Epidemiology of Intermittent Exotropia in Preschool Children in China

PURPOSE: To determine the prevalence, subtypes, and associated risk factors for intermittent exotropia (IXT) in preschool children aged 3 to 6 years in eastern China. METHODS: A population-based study including 5831 preschool children aged 3 to 6 years was conducted from 2011 to 2012 in Yuhua District, Nanjing, China, using an age-stratified random sampling procedure. Clinical examinations including ocular alignment, ocular motility, visual acuity, prism cover test, cycloplegia refraction, stereopsis screening, slitlamp examination, and fundus examination were performed by trained ophthalmologists and optometrists. Intermittent exotropia was defined as an acquired intermittent exodeviation of at least 10 prism diopters in an otherwise healthy child following the classification recommended by the National Eye Institute. RESULTS: The overall prevalence of IXT in this population was 3.24% (95% confidence interval, 2.79 to 3.69%), with no age (p = 0.19) and sex (p = 0.89) differences. Among 166 children with IXT, the "basic type" was the most common type of IXT (74.7%), the "divergence excess" was the second (19.9%), whereas the "convergence weakness" was the rarest (5.4%). In multivariate analysis adjusting for age, sex, and other confounders, the presence of IXT was only associated with a history of hypoxia at birth (odds ratio, 4.41; 95% confidence interval, 2.47 to 7.86). CONCLUSIONS: Intermittent exotropia affected approximately 1 in 30 Chinese preschool-aged children in eastern China, indicating a relatively higher burden of this pediatric eye condition in the world's most populous country. The presence of IXT was strongly associated with a history of hypoxia at birth.