title: Original papers: Prevalence of amblyogenic diseases in a preschool population sample of Valladolid, Spain.
abstract: OBJECTIVE
  Amblyopia is the leading cause of monocular vision loss in people under 40 years, and especially in children. The purpose of the present investigation is to determine the prevalence of amblyopia and ocular pathology, specially the most common causes of amblyopia, in a population of 3-to 6-year-old children.
  
  
  METHODS
  From a total of 8167 children, a geographically defined population of 3-to 6-year-old children, 2000 were randomly selected, and 1179 (58.9%) examined. Ophthalmologic examination included: Personal and familial history, visual acuity, extraocular motility, cover test at near distance, cycloplegic refraction with autorefractometer and fundus eye examination. Amblyopia was considered when corrected visual acuity was < 0.5 with Marquez optotypes and difference in visual acuity of 0.2 or more between eyes. Pathology considered as amblyogenic were strabismus, visual acuity asymmetry and anisometropia.
  
  
  RESULTS
  The family history showed amblyopia in 249 (21.1%), strabismus in 227 (19.2%), and refractive errors in 808 (65.5%). Cover test was positive in 78 children (6.7%). A visual acuity difference of 0.2 or more between eyes was present in 88 (7.5%) children, and anisometropia over 1.5 diopters (in spherical equivalent) was present in 17 (1.4%) subjects. One hundred and twenty-two (10.35%) children did not achieve a normal visual acuity: visual acuity in the better eye was less than 0.5 in 55 children under 5 years and less than 0.6 in 67 children over 5 years. The prevalence of amblyopia was 7.5%.
  
  
  CONCLUSIONS
  The data support the importance of early detection and treatment of amblyopia and the need for visual screening at an early age.
authors.affiliation: Department of Ophthalmology and Epidemiology, University of Valladolid, Spain.
authors.forename: J
authors.initials: J
authors.lastname: Martínez
authors.forename: S
authors.initials: S
authors.lastname: Cañamares
authors.forename: M A
authors.initials: MA
authors.lastname: Saornil
authors.forename: A
authors.initials: A
authors.lastname: Almaraz
authors.forename: J C
authors.initials: JC
authors.lastname: Pastor