title: Comparison of age-specific cataract prevalence in two population-based surveys 6 years apart.
abstract: BACKGROUND
  In this study, we aimed to compare age-specific cortical, nuclear and posterior subcapsular (PSC) cataract prevalence in two surveys 6 years apart.
  
  
  METHODS
  The Blue Mountains Eye Study examined 3654 participants (82.4% of those eligible) in cross-section I (1992-4) and 3509 participants (75.1% of survivors and 85.2% of newly eligible) in cross-section II (1997-2000, 66.5% overlap with cross-section I). Cataract was assessed from lens photographs following the Wisconsin Cataract Grading System. Cortical cataract was defined if cortical opacity comprised > or = 5% of lens area. Nuclear cataract was defined if nuclear opacity > or = Wisconsin standard 4. PSC was defined if any present. Any cataract was defined to include persons who had previous cataract surgery. Weighted kappa for inter-grader reliability was 0.82, 0.55 and 0.82 for cortical, nuclear and PSC cataract, respectively. We assessed age-specific prevalence using an interval of 5 years, so that participants within each age group were independent between the two surveys.
  
  
  RESULTS
  Age and gender distributions were similar between the two populations. The age-specific prevalence of cortical (23.8% in 1st, 23.7% in 2nd) and PSC cataract (6.3%, 6.0%) was similar. The prevalence of nuclear cataract increased slightly from 18.7% to 23.9%. After age standardization, the similar prevalence of cortical (23.8%, 23.5%) and PSC cataract (6.3%, 5.9%), and the increased prevalence of nuclear cataract (18.7%, 24.2%) remained.
  
  
  CONCLUSIONS
  In two surveys of two population-based samples with similar age and gender distributions, we found a relatively stable cortical and PSC cataract prevalence over a 6-year period. The increased prevalence of nuclear cataract deserves further study.
authors.affiliation: Centre for Vision Research, Westmead Millennium Institute, Department of Ophthalmology, University of Sydney, Westmead Hospital, Westmead, NSW, Australia. ava_tan@wmi.usyd.edu.au
authors.forename: Ava Grace
authors.initials: AG
authors.lastname: Tan
authors.forename: Jie Jin
authors.initials: JJ
authors.lastname: Wang
authors.forename: Elena
authors.initials: E
authors.lastname: Rochtchina
authors.forename: Paul
authors.initials: P
authors.lastname: Mitchell
mesh_terms: D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D001315:Australia / Q000453:epidemiology; D002386:Cataract / Q000453:epidemiology*; D003430:Cross-Sectional Studies; D005260:Female; D006306:Health Surveys; D006801:Humans; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D017678:Sex Distribution