Two new stereotests for long distance: examination of stereopsis with regard to the permission of driving.

Abstract

Two differently constructed stereotests for a distance of 4 m are presented (tests A and B), which are based on the three-rod method of Helmholtz. In both tests, eight test objects are offered simultaneously, one of them being displaced toward the subject to a certain extent (100-10 s of arc). In test A the subject sees the eight test objects through eight holes, whereas in test B the test objects are seen directly. Each disparity is offered eight times. The threshold is defined as five of eight answers being correct. A total of 51 subjects without strabismus and with normal stereopsis in conventional tests achieved a mean stereo-acuity of 30 s of arc in test A and 10 s of arc in test B. The same subjects with one eye occluded and 49 patients with severe binocular defects reached chance scores only in test A, whereas in test B the success rate was improved slightly by monocular clues (P = 1/5). In examining stereopsis with regard to driving licenses, only tests for long distance should be used. Both new stereotests differentiate between normal and pathological candidates with high specificity and sensitivity.