The effects of age and glare on driving

Abstract

Purpose: This study aimed to characterise the visual experience and visual competence of commercial drivers. The effects of age and glare on contrast sensitivity, useful field of view and driving performance were evaluated. Methods: In Experiment I, a cross-sectional study was carried out in Hong Kong for collecting the visual experience and studying the visual competence of current commercial drivers by conducting a personal interview and a vision assessment. In Experiments II to IV, three different groups of subjects were recruited from the Optometry Clinic, The Hong Kong Polytechnic University and were divided equally into two age groups, the younger group (20-29 years) and the older group (50-59 years). All subjects had visual acuity of 6/6 or better, were free from ocular structure abnormalities and any history of ocular injury and surgery. In Experiment II, they were investigated for the effect of glare on central and peripheral contrast sensitivity. In Experiment III, they were investigated for the effect of glare on the useful field of view. Different glare eccentricities were tested on contrast sensitivity and useful field of view. In Experiment IV, the driving performance of the subjects in the presence of glare was studied using a self-built driving simulator. The effects of age and its interaction with glare were also investigated. Results: In Experiment I, the awareness of regular eye checks among Hong Kong commercial drivers was found to be low. Tiredness, dry eye, glare intolerance, inadequate road lighting and crowded road signage were the most commonly encountered visual symptoms / difficulties reported by the commercial drivers at work. In Experiment II, peripheral contrast sensitivity was found to deteriorate in the presence of glare but the age was a factor only for central contrast sensitivity, with the older group showing worse contrast sensitivity (younger group: 1.44±0.18; older group: 1.27±0.24). In Experiment III, ageing did not affect the central processing speed in the useful field of view test. Both younger and older subjects had reduced ability to process the information in the divided attention subtest. There was also a selective deterioration of performance when the glare sources were closer to the peripheral task (Younger group: Control: 17.97±3.79 msec, Glare sources at 7.5°: 21.93±7.20 msec; Older group: Control: 31.00±19.99 msec, Glare sources at 7.5°: 59.50±43.97 msec). In the tests of selective attention where visual distracters were presented, the younger subjects demonstrated an improved useful field of view in the presence of glare at different eccentricities (Control: 81.90±32.41 msec; Glare sources at 2.5°: 54.97±40.61 msec; Glare sources at 5.0°: 50.00±35.05 msec; Glare sources at 7.5°: 50.07±17.79 msec), but this effect was not apparent in the older subjects except the glare sources at 2.5° (Control: 159.03±54.44 msec; Glare sources at 2.5°: 129.63±58.53 msec; Glare sources at 5.0°: 135.73±53.65 msec; Glare sources at 7.5°: 152.45±48.69 msec). Younger subjects had better performance than older subjects in both the divided attention and selective attention subtests of the useful field of view. In Experiment IV, different strategies (e.g. lower mean speed, lower mean speed before the road sign, decrease variation of lateral offset and longer completion time) in driving for compensating the glare condition were found in both older and younger drivers. Moreover, glare had significant influence on the reaction time of both older and younger drivers. Conclusion: Glare is a visual disturbance in driving causing a deterioration of contrast sensitivity and useful field of view, especially in middle-aged / elderly drivers. Compensatory strategies in driving are adopted by drivers to cope with this adverse condition while the critical effect of glare cannot be omitted from those younger drivers.