Astigmatism occurs when the front of the eye or the cornea, has an irregular curvature.
Normally astigmatism is treated in the following ways:
If the degree of astigmatism is slight and no other problems like nearsightedness or farsightedness, are present, corrective lenses
may not be needed. If on the other hand astigmatism is great enough to cause eyestrain, headache, or distortion of vision, prescription lenses will be needed for clear and comfortable vision.
More info at
http://www.kellogg.umich.edu/patientcare/conditions/astigmatism.html