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astigmatism

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astigmatism


  2  definitions  found 
 
  From  Webster's  Revised  Unabridged  Dictionary  (1913)  [web1913]: 
 
  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. 
 
  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. 
 
  From  WordNet  r  1.6  [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}] 




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