Astigmatism is a common vision condition where the front surface of your eye, or sometimes the lens inside it, is curved unevenly. Instead of being shaped like a basketball with a uniform curve in every direction, the eye is shaped more like a football or an egg, with one curve steeper than the other. This causes light to focus on two different points instead of one, making vision blurry at all distances. Roughly 1 in 4 children have it, and the numbers are even higher in adults.
How an Astigmatic Eye Differs From a Normal One
In a perfectly shaped eye, the cornea (the clear front dome) bends light evenly so it focuses on a single point on the retina. In an astigmatic eye, the cornea has two principal curves, one steeper and one flatter, set at right angles to each other. Think of it like a spoon: light passing through the rounder part bends differently than light passing through the flatter part. The result is two focal points instead of one, which is why images look stretched or smeared rather than sharp.
The cornea isn’t always the culprit. The lens inside your eye can also be unevenly curved, which adds its own layer of distortion. In fact, total astigmatism is the combined effect of both the cornea and the internal lens. Interestingly, nearly all human eyes have at least a tiny amount of uneven curvature. It only becomes a problem when the mismatch is large enough to noticeably blur your vision.
What Astigmatism Feels Like
Blurry vision is the hallmark symptom, and unlike nearsightedness or farsightedness, the blur affects both close and distant objects. You might struggle to read a menu at arm’s length and also have trouble making out road signs. Some people experience double vision, where images appear to overlap, even with one eye closed.
Other common symptoms include:
- Glare and halos around lights, especially while driving at night
- Squinting to try to sharpen what you see
- Headaches and eye strain, particularly after prolonged reading or screen time
- Fatigue that seems tied to visual tasks
These symptoms tend to be most noticeable at night, in rain, or any time you’re looking at bright lights against a dark background. Many people with mild astigmatism don’t realize they have it because their brain compensates, but that extra effort is often the hidden cause of chronic eye strain or end-of-day headaches.
What Causes It
Most astigmatism is simply the shape you were born with. Genetics play the largest role, and many people have some degree of it from early childhood. Beyond genetics, several things can cause or worsen astigmatism:
- Keratoconus: a progressive condition where the cornea thins and bulges into a cone shape, creating significant irregular astigmatism. Risk factors include vigorous eye rubbing, a family history of the condition, and having certain conditions like Ehlers-Danlos syndrome or Down syndrome.
- Eye injuries or corneal scarring: trauma to the front of the eye can distort the cornea’s surface.
- Previous eye surgery: procedures like cataract removal or corneal transplants can sometimes change the cornea’s curvature.
- Corneal infections: certain infections can leave uneven scarring on the cornea.
There’s also an age-related shift worth knowing about. In younger people, the internal lens partially compensates for corneal astigmatism, effectively reducing it. As you age, the lens changes shape and stops compensating as well, which is why some people notice worsening astigmatism in their 40s and beyond even though their cornea hasn’t changed much.
Regular vs. Irregular Astigmatism
Eye care professionals classify astigmatism into two broad types. Regular astigmatism is by far the more common one. The two principal curves of the cornea sit at a clean 90-degree angle to each other, and each curve is smooth and consistent across the surface. This type is easy to correct with standard glasses or contact lenses.
Irregular astigmatism is more complex. The curves aren’t perpendicular, and the surface may have bumps or inconsistencies. It’s typically caused by conditions like keratoconus, corneal scarring, or surgical changes. Standard soft contact lenses often can’t fully correct it, so rigid gas-permeable lenses or specialty contacts are usually needed.
How It’s Diagnosed
Your eye doctor can detect astigmatism during a routine eye exam. The standard refraction test, where you look through a series of lenses and say which is clearer, measures how much correction you need. But to understand the shape of your cornea in detail, they’ll use one of two tools.
A keratometer is a telescope-like instrument that measures the curvature of the cornea along its steepest and flattest points. It’s quick and gives a good basic reading. More detailed information comes from corneal topography, which maps the entire surface of the cornea in high resolution, almost like a topographic map of a landscape. Topography is becoming the standard approach and is especially useful for detecting irregular astigmatism or keratoconus.
Reading Your Prescription
If you have astigmatism, your eyeglass prescription will include two numbers beyond the basic sphere correction. The “cylinder” (CYL) number tells you how much astigmatism you have, measured in diopters. A higher number means a bigger difference between your steepest and flattest curves. The “axis” is a number between 1 and 180 that indicates the angle where the astigmatism sits on your cornea, essentially telling the lab how to orient the corrective lens.
If your prescription has no cylinder value, you don’t have clinically significant astigmatism. A cylinder of 0.50 to 0.75 diopters is mild, 1.00 to 2.00 is moderate, and anything above 2.00 is considered high.
Correction With Glasses and Contacts
Glasses are the simplest fix. The lenses are ground with a cylindrical correction that compensates for the uneven curvature of your eye. They work reliably because they sit in a fixed position in front of your face and never shift out of alignment.
Contact lenses for astigmatism are called toric lenses. Unlike regular contacts, which are the same power all the way around, toric lenses have different powers in different zones and need to stay oriented correctly on your eye. Older designs used a small weight at the bottom edge to keep the lens from rotating. Modern versions use more sophisticated stabilization, and soft toric lenses have improved dramatically in comfort and visual sharpness. For low amounts of astigmatism, even standard soft or rigid contacts can neutralize the distortion. For moderate to high amounts, toric lenses or rigid gas-permeable lenses are typically needed. Rigid lenses generally provide sharper vision than soft ones for astigmatism because they create a smooth, uniform surface over the irregular cornea.
Surgical Options
LASIK is the most widely known refractive surgery for astigmatism. It reshapes the cornea with a laser to create a more uniform curve. For astigmatism under 2 diopters combined with low to moderate nearsightedness (under 6 diopters), LASIK has a strong track record of producing excellent uncorrected vision with minimal risk of complications. Higher levels of astigmatism can also be treated, though the results become less predictable as the numbers climb. The exact limits depend on the laser system used and local regulatory approvals.
PRK (photorefractive keratectomy) is a similar laser procedure but removes the outer layer of the cornea rather than creating a flap beneath it. Recovery takes longer, but it’s a good option for people with thinner corneas who aren’t candidates for LASIK. For people undergoing cataract surgery, toric intraocular lens implants can correct astigmatism at the same time the clouded natural lens is replaced.
Astigmatism in Children
About 15% of children worldwide have astigmatism greater than 0.5 diopters, and recent data suggest prevalence has been climbing. Studies tracking children before and after the pandemic found that rates of refractive astigmatism rose from about 23% to nearly 35% between 2019 and 2023, likely related to increased near-work and screen time during lockdowns.
Uncorrected astigmatism in young children can affect more than just reading the whiteboard. Research on children ages 4 to 5 found that astigmatism had a significant impact on early academic readiness, particularly in language and literacy skills. Because young children rarely complain about blurry vision (they assume everyone sees the way they do), early vision screening before school age is important for catching it. Left uncorrected during critical years of visual development, significant astigmatism can contribute to amblyopia, sometimes called “lazy eye,” where the brain begins to favor one eye over the other.