title: Lens opacities in adults in Pakistan: prevalence and risk factors.
abstract: OBJECTIVE
  To investigate the prevalence and risk factors for lens opacity (LO) amongst a nationally representative sample of the adult population of Pakistan.
  
  
  METHODS
  This national study of blindness and visual impairment (adults > or =30 years) used multistage, stratified, cluster random sampling. Grading of LO was conducted using the Mehra/Minassian classification system. LO, partly or wholly obscuring the red reflex, or previous cataract surgery were indicators of opacity.
  
  
  RESULTS
  16,402 (94.7%) adults were included in this analysis (study conducted 2002-2003). A total of 4,096 (standardized prevalence 20.9%, 95%CI: 20.3, 21.5%) adults were found to have LO. The highest prevalence of LO was found in Punjab province (22.2%), the lowest in Balochistan Province (18.0%). Significant positive associations were increasing age (multivariable odds ratio (OR) 3.2: 95%CI: 3.1, 3.4), hypertension (OR 1.2, 95%CI: 1.1, 1.3), history of diabetes (OR 2.6: 95%CI 2.0, 3.2) and smoking (OR 1.3: 95%CI: 1.1, 1.5). Higher body mass index (BMI) (OR 0.8: 95%CI 0.7, 0.9, heavy vs. normal BMI) and attendance to school (OR 0.6: 95%CI: 0.5, 0.8) were associated with lower risk of LO. Individuals in districts classified as hot were at significantly increased risk (OR 1.3: 95%CI: 1.1, 1.5), and those in wet districts (> 600 mm annual rainfall) had lower odds than individuals living in dry districts (OR 0.7: 95%CI: 0.6, 0.8).
  
  
  CONCLUSIONS
  Almost a fifth of the adult population had LO. Significant positive associations were age, smoking status, hypertension, diabetes, and increased deprivation level. Protective factors included high BMI and educational achievement. The climatic associations offer novel hypothesis for further research into cataractogenesis.
authors.affiliation: International Centre for Eye Health, Clinical Research Unit, Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London. shaheen.shah@lshtm.ac.uk
authors.forename: Shaheen P
authors.initials: SP
authors.lastname: Shah
authors.forename: Brendan
authors.initials: B
authors.lastname: Dineen
authors.forename: Zahid
authors.initials: Z
authors.lastname: Jadoon
authors.forename: Rupert
authors.initials: R
authors.lastname: Bourne
authors.forename: Mohammad Aman
authors.initials: MA
authors.lastname: Khan
authors.forename: Gordon J
authors.initials: GJ
authors.lastname: Johnson
authors.forename: Bianca
authors.initials: B
authors.lastname: De Stavola
authors.forename: Clare
authors.initials: C
authors.lastname: Gilbert
authors.forename: Mohammad Daud
authors.initials: MD
authors.lastname: Khan
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D002386:Cataract / Q000453:epidemiology* / Q000209:etiology; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D010154:Pakistan / Q000453:epidemiology; D015995:Prevalence; D012189:Retrospective Studies; D018570:Risk Assessment; D012307:Risk Factors