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What is astigmatism?

Astigmatism is distorted vision caused by an unevenly curved cornea. The cornea is the clear outer layer on the front of the eye. As a result of astigmatism, your vision is somewhat blurry all the time.

Astigmatism is a common problem. Many people have astigmatism that is so slight that it does not interfere with their vision. People with worse astigmatism may squint to try to bring objects into focus. Squinting does not hurt your eyes, but it may lead to headaches.

How does it occur?

No one knows for sure what causes uneven corneas. Corneas, like sets of teeth, are rarely perfect. Astigmatism sometimes runs in families. Some people have had irregular corneas since birth. Other people develop astigmatism as they get older. Astigmatism may develop after cataract or cornea surgery. People can have astigmatism along with nearsightedness (myopia) or farsightedness (hyperopia).

What are the symptoms?

The main symptom is vision that is never completely clear and sharp at any distance or in any amount of light, without glasses. Part of your vision may be in focus and part blurry. For example, vertical lines may be in focus while horizontal lines are blurry.

How is it diagnosed?

Your eye care provider will test your vision and examine your eyes. You will be asked to read letters from a chart. Then you will be asked to read the same chart with different lenses in front of your eyes to see which ones improve your vision. Your provider may use a special instrument to focus a circle of light on the cornea and measure its reflection. This helps measure the curve of the cornea's surface.

Your provider will also check if you have any eye diseases.

How is it treated?

For slight astigmatism, you may not need glasses. Greater degrees of astigmatism can be corrected with glasses or contact lenses.

Surgeons can treat astigmatism in some people by reshaping the cornea. Three procedures used are:

  • AK (astigmatic keratotomy): The surgeon cuts small slits in the cornea. This flattens the cornea, which often helps light rays focus better on the retina.
  • PRK (photorefractive keratectomy): The surgeon uses a laser to remove thin layers of the cornea. This changes the shape of the cornea and may help the eyes to focus better.
  • LASIK (laser in situ keratomileusis): The surgeon uses a laser and a very precise tool to reshape the cornea.

The main risks of these procedures are:

  • You may have scarring in the cornea that can cause glare.
  • You may develop dry eyes.
  • You may get more nearsighted or farsighted.
  • The astigmatism may get worse.
  • You may get an infection of the eye.
  • These procedures can weaken the cornea.

Be sure you talk to a qualified ophthalmologist (a medical eye doctor) about all your options before you decide which treatment is best for you.

Can I help prevent astigmatism?

Because there is no known cause for astigmatism, there is nothing you can do to prevent it.

Reviewed for medical accuracy by faculty at the Wilmer Eye Institute at Johns Hopkins. Web site:
Developed by RelayHealth.
Published by RelayHealth.
Last modified: 2009-10-29
Last reviewed: 2010-09-07
This content is reviewed periodically and is subject to change as new health information becomes available. The information is intended to inform and educate and is not a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional.
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