Myopia prevalence in Denmark - a review of 140 years of myopia research.

PURPOSE: To evaluate potential changes in myopia prevalence in Denmark by revising more than 100 years of myopia research. METHODS: A systematic literature search was performed in the PubMed, Embase and Cochrane Library databases. Only studies reporting a myopia prevalence in Denmark were included. Myopia was defined using the definition in individual references. We did not restrict inclusion of studies to specific methods of measuring or evaluating refraction. As refraction changes throughout life, information from available studies was divided in relevant age groups. Chi-squared test was used when analysing the effect of sex and education on myopia prevalence except when the expected values were beneath 5, where Fisher's exact test was used. To further compare the effect of sex, we calculated the odds ratio of being myopic for females compared to males. RESULTS: We identified 29 Danish studies reporting on prevalence of myopia. The studies were performed between year 1882 and 2018. We found no strong evidence of an increase in myopia prevalence in Denmark. Increasing age was associated with an increased myopia prevalence up to the age of 60 years where after the prevalence decreased. Longer education and more intensive educational load were associated with myopia. Fourteen studies compared the prevalence of myopia between males and females and two of these studies found a significant higher prevalence in females. CONCLUSION: We evaluated nearly 140 years of myopia research in Denmark and did not find a convincing change in prevalence of myopia which is in contrast to the high prevalence of myopia reported in some parts of the world and the expected rise in myopia as predicted by WHO.