Are our legal visual requirements for driving adequate?

Prevention of road traffic accidents (RTAs) is a public health priority issue in Oman. It is proposed that the lack of strict driving license policy may be one aspect contributing to this problem.[1] Human error was found to be the main cause of these collisions.[1] Vision is an indisputable factor in this human error. Many visual tests for drivers are inadequate, often failing to stimulate the distractions and wide-ranging contrasts and luminance levels experienced in real-world road conditions.[2] Many drivers delay or avoid seeking evaluation and treatment for vision issues.[3] This begs the question; are the current visual requirements and screening tests for obtaining and maintaining an Omani driver's license adequate? Visual acuity (VA) testing is the most common functional method for determining eligibility for licensure worldwide. It is the only screening test of visual function that forms the foundation of the current Omani drivers licensing requirement. The Directorate General of Traffic at the Royal Oman Police require a best-corrected VA of 6/6 in at least one eye for standard private licensure and at least 6/12 in each eye for the commercial licenses. Some variation exists across countries with the cutoff values for vision, but most require drivers of private vehicles to meet a standard cutoff of 6/12 in the better eye or both eyes tested together. This is more stringent for commercial drivers with a minimum VA of 6/9 in the better eye as a common requirement and restrictions on the VA in the weaker eye.[4] However, there is little to no evidence that this screening test, no matter which pass-fail cutpoint is selected, enhances driver safety and performance. This is not surprising, as the ability to resolve detail is important for particular VA-related driving skills such as road signage recognition for route planning or complying with “rules of the road” rather than safe operation of a vehicle or for collision avoidance. Since VA was designed solely for eye heath diagnostic and monitoring purposes, it does not and should not truly reflect the complexity of driving.[2] Visual field (VF) screening is mandated by many other countries but not in Oman. Requirements vary in both the extent considered compatible with safe driving and the methods for testing. Horizontal field requirements range from 110° to 150° binocular fields with or without a minimum vertical extent of 20°–40° above and below fixation.[4] Methods range from confrontation to perimetry, most commonly the Estermann VF test which is the preferred method of assessment in the UK, Australia, and Canada. It is a binocular supra-threshold test considered important for driving and is fast to perform. Their recommendation is no significant defect within the central 20°.[5] Merging the two monocular fields to form an integrated VF has also been shown to be useful in assessing fitness to drive.[67] A more reliable test identified recently is the useful field of vision test. It assesses total VF area in which useful information can be acquired without eye and head movements.[8] The current literature suggests that severe VF impairments are associated with an increased RTA risk but the impact of mild to moderate VF loss is less clear.[4] Hemianopic and quadrantanopic defects are considered unacceptable for driving by many jurisdictions, despite the lack of clear evidence that all drivers with these defects are unsafe to drive. Individuals with long-standing defects may develop effective adaptive strategies over time through improvements in eye and head movements but this compensation is variable.[2] The impact of binocular vision disorders and driver safety is unknown, but some countries such as Australia and Canada require drivers to have no diplopia inside the central 40° (within 20° of the primary direction of gaze). A restricted license may be considered if the diplopia is controlled for at least 3 months (either by spectacles or occlusion) or is chronic (i.e., ≥6 months) and stable with proof of satisfactory functional adaptation. Other countries require no diplopia within the 120° field of vision.[9] Color vision is tested at the license applications for drivers in majority of the USA. Although there is no evidence that color deficiency by itself increases crash risk, in some circumstances, it may impact the performance of interpreting traffic control devices and signals, especially if other cues (e.g., pattern and position) are insufficiently informative.[2] In the event of acute monocular status, an adaptation period of 6 months is considered necessary in some jurisdictions. Other aspects of vision suggested to predict driver safety include contrast sensitivity, motion perception, and disability glare. No such requirements are listed in any jurisdiction as of yet, since the literature surrounding them are not extensive.[2] As people age, visual deficits become common. Although age is not a reliable predictor of driving safety, physical, and cognitive changes may affect driving safety over time.[10] Therefore, some jurisdictions have tightened license renewal requirements for older drivers and many others are considering similar options. Regulations to be considered may include frequent vision testing, increase the frequency of licensure renewal cycles, on-the-road driving evaluation at renewals, and the need for an ophthalmologist approval. Reporting laws should be in place to obligate health-care providers to report unsafe drivers to the local licensing authorities as it is in the public interest to do so. Unfortunately, what we currently rely upon in the country is drivers to self-declare their vision problems to the authorities or make their own decision for cessation of driving or modifying their driving habits. This can be problematic and relies on public awareness, which is limited. What we lack are clear national guidelines governing the visual assessment of fitness to drive. Since vision is necessary but insufficient for safe driving, there is growing evidence that multi-domain tests may be more relevant. It is imperative that we, as visual health-care professionals, address vision problems that may impact driving, prioritize, and uphold their visual standards as well as help policy-makers develop and implement changes to the current driving regulations. All this while trying to individualize assessments and risk prediction to ensure fairness in preservation of both individual autonomy and public safety.

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