Most countries require that vision meets a pre-defined standard in order to be legally permitted to drive, but these standards vary widely. The primary method by which vision is assessed to determine suitability for driving is by measuring visual acuity (VA) and the most common minimum standard is binocular VA of 6/12 Snellen (0.3 logMAR). Most countries set visual field requirements as well, the most common of which is that visual field (VF) extends to 120 degrees horizontally. Additional assessments including colour vision, colour sensitivity and glare recovery are not frequently performed. Vision standards have been criticised as lacking an adequate evidence base. The authors of this study set out to examine the suitability of current vision screening standards to determine fitness to drive. Anonymised electronic medical records of 81,184 unique patients from 40 participating optometric practices were analysed. There was a high variability between uncorrected (UCVA) and corrected (CVA) visual acuity, a reflection of the refractive errors that affect individuals. Additionally, both UCVA and CVA deteriorate with age, especially from seventh decade onwards. An increasing proportion of measurements fell into borderline (0.2 to 0.4 logMAR in both eyes) or fail (worse than 0.4 logMAR) with increasing age. Increasing time since initial optometric visit was found to negatively affect the likelihood of passing at subsequent visits. A recent meta-analysis observed a 46% increased risk of traffic accidents in those with VA of 6/18 or worse. The authors of this study conclude that the most commonly used VA threshold of 0.3 logMAR excludes a small minority of potential drivers. Up to 99% of potential drivers can comfortably be expected to pass this standard for driving. Other countries with more stringent VA standards would exclude a higher percentage of people from driving, and potentially introduce a bias against the more elderly population, in which VA deteriorates as discussed above. Furthermore, the frequency of driver vision screening assessments appears to be inappropriately long for younger drivers as there appears to be a reduction of 0.022 logMAR vision per year, i.e., loss of approximately two to three lines of VA without correction over a 10-year licence renewal period. The current standards where repeat assessment are only required at an age of 70 years and older would fail to detect such drivers. Commonly this would be due to need to update refraction.
Vision screening standards for fitness to drive
Reviewed by Kurt Spiteri Cornish
Big data analysis of vision screening standards used to evaluate fitness to drive.
CONTRIBUTOR
Kurt Spiteri Cornish
Sheffield Teaching Hospitals NHS Trust, London, UK.
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