The Collaborative International Dictionary of English v.0.48:

Astigmatic \As`tig*mat"ic\, a. (Med. & Opt.)
   Affected with, or pertaining to, astigmatism; as, astigmatic
   eyes; also, remedying astigmatism; as, astigmatic lenses.
   [1913 Webster]

WordNet (r) 3.0 (2006):

astigmatic
    adj 1: of or relating to a defect in the eye or in a lens caused
           by a deviation from spherical curvature which prevents
           light rays from meeting at a common focus and so results
           in distorted images [ant: anastigmatic, stigmatic]