Prevalence, causes and associations of amblyopia in year 1 students in Central China The Anyang childhood eye study (ACES)

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. 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 a parts per thousand currency signaEuro parts per thousand 20/32 (a parts per thousand yen logMar 0.2) in the worse eye and with coexisting anisometropia (a parts per thousand yen 1.00 D SE for hyperopia, a parts per thousand yen 3.00 D SE for myopia, or a parts per thousand yenaEuro parts per thousand 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 a parts per thousand yenaEuro parts per thousand 4 D SE, myopia a parts per thousand currency signaEuro parts per thousand a'6 D SE, or astigmatism a parts per thousand yenaEuro parts per thousand 2.5 D, or past or present visual axis obstruction. 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 a parts per thousand yenaEuro parts per thousand+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. 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.