Astigmatism

3 definitions found

From The Collaborative International Dictionary of English v.0.48 [gcide]:

  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]

From The Collaborative International Dictionary of English v.0.48 [gcide]:

  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]

From WordNet (r) 2.0 [wn]:

  astigmatism
       n 1: (ophthalmology) impaired eyesight resulting usually from
            irregular conformation of the cornea [syn: {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: {astigmia}] [ant: {stigmatism}]