Astigmatism

What is astigmatism?

Astigmatism is distorted vision caused by an unevenly curved cornea (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 more astigmatism may squint to try to bring objects into focus. Squinting does not hurt your eyes, but it may lead to headaches.

Astigmatism can occur with nearsightedness (myopia) or farsightedness (hyperopia). Astigmatism can be treated with eyeglasses, contact lenses, or surgery.

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.

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. 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 examine your eyes with special instruments to see 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.

In recent years, surgeons have been able to treat astigmatism in some people by reshaping the cornea. Three procedures used are:

• AK (astigmatic keratotomy): The surgeon cuts small slits in the peripheral cornea. This procedure 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 allow better focusing.
• 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:

• scarring that causes glare
• getting more nearsighted or farsighted
• a worsening of the astigmatism
• infection of the eye

Not everyone with astigmatism will benefit from these procedures. 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.