Q. I wear corrective glasses for astigmatism, but I don't really understand what astigmatism is.
A. Astigmatism means that the cornea of the eye has an irregular shape. The cornea is the clear covering over the lens and the iris. The iris controls how much light enters the eye. The lens focuses the light on the retina, the light-sensitive area at the rear of the eye. The cornea protects these structures and helps to transmit light through the eye.
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The cornea is normally round, but in people with astigmatism, it may be an oval. As a result, light scatters as it passes through the cornea; the light rays do not focus on a single point on the retina. That focus is what you need for clear vision, just like a camera.
The result of uncorrected astigmatism is blurred vision. The image is distorted, regardless of whether you're looking at something distant or something close. In this respect, astigmatism is different from nearsightedness, where things in the distance are blurry but not things that are close. It's also different from presbyopia, the condition that causes most of us to need reading glasses. (I've put an illustration on my website, AskDoctorK.com.)
Some people describe the blurred vision as double vision but in only one eye. Astigmatism can lead to eyestrain, squinting and headaches from working to focus on near or distant objects.
People are born with astigmatism, but it may not be apparent until a child begins to attend school or learns to read. Astigmatism is a lifelong condition unless it is treated. It may worsen slowly over time, but more typically it remains stable throughout life.
It is possible to correct astigmatism using glasses, certain types of contact lenses or surgery. Glasses are a good, reliable choice.
Patients who prefer contact lenses may find that they are limited to hard lenses. Soft lenses sometimes can be used, but they aren't as effective for severe cases of astigmatism.
Surgery may be a choice, especially for people who have dry eyes or other conditions that prohibit them from wearing corrective lenses. The most common type of surgery used to correct astigmatism is LASIK (laser in situ keratomileusis). In LASIK, a small incision is made on the surface of the eye to create a small flap of tissue, which then is lifted up. A cool laser beam corrects the irregular curvature of astigmatism. The flap is replaced, and recovery is usually quick and painless.
Common eye conditions like astigmatism can be treated much more easily and successfully today than when I began medical school. Back then glasses could be Coke bottle thick; contact lenses were less comfortable than they are today; and LASIK surgery hadn't been developed. We've come a long way.
• Dr. Komaroff is a physician and professor at Harvard Medical School. To send questions, go to AskDoctorK.com.