The Collaborative International Dictionary of English v.0.48:

Anastigmatic \An*as`tig*mat"ic\, a. [Pref. an-not + astigmatic.]
   (Optics)
   Not astigmatic; free of astigmatism; -- pertaining to a lens
   or lens system, and used especially of a lens system which
   consists of a converging lens and a diverging lens of equal
   and opposite astigmatism but different focal lengths, and
   sensibly free from astigmatism.
   [Webster 1913 Suppl. + WordNet 1.5]

WordNet (r) 3.0 (2006):

anastigmatic
    adj 1: pertaining to a lens or lens system free of astigmatism
           (able to form point images) [syn: anastigmatic,
           stigmatic]
    2: not astigmatic [syn: anastigmatic, stigmatic] [ant:
       astigmatic]