Prevalence of amblyopia and strabismus in Hani school children in rural southwest China: a cross-sectional study

Purpose To determine the prevalence rate of amblyopia and strabismus in Chinese Hani ethnic school-aged children. Methods All grade 1 and grade 7 students in Mojiang Hani Autonomous County, located in southwest China, were invited for comprehensive eye examinations performed by experienced ophthalmologists and optometrists, including visual acuity, ocular alignment and movements, cycloplegic autorefraction, anterior segment and fundus examinations. Standard definitions of amblyopia and strabismus were applied to calculate their prevalence rate. Results A total of 1656 (91.0% response rate) grade 1 Hani students and 1394 (92.8% response rate) grade 7 Hani students participated in the study. Amblyopia was present in 25 Hani students (0.82%, 95% CI 0.55% to 1.20%), with no significant differences in grade (p=0.42) and gender (p=0.69). Among these 25 amblyopic children, 17 had unilateral amblyopia and eight had bilateral amblyopia, including 16 anisometropic, eight binocular refractive and one strabismic. Strabismus was found in 59 Hani students (1.93%, 95% CI 1.50% to 2.48%), including 47 with intermittent exotropia, six with constant exotropia, five with constant esotropia and one with unilateral superior oblique palsy. The prevalence rate of strabismus was higher in grade 7 students than grade 1 students with borderline significance (2.44% vs1.50%, p=0.07), but was similar by gender (2.16% in boys vs 1.68% in girls, p=0.36). Conclusion The prevalence of amblyopia and strabismus in Chinese Hani school children are both lower than that previously reported for Chinese Han children in China and for many other racial/ethnic populations from non-China studies. Refractive error is the major cause for amblyopia and intermittent exotropia is the primary strabismus type.