The relevance of stereopsis for motorists: a pilot study

Purpose: To study the influence of stereoscopic depth perception on automobile driving performance. Methods: Ten patients with strabismus and defective stereopsis were compared with ten healthy controls with respect to their performance in a series of automobile driving manoeuvres. The two groups were individually matched as to age, annual miles driven, years of licence holding and type of vehicle owned. After an ophthalmologic examination the subjects in each group performed the following series of driving tests: (1) stopping in front of an obstacle, (2) reversing into a parking space, (3) driving through a slalom course, (4) estimating the relative positions of two cars. All tests were performed binocularly and monocularly (with the non-dominant eye covered). Results: Only in the slalom test did the normal subjects perform significantly better than the stereo-deficient subjects (odds ratio 10.5; P<0.01). In estimating position, normal subjects actually performed significantly worse (odds ratio 0.091; P<0.01). A significant distance ratio of 2.5 (95% CI 1.1-5.5; P=0.033) of the monocular with respect to the binocular performance of the normal subjects was found for the stopping task only, while the subjects with defective stereopsis showed no difference between their monocular and binocular performance. Conclusion: In this study, stereopsis had a positive effect on driving performance only in dynamic situations at intermediate distances.