What Is Astigmatism?

Key Takeaways

• Astigmatism is a common eye problem that makes your vision blurry at near and far distances.
• It occurs when the cornea or lens of the eye is irregularly shaped. 
• When the eye's curvature isn't smooth and even, light rays cannot properly focus, causing blurred vision.
• Other common symptoms are eye strain, seeing glare or starbursts, and poor night vision.
• Your doctor can diagnose astigmatism with a comprehensive eye exam. It’s usually treatable with eyeglasses, contact lenses, or refractive surgery.

What is Astigmatism?

Astigmatism is a common and treatable eye condition that occurs when either the cornea or the lens has an irregular shape. It's a type of refractive error that causes blurred vision at all distances. 

You can have astigmatism in one or both eyes, and it’s often present at birth. It may occur with other refractive errors, including:

• Myopia (nearsightedness). This is known as myopic astigmatism.
• Hyperopia (farsightedness). This is called hyperopic astigmatism.

Mixed astigmatism involves symptoms of myopia (blurred distance vision) and hyperopia (distorted up-close vision).

How Does Astigmatism Affect Your Vision? 

People with astigmatism experience distorted vision when looking at near and distant objects. This is because the eye’s lens or cornea has an irregular shape. 

The cornea and lens are structures that bend (refract) light onto your retina so you can see.

A perfectly shaped eye is round, like a smooth ball. As light passes through the eye, the smooth curvature of the cornea and the lens bend light evenly to properly focus an image.

Astigmatism occurs when the eye is shaped like an oval or egg. This irregular shape prevents light from focusing properly. It causes blurred or distorted vision.

What Are the Types of Astigmatism?

There are two types of astigmatism. It’s possible to have both types in one eye. The type of astigmatism you have depends on whether the cornea or lens is affected:⁴

• Corneal astigmatism. The surface of your eye (cornea) has an abnormal, egg-shaped curve.
• Lenticular astigmatism. The eye lens is misshaped.

Regular vs. Irregular Astigmatism

Astigmatism can also be described as regular or irregular:

• Regular astigmatism. This type happens when the eye is evenly shaped like an oval or football.
• Irregular astigmatism. This type occurs when the eye’s curvature is uneven. Irregular astigmatism is less common than the regular type.

What Causes Astigmatism?

The exact cause of astigmatism is unknown. However, genetics may play a role. Astigmatism is often present at birth, but some people develop it later in life. 

Factors that may cause you to develop astigmatism include:

• Eye injury 
• Eye disease such as keratoconus
• Complications of eye surgery 

Who is at Risk for Astigmatism?

Studies show these factors increase your risk for astigmatism:^1,2

• Older age
• Eye injuries that cause corneal scarring or thinning
• Eye surgery, such as cataract surgery or LASIK
• Having a parent with astigmatism
• Family history of eye disorders
• Having a mother who smoked while pregnant
• Having refractive errors (e.g., myopia and hyperopia)

Astigmatism affects 36.2% of Americans and is the most common refractive error in the U.S.³ It is not caused by squinting, reading in dim light, or watching the television up close.

Symptoms of Astigmatism

Most people with astigmatism have blurry vision when looking at objects up close and far away. However, people who only have slight astigmatism and no other vision problems may not have symptoms.

Other common astigmatism symptoms include:⁵

• Blurry vision when looking at near or far objects
• Straining or squinting to see objects more clearly
• Seeing glare or starbursts around lights at night
• Headaches 
• Eye strain or discomfort
• Difficulty seeing at night or in low light conditions

Astigmatism Symptoms in Children

Symptoms of astigmatism may be harder to detect in younger children. They may not notice they have a vision problem, so they won't report it. This is why early childhood screenings for eye diseases and vision problems are important.

If your child has frequent headaches or sudden changes in school performance, astigmatism may be the cause. Talk to your pediatrician, family physician, or other eye health professional if you suspect your child has a vision condition.

How Is Astigmatism Diagnosed?

An eye doctor can diagnose astigmatism with a comprehensive eye exam. They'll start by performing a slit-lamp exam, which involves looking into your eye with a special lighted microscope. This is to test the eyes’ health and is not necessary to diagnose astigmatism.

Your doctor may perform the following tests to arrive at an astigmatism diagnosis:

• Visual acuity test. Visual acuity describes your sharpness of vision. Testing it involves having you read letters from a chart at certain distances.
• Refraction test. This uses an instrument called a phoropter. It contains a series of lenses to help your doctor determine which one gives you the clearest vision. 
• Autorefraction. This measures refractive errors like astigmatism by shining a bright light into your eye and measuring how it bends. 
• Keratometry or corneal topography. Both these tests measure the curvature of your cornea. Corneal topography provides more information about your cornea’s shape.

How Is Astigmatism Measured?

Eye doctors use a keratometer to measure astigmatism in diopters (D). The astigmatism severity scale is as follows:

• Mild. 0.10 to 1.00 D
• Moderate. 1.00 to 2.00 D
• Severe. 2.00 to 4.00 D
• Extreme. over 4.00 D

Can You Fix Astigmatism?

Yes. Regular astigmatism is easily treatable with corrective lenses or refractive surgery. Eye doctors can accurately measure it and prescribe appropriate treatment.

Irregular astigmatism is not as easy to treat, and eyeglasses don’t help. Specialty contacts (like rigid or sclerals) are a treatment option for irregular astigmatism. Laser or other corneal surgery can also treat irregular astigmatism, depending on its cause.⁶

Treatment Options

There are many ways to treat astigmatism, but corrective lenses like glasses or contacts are the most common. Depending on your needs, your doctor may recommend one of the following options:

Eyeglasses

Corrective lenses like glasses are a simple and economical way to improve vision. When worn, they help your eyes focus light rays on your retina.

Astigmatism glasses are different from normal glasses. They have cylinder (CYL) and AXIS specifications. These denote lens power and the rotation of astigmatism correction.

Moderate to extreme astigmatism that measures 1.50 to 4.00 diopters can be corrected with glasses. However, an eye doctor can determine if eyeglasses or other treatments are the best option.

If your astigmatism occurs with another type of refractive error, such as presbyopia, your doctor may recommend progressive lenses.

Contact Lenses

Contacts are another type of corrective lenses. Many people prefer them for their comfort and convenience. Like eyeglasses, contacts bend light rays and focus them on your retina.

Disposable and rigid gas-permeable lenses with a cylindrical (toric) design are ideal for astigmatism. They can correct astigmatism and other refractive errors.

Depending on your needs, your doctor may also prescribe:

• Soft lenses 
• Rigid contact lenses (gas permeable contact lenses)
• Toric lenses

You can choose contacts based on your budget and convenience. To explore options, check out our review of the Best Contacts for Astigmatism.

Laser Eye Surgery

Also called refractive surgery, laser eye surgery treats astigmatism by changing the shape of the cornea. 

• Laser-assisted in situ keratomileusis (LASIK). LASIK treats astigmatism and other refractive errors. The surgical procedure involves cutting a thin flap in your cornea and reshaping it with a laser. Not everyone is a candidate for LASIK.
• Photorefractive keratectomy (PRK). PRK also changes the shape of the cornea with a laser. This procedure doesn’t involve a corneal flap, making it a better option for people with thin corneas.
• Laser-assisted subepithelial keratectomy (LASEK). LASEK surgery is similar to LASIK and PRK. While PRK involves removing the outer layer of corneal tissue (epithelium), LASEK cuts a small flap in the epithelial tissue.

Orthokeratology (Ortho-K)

Orthokeratology is a non-invasive lens correction therapy. The treatment lasts 2 weeks and involves wearing rigid gas-permeable contact lenses. 

These lenses are designed to fit your eyes and gently reshape your cornea. You wear them for a period of time, such as overnight, then remove them.

Once the cornea adjusts to a normal shape, the ophthalmologist provides retainer lenses to help maintain clear vision.

Lens Replacement Surgery

Also known as refractive lens exchange, lens replacement surgery is an invasive surgical procedure that removes the misshapen eye lens. The surgeon replaces the natural lens with a toric lens.

Lens replacement surgery is recommended for:

• Lenticular astigmatism
• People with or at risk of cataracts

Phakic Intraocular Lenses (IOLs)

The treatment is an invasive surgery that inserts phakic lenses into your eye. But instead of replacing your eye's natural lens, it is either placed at the front of the iris or behind it. Phakic lenses treat severe myopia and myopic astigmatism.