The Collaborative International Dictionary of English v.0.48:

ametropia \am`e*tro"pi*a\ ([a^]m`[-e]*tr[=o]"p[i^]*[.a]), n.
   [Gr. 'a`metros irregular + 'w`ps, 'wpo`s, eye.] (Med.)
   A visual impairment resulting from faulty refraction of light
   rays in the eye. Subtypes include myopia astigmatism and
   hyperopia. -- Am`e*trop"ic ([a^]m`[-e]*tr[o^]p"[i^]k), a.
   AS
   [1913 Webster +PJC]

The Collaborative International Dictionary of English v.0.48:

Astigmatism \A*stig"ma*tism\, n. [Gr. 'a priv. + ?, ?, a prick
   of a pointed instrument, a spot, fr. ? to prick: cf. F.
   astigmatisme.] (Med. & Opt.)
   A defect of the eye or of a lens, in consequence of which the
   rays derived from one point are not brought to a single focal
   point, thus causing imperfect images or indistinctness of
   vision.
   [1913 Webster]

   Note: The term is applied especially to the defect causing
         images of lines having a certain direction to be
         indistinct, or imperfectly seen, while those of lines
         transverse to the former are distinct, or clearly seen.
         [1913 Webster]

WordNet (r) 3.0 (2006):

astigmatism
    n 1: (ophthalmology) impaired eyesight resulting usually from
         irregular conformation of the cornea; common in nearsighted
         people [syn: astigmatism, astigmia]
    2: (optics) defect in an optical system in which light rays from
       a single point fail to converge in a single focal point [syn:
       astigmatism, astigmia] [ant: stigmatism]