title: The Pakistan national blindness and visual impairment survey--research design, eye examination methodology and results of the pilot study.
abstract: OBJECTIVE
  To establish age- and sex-specific prevalence rates and causes of blindness and low vision in children aged 10 to 15 years and adults aged 30 years and older in Pakistan.
  
  
  METHODS
  Multi-stage, stratified (rural/urban), cluster random sampling, with probability proportional-to-size procedures, was utilised to select a cross-sectional, nationally representative sample of adults (16,600 subjects) and children (6,000 subjects). Each subject underwent: interview, visual acuity (logMAR), autorefraction and optic disc examination. Those that saw < 6/12 in either eye underwent corrected visual acuity and dilated posterior segment examination.
  
  
  RESULTS
  The results of a pilot survey are reported in this paper. In the two rural pilot sites, 159 subjects (including 47 children) were examined; 50% were male. Thirty seven adults (23.3%) but no children saw worse than 6/12 in either eye. Two subjects were blind (corrected visual acuity) in the better eye, and 11 were visually impaired. Refractive error was the main cause (in 22 eyes (39% of the total of 56 eyes)) of < 6/12 visual acuity, followed by cataract (12 eyes), uncorrected aphakia (6 eyes) and age-related macular disease (3 eyes).
  
  
  CONCLUSIONS
  The pilot survey demonstrated that the proposed examination process for the main survey is feasible. Particular strengths of this survey include the use of logMAR visual acuity testing and autorefraction of all subjects, a dilated posterior segment examination, and the use of a 'less than 6/12' threshold for further examination. This lower threshold addresses the burden of refractive error, which, with cataract, are two of the diseases specifically targeted by Vision 2020.
authors.affiliation: Clinical Research Unit, Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, England, UK. rupert.bourne@lshtm.ac.uk
authors.forename: Rupert
authors.initials: R
authors.lastname: Bourne
authors.forename: Brendan
authors.initials: B
authors.lastname: Dineen
authors.forename: Zahid
authors.initials: Z
authors.lastname: Jadoon
authors.forename: Pak S
authors.initials: PS
authors.lastname: Lee
authors.forename: Aman
authors.initials: A
authors.lastname: Khan
authors.forename: Gordon J
authors.initials: GJ
authors.lastname: Johnson
authors.forename: Allen
authors.initials: A
authors.lastname: Foster
authors.forename: Daud
authors.initials: D
authors.lastname: Khan
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000368:Aged; D001766:Blindness / Q000453:epidemiology* / Q000209:etiology; D002648:Child; D003430:Cross-Sectional Studies; D003941:Diagnostic Techniques, Ophthalmological; D015340:Epidemiologic Research Design; D005260:Female; D006306:Health Surveys; D006801:Humans; D008297:Male; D008875:Middle Aged; D010154:Pakistan / Q000453:epidemiology; D010865:Pilot Projects; D015995:Prevalence; D012030:Refractive Errors / Q000150:complications / Q000453:epidemiology; D012424:Rural Population / Q000706:statistics & numerical data; D017678:Sex Distribution; D014505:Urban Population / Q000706:statistics & numerical data; D015354:Vision, Low / Q000453:epidemiology* / Q000209:etiology; D014792:Visual Acuity / Q000502:physiology; D019987:Persons with Visual Disabilities / Q000706:statistics & numerical data*