Relationship between night myopia and night-time motor vehicle accidents

Purpose: To investigate the relationship between night myopia and the occurrence of night-time motor vehicle accidents in a group of professional drivers. Methods: We examined 136 professional drivers. Refraction was determined in full illumination (100 cd/m(2)) and after sitting in darkness for 5 mins. The change in refraction, indicative of night myopia, was correlated with the number of motor vehicle accidents in which each driver was involved (detailed in their personal files) and with the results of a visual complaints questionnaire. Results: The mean age of the study group was 21.0 years. Mean spherical refraction changed from + 0.11 dioptres (D) in light to - 0.17 D after dark adaptation for 5 mins. Night myopia was found in 34 drivers (25%), at a mean of - 1.2 D (range - 0.75 D to - 3.50 D). There was no statistically significant difference between these drivers and the rest of the group in the results of the visual complaints questionnaire, or in the number of accidents occurring during the day. However, drivers with a myopic shift > 0.75 D were involved in more accidents at night than the rest of the group (p = 0.044). Conclusions: In this study population, drivers with night myopia of > 0.75 D were more likely to be involved in night-time accidents. This may imply that selected groups of drivers should be examined for night myopia.