Jennifer Colt, age 13, of Erie, Pa., for her question:

WHAT CAUSES ASTIGMATISM?

Astigmatism is an eye condition that makes objects appear blurred. This happens because rays of light from different parts of an Abject being viewed do not all focus equally on the retina.

Almost everyone has some astigmatism caused by abnormalities in the curve of the cornea. Some people are born with it. Others occasionally get it from an injury or disease of the cornea.

Eyeglasses or contact lenses can often correct astigmatism. Extreme cases can be corrected often by corneal transplantation, an operation in which the scarred cornea is replaced by clear corneal tissue from another person.

Astigmatism sometimes produces symptoms of eyestrain and headache.