title: Five-year change in refraction and its ocular components in the 40- to 64-year-old population of the Shahroud eye cohort study.
abstract: BACKGROUND
  To assess 5-year refractive changes and their related factors in the 40- to 64-year-old population of Shahroud, Iran.
  
  
  METHODS
  Prospective cohort study.
  
  
  METHODS
  Of the 5190 participants of Phase I, 4737 participated in Phase II (response rate = 91.3%).
  
  
  METHODS
  Participants were tested by refraction, visual acuity, slit-lamp biomicroscopy, ophthalmoscopy and biometry. Myopia was defined as a spherical equivalent more negative than -0.5 dioptre (D) and hyperopia as a spherical equivalent more positive than +0.5 D.
  
  
  METHODS
  Mean 5-year change in spherical equivalent refraction.
  
  
  RESULTS
  The mean 5-year change in spherical equivalent refraction was +0.24 D (95% CI: +0.22 to +0.25). After 5 years, 4.77% (95% CI: 4.08 to 5.46) of subjects developed at least 0.5 D of myopia and 22.27% (95% CI: 20.97 to 23.57) developed at least 0.5 D of hyperopia. Five-year changes in refraction included a hyperopic shift in all age groups. The greatest hyperopic shift was seen in middle-aged women. The greatest loss of lens power was observed in hyperopic women and the least in myopic men. Nuclear cataract was associated with a myopic shift in refraction. The axial length and the corneal power had very small changes during this period. Myopes showed the greatest increase in axial length. Corneal power increased by a very small amount in all refractive groups.
  
  
  CONCLUSIONS
  The most important biometric index related to hyperopic shifts, which were greater in magnitude in women, was loss of lens power, whereas nuclear cataract was associated with myopic shifts.
authors.affiliation: Noor Research Center for Ophthalmic Epidemiology, Noor Eye Hospital, Tehran, Iran.
authors.forename: Hassan
authors.initials: H
authors.lastname: Hashemi
authors.affiliation: Noor Ophthalmology Research Center, Noor Eye Hospital, Tehran, Iran.
authors.forename: Mehdi
authors.initials: M
authors.lastname: Khabazkhoob
authors.affiliation: Department of Ophthalmology, Centro Médico San Luis, Buenos Aires, Argentina.
authors.forename: Rafael
authors.initials: R
authors.lastname: Iribarren
authors.affiliation: Department of Epidemiology, School of Public Health, Shahroud University of Medical Sciences, Shahroud, Iran.
authors.forename: Mohammad Hassan
authors.initials: MH
authors.lastname: Emamian
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Akbar
authors.initials: A
authors.lastname: Fotouhi
mesh_terms: D000328:Adult; D000375:Aging / Q000502:physiology; D001699:Biometry; D015331:Cohort Studies; D005260:Female; D006801:Humans; D006956:Hyperopia / Q000503:physiopathology*; D007492:Iran; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000503:physiopathology*; D009887:Ophthalmoscopy; D011446:Prospective Studies; D012029:Refraction, Ocular / Q000502:physiology*; D066167:Slit Lamp; D013997:Time Factors; D014786:Vision Disorders / Q000503:physiopathology*; D014792:Visual Acuity / Q000502:physiology*
keywords: adult; cohort study; ocular biometry; refractive errors