Refractive Blur Reduces Both Day and Night-Time Driving Performance and Alters Driver Gaze Patterns

Purpose: : To investigate the effect of different levels of refractive blur on real world driving performance and eye movements measured under day and night-time conditions.

Methods: : Participants included 12 visually normal, young adults (mean age=25.6 ± 5.2 years) who drove an instrumented research vehicle around a 4 km closed road circuit with 4 different levels of binocular spherical refractive blur (0.00 D, +0.50 D, +1.00 D, +2.00 D). The subjects wore optimal sphero-cylinder correction and the additional blur conditions were mounted in modified full-field goggles. The order of testing the blur conditions was randomized. Driving performance was assessed separately under day and night-time conditions with measures including road signs recognized, sign recognition distance, hazard detection and avoidance, gap detection, lane-keeping, speed and time to complete the course. Driving eye movements were also recorded using an ASL Mobile Eye tracking system.

Results: : Refractive blur and time of day had significant effects on driving performance (p<0.05), such that increasing blur and night-time driving reduced performance on all driving tasks except gap judgment and lane keeping. There was also a significant interaction between blur and time of day (p<0.05), where the effects of blur were exacerbated under night-time driving conditions. Post hoc testing indicated that all blur conditions were different to one another except for the number of hazards hit, where only the difference between +0.50 D blur and baseline 0.00 D failed to reach significance. Refractive blur also significantly increased the number of eye movement fixations and the duration of fixations on roadside signs while driving.

Conclusions: : The effects of blur were greatest under night-time conditions, even for levels of refractive blur as low as +0.50 D. Drivers also spent more time looking at signs rather than scanning the road ahead when driving with blur. These findings imply that the correction of refractive errors is essential for safe driving.