1. Eye Care Glossary
  2. What Is Astigmatism?

Astigmatism

Astigmatism is a condition commonly affecting adults, but can affect children as well. While it’s often associated with nearsightedness and farsightedness, astigmatism causes blurry vision regardless of distance. The good news is that astigmatism is not a dangerous condition and can be treated, usually quite successfully. Continue reading for additional information about causes, symptoms, diagnosis, and treatment options.

What is Astigmatism?

Astigmatism is an irregular shape in the curvature of the eye’s cornea or lens (the cornea takes on the shape of a football). A normal cornea is perfectly spherical in shape, which helps focus light rays. When the cornea is irregularly shaped, light rays are not refracted (bent) properly. This causes vision on both near or far objects to be distorted and blurry. Astigmatism often accompanies myopia (nearsightedness) or hyperopia (farsightedness).

Together, these conditions are known as “refractive errors”, because they involve errors in how the eyes refract light.

Adults are more likely than children to notice that astigmatism is affecting their vision. However, if not corrected astigmatism may impair a child’s performance in school and sports. This condition can be present at the time of birth or may develop over time. It is important that children have regular eye exams so that these problems can be detected and corrected as early as possible.

Causes

Most people with astigmatism are born with it, but it can also develop over time or result from an eye injury.

Additionally, astigmatism can occur due to a relatively rare condition called Keratoconus. This condition can cause astigmatism by making the cornea thinner and more cone-shaped. This condition cannot be corrected with eyeglasses. People with Keratoconus typically require contact lenses to be able to see clearly.

Symptoms

Symptoms of astigmatism may include:

  • Blurry or distorted vision
  • Headaches
  • Eyestrain
  • Squinting
  • Trouble seeing at night

If you are having any of these symptoms, visit your local eye doctor. These symptoms may be indicative of other vision or health problems. Your eye doctor can conduct tests to determine the cause of the symptoms.

Diagnosis

Astigmatism is easily detected with an eye exam performed by your eye doctor using the following tests.

Refraction

Refraction tests are used to determine whether you have a refractive error, including one related to astigmatism. During the manual refraction, the doctor has you look at an eye chart and pairs of lenses are placed in front of your eyes, asking you, “Which lens makes things clearer—lens 1 or lens 2?”

Visual acuity test

During your eye exam, the doctor tests your visual acuity—meaning how well you can see—using an eye chart and scoring your vision (20/40, 20/20, etc.). This measurement is done while you wear your current eyeglasses (or without corrective lenses if you don’t currently wear them) and then again after a refraction. Your visual acuity test helps determine the severity of your astigmatism or other refractive error.

Keratometry

In this astigmatism test, an instrument called a keratometer is used to measure the curvature of your cornea. Your eye doctor uses this test to map the exact shape of your eye to determine the glasses or contacts prescription that best compensates for the astigmatism.

Severity Scale

You may have seen the word "diopter" on a glasses or contact lens prescription. It's a technical term for specifying how lenses should be engineered to correct vision—and also indicates the degree(severity) of astigmatism.

  • 0 diopters - a perfectly-shaped eye with no astigmatism
  • 0.5 to 0.75 diopters - most people have this degree of astigmatism
  • 1.5 diopters or more - with this degree of astigmatism, glasses or contacts are likely needed to correct vision

Treatment Options

Almost all cases of astigmatism can be corrected with eyeglasses or contact lenses. If you have just slight astigmatism and no other vision problems, you might not need vision correction. There are two main treatments for astigmatism:

  • Corrective lenses - both eyeglasses and contact lenses.
    • Eyeglasses - People with astigmatism generally choose eyeglasses to improve their vision.
    • Contact lenses - Some people have more success with contact lenses than eyeglasses. They can provide clearer vision and a wider field of view.
  • Laser and other refractive surgery - Laser and refractive surgery such as LASIK. Surgical options are less common as they come with more expense and the risks associated with most surgeries.

It is common for astigmatism to change over time. After astigmatism is diagnosed, eye exams should be performed annually by your local eye doctor or more often as directed.

Frequently Asked Questions

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