title: The Nigerian national blindness and visual impairment survey: Rationale, objectives and detailed methodology.
abstract: BACKGROUND
  Despite having the largest population in Africa, Nigeria has no accurate population based data to plan and evaluate eye care services. A national survey was undertaken to estimate the prevalence and determine the major causes of blindness and low vision. This paper presents the detailed methodology used during the survey.
  
  
  METHODS
  A nationally representative sample of persons aged 40 years and above was selected. Children aged 10-15 years and individuals aged <10 or 16-39 years with visual impairment were also included if they lived in households with an eligible adult. All participants had their height, weight, and blood pressure measured followed by assessment of presenting visual acuity, refractokeratomery, A-scan ultrasonography, visual fields and best corrected visual acuity. Anterior and posterior segments of each eye were examined with a torch and direct ophthalmoscope. Participants with visual acuity of < = 6/12 in one or both eyes underwent detailed examination including applanation tonometry, dilated slit lamp biomicroscopy, lens grading and fundus photography. All those who had undergone cataract surgery were refracted and best corrected vision recorded. Causes of visual impairment by eye and for the individual were determined using a clinical algorithm recommended by the World Health Organization. In addition, 1 in 7 adults also underwent a complete work up as described for those with vision < = 6/12 for constructing a normative data base for Nigerians.
  
  
  CONCLUSIONS
  The field work for the study was completed in 30 months over the period 2005-2007 and covered 305 clusters across the entire country. Concurrently persons 40+ years were examined to form a normative data base. Analysis of the data is currently underway.
  
  
  CONCLUSIONS
  The methodology used was robust and adequate to provide estimates on the prevalence and causes of blindness in Nigeria. The survey would also provide information on barriers to accessing services, quality of life of visually impaired individuals and also provide normative data for Nigerian eyes.
authors.affiliation: International Centre for Eye Health, London School for Hygiene and Tropical Medicine, UK. brendan.dineen@nuigalway.ie
authors.forename: Brendan
authors.initials: B
authors.lastname: Dineen
authors.forename: Clare E
authors.initials: CE
authors.lastname: Gilbert
authors.forename: Mansur
authors.initials: M
authors.lastname: Rabiu
authors.forename: Fatima
authors.initials: F
authors.lastname: Kyari
authors.forename: Abdull M
authors.initials: AM
authors.lastname: Mahdi
authors.forename: Tafida
authors.initials: T
authors.lastname: Abubakar
authors.forename: Christian C
authors.initials: CC
authors.lastname: Ezelum
authors.forename: Entekume
authors.initials: E
authors.lastname: Gabriel
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Elhassan
authors.forename: Adenike
authors.initials: A
authors.lastname: Abiose
authors.forename: Hannah
authors.initials: H
authors.lastname: Faal
authors.forename: Jonathan Y
authors.initials: JY
authors.lastname: Jiya
authors.forename: Chinenyem P
authors.initials: CP
authors.lastname: Ozemela
authors.forename: Pak Sang
authors.initials: PS
authors.lastname: Lee
authors.forename: Murthy V S
authors.initials: MV
authors.lastname: Gudlavalleti
mesh_terms: D000293:Adolescent; D000328:Adult; D001766:Blindness / Q000175:diagnosis / Q000453:epidemiology* / Q000209:etiology*; D002387:Cataract Extraction; D002648:Child; D005654:Fundus Oculi; D006306:Health Surveys; D006801:Humans; D008722:Methods; D009549:Nigeria / Q000453:epidemiology; D010781:Photography; D011184:Postoperative Period; D015995:Prevalence; D012029:Refraction, Ocular; D014065:Tonometry, Ocular; D014787:Vision Tests; D015354:Vision, Low / Q000175:diagnosis / Q000453:epidemiology* / Q000209:etiology*; D014792:Visual Acuity; D014794:Visual Fields