Purpose: To study whether physical activity has a protective effect on the development and progression of myopia in medical students.
Methods: In a 2-year longitudinal cohort study, 156 Caucasian first-year medical students from the University of Copenhagen were enrolled. The baseline examination included visual acuity, subjective refraction, Maddox Wing test (Clement Clarke International Ltd., Harlow, UK), partial coherence interferometry, slit lamp examination, automated refraction in cycloplegia, an oral questionnaire, and a cycle ergometer test. Measurements were repeated at the follow-up. A total of 151 (97%) participants completed the study.
Results: The prevalence of myopia (spherical equivalent [SE] <or= -0.5 D) increased from 37% (95% confidence interval [CI]: 29.1-44.9) to 43% (95% CI: 34.6-50.8, P < 0.001). The incidence rate of myopia was 6.1/100 person years of observation. The mean refractive error (SE) decreased from -0.50 (1.81) to -0.74 (1.95) D (P < 0.001), and the mean axial length increased from 23.81 (1.06) to 23.94 (1.09) mm (P < 0.001). In a multiple regression analysis, time spent reading scientific literature (P = 0.024) and younger age (P = 0.022) were associated with a refractive change toward myopia, whereas physical activity was inversely associated with a refractive change toward myopia (P = 0.015). Myopic eyes progressed significantly more than did emmetropic and hyperopic eyes (P = 0.002).
Conclusions: An association between physical activity and myopia was observed, suggesting a protective effect of physical activity on the development and progression of myopia in university students. The results confirm that intensive studying is a risk factor of myopia and that myopic progression or development is more likely in medical students in their early 20s than in their late 20s.