Binocular visual field loss and motor vehicle crash frequency and severity: A generalized structural equation modeling study using linked data

Introduction Previous research has demonstrated an association between visual field loss (VFL) and motor vehicle crashes, however, the direct and indirect effects of demographic and clinical factors, including VFL, on crash frequency and severity remain poorly understood. Method A database of visual field tests obtained from Ophthalmologists in Western Australia was linked to population-based crash and health datasets (1990-2019). A generalized structural equation model (GSEM) was used to examine the direct and indirect effects of demographic and clinical factors on crash frequency and severity among crash-involved drivers. Results A total of 4307 (13.76%) older adults aged 50+ years were involved in 5537 crashes, of whom 55.84% had binocular VFL. Among crash-involved drivers, binocular VFL was directly associated with a 3% higher crash frequency (IRR = 1.03, β = 0.03, 95% CI: 0.01 to 0.07) but not crash severity (OR = 1.01, logit = 0.01, 95% CI: −0.12 to 0.15). Female sex (IRR = 0.95, β = −0.05, 95% CI: −0.08 to −0.03) and previous cataract surgery (IRR = 0.96, β = −0.04, 95% CI: −0.08 to −0.01) were directly associated with lower crash frequency. Older age (70+ years) was indirectly associated with increased crash frequency through VFL, whereas female sex was indirectly associated with lower crash frequency through binocular VFL. Binocular VFL was not directly or indirectly associated with crash severity, which was primarily explained by crash type (OR = 2.40, logit = 0.87, 95% CI: 0.59 to 1.13). Conclusions Binocular VFL was associated with increased crash frequency but not crash severity among older crash-involved drivers. VFL also acted as a pathway through which demographic factors influenced crash frequency. These findings support consideration of objective visual field assessment as part of fitness-to-drive evaluations and suggest that strategies to reduce crash severity should focus on factors beyond visual impairment.