It is caused usually when the cornea is shaped irregularly so light bends differently depending upon the angle of light when it hits the eye. Because light rays bend in different directions, the lens cannot focus in a sharp point to create a clear image of light on the retina.
Many people have slight astigmatism.
People with myopia or hyperopia may have astigmatism, as well. Lenses prescribed to correct astigmatism must be perfectly aligned with your eye. Proper eyeglass or contact lens fitting is a must for optimal visual comfort. Because the degree of astigmatism can change, regular vision checks are important to maintaining the best possible vision. Astigmatism causes scattered focal points.