At night, astigmatism turns point sources of light into smeared, distorted shapes. Headlights, streetlights, and traffic signals can appear surrounded by halos, starbursts, or streaky lines that spread outward from the light source. During the day, you might barely notice your astigmatism. After dark, it can feel like looking through a smudged windshield.
The Three Main Light Distortions
People with astigmatism typically describe three distinct effects when they look at lights in the dark:
- Halos: Bright, fuzzy circles that surround each light source, almost like a glowing ring. Oncoming headlights and streetlights are the most common triggers.
- Starbursts: Radiating lines or spikes that shoot outward from a light, giving it a star-like or spiky appearance. These can make it hard to judge the exact position of a light.
- Glare: An overall wash of brightness that bleeds into your field of vision, reducing contrast and making everything around the light source harder to see.
Some people also notice that lights appear to have streaks or tails, almost like a comet. The specific pattern you see depends on the axis and severity of your astigmatism, so two people with the condition can experience slightly different distortions from the same light source.
Why It Gets Worse in the Dark
Your pupils dilate in low light to let in more of the available light. This is exactly what makes astigmatism more noticeable at night. A wider pupil allows light to pass through more of the irregularly shaped cornea (or lens), which magnifies the distortion. Research measuring visual acuity at different pupil sizes found a clear, statistically significant relationship: as the pupil widens from 1 mm to 5 mm, visual sharpness in astigmatic eyes drops progressively. At a 5 mm pupil, which is common in dim conditions, the blur is substantially worse than in bright daylight when the pupil is small and acts almost like a pinhole.
In normal eyes, the cornea curves evenly like a basketball, bending light to a single focal point on the retina. With astigmatism, the cornea is shaped more like a football, with one meridian curving more steeply than another. Instead of focusing light to one sharp point, this creates two separate focal lines. The gap between them is what produces the blur, and that gap matters more when the pupil is wide open.
How It Affects Night Driving
Night driving is where astigmatism causes the most practical trouble. Oncoming headlights can flare into distracting starbursts or halos, pulling your focus away from the road. Blurred vision becomes more pronounced in low light, making road signs harder to read until you’re closer than usual. Reduced contrast sensitivity, the ability to distinguish dark objects against a dark background, makes it harder to spot pedestrians, curbs, or obstacles in poorly lit areas.
These effects compound each other. Glare from one car’s headlights can temporarily reduce your ability to see the dimly lit road ahead, and if you’re also dealing with starbursts, your brain has to work harder to interpret what you’re seeing. For people with moderate to high astigmatism (above 1.25 diopters), uncorrected nighttime driving can meaningfully increase accident risk.
Severity Makes a Difference
Not everyone with astigmatism struggles at night. The condition is extremely common, affecting roughly 40% of adults worldwide, and many people have such a mild degree that they never notice symptoms. Eye doctors often categorize astigmatism by diopter measurement:
- Insignificant (0.25 to 0.50 diopters): Rarely causes noticeable night vision issues.
- Low (0.75 to 1.00 diopters): You may notice slight halos or softness around lights.
- Moderate (1.25 to 2.25 diopters): Starbursts and glare become clearly visible and can interfere with driving.
- High (2.50 diopters and above): Significant distortion around any light source, with pronounced blur in low-light conditions.
If your prescription lists a cylinder value (the number that measures astigmatism), that tells you where you fall. Many people with insignificant or low astigmatism only realize they have it when they get an eye exam.
What Helps With Nighttime Vision
The most effective fix is wearing the correct prescription. Glasses or contact lenses that include your cylinder correction reshape how light enters the eye, collapsing those two focal lines back into one point. For nighttime driving specifically, lenses with an anti-reflective coating can reduce glare by up to 78%, which makes a noticeable difference in how comfortable headlights and streetlights feel.
Toric contact lenses are designed specifically for astigmatism. They have different corrective powers along different meridians of the lens and are weighted to stay properly oriented on the eye. For people who prefer not to wear daytime correction, toric orthokeratology lenses are rigid lenses worn overnight that temporarily reshape the cornea, reducing both nearsightedness and astigmatism during the following day.
LASIK and similar refractive surgeries can permanently correct astigmatism by reshaping the cornea with a laser. However, it’s worth knowing that night vision disturbances are one of the most common post-surgical complaints, even after procedures considered fully successful by clinical standards. One study in the British Journal of Ophthalmology found that halo effects around lights roughly doubled after LASIK, and nearly 44% of refractive surgery patients in a separate review reported some degree of night vision difficulty. These effects often improve over the first several months as the eye heals, but for some people they persist. If nighttime vision is your primary concern, this is worth discussing in detail before choosing surgery.
When the Problem Might Be Something Else
Astigmatism that worsens noticeably over time, especially if your glasses prescription keeps changing, could signal keratoconus. This is a progressive condition where the cornea thins and bulges into a cone shape, creating irregular astigmatism that’s harder to correct with standard lenses. The night vision symptoms overlap significantly: increased light sensitivity, glare, and distorted vision. The key difference is the pattern of change. Stable astigmatism that’s been roughly the same for years is almost certainly ordinary. Rapidly worsening distortion, sudden clouding of vision, or a prescription that shifts at every visit warrants a closer look from an eye doctor who can map the shape of your cornea.