Inability of the Mini-Mental State Exam (MMSE) and high-contrast visual acuity to identify unsafe drivers

To examine the validity of high-contrast visual acuity and the Mini-Mental State Exam (MMSE) as tools for identifying at-risk older drivers.

Prospective multi-site observational cohort study.

Community sample drawn from cities of Brisbane and Canberra, Australia.

560 licensed drivers aged 65-96 years recruited between 2013 and 2016, from the community, an optometry clinic and driver referral service.

50-minute standardized on-road driving test conducted on a standard urban route in a dual-brake vehicle with a driver trained Occupational Therapist assessor masked to participants' cognitive, visual and medical status.

Of 560 participants who completed the on-road test, 68 (12%) were classified as unsafe. Binary logistic regression models adjusted for age, gender, site, comorbidity and driving exposure indicated that a 1-point decrease in MMSE score was associated with a 1.35 (95%CI: 1.12-1.63) increase in odds of unsafe driving, and for each line reduction in binocular visual acuity (increase of 0.1 logMAR) was associated with 1.39 (95%CI: 1.07-1.81) increased odds of unsafe driving. However, Receiver Operating Characteristic (ROC) analysis showed low discriminative power for both measures (MMSE: AUC = 0.65 (95%CI: 0.58-0.73), visual acuity: AUC = 0.65 (95%CI: 0.59-0.72)) and typical cut-offs were associated with very low sensitivity for identifying unsafe drivers (MMSE <24/30: 2%; visual acuity worse than 6/12 Snellen (logMAR >0.30): 3%).

The MMSE and high-contrast visual acuity tests do not reliably identify at-risk older drivers. They have extremely low sensitivity for detecting unsafe drivers, even when used together, and poor prognostic properties relative to validated screening instruments that measure cognitive, vision and sensorimotor functions relevant to driving. Clinicians should select alternate validated driver screening tools where possible.