There's no such thing as a perfect world or a perfect golf swing. Likewise, there are no perfect eyeballs. Elongated eyeballs are nearsighted, or myopic. Eyeballs that are too short and squat are farsighted, or hyperopic. And some eyeballs have an uneven surface, a condition called astigmatism. Irregularly shaped eyeballs can't focus light effectively.
A “normal” cornea has a smooth, unvarying curvature, like that of a gumball. In an eye with astigmatism, the corneal curvature is steeper and more peaked, like the bowed curve of a lemon drop. Problems caused by the shape of the cornea are said to be mechanical, or related to a physical mechanism, as opposed to pathological, or related to a disease process. They're called refractive errors because the light doesn't bend properly as it moves through the eye.
Refraction refers to the change of direction of a light ray as it passes into and through the structures of the eye. Its velocity is faster or slower depending on what medium (substance) it's moving through. The principle is similar to that of an arrow hitting its target. The arrow will slice through a block of styrofoam faster than it will penetrate a stack of cardboard. The word refraction, in fact, comes from a Latin word meaning “to break” or “to force back.”
If you have astigmatism, you're in good company. The National Health and Nutrition Examination Survey (NHANES), an ongoing data collection initiative conducted by the National Center for Health Statistics, shows that among men and women age 20 or older, more than one third have astigmatism. The condition is often accompanied by another refractive error (myopia or hyperopia).
Since astigmatism can be hereditary, it's often present from birth. Anyone of any age can have astigmatism. Like many eye disorders, it's more common among people in older age groups. However, astigmatism among children is of special concern, since adults may not suspect it and children may not know that their vision isn't sharp. A recent study found, in fact, that nearly 30% of children have astigmatism.
Contrary to what your aunt or grandmother may have told you, astigmatism isn't caused by squinting at comics in dim light, or by always having your nose in a book, or by parking yourself two feet from the screen to watch reruns of. More likely, it's the other way around—that is, you squint, hold your book close, or sit near the TV because you have astigmatism.
Astigmatism can also occur after some types of eye injury or surgery, or in the presence of certain eye diseases. It's associated, for instance, with keratoconus, a progressive disease that causes the cornea to thin and bulge into an elliptical (arched) shape.
The symptoms of astigmatism can mimic those of other eye disorders, such as Age-Related Macular Degeneration (AMD) or simple eye strain. Some of these conditions, including AMD, can pose a threat to your vision. See your vision care provider if you have any of the following symptoms of astigmatism:
- Blurred vision at all distances
- Distorted vision
- Eye strain or fatigue
- Trouble driving at night
If you have no blurred vision or other symptoms of astigmatism and no risk factors for cataracts, glaucoma, AMD, or diabetic retinopathy, have a baseline eye exam at age 40. Even if no astigmatism is found, your provider will take measurements of your eye, such as pressure and corneal curvature, that can provide a standard against which future exam results may be compared. (Of course, if you have risk factors for cataracts, glaucoma, AMD, or diabetic retinopathy, or if you fall into a high-risk ethnic group, you should receive comprehensive dilated eye examinations sooner and more often, as advised by your provider.)
Your eye doctor can diagnose astigmatism with a simple eye exam consisting of refraction testing and keratometry:
- Keratometry. Keratometry uses a specialized instrument called a keratometer to calculate the cornea's curvature by measuring its steepest and flattest parts. It works by projecting rings of light onto your cornea and measuring the amount of light reflected back. Your provider will note any distortion of the rings and calculate the distance of the intervals between them to glean information about the degree of astigmatism in the eye.
If your astigmatism is pronounced enough to keep you from engaging safely in tasks such as driving, using a sewing machine, or operating a weed whacker, you should have it corrected. You should also correct your vision if it interferes with your enjoyment of activities you're interested in, whether it's playing ping-pong or making handmade picture frames. Treatment options for people with astigmatism include standard eyeglasses, contact lenses, refractive surgery, and orthokeratology, depending on what works best for your health needs, age, and lifestyle.
- Eyeglasses. They may not be high-tech, but standard spectacles still do a great job of correcting vision for people with astigmatism.
- Contact lenses. Rigid or soft contact lenses are also effective in correcting astigmatism. For people who have hyperopia or myopia with astigmatism, toric lenses-
soft contacts with two powers in them, like bifocals-are a good option.
- Refractive surgery. The goal of refractive surgery is to reshape the cornea as an alternative to wearing contacts or glasses for astigmatism. Methods of refractive surgery include various laser procedures, such as LASIK surgery and photorefractive keratectomy (PRK). A newer surgical option flattens the cornea by means of two tiny, transparent crescents implanted along its perimeter. The crescents, called INTACS, are made of a medical polymer and can be replaced if your prescription changes.
- Orthokeratology. Orthokeratology uses a series of specially fitted rigid contact lenses, worn while you sleep, to reshape your corneas. This procedure is attractive to those who don't want to wear contact lenses during the day, such as those who enjoy swimming. The process can be used to treat mild astigmatism; however, retainer lenses must be worn at night every few days, or your eyes will gradually return to their previous curvature.