The Driving Visual Field and a History of Motor Vehicle Collision Involvement in Older Drivers: A Population-Based Examination

PURPOSE. We designed a visual field test focused on the field utilized while driving to examine associations between field impairment and motor vehicle collision involvement in 2000 drivers aged 70 years or older. METHODS. The "driving visual field test'' involved measuring light sensitivity for 20 targets in each eye, extending 15 degrees superiorly, 30 degrees inferiorly, 60 degrees temporally, and 30 degrees nasally. The target locations were selected on the basis that they fell within the field region utilized when viewing through the windshield of a vehicle or viewing the dashboard while driving. Monocular fields were combined into a binocular field based on the more sensitive point from each eye. Severe impairment in the overall field or a region was defined as average sensitivity in the lowest quartile of sensitivity. At-fault collision involvement for 5 years prior to enrollment was obtained from state records. Poisson regression was used to calculate crude and adjusted rate ratios (RRs) examining the association between field impairment and at-fault collision involvement. RESULTS. Drivers with severe binocular field impairment in the overall driving visual field had a 40% increased rate of at-fault collision involvement (RR, 1.40; 95% confidence interval [CI]: 1.07-1.83). Impairment in the lower and left fields was associated with elevated collision rates (RR, 1.40; 95% CI: 1.07-1.82 and RR, 1.49; 95% CI: 1.15-1.92, respectively), whereas impairment in the upper and right field regions was not. CONCLUSIONS. Results suggest that older drivers with severe impairment in the lower or left region of the driving visual field are more likely to have a history of at-fault collision involvement.