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Editors Selection IGR 11-2

Quality of Life: Risk factors for motor vehicle collision involvement

Comment by George Lambrou on:

22614 Visual and medical risk factors for motor vehicle collision involvement among older drivers, Cross JM; McGwin G Jr; Rubin GS et al., British Journal of Ophthalmology, 2009; 93: 400-404

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Do eye diseases and, more specifically, visual impairment have a direct impact on the ability to drive safely? Most of us would probably give an affirmative answer to that question, based on our intuitive assumption that 'better vision implies better driving skills' and by the fact that in most countries a vision test is mandatory in order to obtain and maintain a driver's license. But is that really so? Can one really infer that drivers with a significantly (though not dismally) reduced visual acuity are taking risks with their own and other people's safety? And what about drivers with reduced contrast sensitivity? Or those with cataracts? Or those with glaucoma? Most of us would refrain from a clear Yes or No and would use conditional statements or, more wisely, would turn to cohort studies for evidence. Cross et al. (480) provide a pooled-data analysis from four such cohort studies of older drivers from three US states, conducted in the nineties. The actual outcome parameter was not driving skills per se, but involvement in Motor Vehicle Collision (MVC) either at-fault or not. The total number of enrolled drivers was 3158 (with a majority of 2037 from the single Maryland cohort), with a mean age of 72 years and a male:female ratio of 48:52. The analysis looked at the risk ratios for the association between various medical (non-ocular and ocular/visual) characteristics and MVC involvement. With respect to eye diseases, there was no significant association between any of the conditions examined (cataract, glaucoma, macular degeneration and diabetic retinopathy) and any type of MVC. The overall prevalence of these conditions was 36.9%, 7.9%, 2.8% and 3.1% respectively ‐ very close to the prevalence in the ageing general population. More interestingly, there was no significant association between binocular visual acuity and MVC involvement. Vision worse than 20/20 but better than 20/40 had no impact whatsoever, whereas vision levels below 20/40 were mildly but not significantly linked to MVC involvement. Similarly, there was no hint of an association between MVCs and reduced contrast sensitivity. The one visual parameter that significantly increased the risk ratio of MVC was the UFOV or Useful Field of View, a concept that takes into account visual processing speed and higher-order processing skills, such as divided visual attention. Performance on this test is a function of: (1) the minimum target duration required to perform a central discrimination task, (2) the ability to divide attention between central and peripheral visual tasks, and (3) the ability to filter out distracting stimuli.

We may be using the wrong visual tests for granting driving licenses

The take-home message of this pooled-data analysis with respect to visual disturbances is that we may be using the wrong visual tests for granting driving licenses. In the light of these and other findings, a serious need seems to exist for evidence-based research to develop a battery of vision tests able to identify high-risk drivers. Although this was not discussed in the present paper, visual field testing is likely to be one of this battery of tests.

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