Vision impairment and traffic safety outcomes in LMICs
Authors: Alain Chichom-Mefire
Journal: The Lancet Global Health (2021)

Vision is generally considered to be the most important sensory ability for safe driving. The legislation of most countries globally imposes visual assessment for all candidates for a driving licence. In high-income countries, specific regulations that are inspired by apparently objective and frequently updated criteria are developed and implemented to guide the assessment of fitness to drive as a holistic and legal concept.1Charman WN Vision and driving—a literature review and commentary.Ophthalmic Physiol Opt. 1997; 17: 371-391PubMed Google Scholar, 2Mérour A Favrat B Borruat FX Pasche C Exigences visuelles pour la conduite: y voir plus clair.Rev Med Suisse. 2014; 10 (2256–57 (in French).): 2252-2254PubMed Google Scholar, 3Detry-Morel M Aptitude visuelle àla conduite d'un véhicule.Bull Soc Belge Ophtalmol. 2004; 291 (in French).: 5-15Google Scholar However, the proportion of drivers in many low-income and middle-income countries (LMICs), including those drivers involved in transportation of the public in large numbers, who are still able to secure a driving licence without ever having their vision assessed might seem shocking4Vofo BN Ayuk DA Pe'er J Chichom-Mefire A Tendongfor N Nche EN Visual assessment of commercial drivers in the South West Region of Cameroon.BMC Ophthalmol. 2021; 21: 148Crossref PubMed Scopus (1) Google Scholar, 5Pepple G Adio A Visual function of drivers and its relationship to road traffic accidents in Urban Africa.Springerplus. 2014; 3: 47Crossref PubMed Scopus (14) Google Scholar and reveals challenges in law implementation. Paradoxically, it is observed that these shortcomings do not necessarily translate into a higher proportion of drivers with visual defects and the methods to assess visual function of drivers needs to be revisited. Several studies have attempted to estimate the proportion of drivers with visual defects in all settings and some often attempt to associate the presence of such defects with the risk of occurrence of road traffic crashes.4Vofo BN Ayuk DA Pe'er J Chichom-Mefire A Tendongfor N Nche EN Visual assessment of commercial drivers in the South West Region of Cameroon.BMC Ophthalmol. 2021; 21: 148Crossref PubMed Scopus (1) Google Scholar, 5Pepple G Adio A Visual function of drivers and its relationship to road traffic accidents in Urban Africa.Springerplus. 2014; 3: 47Crossref PubMed Scopus (14) Google Scholar, 6Boadi-Kusi SB Kyei S Asare FA Owusu-Ansah A Awuah A Darko-Takyi C Visual function among commercial vehicle drivers in the central region of Ghana.J Optom. 2016; 9: 54-63Crossref PubMed Scopus (8) Google Scholar The Article by Prabhath Piyasena and colleagues in The Lancet Global Health is an interesting overview of the problem, specifically in LMICs, with a focus on the prevalence of visual defects, adherence to visual parameters included in driving licensure requirements, and the possible association with the risk of poor driving outcomes.7Piyasena P Olvera-Herrera VO Chan VF et al.Vision impairment and traffic safety outcomes in low-income and middle-income countries: a systematic review and meta-analysis.Lancet Glob Health. 2021; 9: e1411-e1422Summary Full Text Full Text PDF PubMed Scopus (3) Google Scholar The systematic review and meta-analysis of 15 394 participants (mean age 39·3 years [SD 9·65]; 1167 [7·6%] of 15 279 female) found that the prevalence of vision impairment among road users ranged from 1·2% to 26·4%, colour vision defects from 0·5% to 17·1%, and visual field defects from 2·0% to 37·3%. The meta-analysis revealed a 46% greater risk of having a road traffic crash among those with central acuity visual impairment (risk ratio [RR] 1·46 [95% CI 1·20–1·78]; p=0·0002) and a greater risk among those with colour vision defects (RR 1·36 [1·01–1·82]; p=0·041) or defects of the visual field (RR 1·36 [1·25–1·48]; p<0·0001). It also shows a poor adherence to licensure requirements.7Piyasena P Olvera-Herrera VO Chan VF et al.Vision impairment and traffic safety outcomes in low-income and middle-income countries: a systematic review and meta-analysis.Lancet Glob Health. 2021; 9: e1411-e1422Summary Full Text Full Text PDF PubMed Scopus (3) Google Scholar Assessment of vision as a component of fitness to drive is historically based on perceptual parameters ranging from the most basic—ie, visual acuity, colour vision, and visual fields—to more specific ones such as stereopsis (the ability to appreciate depth), contrast sensitivity, and peripheral vision. Such parameters play an important role in safe driving. For example, poor colour vision might result in poor interpretation of road signs and traffic lights exposing the individual to a greater risk of driving errors. Stereopsis could be of great importance in assessing distances in some driving situations such as overtaking or change of lane. However, it is still difficult to associate abnormalities of these parameters with the risk of adverse events while driving. Driving should not be viewed as a function of vision as a sensorial perception but rather a multifactorial and multifunctional competence, with necessity for assessing and adjusting to orientation, navigation, estimation of distances, and scanning of the environment. Other competencies that partly use visual function include more judgment-based situations such as giving way or adjustment of speed. Perceptual parameters often show age-dependent differences. However, although older drivers might have more visual defects and more visual defects lead to more crashes, younger drivers still have more crashes for other reasons.1Charman WN Vision and driving—a literature review and commentary.Ophthalmic Physiol Opt. 1997; 17: 371-391PubMed Google Scholar Consequently, relying on these tests to determine fitness to drive might result in other consequences, including the unfair disqualification of many safe drivers. The current parameters assess vision as an isolated sensory function rather than a component of cognitive function as a whole. The challenge is to develop a test or group of tests capable of clearly identifying driving licence candidates with visual defects associated with a higher risk of traffic-related incidents. Some reports have attempted to compare these perceptual visual parameters to the more holistic concept of visual attention, which combines the two aspects with psychometric performance and is anticipated to be more discriminative.8Grundler W Strasburger H Visual attention outperforms visual-perceptual parameters required by law as an indicator of on-road driving performance.PLoS One. 2020; 15e0236147Crossref PubMed Scopus (4) Google Scholar, 9Kotecha A Spratt A Viswanathan A Visual function and fitness to drive.Br Med Bull. 2008; 87: 163-174Crossref PubMed Scopus (23) Google Scholar The main challenge of this approach might be its feasibility and the potential for its conversion into driving prerequisites and legal dispositions. I appreciate that the authors of this Article highlight the absence of randomised trials assessing the effect of interventions to improve vision on traffic outcomes. In the absence of such trials, the relevance of any approach to assess vision as a driving requirement will lack objectivity. However, current available data summarised in the report suggest that ensuring accurate and systematic assessment of perceptive visual parameters of candidates for driving licences during initial application and renewal in all LMICs could be a good starting point. I declare no competing interests. Vision impairment and traffic safety outcomes in low-income and middle-income countries: a systematic review and meta-analysisThis systematic review shows a positive association between vision impairment and traffic crashes in LMICs. Our findings provide support for mandatory vision function assessment before issuing a driving licence. Full-Text PDF Open Access