Refractive lens power and lens thickness in children (6-16 years old)

To examine the refractive lens power (RLP) and lens thickness and their associated factors in children from North-Western China. Children from two schools (primary school and junior high school) in the North-Western Chinese province of Qinghai underwent a comprehensive ophthalmic examination including biometry and cycloplegic refractometry. The RLP was calculated using Bennett's equation. The study included 596 (77.9%) individuals (mean age: 11.0 ± 2.8 years; range: 6-16 years) with a mean axial length of 23.65 ± 1.24 mm (range: 20.02-27.96 mm). Mean lens thickness was 3.30 ± 0.16 mm (range: 2.85-3.99 mm) and mean RLP was 24.85 ± 1.98D (range: 19.40-32.97). In univariate analysis, girls as compared to boys had a significantly thicker lens and greater RLP, shorter axial length, smaller corneal curvature radius and shorter corneal curvature radius (all P < 0.001). Both sexes did not differ significantly in refractive error (P = 0.11) and corneal thickness (P = 0.16). RLP was positively associated with refractive error (correlation coefficient r = 0.33; P < 0.001) and lens thickness (r = 0.62; P < 0.001) and negatively with axial length (r =  - 0.70; P < 0.001). In univariate analysis, RLP decreased significantly with older age in the age group from age 6-13, while it plateaued thereafter, with no significant difference between boys and girls. In multivariate regression analysis, a higher RLP was associated with younger age (P < 0.001; standard regression coefficient β =  - 0.07), female sex (P < 0.001; β =  - 0.08), shorter axial length (P < 0.001; β =  - 0.48) and higher lens thickness (P < 0.001; β = 0.42). In Chinese children, RLP with a mean of 24.85 ± 1.98D decreases with older age, male sex, longer axial length, and thinner lens thickness. Changes in RLP and axial length elongation are important players in the emmetropization and myopization.