Association of Axial Length and Refraction With Near Horizontal Heterophoria in Chinese Children

Myopia is becoming a global public health burden which is believed to have a multifactorial etiology. The relationship between heterophoria and refraction remains controversial. We describe the association of refraction and axial length (AL) with heterophoria in a large population-based study of school-aged Chinese children. Eleven thousand thirteen elementary school children grades 1-6, were included in this school-based, cross-sectional study. Near phoria data was quantified by using Maddox rod test and prism at 33 cm. Children in each grade level were sorted into three groups based upon phoria: 1) those with more than six prism diopters (PD) exophoria, 2) those with zero to six PD exophoria, and 3) those with any amount of esophoria. Autorefraction was measured by autorefractor (Topcon KR8900, Japan) and AL was measured by Optical Biometer AL-Scan (Nidek AL-Scan, Japan). A generalized additive model (GAM) was applied with a Gaussian link to explore the association between the refractive error or axial length and heterophoria. An additional age-adjusted model was also employed for analysis.