Abstract
AIM: To investigate the proportion and characteristic of emmetropia in schoolchildren aged 6-11, especially estimate the normal value of ocular biometric parameters of emmetropia. METHODS: A population-based cross-sectional study was conducted on children aged 6-11y in Shenzhen. Totally, 2386 schoolchildren from two primary schools were involved. The axial length (AL) and the corneal radius of curvature (CRC) were measured by partial coherence laser interferometry. Noncycloplegic refraction and refractive astigmatism (RA) was measured using autorefraction. The axial length-to-corneal radius of curvature ratio (AL/CRC), corneal astigmatism (CA) and spherical equivalent refraction (SER) were calculated. RESULTS: The proportion of emmetropia in elementary school students was 41.30%. This percentage decreased gradually from 6 to 11 years of age and decreased rapidly after 9 years of age. The mean and 95%CI of each parameter were provided for boys and girls aged 6 to 11 years of age with emmetropia according to each age group. The change trend of parameters of boys and girls are similar. After 7 years of age, the AL of non-emmetropia started to increase faster than that of emmetropia. The change trend of AL/CRC was the same as that of AL. The other parameters tend to be stable after 7 years of age. CONCLUSION: The age of 7-9 is an important period for the changes of refractive state and ocular biometric parameters of primary school students, and it is a special focus period for children myopia prevention. The normal value and variation of ocular biometric parameters of emmetropia can provide the basis for the clinical judgment of whether or not children's ocular biometric parameters obtained by single measurement and changes obtained by multiple measurements are abnormal.