title: Refractive status of indigenous people in the northwestern Amazon region of Brazil.
abstract: OBJECTIVE
  The purpose of this study was to investigate the refractive status of the illiterate indigenous people of the upper Rio Negro region of the Amazon rain forest in northwestern Brazil.
  
  
  METHODS
  From an overall sample of 486 people, 259 indigenous people and 78 Brazilians between 12 and 59 years of age with no compromising optical opacities were refracted with cycloplegic retinoscopy. Subjects were categorized as indigenous if they had at least three generations of indigenous ancestry with no folklore suggesting other ancestors.
  
  
  RESULTS
  Myopia was rare among the indigenous population. Only 2.7% of eyes showed myopia of -1.00 D or more and 1.6% (four people) had bilateral myopia of -1.00 D or more. Half of this small group were the only educated indigenous people examined. The prevalence of astigmatism and anisometropia equal to or >1.00 D was 15.5% and 8.2%, respectively. Most of the astigmatism in the indigenous people had an against-the-rule axis. Age was not associated with the refractive errors of the indigenous people. Brazilians from the small city in which the study was performed had higher rates of myopia (6.4% of eyes and 5.1% of subjects bilaterally). Older preeducation adults also had a very low prevalence of myopia (3.2% of eyes and 2.0% of subjects), whereas the younger, slightly educated Brazilians had a higher prevalence of myopia (11.3% of eyes and 9.7% of subjects).
  
  
  CONCLUSIONS
  The low prevalence of myopia in the illiterate indigenous people is consistent with other studies and suggests that myopia is related to literacy. The generational change among the local mixed race Brazilians further supports this conclusion. The relatively high rates of astigmatism and anisometropia in the indigenous people were unusual for a predominantly emmetropic sample.
authors.affiliation: New England College of Optometry, Boston, Massachusetts 02115, USA. thornf@ne-optometry.edu
authors.forename: Frank
authors.initials: F
authors.lastname: Thorn
authors.forename: Antonio A V
authors.initials: AA
authors.lastname: Cruz
authors.forename: André J
authors.initials: AJ
authors.lastname: Machado
authors.forename: Ricardo A C
authors.initials: RA
authors.lastname: Carvalho
mesh_terms: D000293:Adolescent; D000328:Adult; D015858:Anisometropia / Q000453:epidemiology*; D001251:Astigmatism / Q000453:epidemiology*; D001938:Brazil / Q000453:epidemiology; D002648:Child; D004522:Educational Status; D006801:Humans; D008875:Middle Aged; D009216:Myopia / Q000453:epidemiology*; D044382:Population Groups / Q000706:statistics & numerical data*; D015995:Prevalence