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[Effect of interpupillary distance on acuity of depth perception].

BACKGROUND
Until today it is not really known, what kind of influence the interpupillary distance (IPD) has on depth perception. Actual literature says that haploscopic separation of pictures is of disadvantage for subjects with small IPD. This study intended to verify the influence of IPD on stereopsis in order to get valid and comparable results when testing the depth perception of different subjects.


SUBJECTS AND METHODS
We examined 58 normosensoric soldiers for their stereoscopic sensation while changing their individual IPD. By using flexible flat plates of glass, the subjects' IPD could be changed infinitely variable to fix depth perception in haploscopic stereotesting.


RESULTS
The variety of the interpupillary distance (IPD) of different people has to be strictly differentiated from the intraindividual changes of interpupillary distance, which, by a change of convergence, lead to a change of depth perception. A decrease in intraindividual IPD reveals an increase of depth perception. This change of perception follows, in mathematical terms, the law of logarithm. In case of intraindividual change of IPD the size of objects is also influenced.


CONCLUSIONS
Using conventional stereotests, the IPD of different subjects has negligible influence on the depth perception. Different results of depth perception obtained with the help of stereoscopic examination of normosensoric subjects probably correspond with an individual and egocentric dealing with the visual localization of distances (distance between objects, size of objects, depth of objects).