What is Astigmatism?

The normal cornea is semi-spherical. Vertical as well as horizontal lines are clearly pictured. A dot-shaped light source, e.g. a light bulb, is pictured as a light spot. If the cornea is bent unevenly, i.e. rather elliptical, an astigmatism is the result and the view gets blurry. A point for instance is pictured as a line.