title: Prevalence, causes and associations of amblyopia in year 1 students in Central China : The Anyang childhood eye study (ACES).
abstract: BACKGROUND
  Earlier diagnosis and treatment of amblyopia are associated with improved visual outcomes. This study reports the prevalence of amblyopia and associated factors in year 1 primary school students in central China.
  
  
  METHODS
  The school-based, cross-sectional study involved 3,112 year 1 primary school students . All the participants underwent a comprehensive eye examinations including cycloplegic refraction, cover test and ocular movement examinations. The unaided and best corrected visual acuity (BCVA) was recorded. Unilateral amblyopia was defined as a 2-line interocular difference with BCVA ≤ 20/32 (≥ logMar 0.2) in the worse eye and with coexisting anisometropia (≥ 1.00 D SE for hyperopia, ≥ 3.00 D SE for myopia, or ≥ 1.50 D for astigmatism), strabismus or past or present visual axis obstruction. Bilateral amblyopia was defined as BCVA in both eyes<20/40 (> logMar 0.3), with coexisting hyperopia ≥ 4 D SE, myopia ≤ -6 D SE, or astigmatism ≥ 2.5 D, or past or present visual axis obstruction.
  
  
  RESULTS
  Out of the 3,112 eligible students, 2,893 (93.0 %) students completed the examinations. The average age of the students was 7.1 ± 0.4 (mean ± standard deviation SD) years old. The prevalence of amblyopia was 1.0 % (95 % confidence interval [CI], 0.6 %-1.3 %) with no difference between the sexes (P = 0.88). Of the 27 amblyopic students, unilateral amblyopia was found in 18 (66.7 %) students, and bilateral amblyopia in 9 (33.3 %) students. Of 18 unilateral amblyopia, 13 were anisometropic amblyopia, 4 were strabismus amblyopia, 1 was mixed amblyopia. Of 9 bilateral amblyopia, 7 were isoametropic amblyopia, 2 were stimulus deprivation. The mean corrected VA of the amblyopic eyes was 30.50 logMAR letters (Snellen VA equivalent 4/12.6), and the range was 5 to 45 logMAR letters (Snellen VA equivalent 4/40-4/6.3). Most amblyopic eyes (38.9 %) were significantly hyperopic (spherical equivalent ≥ +3.00 D); 25.0 % were myopic. In addition, 58 (2.1 %) students had a previous amblyopia history of amblyopia that was not corroborated in this study.
  
  
  CONCLUSIONS
  The study shows a relatively low prevalence of amblyopia (1.0 %) in year 1 students in central China. Amblyopia is usually caused by abnormal refractive error.
authors.affiliation: Beijing Tongren Eye Center, Beijing Tongren Hospital, Beijing Ophthalmology & Visual Sciences Key Lab, Capital Medical University, No. 1 Dongjiao Min Xiang, Dongcheng District, Beijing, 100730, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Fu
authors.forename: Shi Ming
authors.initials: SM
authors.lastname: Li
authors.forename: Si Yuan
authors.initials: SY
authors.lastname: Li
authors.forename: Jin Ling
authors.initials: JL
authors.lastname: Li
authors.forename: He
authors.initials: H
authors.lastname: Li
authors.forename: Bi Dan
authors.initials: BD
authors.lastname: Zhu
authors.forename: Zhou
authors.initials: Z
authors.lastname: Yang
authors.forename: Lei
authors.initials: L
authors.lastname: Li
authors.forename: Ning Li
authors.initials: NL
authors.lastname: Wang
mesh_terms: D000550:Amblyopia / Q000453:epidemiology* / Q000209:etiology*; D002648:Child; D002681:China / Q000453:epidemiology; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D015995:Prevalence; D012029:Refraction, Ocular / Q000502:physiology; D012030:Refractive Errors / Q000150:complications; D012307:Risk Factors; D013285:Strabismus / Q000453:epidemiology; D013334:Students; D011795:Surveys and Questionnaires; D014792:Visual Acuity / Q000502:physiology