Astigmatism is very common. Some experts believe that almost everyone
has a degree of astigmatism, often from birth, which may remain the same
throughout life. It is said that the tendency to develop astigmatism
(not astigmatism in itself) is inherited and that therefore some people are more prone to develop astigmatism than others.
Some cases of astigmatism are caused by problems in the lens of the
eye. Minor variations in the curvature of the lens can produce minor
degrees of astigmatism (lenticular astigmatism).
In these patients, the cornea is usually normal in shape. Infants, as a
group, have the least amount of astigmatism. Astigmatism may increase
during childhood, as the eye is developing. Source: http://www.eyerobics.com.au/astigmatism.html