In a perfectly shaped eye, the cornea and lens are round, like a football. Therefore, all light entering the cornea and lens will bend equally in order to make a sharply focused image on the retina (back of the eye). If either your cornea or lens is rugby ball shaped, the light rays aren't bent the same, forming two different images and resulting in blurred vision. The astigmatism will occur when your cornea or lens is curved more steeply in one direction than in another.
