THE FREIBURG STEREOTEST IN THE ASSESSMENT OF STEREOPSIS FOR DRIVING LICENSES

Background: The ''Freiburg Stereotest'' is a new instrument where disp arate pictures are generated by a computer and displayed on one single high resolution video monitor. In the present work, the Freiburg Ster eotest was used to check the stereo qualification for certain categori es of driver's licence. For this purpose, a determination of the small est detectable disparity is not reasonable. Rather, it should be check ed whether or not a certain disparity, usually well above threshold, i s recognized with a sufficient reliability. We have chosen a disparity of 100 arcsec; this value is considered to be an acceptable requireme nt for certain categories of driver's licence. Subjects and Methods: 6 strabismic subjects were examined binocularly and 10 normal subjects were examined both binocularly and monocularly. Two targets (''busses' '), side by side and different in depth by a disparity of 100 arcsec, were presented 78 times and, in a two-alternative forced-choice proced ure, a minimum of 66 hits was required to pass the test. Monocular cue s were excluded by a systematic variation of the lateral distance betw een the two targets. Results: The strabismic subjects and the monocula rly occluded normal subjects reached random scores only. With both eye s open, 8 of the 10 normal subjects reached scores near 100%, while 2 of them passed the test only when the lateral distance between the two targets was 15 minarc or less. For a lateral distance between the two targets of more than 15 minarc, these 2 subjects showed a learning ef fect. Conclusions: The Freiburg Stereotest allows to determine with st atistical significance whether or not a proband can recognize a certai n disparity which may be required for a driver's licence.