Despite years of experience on the road, older drivers are involved in car crashes nearly as often as young individuals, who have notoriously high crash rates. Research now suggests impaired contrast sensitivity may be part of the problem. When testing this theory, a team of investigators found that mesopic contrast sensitivity testing, but not photopic testing, may help predict future crash risk in older drivers.

This prospective, population-based study evaluated drivers who were at least 60 years old. In total, 844 participants underwent photopic contrast sensitivity testing and 854 underwent mesopic testing for targets from 1.5 to 18 cycles per degree. The team analyzed continuous driving data captured by vehicle sensors.

While photopic contrast sensitivity function and peak contrast sensitivity were not associated with crash rate, mesopic testing was.

“Results highlight a previously unappreciated association between older adults’ mesopic contrast sensitivity deficits and crash involvement regardless of the time of day,” the study authors wrote in their paper. “Given the wide variability of light levels encountered in both day and night driving, mesopic vision tests, with their reliance on both cone and rod vision, may be a more comprehensive assessment of the visual system’s ability to process the roadway environment.”