Eyesight and Driving

Eyesight and Driving

How Effective?

The Eyesight Test

  • The main methods of assessing whether a driver’s vision meets accepted safety standards, and of preventing those drivers whose vision fails to meet these standards from driving are the minimum legal eyesight standards and the eyesight test in the Driving Test. The UK eyesight standards and test are described above.

  • However, many of the research studies have found that some drivers who pass the vision test still exhibit impaired driving due to poor eyesight. For example, drivers’ ability to see and respond to pedestrians at night was degraded by modest but common visual impairments, even when their visual acuity met the standard for driver licensing. (Chu et al, 2010) Moderate levels of simulated cataract slowed drivers' ability to detect and anticipate traffic hazards, despite the fact that their vision still complied with the minimum legal standard required for driving. (Marrington, 2008)

  • The 2010 literature review of the role of vision in driving identified many studies indicating that visual acuity is very weakly linked to crash risk and is a poor screening test for identifying drivers who are at-risk. However, it reasoned that visual acuity is related to certain aspects of driving performance (e.g., road sign recognition) and licensing authorities are unlikely to give up visual acuity screening tests. (Owsley and McGwin, 2010)

  • The authors suggested that a more practical approach to improving the efficacy of vision screening is to examine how current tests could be supplemented by other types of screening approaches, like contrast sensitivity, visual field, processing speed, and divided attention tests, some of which have a large evidence-basis for their relevance to driver safety. (Owsley and McGwin, 2010)

  • The Optical Confederation in the UK (a coalition of Opticians, Contact Lens Manufacturers, Optometrists, Manufacturing Opticians, and Ophthalmists) believe that the Number Plate Test is an unfair and unreliable test of visual acuity, and is not comparable to the Snellen standards required by the EU Directive or by the UK law. They are also concerned about the variability of the Test caused by differing lighting and weather conditions or by the examiner’s estimate of 20 metres. The Optical Confederation, therefore, believes that the Number Plate test should be replaced with a proper assessment of visual acuity performed under controlled conditions. (Optical Federation, 2011)

  • Several studies suggest that incorporating a Useful Field of Vision test would make the driver’s eyesight test more effective at identifying drivers whose vision is not good enough for driving. A meta-analysis of eight studies that reported relationships between UFOV and driving performance concluded that the evidence confirms that the UFOV assessment is a valid and reliable index of driving and safety. (Clay et al, 2005)

  • An Australian study of older drivers who were rated as higher risk on the UFOV test, suggested that the selective attention subtest of the UFOV may be more effective in predicting driving difficulties in situations of divided attention. (Wood et al, 2012) A 2002 Australian study concluded that motion sensitivity and the UFOV tests significantly improve the predictive power of vision tests for driving performance. It added that although such measures may not be practical for widespread screening, their application in selected cases should be considered.

  • A UK study compared the results of the Snellen test with those of the number plate test for 100 Ophthalmology outpatients with 6/9 vision or 6/12 vision. It found that 26% of patients with 6/9 vision failed the number plate test, but 34% of patients with 6/12 vision passed the number plate test. (Currie et al, 2000)

  • It also found uncertainty among eye health professionals in deciding which patients should be advised not to drive. 76% of GPs advised patients with 6/9 vision that they could drive, 13% said they should not drive, and 11% were unsure. 21% said patients with 6/12 vision could drive, 54% said they should not drive, and 25% were unsure. (Currie et al, 2000)

  • The level of acuity at which optometrists, opticians, and ophthalmologists would advise drivers against driving ranged from 6/9−2 (ability to read all except two letters on the 6/9 line of the Snellen chart) to less than 6/18. The report concluded that Snellen acuity is a poor predictor of an individual's ability to meet the required visual standard for driving. (Currie et al, 2000)

Individual Driving Assessments

  • Several studies suggest that their findings of the problems caused by vision impairments, and ways of compensating for some of these (for example, head movements) should be used to inform driver training programmes. (Wood et al 2011, Parker et al 2011, Owsley and McGwin 2010, Elgin et al 2010)

  • A review of 131 patients with visual field loss who had taken an on-road driving assessment showed that some with visual field loss were rated as “safe” during on-road driving assessments, and that it is difficult to predict whether a patient with a visual field defect will be able to drive safely based on the extent and location of the deficit. It highlighted the need for individual on-road assessments for patients with visual field defects. (Racette and Casson, 2005)

Driver Adaptations

  • Research also shows that drivers make adaptations to compensate for their impaired vision, most typically by wearing corrective spectacles or contact lenses (although the effects of these vary as discussed above), by making more head and shoulder movements, by avoiding driving at night and ultimately by stopping driving altogether. Also, as discussed above, cataract surgery is effective at returning a driver’s vision, and their driving, to the standard of drivers with good vision.

  • Analysis of data from a cohort study of 2,520 older adults followed over 8 years with data collected every two years indicated that older drivers who achieved worse scores at the start of the study in visual acuity, contrast sensitivity, and central or lower peripheral visual fields were more likely to stop driving. Those who experienced 2-year losses in acuity, contrast sensitivity, or lower peripheral visual fields were more likely to stop driving. (Freeman et al, 2005)

Other Approaches

  • One study suggested that there are possible consequences for road design and that creating high contrast driving environments may improve hazard detection for those with poor contrast sensitivity. (Marrington et al, 2008)

 

  • Date Added: 14 Mar 2013, 11:55 AM
  • Last Update: 26 Jan 2017, 04:31 PM