Stereoacuity versus fixation disparity as indicators for vergence accuracy under prismatic stress.
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.
Kromeier
Miriam
M
Abteilung Neuroophthalmologie und Schielbehandlung, Universitäts-Augenklinik Freiburg, Killianstr 5, 79106 Freiburg, Germany. kromeier@aug.ukl.uni-freiburg.de
Schmitt
Christina
C
Bach
Michael
M
Kommerell
Guntram
G
D000328:Adult; D001248:Asthenopia / Q000209:etiology; D005133:Eye Movements; D005139:Eyeglasses; D006801:Humans; D015357:Vision Disparity; D015348:Vision, Binocular; D014792:Visual Acuity