Assessing Driving Performance with Moderate Visual Field Loss

The minimum binocular horizontal field extent for driver licensing varies widely between states in the USA. The authors examined the relationship between visual field extent and open-road driving performance using a scoring method that measured the quality of specific skills for a range of general driving maneuvers, as well as maneuvers that the authors expected to be difficult for people with restricted fields. Twenty-eight current drivers with mild to moderate peripheral visual field restrictions (123 + or - 20 degrees, V4e target) drove the 14-mile route. While most subjects were scored as safe drivers, those with more restricted horizontal and vertical binocular field extents showed significantly poorer skills in maneuvers for which a wide field of vision is likely to be important (p < or = 0.05): speed matching when changing lanes, and maintaining lane position and keeping to the path of the curve when driving around curves. Further studies using similar assessment methods with drivers with more restricted fields are necessary to determine the minimum field extent for safe driving.