title: Refractive, biometric and topographic changes among Portuguese university science students: a 3-year longitudinal study.
abstract: OBJECTIVE
  The aim of this study was to investigate the changes in refractive, biometric and topographic ocular parameters among university students in Portugal during a 3-year period.
  
  
  METHODS
  A 3-year longitudinal study comprised 118 Portuguese university students from the School of Science (34 males and 84 females; mean age 20.6 +/- 2.3 years). Ocular refraction, corneal curvature (CR) and eccentricity, and A-scan biometry were conducted under cycloplegia. The sphero-cylindrical refractive results were converted into vector representations (M, J(0) and J(45)) for statistical analysis. Myopia was defined as M < or = -0.50 D, emmetropia as M > -0.50 D and < +0.50 D and hyperopia as M > or = +0.50 D.
  
  
  RESULTS
  At the beginning of the study sphero-cylindrical refraction (M) ranged from -6.75 to +3.00 D, with a mean value of 0.23 +/- 1.46 D [mean +/- standard deviation (S.D.)]. Eighty-three students presented astigmatism with a mean value (+/-S.D.) of -0.52 +/- 0.41 D, and a maximum of -2.25 D. After 3 years the mean refractive change for the M component was -0.29 +/- 0.38 D (p < 0.001) and non-significant changes of 0.02 +/- 0.16 D (p = 0.281) for the J(0) component and 0.01 +/- 0.09 D (p = 0.784) for the J(45) component. Prevalence of myopia increased by 5.1%, while the prevalence of hyperopia decreased by 9.4%. Myopia progression > or =0.5 D was observed in 22% of the population. Axial length, vitreous chamber depth and lens thickness increased significantly while anterior chamber depth and central CR did not change significantly.
  
  
  CONCLUSIONS
  This study shows a change in refraction towards myopia accompanied by a vitreous chamber elongation in a Portuguese population comprising science students during the first three years of their university course. Younger students were more likely to show clinically significant myopia progression.
authors.affiliation: Department of Physics (Optometry), School of Sciences, University of Minho, Campus de Gualtar, Braga, Portugal. jorge@fisica.uminho.pt
authors.forename: J
authors.initials: J
authors.lastname: Jorge
authors.forename: J B
authors.initials: JB
authors.lastname: Almeida
authors.forename: M A
authors.initials: MA
authors.lastname: Parafita
mesh_terms: D000328:Adult; D003315:Cornea / Q000502:physiology*; D018450:Disease Progression; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D009216:Myopia / Q000175:diagnosis*; D011174:Portugal / Q000453:epidemiology; D012029:Refraction, Ocular / Q000502:physiology*; D012030:Refractive Errors / Q000175:diagnosis*