visual field, along with a constellation of other symptoms including halos, afterimages, light sensitivity, and poor night vision. Research using brain imaging and electrical recordings has found that people with visual snow syndrome show overactive responses in visual brain areas, along with structural and connectivity changes in regions connecting the cortex and thalamus.11PubMed Central. Visual snow syndrome: recent advances in understanding the pathophysiology and potential treatment approaches The halos in this condition likely arise from the brain amplifying normal visual noise rather than from any structural problem in the eye.
Migraine with aura can also produce transient halos or glowing edges around objects, though these episodes typically last minutes to an hour and resolve as the migraine progresses. The key distinction for someone trying to figure out their own symptoms: halos from eye conditions are usually tied to looking at a specific light source and are consistent each time, while halos from neurological conditions tend to accompany other perceptual oddities like visual static, trailing images, or flashing lights, and may appear even in uniform lighting.
Pupil Size and Low-Light Conditions
Your pupils naturally dilate in dim light to let in more photons, and this dilation alone can unmask halos that are invisible during the day. When the pupil is small, light passes through only the central, most optically precise part of the cornea and lens. When it opens wide, peripheral zones with more optical imperfections contribute to the image, spreading light into rings and streaks. This is why many people notice halos only at night or in dark environments, and why the complaint is so common after LASIK, where the treated zone on the cornea has a defined edge that a dilated pupil can exceed.
Age compounds the effect. The lens becomes less flexible and slightly cloudier decade by decade, so even without a diagnosable cataract, a 60-year-old will typically scatter more light than a 25-year-old. Combine that with the normal age-related changes in pupil dynamics, and it is not unusual for mild halos around streetlights to appear in middle age without any specific disease being present. These “physiologic” halos are faint and consistent, and they do not worsen rapidly. If halos are new, intensifying, colored, or accompanied by pain or vision loss, the cause is more likely pathological.
How Eye Doctors Evaluate Halos
Describing halos to a doctor can feel subjective, so researchers have developed tools to quantify them. One approach uses a halometer, which presents a bright central light and measures how far from that light a patient can still detect a dimmer target. The larger the “dead zone” around the light where dim targets vanish, the bigger the halo. A tablet-based halometer has been developed to make this assessment more accessible, using a straylight meter alongside the halo measurement to link the subjective complaint to an objective light-scatter value.12PubMed. Tablet App halometer for the assessment of dysphotopsia Separate research confirmed that halo radius and forward light scatter are directly related, meaning the physical measurement of straylight reliably predicts how bothersome halos will be.2PubMed. Relationship between halo size and forward light scatter
In routine clinical practice, though, your doctor is more likely to rely on a slit-lamp exam, which lets them inspect the cornea and lens under magnification to look for opacities, deposits, or swelling. Corneal topography maps the shape of the corneal surface and can reveal irregularities that contribute to halos, while tonometry checks eye pressure to rule out glaucoma. If the eye exam is normal but halos persist, that raises the possibility of a neurological cause, and further workup may be warranted.
When Halos and Starbursts Are Not the Same Thing
People often use “halos,” “starbursts,” and “glare” interchangeably, but they are distinct phenomena with different underlying causes. Halos are smooth, ring-shaped glows around a light. Starbursts are spiky rays radiating outward from a light, like the points of a star. Glare is a more diffuse wash of brightness that reduces contrast without necessarily forming a distinct shape. The early PRK research described above found that starbursts were driven by corneal transparency problems, while halos were driven by defocusing effects and pupil size.7Eye. Disturbances in night vision after excimer laser photorefractive keratectomy This distinction is clinically useful because the treatments differ: a starburst caused by corneal haze may resolve on its own as the cornea heals, while a halo caused by a large pupil exceeding the optical zone may need a different intervention, like pupil-constricting drops at night.
If you are trying to communicate your symptoms to an eye care provider, paying attention to the shape and behavior of the light disturbance gives them a head start. A smooth ring that appears around every light source in the dark suggests a diffuse scattering cause like early cataract or corneal edema. Spiky rays from point sources suggest surface irregularity. A general washed-out feeling around bright lights without a distinct ring shape points toward forward scatter from lens or corneal opacity. All three can coexist, and many conditions produce more than one type, but the dominant pattern narrows the differential.
Dry Eyes and Tear Film Instability
One of the most overlooked causes of halos is an uneven tear film. The tear layer is technically the eye’s outermost optical surface, and when it breaks up between blinks or becomes patchy from dry eye disease, it introduces tiny irregularities that scatter light just like a smudged windshield does. Drivers who notice halos around oncoming headlights that briefly clear with a blink are likely experiencing tear-film-related scatter rather than a structural problem. Artificial tears or treatment of the underlying dry eye condition often resolves or reduces these halos without any surgical or medical intervention, making it one of the simplest fixes on this list.
Tear film disruption can also complicate the assessment of halos from other causes. If a patient with early cataracts also has dry eyes, some of the halo they perceive may be tear-related and correctable without cataract surgery. This is why many ophthalmologists optimize the ocular surface before making surgical decisions, to get a clearer picture of how much of the visual complaint is coming from the lens versus the front of the eye.