Astigmatism is one of the most common vision conditions in the world, affecting roughly one in three people in the United States. Despite how widespread it is, many people are unfamiliar with what astigmatism actually means, what causes it, or why it makes vision blurry at all distances rather than just near or far.
This guide explains what astigmatism is, what causes the irregular cornea shape behind it, the symptoms it produces, the different types, how common it is, and the full range of treatment options available.
Note: This article is general information. An eye care professional should diagnose astigmatism and determine the appropriate prescription or treatment.
What Is Astigmatism?
Astigmatism is a refractive error caused by an irregularly shaped cornea (the clear dome-shaped tissue covering the front of the eye) or, less commonly, an irregularly shaped lens inside the eye. The irregular curvature prevents light from focusing evenly on the retina — the light-sensing layer at the back of the eye — resulting in blurred or distorted vision at all distances.
In a normal eye, the cornea is spherical — evenly curved in all directions, like a basketball. In an eye with astigmatism, the cornea is elongated and curved more steeply in one direction than another — shaped more like a football or the back of a spoon. This uneven curvature means light entering the eye focuses at multiple points on the retina rather than a single sharp point, which is what creates the characteristic blurring.
The word astigmatism comes from the Greek ‘a’ (without) and ‘stigma’ (point) — literally meaning ‘without a focal point.’ This describes the optical problem precisely.
How Common Is Astigmatism?
Astigmatism is extremely common. According to the American Academy of Ophthalmology, approximately one in three people in the United States has astigmatism to some degree. Global estimates suggest around 33 to 40 percent of the general population has clinically significant astigmatism.
Key facts about how common astigmatism is:
- It affects all ages — babies can be born with astigmatism, though most outgrow it in infancy
- It affects all races and ethnicities, with some population-level variation in prevalence
- It frequently occurs alongside other refractive errors — people who are nearsighted (myopic) or farsighted (hyperopic) are more likely to also have astigmatism
- Low levels of astigmatism are present in the majority of people; only clinically significant levels require correction
What Causes Astigmatism?
The cause of most astigmatism is simply the shape the eye develops — often hereditary. In the majority of cases, astigmatism is present from birth or develops in early childhood as the eye grows, and there is no identifiable external cause.
Hereditary Factors
The most significant risk factor for astigmatism is family history. If parents or siblings have astigmatism, a person is more likely to develop it. The irregular corneal shape is often an inherited anatomical feature, like eye color or foot shape.
Eye Rubbing
Frequent, vigorous eye rubbing is one of the few modifiable factors associated with developing or worsening astigmatism. Repeated mechanical pressure on the cornea can gradually alter its shape over time. Eye rubbing is particularly associated with keratoconus — a progressive condition in which the cornea thins and develops a cone-like bulge rather than a dome shape. People with dry eyes or allergies who habitually rub their eyes are at elevated risk.
Eye Injury or Surgery
Trauma to the eye — a cut, puncture, or other injury affecting the cornea — can alter the corneal shape and produce astigmatism. Some eye surgeries can also cause or worsen astigmatism, particularly if they alter the corneal surface as part of the procedure.
Keratoconus
Keratoconus is a progressive eye disease in which the cornea thins and gradually bulges outward into a cone shape rather than remaining dome-shaped. This produces significant and often irregular astigmatism. Keratoconus typically develops in the teenage years and progresses into the mid-thirties, and it is a distinct condition from ordinary astigmatism.
What Does NOT Cause Astigmatism
Despite common beliefs, the following do not cause astigmatism:
- Reading in low light — a very widespread myth; low light affects eye strain and comfort, not corneal shape
- Sitting too close to a television or screen — no evidence supports this causing any refractive error
- Excessive screen use — screens cause eye strain and dry eyes but do not physically alter corneal shape
Types of Astigmatism
| Type | Description |
| Corneal astigmatism | Most common type — irregular curvature of the cornea |
| Lenticular astigmatism | Irregular shape of the lens inside the eye (cornea may be normal) |
| Myopic astigmatism | Astigmatism combined with nearsightedness in one or both meridians |
| Hyperopic astigmatism | Astigmatism combined with farsightedness in one or both meridians |
| Mixed astigmatism | One meridian is nearsighted, the other is farsighted |
| Regular astigmatism | Principal meridians are perpendicular to each other — most common and most correctable form |
| Irregular astigmatism | Meridians are not perpendicular — often from keratoconus or injury; harder to fully correct with glasses |
Symptoms of Astigmatism
Unlike nearsightedness (which blurs only distant objects) or farsightedness (which primarily blurs close objects), astigmatism causes blurring at all distances. Symptoms vary depending on the degree of astigmatism:
- Blurred or distorted vision at all distances — the most characteristic symptom
- Eye strain — the eyes work harder to compensate for the blurring, causing fatigue
- Headaches — particularly after prolonged reading, screen use, or driving
- Squinting — an automatic attempt to improve focus
- Difficulty with night vision — lights may appear to have glare, halos, or streaks
- Sensitivity to glare — particularly in bright light or oncoming headlights
- Difficulty reading comfortably — text may appear distorted or difficult to track
- Depth perception issues — blurring at all distances can affect the ability to judge distances accurately
In mild astigmatism, symptoms may be minimal or absent. Significant astigmatism typically produces noticeable symptoms that affect daily activities.
Astigmatism vs Nearsightedness vs Farsightedness
| Feature | Astigmatism | Nearsightedness (Myopia) | Farsightedness (Hyperopia) |
| Cause | Irregular cornea/lens shape | Eye too long or cornea too curved | Eye too short or cornea too flat |
| Blurry at distance? | Yes | Yes | Sometimes |
| Blurry up close? | Yes | No | Yes |
| Night vision issues? | Yes — halos/glare | Yes — blurry | Less common |
| Can occur together? | Often occurs with both | Common combination | Common combination |
How Is Astigmatism Diagnosed?
An eye care professional diagnoses astigmatism during a comprehensive eye exam using several tests:
- Visual acuity test: The standard eye chart test (reading letters at a distance) provides a baseline measure of how clearly you see at different distances
- Keratometry: Measures the curvature of the corneal surface; the primary tool for detecting and quantifying corneal astigmatism
- Corneal topography: A detailed map of the corneal surface that shows the full pattern of curvature; particularly useful for detecting irregular astigmatism and keratoconus
- Refraction: The process of determining the exact lens prescription needed to correct your vision, including the cylinder correction for astigmatism
In your eyeglass or contact lens prescription, astigmatism is represented by the ‘cylinder’ (CYL) value and the ‘axis’ — the degree indicates how strong the correction is, and the axis (0–180 degrees) indicates the orientation of the astigmatism.
Astigmatism Treatment Options
Eyeglasses
The simplest and most common correction for astigmatism. Lenses prescribed for astigmatism have a cylindrical correction (in addition to any spherical correction for nearsightedness or farsightedness) that compensates for the irregular corneal curvature. Most people with astigmatism can achieve excellent vision correction with standard eyeglass lenses. High-power astigmatism prescriptions may benefit from thinner lens materials.
Contact Lenses
Standard soft contact lenses are spherical and do not correct astigmatism. Toric contact lenses are specifically designed to correct astigmatism — they have different powers in different meridians and are weighted to stay in proper orientation on the eye. Gas-permeable (rigid) contact lenses can also correct astigmatism, sometimes more effectively than soft lenses, because the rigid lens replaces the irregular corneal surface with a smooth refracting surface.
Orthokeratology (Ortho-K)
Orthokeratology involves wearing specially designed rigid gas-permeable contact lenses overnight. The lenses gently reshape the corneal surface during sleep. When removed in the morning, the cornea retains a more regular shape for the day, allowing clear vision without correction during waking hours. The effect is temporary and requires nightly wear to maintain. Ortho-K is an option for people who want freedom from daytime glasses or contacts, particularly children and young adults.
LASIK Surgery
LASIK (Laser-Assisted In Situ Keratomileusis) uses a laser to permanently reshape the cornea, correcting the irregular curvature that causes astigmatism. The procedure involves creating a thin corneal flap with a laser, reshaping the underlying tissue, and replacing the flap. LASIK can correct astigmatism alongside nearsightedness and farsightedness in a single procedure. Most patients achieve significantly improved vision; results are typically permanent, though age-related changes can occur.
Candidacy for LASIK depends on corneal thickness, the stability of the prescription, pupil size, and overall eye health. Not everyone is a candidate.
PRK (Photorefractive Keratectomy)
PRK is an alternative laser procedure for people who are not suitable candidates for LASIK — typically due to insufficient corneal thickness or other corneal factors. In PRK, the outer surface of the cornea is removed and a laser reshapes the exposed tissue. The outer layer regrows as healing occurs. Recovery from PRK is slower than LASIK (several days versus several hours for usable vision), but the long-term visual outcomes are comparable.
Can Astigmatism Be Prevented?
Most astigmatism cannot be prevented — hereditary astigmatism is structural and not influenced by behavior. Avoiding frequent vigorous eye rubbing is the main behavioral measure that can reduce the risk of progressive corneal shape changes. Protecting the eyes from injury with appropriate eyewear in high-risk activities reduces traumatic astigmatism risk.
Living With Astigmatism
- Mild astigmatism (under 1.00 diopter) often causes minimal symptoms and may not require correction
- Moderate to significant astigmatism is easily managed with glasses or toric contact lenses
- Astigmatism does not worsen vision permanently — with correction, most people with astigmatism achieve 20/20 vision or better
- Astigmatism can change over time, particularly during childhood, adolescence, and as part of normal aging — regular eye exams allow prescriptions to be updated as needed
- Astigmatism is not ‘cured’ by glasses or contacts — they compensate for it optically. Surgical options (LASIK, PRK) can correct the underlying corneal shape permanently.
Frequently Asked Questions
What is astigmatism?
Astigmatism is a refractive error caused by an irregularly shaped cornea (or lens), which prevents light from focusing evenly on the retina. Instead of a single focal point, light focuses at multiple points, producing blurred or distorted vision at all distances. It affects approximately one in three people and is usually correctable with glasses, contact lenses, or laser surgery.
What causes astigmatism?
Most astigmatism is hereditary — an irregularly shaped cornea or lens that develops as part of how the eye grows. Eye rubbing over time, eye injuries, certain eye conditions (such as keratoconus), and some eye surgeries can also cause or worsen astigmatism. Reading in low light and sitting close to screens do not cause astigmatism — these are myths.
How common is astigmatism?
Very common — approximately one in three people in the United States has clinically significant astigmatism, according to the American Academy of Ophthalmology. Low-level astigmatism is present in the majority of the population; only significant levels require correction.
Can astigmatism be cured?
Glasses and contact lenses correct astigmatism optically but do not cure it — the correction is needed as long as the corneal shape remains irregular. LASIK and PRK laser surgery can permanently reshape the cornea to correct astigmatism, offering a long-term solution. Orthokeratology (overnight contact lenses) provides temporary corneal reshaping.
Can you develop astigmatism as an adult?
Yes, though it is less common than childhood astigmatism. Adults can develop astigmatism from eye injuries, eye surgery, or progressive corneal conditions like keratoconus. Prescription changes in existing astigmatism are normal and can occur at any age. Regular eye exams — at least every two years for adults — catch these changes.
Final Thoughts
Astigmatism is one of the most common and most manageable eye conditions — affecting a third of the population but easily corrected in most cases with a simple prescription adjustment. Understanding what astigmatism is (an irregular corneal shape, not a disease), what causes it (mostly hereditary), and what can be done about it (glasses, contacts, or surgery) removes much of the mystery from a condition that many people are told they have without a clear explanation of what it means.
If you notice blurred vision at all distances, eye strain, headaches after reading, or difficulty with night vision and glare, an eye exam is the appropriate first step. An optometrist or ophthalmologist can diagnose astigmatism precisely and determine whether and what type of correction is appropriate for your specific prescription.