The Eye Institute©

The Eye Institute©

Astigmatism is the most common vision problem, but 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 eyeglasses, contact lenses or refractive surgery.

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.

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 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.

Astigmatism Treatment
Unless it is extreme, astigmatism can be compensated for satisfactorily with eyeglasses or contact lenses.