title: Cataract prevalence varies substantially with assessment systems: comparison of clinical and photographic grading in a population-based study.
abstract: OBJECTIVE
  Cataract is the major cause of blindness worldwide yet there is no consensus on its assessment and definition. This study compares age-related cataract prevalence derived from two commonly used methods: clinical assessment using the Lens Opacity Classification System (LOCS III) and photographic grading using the Wisconsin Cataract Grading System (Wisconsin System).
  
  
  METHODS
  The Singapore Malay Eye Study is a population-based study of 3,280 Singapore Malays aged 40-80 years. Presence of nuclear, cortical and posterior sub-capsular cataract was assessed clinically during slit-lamp examination using LOCS III, and via slit-lamp and retro-illumination photographic grading using the Wisconsin System. Analyses were conducted to determine agreement in cataract prevalence estimates between the two grading Systems and approaches.
  
  
  RESULTS
  Poor agreement was found between severity levels of the two grading scales for all three cataract types. Using currently accepted cut-offs to define nuclear (≥ 4 on both LOCS III and Wisconsin System), cortical (≥ 2 in LOCS III, ≥ 25% in Wisconsin) and PSC (≥ 2 in LOCS III, ≥ 5 % in Wisconsin) cataract, the LOCS III overestimated the prevalence of significant cataract as compared to the Wisconsin System, with nuclear cataract prevalence, 27.5% (LOCS III) versus 17.0% (Wisconsin System), cortical cataract prevalence, 27.9% versus 7.0% and posterior sub-capsular cataract prevalence, 7.8% versus 5.1%.
  
  
  CONCLUSIONS
  The prevalence of cataract in a population varies substantially by measurement methods, with systematically different estimates found using the two most frequent cataract grading systems. This study re-emphasizes the need for global standards to assess and define cataract for epidemiologic and clinical studies.
authors.affiliation: Singapore National Eye Centre, Singapore.
authors.forename: Anna C S
authors.initials: AC
authors.lastname: Tan
authors.forename: Jie Jin
authors.initials: JJ
authors.lastname: Wang
authors.forename: Ecosse L
authors.initials: EL
authors.lastname: Lamoureux
authors.forename: Wanling
authors.initials: W
authors.lastname: Wong
authors.forename: Paul
authors.initials: P
authors.lastname: Mitchell
authors.forename: Jialiang
authors.initials: J
authors.lastname: Li
authors.forename: Ava Grace
authors.initials: AG
authors.lastname: Tan
authors.forename: Tien Y
authors.initials: TY
authors.lastname: Wong
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D044466:Asian People / Q000208:ethnology; D002386:Cataract / Q000145:classification* / Q000175:diagnosis / Q000453:epidemiology*; D003941:Diagnostic Techniques, Ophthalmological / Q000592:standards*; D006302:Health Services Research; D006801:Humans; D008875:Middle Aged; D010781:Photography / Q000592:standards*; D015995:Prevalence; D012846:Singapore / Q000453:epidemiology