Accelerated loss of crystalline lens power initiating from emmetropia among young school children: a 2-year longitudinal study.

PURPOSE To determine the characteristics of crystalline lens with varying refractive errors and relationship with axial elongation in young school children. METHODS A total of 1465 children aged 6-8 years were examined annually for 2 years. Each participant underwent a series of ophthalmic examinations, including cycloplegic autorefraction, crystalline lens and axial length measurement. Crystalline lens power was determined, and factors associated with different refractive statuses were investigated. RESULTS Crystalline lens power decreased with time; reduction in lens power in Year 1 was greater in children with emmetropia (-0.69 ± 0.59 dioptre [D]) than in those with hyperopia (-0.49 ± 0.56 D) or myopia (-0.45 ± 0.55 D) (p   0.05) visits. Among myopes at Year 1 visit, there was a greater reduction at Year 2 in those who had baseline emmetropia (-0.61 ± 0.51 D) than those who had baseline myopia (-0.26 ± 0.49 D, p < 0.001). The trend was similar among children of the same age. There was a significant correlation between changes in lens power and axial elongation in non-myopia (β = -0.954, p < 0.001) and new myopia (β = -1.178, p < 0.001), but not in established myopia (β = -0.001, p = 0.539). CONCLUSIONS There is accelerated loss of lens power in emmetropia and early stage of myopia. However, this loss is retarded when myopia persists and is accompanied by disappearance of the compensatory effect of lens power against axial elongation. These findings provide new insights into human refractive development.