Astigmatism (often mistakenly called “a stigmatism”) is a common vision condition where the front of your eye or the lens inside it is curved unevenly, causing blurry or distorted vision at all distances. It affects roughly one in four people and is one of the most frequently diagnosed refractive errors alongside nearsightedness and farsightedness.
How Astigmatism Affects Your Vision
A normally shaped eye is round like a basketball. Light enters through the curved front surface (the cornea), passes through the lens, and lands on a single focal point at the back of the eye. That single point of focus is what gives you a sharp image.
With astigmatism, the eye’s cornea or lens is shaped more like a football, with one curve steeper than the other. This means light entering the eye bends at two different angles and creates two focal points instead of one. Neither focal point lands cleanly on the retina, so the image your brain receives is blurred or stretched. The distortion can affect objects up close, far away, or both.
What Causes It
Astigmatism is usually something you’re born with. The uneven curvature develops as the eye forms, and most people who have it have always had it. It can also appear after an eye injury, certain eye diseases, or surgery. Despite what you may have heard, reading in dim light, sitting close to the TV, or squinting does not cause astigmatism or make it worse.
There are two main types based on where the irregular curve sits. Corneal astigmatism is the more common form, where the front surface of the eye has mismatched curves. Lenticular astigmatism happens when the lens inside the eye, which sits behind the cornea, has the uneven shape instead. Both types blur your vision in the same way.
Symptoms to Recognize
The most obvious symptom is blurry vision that doesn’t fully clear up whether you’re looking at something nearby or across the room. Many people also experience eye strain, headaches (especially after reading or screen work), and a habit of squinting to try to sharpen what they see.
Nighttime is often when astigmatism becomes most noticeable. During the day, your pupils are smaller and can partially compensate for the uneven curvature, so you may not realize anything is off. Once it gets dark and your pupils widen, bright lights from headlights and streetlamps can look surrounded by halos or starbursts. If you’ve ever felt like driving at night was harder than it should be, with glowing streaks radiating from every light source, astigmatism is a likely explanation. Dry eyes can make this worse, because an uneven tear film scatters light even further.
How It’s Measured
An eye care professional checks for astigmatism during a standard eye exam using a few different tools. One common method is keratometry, where you look into an instrument that resembles a small telescope and focus on a target image (usually a set of circles with plus and minus signs). The device measures how steeply your cornea curves in different directions. If the curve is the same all the way around, you’ll get one consistent reading. If you have astigmatism, the instrument picks up two different values: one for the steepest part and one for the flattest.
More advanced clinics use corneal topography, which creates a detailed color-coded map of your entire corneal surface. This is becoming the preferred method because it captures subtle irregularities that keratometry can miss.
The amount of astigmatism is measured in units called diopters. Less than 1.00 diopter is considered mild, and many people in this range barely notice symptoms. Between 1.00 and 2.00 diopters is moderate. Severe astigmatism falls between 2.00 and 3.00 diopters, and anything above 3.00 is classified as extreme. Most people fall in the mild to moderate range.
Reading Your Prescription
If you have astigmatism, your glasses or contact lens prescription will include two extra numbers beyond the basic sphere (nearsighted or farsighted) correction. The first is the cylinder value, often abbreviated CYL. This number tells you how much astigmatism correction you need, measured in diopters. The second is the axis, a number between 1 and 180 that indicates the angle on your cornea where the astigmatism sits. Together, these two values let the lens correct the exact direction and degree of your eye’s uneven curve.
Correction Options
Glasses are the simplest fix. The lenses are ground with different curvatures at specific angles to counteract the uneven shape of your eye, collapsing those two focal points back into one.
Contact lenses designed for astigmatism are called toric lenses. Unlike standard round contacts that have the same power across the entire surface, toric lenses have different corrective powers built into different zones of the lens. They also need to sit on your eye in a specific orientation to line up with your axis, so they’re designed with weighting or other features that keep them from rotating out of position when you blink.
Laser eye surgery, including LASIK, can permanently reshape the cornea to correct astigmatism. The procedure uses a laser to remove microscopic amounts of tissue, evening out the curvature so light focuses on a single point again. Modern femtosecond laser techniques offer better precision and lower rates of needing a follow-up procedure compared to older methods. The maximum amount of astigmatism that can be corrected surgically depends on the specific laser system and regulatory approvals, so your eligibility will depend on the severity of your prescription and other factors like corneal thickness.
Astigmatism in Children
Astigmatism is especially common in young children and can change as the eye grows. A large study of children aged 6 to 8 found that about 23% had measurable astigmatism before 2020, with rates climbing to nearly 35% by 2022-2023. The increase may be linked to more time spent on close-up work and less time outdoors, though the exact relationship is still being studied. Because children rarely complain about blurry vision (they assume everyone sees the way they do), regular eye exams are the most reliable way to catch it early. Uncorrected astigmatism in young kids can contribute to amblyopia, sometimes called lazy eye, where the brain starts ignoring the blurry image from one eye.