title: The prevalence and causes of visual impairment in Tehran: the Tehran Eye Study.
abstract: OBJECTIVE
  To determine the prevalence and causes of visual impairment in Tehran, Iran, through a population based study.
  
  
  METHODS
  In a population based, cross sectional study, 6497 Tehran citizens were sampled from 160 clusters using a stratified, random, cluster sampling strategy. The eligible people were enumerated through a door to door household survey in the selected clusters and were invited. All participants were transferred to a clinic for an extensive eye examination and interview. Visual impairment was determined using presenting and best corrected visual acuity (low vision: visual acuity of less than 6/18 to 3/60 in the better eye; blindness: visual acuity of less than 3/60 in the better eye).
  
  
  RESULTS
  Of those sampled, 4565 (70.3%) people participated in the study. The age and sex standardised prevalences of visual impairment on the basis of best corrected and presenting visual acuity were 1.39% (95% confidence interval (CI), 1.07 to 1.71) and 2.52% (95% CI, 2.07 to 2.97), respectively. 15 people (0.28%; 95% CI, 0.14 to 0.42) were blind with corrected vision while 22 (0.39%; 95% CI, 0.23 to 0.56) were blind with presenting vision. Using the corrected and presenting vision, the prevalence of low visual impairment was 1.11% (95% CI, 0.84 to 1.39) and 2.13% (95% CI, 1.71 to 2.55), respectively. The causes of visual impairment according to the best corrected vision were cataract (36.0%), macular degeneration (20.0%), and amblyopia (10.7%). However, according to the presenting vision, uncorrected refractive errors were the most frequent primary cause (33.6%) and cataract (25.4%), macular degeneration (12.7%), and amblyopia (8.2%) were the other main causes of visual impairment in the study sample. The prevalence of visual impairment was associated with advancing age and lower education.
  
  
  CONCLUSIONS
  The results indicate that the burden of visual impairment is important and, although easily preventable, uncorrected refractive errors and cataract have a major role as causes of visual impairment in this population. Results also highlight the need for visual impairment prevention programmes, with emphasis on treatment of refractive errors and cataract.
authors.affiliation: Epidemiology and Biostatistics Department, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran. afotouhi@sina.tums.ac.ir
authors.forename: A
authors.initials: A
authors.lastname: Fotouhi
authors.forename: H
authors.initials: H
authors.lastname: Hashemi
authors.forename: K
authors.initials: K
authors.lastname: Mohammad
authors.forename: K H
authors.initials: KH
authors.lastname: Jalali
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000550:Amblyopia / Q000150:complications; D002386:Cataract / Q000150:complications; D002648:Child; D002675:Child, Preschool; D016000:Cluster Analysis; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007223:Infant; D007492:Iran / Q000453:epidemiology; D008268:Macular Degeneration / Q000150:complications; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D014786:Vision Disorders / Q000453:epidemiology* / Q000209:etiology