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Vision Problems: Astigmatism

An astigmatic cornea is irregularly shaped, causing blurred or distorted vision.

Overview

Astigmatism (uh-STIG-muh-tizz-um) is an uneven or irregular curvature of the cornea or lens, causing blurred or distorted vision – such as letters or shapes appearing to be compressed, stretched, or tilted. It is treated with corrective lenses or surgery.

Most commonly, astigmatism occurs because the cornea is oval or egg-shaped instead of round. Along with an irregularly shaped lens, this causes, light rays entering the astigmatic eye scatter instead of focusing to a single focal point on the retina — some rays fall on the retina while others focus in front of or behind it.

Most people have some degree of astigmatism, which is usually present at birth and is believed to be hereditary. It can also result from injury or conditions such as keratoconus or chalazion.

Astigmatism tends to occur with other refractive disorders; for instance, about half of those with myopia (nearsightedness) are also astigmatic.

Symptoms

The most common symptom is blurred vision in both near and distant vision. Those with mild cases may have blurred vision only at certain distances, or see fine but experience headaches or eye strain (from squinting). If you have astigmatism, you may see better in some directions than others (vertically, horizontally or diagonally) or recognize some letters or shapes more easily than others (O versus X).

Although we are usually born with astigmatism, it is often not diagnosed until a child begins to read. Other symptoms can include:

  • The need to squint
  • Headaches
  • Eyestrain
  • Eye fatigue

Prevention

Astigmatism cannot be prevented. However, your degree of astigmatism can increase with age, and regular eye exams can determine the need for increased strength of corrective lenses. If your astigmatism seems to be rapidly growing worse, you may be experiencing the onset of a more serious eye disease such as keratoconus or in which the center of the cornea thins and develops a cone-shaped bulge that blurs and distorts vision.

Parents and those who work with children should be aware that astigmatism could contribute to poor performance in school. Routine eye tests conducted in schools may not detect astigmatism, so regular exams by a qualified eye doctor are recommended.

Treatment

Since most people have some degree of astigmatism, it is considered normal. If minor, treatment may not be required but is certainly beneficial. Moderate or severe astigmatism can be treated with a variety of methods:

  • Corrective Eyewear
    • Eyeglasses. If you already wear glasses for another refractive error (such as nearsightedness), correction for your astigmatism may be included in your prescription.
    • Contact lenses are another option. Toric contacts are specifically designed for people with astigmatism; they compensate for an irregularly shaped lens or cornea by having different powers of correction at different points on the lens. And rigid gas-permeable contact lenses may actually help prevent astigmatism from progressing.
  • Laser Surgery may benefit some astigmats with irregularly shaped corneas. LASIK (laser in-situ keratomileusis) is a procedure in which a surgeon slices a flap into the cornea and a laser removes some tissue from beneath the sliced area to reshape the cornea. But corrective lenses may still be required following the surgery for certain activities.