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Astigmatism may accompany farsightedness or nearsightedness. Usually it is caused by an irregularly shaped cornea (called corneal astigmatism). But sometimes lenticular astigmatism results from an irregularly shaped lens, which is located behind the cornea. Either kind of astigmatism can usually be corrected with eyeglasses, contact lenses, or refractive surgery. Astigmatism Symptoms and Signs You may not notice small amounts of astigmatism at all or have just slightly blurred vision. But sometimes uncorrected astigmatism can give you headaches or eye strain and distort or blur your vision at all distances. Because not only adults can be astigmatic, you need to make sure you schedule an eye exam for your child. Dr. Karla Zadnik, an optometrist at The Ohio State University School of Optometry, found in a recent study of 2,523 children that more than 28 percent of them had astigmatism. Children may be even more unaware of the condition than adults, and they are unlikely to complain about blurred or distorted vision. But astigmatism can affect a child's ability to see well in school and during sports, which is why it's important that eye exams be scheduled at regular intervals to detect any astigmatism early on. What Causes Astigmatism? Astigmatism occurs when the cornea is shaped more like an oblong football than a spherical baseball, which is the normal shape. In most astigmatic eyes, the oblong or oval shape causes light rays to focus on two points in the back of your eye, rather than on just one. This is because, like a football, an astigmatic cornea has a steeper curve and a flatter one. In regular astigmatism, the meridians in which the two different curves lie are located 90 degrees apart. In irregular astigmatism, the two meridians may be located at something other than 90 degrees apart; or there are more than two meridians. Regular astigmatism is usually easy to correct (see treatments below), but irregular astigmatism can be complicated and more difficult to correct, depending on the extent of the irregularity and its cause. Usually astigmatism is hereditary: many people are born with an oblong cornea, and the resulting vision problem may get worse over time. But astigmatism may also result from an eye injury that has caused scarring on the cornea, from certain types of eye surgery or from keratoconus, a disease that causes a gradual thinning of the cornea. Astigmatism Treatment Unless it is extreme, astigmatism can be compensated for satisfactorily with eyeglasses or contact lenses. If your eyeglass or contact lens prescription contains three parts rather than one, your eyecare practitioner has found some astigmatism in one or both of your eyes. A prescription with three parts looks like this: -2.75 -1.25 x 90. - The first part indicates your main spherical correction, meaning the amount of power (in diopters) required in a lens to sharpen your visual acuity to an acceptable level, usually 20/20. In this example, the person has myopia and requires a negative (concave) lens to correct it.
- Part two shows the extent of the astigmatism in diopters. Again, the minus sign means a concave lens is needed.
- Part three is the axis (in degrees) of the cylinder required to bend certain light rays to compensate for the cornea's oval shape.
Many people with astigmatism believe that they can't wear contact lenses or that only rigid contact lenses (RGPs, also called GP lenses) can correct astigmatism. This was true many years ago, but now soft toric contact lenses can correct astigmatism. Toric lenses have a special correction built into them and may also contain a prescription for nearsightedness or farsightedness if you need it. While soft torics work well for many people, if you have severe astigmatism, you'll likely do better with RGP contact lenses or eyeglasses. Your eyecare practitioner will advise you. Depending on the type and severity of your astigmatism, you may also be able to have it corrected with refractive surgery. Discuss with your eye doctor which procedure is best to correct your astigmatism, and review your options in our LASIK & Vision Surgery section. All About Vision. “Astigmatism.” March 1, 2010 http://www.allaboutvision.com/conditions/astigmatism.htm
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