title: Does the level of physical activity in university students influence development and progression of myopia?--a 2-year prospective cohort study.
abstract: OBJECTIVE
  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.
authors.affiliation: Kennedy Center, National Eye Clinic, Hellerup, Denmark. njac@dadlnet.dk
authors.forename: Nina
authors.initials: N
authors.lastname: Jacobsen
authors.forename: Hanne
authors.initials: H
authors.lastname: Jensen
authors.forename: Ernst
authors.initials: E
authors.lastname: Goldschmidt
mesh_terms: D000328:Adult; D003718:Denmark; D018450:Disease Progression; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D005260:Female; D006801:Humans; D007368:Interferometry; D008297:Male; D009216:Myopia / Q000209:etiology / Q000503:physiopathology* / Q000517:prevention & control; D015995:Prevalence; D011446:Prospective Studies; D011932:Reading; D012029:Refraction, Ocular / Q000502:physiology; D012307:Risk Factors; D013337:Students, Medical; D011795:Surveys and Questionnaires; D014495:Universities; D014792:Visual Acuity / Q000502:physiology; D044465:White People