Astigmatism or also referred to as an "refractive error" is a medical condition where the entering light does not "refract" evenly on the surface of the eye cornea.
In the general there exist 2 different types of astigmatism:
Regular astigmatism cause by an abnormal shape of the cornea can be treated with toric contact lenses.
The irregular type of astigmatism is often the consequence of operations, accidental wounds or birth related defects. Causes for the effects on the vision of a patient with astigmatism can be scars on the cornea, which cannot be treated with regular eye glasses but with corrective contact lenses.
Refractive errors are caused by the effects of astigmatism, because curvature of the 2 meridians deviated from normal.
The majority of patientes with astigmatism do well either with glasses and special astigmatic lenses. Some astigma patients with extreme conditions may wish to undergo a laser treatment called Lasik.