title: Prevalence of blindness and visual impairment in Nigeria: the National Blindness and Visual Impairment Study.
abstract: OBJECTIVE
  To determine the prevalence of blindness and visual impairment among adults aged > or = 40 years in Nigeria.
  
  
  METHODS
  Multistage, stratified, cluster random sampling with probability proportional to size procedures was used to identify a cross-sectional nationally representative sample of 15,027 persons > or = 40 years of age from all 36 states in Nigeria and the Federal Capital Territory. Distance visual acuity (VA) was measured with a reduced logMAR tumbling-E chart at 4 and 1 m. Presenting and best corrected visual acuities were recorded. Autorefraction was performed in all examined adults. Clinical evaluations included examination under dilation for those with presenting vision < 6/12 in either eye.
  
  
  RESULTS
  In the study, 15,122 persons aged > or = 40 years were enumerated and 13,599 (89.9%) examined. Prevalence of blindness (< 20/400 in the better eye) and severe visual impairment (< 20/200-20/400; presenting vision) was 4.2% (95% confidence interval [CI]: 3.8%-4.6%) and 1.5% (95% CI: 1.3%-1.7%), respectively. Blindness was associated with increasing age, being female, poor literacy, and residence in the North. Participants residing in the South West had the lowest prevalence while those in the North East had the highest prevalence of blindness. It is estimated that 4.25 million adults aged > or = 40 years have moderate to severe visual impairment or blindness (< 20/63 in the better eye).
  
  
  CONCLUSIONS
  There is a high prevalence of blindness and severe visual impairment among those aged > or = 40 years in Nigeria. Significant differences exist between the geopolitical zones and emphasis should be on ensuring eye services across Nigeria, which means that planning at the regional level is necessary.
authors.affiliation: National Eye Centre, Kaduna, Nigeria.
authors.forename: Fatima
authors.initials: F
authors.lastname: Kyari
authors.forename: Murthy V S
authors.initials: MV
authors.lastname: Gudlavalleti
authors.forename: Selvaraj
authors.initials: S
authors.lastname: Sivsubramaniam
authors.forename: Clare E
authors.initials: CE
authors.lastname: Gilbert
authors.forename: Mohammed M
authors.initials: MM
authors.lastname: Abdull
authors.forename: Gabriel
authors.initials: G
authors.lastname: Entekume
authors.forename: Allen
authors.initials: A
authors.lastname: Foster
mesh_terms: D000328:Adult; D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D001766:Blindness / Q000453:epidemiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009549:Nigeria / Q000453:epidemiology; D015995:Prevalence; D012307:Risk Factors; D017678:Sex Distribution; D015354:Vision, Low / Q000453:epidemiology*; D014792:Visual Acuity; D019987:Persons with Visual Disabilities / Q000706:statistics & numerical data*