Astigmatism is a common vision condition where your eye’s front surface, the cornea, curves unevenly, causing light to focus at two different points instead of one. The result is blurry or distorted vision at all distances. It’s the most common refractive error worldwide, affecting an estimated 40% of adults across all regions.
How a Normal Eye Differs From One With Astigmatism
In a normally shaped eye, the cornea is round like a basketball. Light passes through it and converges on a single point at the back of the eye, producing a sharp image. With astigmatism, the cornea is shaped more like a football, with one meridian curving more steeply than another. This uneven curvature bends light in two different directions, creating two focal lines instead of one focal point. The gap between those two focal lines is what makes your vision blurry.
Think of it this way: if you look at a plus sign (+), one line might appear sharp while the other looks fuzzy. That’s because each direction of the curve is focusing light at a slightly different depth inside your eye.
Corneal vs. Lenticular Astigmatism
Most astigmatism comes from the shape of the cornea, but the lens inside your eye can contribute too. The total astigmatism you experience is actually a combination of both. The cornea is typically the bigger factor. Interestingly, the lens often has its own mild astigmatism that partially cancels out the corneal version, especially in younger people. This natural compensation tends to fade with age as the lens changes, which is one reason astigmatism often gets worse over time.
What Astigmatism Feels Like
Blurry vision is the hallmark, but it’s not always the most noticeable symptom, especially if your astigmatism is mild. Many people first notice secondary effects: headaches after reading or screen work, eye strain that builds throughout the day, or unusual fatigue even after a full night’s sleep. You might find yourself squinting frequently without realizing it.
At night or in low light, the symptoms tend to get worse. You may see glare, halos, or starburst patterns around headlights and streetlights. This happens because your pupil dilates in dim conditions, allowing more of the unevenly curved cornea to participate in focusing light.
Some people with mild astigmatism don’t notice any symptoms at all. Their brain compensates by constantly adjusting focus, which works fine until it doesn’t, often showing up as unexplained headaches or eye fatigue rather than obviously blurry vision.
What Causes It
Nearly all human eyes have at least a small amount of asymmetry in their corneal curvature. In most cases, astigmatism is simply inherited. If your parents have it, you’re more likely to as well. It’s present from birth in many people and often detected during childhood eye exams.
Beyond genetics, certain conditions and events can cause or worsen astigmatism. Keratoconus, a progressive thinning of the cornea that causes it to bulge into a cone shape, is one of the more significant causes of irregular astigmatism. Eye injuries, corneal scarring, and previous eye surgeries can also change the cornea’s curvature. Even something as simple as habitually rubbing your eyes has been associated with corneal shape changes over time.
How Prevalence Changes With Age
Astigmatism becomes more common as you get older. Data from large population studies in South Korea illustrate this strikingly: roughly 54% of people in their twenties had astigmatism, rising to 79% in the 60 to 69 age group, and 92% in people 70 and older. People over 70 had 2.5 times the odds of astigmatism compared to those in their fifties. This age-related increase is largely driven by changes in the lens, where shifting internal structures gradually alter how light bends inside the eye.
Reading Your Prescription
If you have astigmatism, your glasses or contact lens prescription will include two extra numbers beyond the basic sphere (nearsightedness or farsightedness) correction. The first is the cylinder value, abbreviated CYL. This number, measured in diopters, tells you how much astigmatism correction you need. A higher number means more unevenness in your cornea’s curvature.
The second is the axis, written as a number between 1 and 180 degrees. This indicates the orientation of your astigmatism, essentially telling the lab which angle to position the corrective lens so it lines up with your cornea’s specific curve. Without the axis, the cylinder correction would be useless because it wouldn’t be aimed in the right direction.
A prescription reading something like -2.00 +1.50 x 90 means you have 2 diopters of nearsightedness, 1.5 diopters of astigmatism, and the astigmatism is oriented at 90 degrees (vertical).
Glasses and Contact Lenses
Most astigmatism is corrected with glasses or contact lenses, and for the majority of people, this is all they’ll ever need. Standard glasses use cylindrical lenses that compensate for the uneven curvature by bending light more in one direction than the other.
Contact lenses for astigmatism, called toric lenses, work on the same principle but need to stay oriented correctly on your eye. They’re designed with slight weighting or special edge shapes that keep them from rotating. If you’ve tried regular contacts and found your vision inconsistent or slightly off, toric lenses designed for your specific cylinder and axis measurements typically solve that problem. Both soft and rigid gas-permeable toric options exist, with rigid lenses sometimes providing sharper correction for higher amounts of astigmatism.
Surgical Options
For people who want to reduce or eliminate their dependence on glasses, laser eye surgery is an option. Both LASIK and PRK can correct astigmatism by reshaping the cornea with an excimer laser. The treatment limits depend on whether your astigmatism is combined with nearsightedness or farsightedness. For nearsighted patients, up to 6 diopters of astigmatism can typically be treated. For farsighted patients, the limit is around 5 diopters. Mixed astigmatism, where one meridian is nearsighted and the other farsighted, can be corrected up to about 6 diopters.
Both LASIK and PRK use the same laser platform, so the correction limits are identical. The difference between the two procedures is in how the surgeon accesses the cornea: LASIK creates a thin flap, while PRK removes the outer layer entirely and lets it regenerate. PRK has a longer recovery period (days to weeks of discomfort versus hours to days with LASIK) but avoids flap-related complications, making it a better fit for people with thinner corneas or certain lifestyles.
For people with very high astigmatism or corneas that aren’t good candidates for laser surgery, implantable lenses or lens replacement surgery are alternatives, though these are less common and involve more complex procedures.
Regular vs. Irregular Astigmatism
There’s an important distinction between regular and irregular astigmatism. Regular astigmatism, the far more common type, has two principal curves oriented at right angles to each other. It’s predictable and correctable with standard glasses or contacts. Irregular astigmatism, where the curvature varies unpredictably across the cornea, is harder to correct. It’s typically caused by corneal disease like keratoconus, scarring, or complications from surgery. Rigid gas-permeable contact lenses or specialty scleral lenses are often the best nonsurgical option for irregular astigmatism, because the rigid lens creates a smooth new optical surface over the uneven cornea.