Objective: To investigate the distribution of spherical equivalent and ocular biometric parameters in a population of grade 7 children in central China.
Methods: 2 363 grade 7 students of junior high schools were randomly sampled. The students have been examined at baseline and followed up annually. Detailed questionnaires and most of the ocular examinations were performed. Spherical equivalent (Seq) was calculated as sphere +1/2 cylinder from cycloplegic autorefraction. Myopia was defined as spherical equivalent ≤ -0.5D, hyperopia as spherical equivalent ≥ +0.5D and emmetropia between -0.5D and +0.5D. The Lensar LS900 was used to measure corneal curvatures, axial length and anterior chamber depth. Right eyes results were analyzed.
Results: Among 2 267 children who have the baseline examination, 1 839 children participated the follow up examination(response rate, 81.1%), with an mean age of 14.7 years (range, 12.9-17.6) and male ratio of 48.4%. The mean spherical equivalent refraction was (-2.62 ± 2.19)D. The prevalence rates of myopia, high myopia, emmetropia and hyperopia were 82.7%, 7.1%, 9.8% and 7.5%. The cumulative incidence rates of myopia and high myopia were 47.1% and 4.5% respectively. Axial length, anterior chamber depth, and corneal curvature were normally distributed. The mean axial length, anterior chamber depth, and corneal curvature were (24.8 ± 1.1)mm, (3.18 ± 0.25)mm, (42.8 ± 1.4)D and (43.9 ± 1.6)D respectively. Axial length was longer, anterior chamber depth was deeper, and corneal were flatter in the male(P = 0.000). Axial length and anterior chamber depth correlated negatively with refraction.
Conclusions: A moderate myopic distribution of refraction was present in the grade 9 students in central China. The prevalence rates of myopia and high myopia were relatively high in this 14-year-old population compared to other countries. It is necessary to strengthen the prevention of juvenile myopia.