title: Stereoacuity versus fixation disparity as indicators for vergence accuracy under prismatic stress.
abstract: BACKGROUND
  Fixation disparity has been widely used as an indicator for vergence accuracy under prismatic stress. However, the targets used for measuring fixation disparity contain artificial features in that the fusional contours are thinned out. We considered that stereoacuity might be a preferable indicator of vergence accuracy, as stereo targets represent natural viewing conditions.
  
  
  METHODS
  We measured fixation disparity with a computer adaptation of Ogle's test and stereoacuity with the automatic Freiburg Stereoacuity Test. Eight subjects were examined under increasing base-in and base-out prisms.
  
  
  RESULTS
  The response of fixation disparity to prismatic stress revealed the curve types described by Ogle and Crone. All eight subjects reached a stereoscopic threshold below 10 arcsec. In seven subjects the stereoscopic threshold increased before double vision occurred.
  
  
  CONCLUSIONS
  Our data suggest that stereoacuity is suitable to assess the range of binocular vision under prismatic stress. As stereoacuity bears the advantage over fixation disparity in that it can be measured without introducing artificial viewing conditions, we suggest exploring whether stereoacuity under prismatic stress would be more meaningful in the work-up of asthenopic patients than is fixation disparity.
authors.affiliation: Abteilung Neuroophthalmologie und Schielbehandlung, Universitäts-Augenklinik Freiburg, Killianstr 5, 79106 Freiburg, Germany. kromeier@aug.ukl.uni-freiburg.de
authors.forename: Miriam
authors.initials: M
authors.lastname: Kromeier
authors.forename: Christina
authors.initials: C
authors.lastname: Schmitt
authors.forename: Michael
authors.initials: M
authors.lastname: Bach
authors.forename: Guntram
authors.initials: G
authors.lastname: Kommerell
mesh_terms: D000328:Adult; D001248:Asthenopia / Q000209:etiology; D005133:Eye Movements; D005139:Eyeglasses; D006801:Humans; D015357:Vision Disparity; D015348:Vision, Binocular; D014792:Visual Acuity