For normal, un-distorted vision, the cornea should be smooth and equally curved in all directions. In an astigmatic eye, the cornea curves more in one direction than the other so that the surface is more like the shape of a football or rugby ball rather than a soccer ball.
Astigmatism distorts or blurs vision for objects at any distance. It is usually evident from an early age and will require some form of vision correction. Low level astigmatism is very common, and may not be bothersome. Astigmatism commonly occurs together with myopia or hypermetropia.