Objectives: To determine the distribution of keratoconus indices in normal children 6 to 12 years of age.

Methods: This cross-sectional study was conducted in children living in urban and rural areas of Shahroud, northeast Iran in 2015. After careful optometric examinations, the Pentacam was used for corneal imaging and measurement of keratoconus indices.

Results: Of 5,620 students who participated in the study, the data of the right eye of 4,947 children were analyzed after applying the exclusion criteria. The mean age of all children was 9.23±1.71 years (range: 6-12 years). The mean and 95% confidence intervals (in the parentheses) of index of surface variance (ISV), index of vertical asymmetry, keratoconus index (KI), central keratoconus index (CKI), index of height asymmetry, index of height decentration (IHD), and average pachymetric progression index (PPIAve) was 17.770 (17.610-17.930), 0.137 (0.135-0.139), 1.022 (1.022-1.023), 1.010 (1.010-1.010), 3.299 (3.230-3.368), 0.007 (0.007-0.008), and 0.948 (0.943-0.952), respectively. The results of multilevel mixed-effects linear regression analysis showed that ISV, KI, CKI, IHD, and PPIAve were significantly higher in girls. Index of surface variance and CKI were higher in urban students, and PPIAve was higher in rural students. Except for PPIAve, which was increased with increasing age, the mean values of other keratoconus indices were significantly lower in 12-year-old students compared with 6-year-old ones.

Conclusion: The results provide valuable information about normal distribution of keratoconus indices in children aged 6 to 12 years. These findings can be used in future research and detection of abnormal cases in the clinical setting.