title: Prevalence of visual impairment and uncorrected refractive error - report from a Canadian urban population-based study.
abstract: OBJECTIVE
  The prevalence of visual impairment due to uncorrected refractive error has not been previously studied in Canada. A population-based study was conducted in Brantford, Ontario.
  
  
  METHODS
  The target population included all people 40 years of age and older. Study participants were selected using a randomized sampling strategy based on postal codes. Presenting distance and near visual acuities were measured with habitual spectacle correction, if any, in place. Best corrected visual acuities were determined for all participants who had a presenting distance visual acuity of less than 20/25.
  
  
  RESULTS
  Population weighted prevalence of distance visual impairment (visual acuity <20/40 in the better eye) was 2.7% (n = 768, 95% confidence interval (CI) 1.8-4.0%) with 71.8% correctable by refraction. Population weighted prevalence of near visual impairment (visual acuity <20/40 with both eyes) was 2.2% (95% CI 1.4-3.6) with 69.1% correctable by refraction. Multivariable adjusted analysis showed that the odds of having distance visual impairment was independently associated with increased age (odds ratio, OR, 3.56, 95% CI 1.22-10.35; ≥65 years compared to those 39-64 years), and time since last eye examination (OR 4.93, 95% CI 1.19-20.32; ≥5 years compared to ≤2 years). The same factors appear to be associated with increased prevalence of near visual impairment but were not statistically significant.
  
  
  CONCLUSIONS
  The majority of visual impairment found in Brantford was due to uncorrected refractive error. Factors that increased the prevalence of visual impairment were the same for distance and near visual acuity measurements.
authors.affiliation: School of Optometry, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada. robinson@uwaterloo.ca
authors.forename: Barbara
authors.initials: B
authors.lastname: Robinson
authors.forename: Yunwei
authors.initials: Y
authors.lastname: Feng
authors.forename: Craig A
authors.initials: CA
authors.lastname: Woods
authors.forename: Desmond
authors.initials: D
authors.lastname: Fonn
authors.forename: Deborah
authors.initials: D
authors.lastname: Gold
authors.forename: Keith
authors.initials: K
authors.lastname: Gordon
mesh_terms: D000328:Adult; D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D009864:Ontario / Q000453:epidemiology; D015995:Prevalence; D012030:Refractive Errors / Q000453:epidemiology* / Q000628:therapy; D012307:Risk Factors; D017678:Sex Distribution; D014505:Urban Population / Q000706:statistics & numerical data*; D014786:Vision Disorders / Q000453:epidemiology*; D014792:Visual Acuity / Q000502:physiology; D019987:Persons with Visual Disabilities / Q000706:statistics & numerical data*