Astigmatism is the most common vision problem, however most people don’t know what it is. It may accompany nearsightedness or farsightedness. Usually it is caused by an irregularly shaped cornea (called corneal astigmatism). But sometimes it is the result of an irregularly shaped lens, which is located behind the cornea; this is called lenticular astigmatism. Either kind of astigmatism can usually be corrected with spectacles or contact lenses.
Astigmatism symptoms and signs
If you have only a small amount of astigmatism, you may not notice it or have just slightly blurred vision. But sometimes uncorrected astigmatism can give you headaches or eyestrain, and distort or blur your vision at all distances. It’s not only adults who can be astigmatic. Dr. Karla Zadnik, an optometrist at Ohio State University School of Optometry, found in a recent study of 2,523 children that more than 28% of them had astigmatism.
Children may be even more unaware of the condition than adults, and they are unlikely to complain of the blurred or distorted vision. Unfortunately, astigmatism can affect their ability to see well in school and during sports, so it’s important to have their eyes examined at regular intervals in order to detect any astigmatism early on.
What causes Astigmatism?
Astigmatism occurs when the cornea is shaped more like an Australian Rules football than a spherical tennis ball, 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 an Australian rules 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 180 degrees apart. In irregular astigmatism, the two meridians may be located at something other than 180 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.
Unless it is extreme, astigmatism can be compensated for satisfactorily with spectacles or contact lenses. If your spectacles or contact lens prescription contains three parts rather than one, your eyecare practitioner has found some astigmatism in one or both of your eyes.
Many people with astigmatism believe that they can’t wear contact lenses, or that only rigid gas permeable contact lenses can correct astigmatism. This was true many years ago, but now there are soft contacts that correct astigmatism; they are called toric contact lenses.
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 Rigid Gas Permeable contact lenses or spectacles. At Ezekiel Eyes we can advise you.