Astigmatism 

Astigmatism is a common vision problem that leads to blurred vision. Astigmatism is caused by an irregularly shaped cornea or a curved lens inside the eye. This keeps light that comes in from being correctly focused on the retina and results in blurry vision -- both near and far. 

Astigmatism is so common that just about everybody has some amount of it. Small amounts of astigmatism -- slightly irregularly shaped corneas -- do not usually cause severe problems and usually do not cause problems or require glasses. More severe cases of astigmatism, or more irregularly shaped corneas, can create distorted or blurry vision, headaches and eye discomfort. 

Many times, astigmatism occurs with other vision problems, such as nearsightedness or farsightedness.