Myopia and natural lighting extremes: risk factors in Finnish army conscripts.

PURPOSE To establish whether features of environmental lighting in far northern latitudes might be associated with prevalence of myopia. METHODS Using both questionnaires and military medical examinations, this cross-sectional survey of Finnish conscripts assessed both light exposure and conventional risk factors for myopia. RESULTS While myopia was not associated with the month of birth, there was a trend towards a higher prevalence of myopia among conscripts living above the Arctic Circle, consistent with the hypothesis that ambient lighting might influence refractive development. Other novel associations with myopia were decreased sunglasses use and brown iris colour. As indicated by other reports, myopia was found to be associated with family history, education and nearwork. CONCLUSION Although constraints inherent in surveying this military population may have limited our ability to detect associations, the positive findings suggest that studying northern populations may prove useful in clarifying any potential role of the light/dark cycle in refractive development.