Astigmatism is a common refractive error. People who have astigmatism experience blurred or distorted vision at all distances. Astigmatism occurs when light entering the eye comes into focus at multiple points, either in front of or behind the retina, instead of precisely on the retina. This can be caused by a cornea that is irregularly shaped, and differs from the rounded shape of a normal cornea. Sometimes it can be caused by an irregularly shaped lens inside the eye. People with mild astigmatism can experience slightly blurred or distorted vision at all distances, but people with severe astigmatism can have vision affected so much, that it prevents them from performing their daily activities.