Aims: To evaluate lens power (LP) in schoolchildren aged 6-12 years.

Methods: This cross-sectional study was conducted in Shahroud, northeast Iran. The students were selected through random cluster sampling and underwent the measurements of biometry, uncorrected and corrected visual acuity, non-cycloplegic and cycloplegic refraction. The LP was calculated using the Bennett formula.

Results: Of 6624 invited children, 5620 (84.8%) participated in the study and data of 4870 children were finally analysed. The mean age of the participants was 9.7 years and 2277 participants (46.02%) were girls. The mean LPs were 22.86 dioptres (D) in total study population, 23.91 D in 6 and 22.10 D in 12-year-old children. The mean LP was higher in girls than boys (23.48 D vs 22.34 D), in rural children than urban children (23.17 D vs 22.83 D) and in children with hyperopia (23.25 D) than children with myopia or emmetropia (22.64 D and 22.86 D, respectively). In the multiple linear regression model, lens thickness (β=1.59, p<0.001), anterior chamber depth (β=2.21, p<0.001) and female sex (β=0.016, p=0.015) were associated with an increase in the LP, while axial length (AL) (β=-4.41, p<0.001), corneal power (CP) (β=-1.47, p<0.001), spherical equivalent (SE) (β=-1.50, p<0.001) and age (β=-0.005, p=0.001) were associated with a decrease in the LP. AL and sex had the highest and lowest impact on LP, respectively. Conclusion: LP decreased with age between 6 and 12 years and was associated with a shorter AL, deeper ACD, higher SE, thicker lens and lower CP.