Prevalence of amblyopia among preschool children in central south China

AIM: To determine the prevalence and factors associated with amblyopia among children aged 30-83mo in central south of China. METHODS: A population-based, cross-sectional study was conducted in children aged 30-83mo in Changsha (an urban city) and Zhangjiajie (a rural area) in central south of China. Clinical examinations including ocular alignment, ocular motility, visual acuity (VA), prism cover test, cycloplegic refraction, slit lamp examination and fundus examination were performed by trained study ophthalmologists and optometrists. Unilateral amblyopia was defined as a 2-line difference between eyes with VA<20/32 in the worse eye and with coexisting anisometropia [>= 1.00 D spherical eutivalent (SE) for hyperopia, >= 3.00 D SE for myopia, and >= 1.50 D for astigmatism], strabismus, or past or present visual axis obstruction. Bilateral amblyopia was defined as VA in both eyes <20/40 (>= 48-month-old) and <20/50 (< 48-month-old), with coexisting hyperopia >= 4.00 D SE, myopia <=-6.00 D SE, and astigmatism >= 2.50 D, or past or present visual axis obstruction. RESULTS: There were 8042 children enrolled and 7713 children were screened. The amblyopia prevalence in children aged 30-83mo was 1.09% (95% confidence interval, 0.86%-1.35%) with no age (P=0.81), gender (P=0.46) or area distribution (P=0.93) differences. Of these, 0.68% were unilateral cases and 0.41% were bilateral cases. Underlying causes included anisometropia (40%), binocular refractive error (36%), strabismus (14%) and deprivation (10%). Hyperopia combined with astigmatism was the frequent refractive error for ametropic and anisometropic amblyopia. CONCLUSION: In this rural and urban Chinese population, 1.09% of children with 30-83mo of age had amblyopia, a prevalence rate similar to that of many other studies. Anisometropia and refractive error are the most common causes of unilateral and bilateral amblyopia respectively.