In order for the
eye to work properly, light coming into the eye must be properly focused
on the retina (or the back of the eye). When the image is not focused,
there is an irregularity in the eye. This irregularity can be the overall
shape of the eye or the curvature of the cornea (the clear outer covering
of the eye), or both. The cornea should be curved equally in all directions.
Astigmatism occurs when the cornea is curved more in one direction than
Astigmatism is quite common and, in the vast majority of cases, it is
due simply to variations between people. Just as different people have
different shaped feet or hands, people also have different shaped corneas.
Rarely astigmatism is caused by lid swellings such as chalazia, and
corneal scars, or by keratoconus (a rare condition in which the cornea
becomes misshapen and pointed rather than smooth and rounded).
Astigmatism may cause blurred vision, eye strain or even headaches.
It can also cause images to appear doubled, particularly at night. Small
amounts of astigmatism can be ignored. But if any of its symptoms are
present, astigmatism can be corrected by glasses or contact lenses.
In most patients hard contact lenses do a better job of correcting for
astigmatism than soft contact lenses.