The cause of astigmatism is usually the irregularity of the cornea. For normal vision, the cornea should be smooth and equally inclined in all directions. In astigmatism, the direction of the cornea is more in one direction. In other words, cornea is very similar to american football ball than basketball. In astigmatism, the image surface is similar to a wavy mirror or a very long, too fat or weak image in the circles. Astigmatism is hereditary. It can be at birth and usually remains unchanged for life. Low-grade astigmatism is very common and usually does not need correction.