Prevalence of myopia in Danish conscripts

Purpose: This study aimed to determine the prevalence of myopia among Danish conscripts and compare the results with those from similar Danish studies carried out in 1882 and 1964. Furthermore, the relationships between myopia and educational level, ethnicity, intelligence (IQ), body mass index (BMI) and height were analysed. Methods: We carried out a cross-sectional study based on medical reports for 4681 male conscripts. The following data were collected from September to December 2004: age; place of birth; weight; height; power of spectacles or contact lenses; visual acuity; number of years at school (8-13 years); occupation; intelligence test (IQ test) score, and ethnicity. Results: The prevalence of myopia (<= - 0.5 D, spherical equivalent) was 12.8% (95% confidence interval [CI] +/- 0.96); the prevalence of high myopia (< - 6.5 D) was 0.3% (95% CI +/- 0.15). Myopes scored higher (45.3 [SD 9.4]) on IQ tests than emmetropes (41.4 [SD 10.4]) (p < 0.001) and had a higher educational level. No relationship was found between myopia and BMI, height or ethnicity. Conclusions: The study reports a significantly decreasing prevalence of low myopia among Danish conscripts in 2004 compared with 1964. Compared with the results from the 1882 study, the prevalence of low myopia seems stable. The prevalence of high myopia has decreased significantly since 1882 and has also tended to decrease from 1964. Number of years in education and IQ test score were related to myopia.