The Facts

The cornea is a special layer on the surface of the eye that does most of the work of bending light as it enters the eye. Light must be bent properly so that it creates a sharp image. Theoretically, the eye's cornea should be perfectly round, like a slice off the surface of a ping-pong ball. Astigmatism is a condition in which the cornea is oval, like the bottom of a dessert spoon. This means that the focus is smeared so that while lines in one direction may be sharp, lines in another direction will be blurry.

Causes

We don't know what causes astigmatism, but we know it tends to run in families. Some people are born with astigmatism. Others get astigmatism later in life, sometimes after eye damage. Everyone has a tiny degree of astigmatism - no cornea is perfectly round. It's only a problem when it interferes with vision.

Symptoms and Complications

If you have astigmatism, you may be able to focus on an object just fine, but the peripheral field of view won't be perfectly clear. Often, people with astigmatism have myopia (nearsightedness) as well. If their vision isn't corrected, everything will be blurred, but still some areas of the field of view will be more focused than others.

Astigmatism shouldn't cause halos, dimming, or brightness, or any changes to the outward appearance of the eye. These symptoms suggest other problems like glaucoma, cataracts, diabetic retinopathy, and conjunctivitis. The degree of astigmatism may change over the years, but there shouldn't be any sudden changes in ability to see and make out detail.

Making the Diagnosis

A thorough eye test will include various tests for astigmatism. This is usually done by an optometrist (a doctor who tests vision and prescribes glasses and contact lenses) or an ophthalmologist (a doctor who specializes in eye problems and eye surgery).

Treatment and Prevention

There are three ways to treat astigmatism: glasses, contact lenses, and surgery.

Glasses and contact lenses for people with an astigmatism have an extra component called a toric lens. This bends light to counterbalance the effects of astigmatism. These lenses are usually a bit more expensive.

Toric contact lenses may be slightly heavier on one side. This side slips to the bottom of the eye, ensuring that the right part of the lens is over the right part of the eye. Some people have found these lenses less comfortable than normal lenses. But contact lens technology is improving all the time, so if you found toric lenses uncomfortable in the past, you might not if you try them now.

Surgery is an option either for very severe astigmatism or for people who are also nearsighted. In the latter case, the astigmatism is corrected at the same time as the surgery.

There are a few basic types of operations: laser-assisted in situ keratomileusis, photorefractive keratectomy, and radial keratotomy. These surgeries are usually done in an eye clinic.

With laser-assisted in situ keratomileusis (LASIK), the doctor makes a small cut into the top layer of the cornea, then folds back this layer like a flap. A laser is then used to mould the tissue of the cornea underneath into a better shape. The flap is then replaced.

Photorefractive keratotomy (PRK) is done with a computer-guided laser. It removes a thin layer of cornea, leaving a shape that will refract (bend) light correctly.

Radial keratotomy may be performed by a surgeon or a special machine. Based on the results of an eye test, the ophthalmologist (a doctor that specializes in eye disorders and eye surgery) will calculate a pattern of radial cuts like wheel spokes around the iris. These cuts cause the cornea to settle into the desired spherical shape.

Radial keratotomy, though cheaper than the laser versions, is no more dangerous nor less effective at treating astigmatism. People with myopia, however, tend to have better vision after photorefractive keratotomy. There is also some risk that radial keratotomy may lead to farsightedness later on.