Astigmatism

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 human lens, which is located inside the eye, behind the iris (the colored part of the eye).

The blurred vision caused by 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.

Children can also have astigmatism as well as adults, and should have their eyes examined before starting dindergarden to ensure that they have clear vision.

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 basketball, which is the normal shape. In most astigmatic eyes, the oblong or oval shape causes light rays to focus on two separate points in the back of the eye, rather than on just one. This is because, like a football, an astigmatic cornea has a steeper curve and a flatter one that split the focus into two points.

In regular astigmatism, the two different curves lie 90 degrees apart, like at 12:00 o'clock and 3:00 o'clock. In irregular astigmatism, the two curves may be located at something other than 90 degrees apart; or there are more than two curves.

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.