A two-year longitudinal study of myopia progression and optical components changes among Hong Kong schoolchildren

Purpose. To investigate myopia progression and optical components changes in a group of Hong Kong schoolchildren from age six to 17 years over two years between 1991 and 1993. Methods. Subjects were refracted subjectively. Corneal curvatures were measured with the Topcon CK-1000 keratometer and biometry with the Storz Omega Biometer. The children were followed longitudinally, with a visit in 1991 and a second visit in 1993. Results. 142 schoolchildren were investigated. Mean shift in spherical equivalent refraction (SER) was -0.69D in girls and -0.57D in boys. This myopic shift was mainly contributed by the spherical component. Cylindrical component is rather stable. Rate of myopia progression was greatest at age 8 to 9 years (-0.70D/yr., girls; -0.48D/yr., boys) and decreased gradually with increasing age. 56% of girls and 49% of boys had a myopic shift of more than -0.50D. Mean SER was -1.83D (girls) and -1.90D (boys) at the end of the study. Paired t-test comparing the two visits showed significant increase in anterior segment distance, vitreous/axial length except corneal curvatures. Conclusions. 62% of the schoolchildren were myopic with mean SER of -1.85D. Mean rate of myopic shift was -0.3D/yr.; it was greatest at age 8 to 9 years. By extrapolation, refraction stabilizes at age 18 to 19 years. Axial length elongation is still the main component that contributes to the progression of myopia.