To better understand the visual deficits that can lead to car accidents, particularly in the elderly, researchers recently examined driving tasks in a study using methods that measured real-time, on-road circumstances. In-car instrumentation can objectively measure crashes and near crashes as they occur on the road using video and vehicle motion data.

This prospective cohort study was conducted from 2015 to 2018 among 154 adults 70 years of age or older who were legally licensed in Alabama and reported currently driving at least four days per week, with over 90% of the participants having an age-related eye condition in at least one eye. Drivers participated in a baseline visual function assessment followed by installation of a data acquisition system with video recording in their vehicle. They were instructed to drive for six months as they normally would during everyday life.

Visual functions associated with crash and near-crash involvement included impaired contrast sensitivity with a rate ratio (RR) of 5.0, moderate with a RR of 2.3 and severe with a RR of 5.0 slowing in visual processing speed, and elevated motion perception thresholds for a drifting grating with a RR of 1.9. Those with impaired peripheral visual field sensitivity had increased rates of crashes and near crashes. However, this finding was not statistically significant.

The authors noted that the visual risk factors found— impaired contrast sensitivity, slowed visual processing speed and impaired motion—were linked with motor vehicle crash reports in previous studies.

“Both moderate and severe slowing in visual processing speed elevated collision risk for older drivers, agreeing with accident report research,” the authors explained in their study. “This finding is also reflective of studies on driving performance problems among older adults for whom slowed processing speed is associated with performance errors.” Contrast sensitivity impairment was also associated with crash and near-crash involvement, they noted. Relative inability to discern object movement was also implicated, a finding “consistent with previous research identifying motion perception impairment as associated with driving performance problems among older adults.”

Lastly, the authors noted this “naturalistic” driving study is distinct from previous studies that used near crashes as a surrogate measure, “because they are impossible to examine in motor vehicle crash report studies.”

“Near crashes and crashes have similar causal mechanisms, yet they have different safety outcomes because of the rapid evasive maneuver of a near crash,” the authors explained. “In the present study, near crashes occurred at approximately twice the rate of crashes.”