Mesopic contrast sensitivity in the presence or absence of glare in a large driver population

Background: To evaluate mesopic contrast sensitivity in conditions of glare and no glare in a vehicle driver population, and to explore the effects of age, habitual spectacle correction, photopic visual acuity and driving exposure. Methods: A cross-sectional study was performed on 297 drivers stratified by age into six groups. The mesopic contrast sensitivity was measured in the absence or presence of glare using the Mesotest II (Oculus, Germany) in each subject both with habitual and best spectacle correction. A questionnaire on the subject's driving habits was completed. Results: There were no significant differences between contrast sensitivity measured with habitual or best spectacle correction. In conditions of no glare, the mesopic contrast sensitivity gradually got worse from 51 to 60 years onwards, and from 41 to 50 years onwards in the presence of glare. In both conditions, the total decrease in contrast sensitivity was 0.3 log units. The with-glare and without-glare mesopic contrast sensitivity improved as photopic visual acuity increased. Forty-five per cent of drivers who reported difficulties in driving at night were unable to perform any of the tests with glare, compared to 20% without glare. However, the effect of driving habits on contrast sensitivity was only significant in the oldest age group. Conclusions: The mesopic contrast sensitivity and glare sensitivity seem to be stable until the age of 50 years, from which point they start to decline at a rate of 0.1 log contrast sensitivity loss per decade. Drivers with poor visual acuity and/ or older drivers who avoided night driving presented worse mesopic contrast sensitivity and greater glare sensitivity.