Corneal resistance factor and corneal hysteresis in a 6-to 18-year-old population

PURPOSE: To determine the distribution and normal range of the corneal resistance factor (CRF) and corneal hysteresis (CH) in the 6- to 18-year age range and their relationship with biometric components. SETTING: Dezful, Iran. DESIGN: Cross-sectional study. METHODS: This study of Dezful school children used a multistage, stratified, cluster approach sampling. All students had examinations for biometry, noncycloplegic refraction, and corneal biomechanical properties; the examinations were performed in the same order in all cases. RESULTS: Of the 864 selected students, 683 participated in the study. The mean CRF and CH was 11.74 mm Hg +/- 1.77 (SD) (95% confidence interval [CI], 11.58-11.89) and 11.49 +/- 1.91 mm Hg (95% CI, 11.33-11.65), respectively. In a linear multiple regression model, the CRF significantly correlated with female sex (beta coefficient = 0.488, P=.013), central corneal thickness (CCT) (beta coefficient =.034, P=.001), and keratometry (beta-coefficient = 0.157, P=.003) and CH significantly correlated with CCT (beta coefficient = 0.025, P<.001), axial length (beta coefficient = -0.303, P=.011), and keratometry (beta coefficient = 0.11, P=.043). Each year increase in age was associated with a 42-unit decrease in the peak 1 area (P=.003). CONCLUSIONS: The distribution of CRF and CH in an Iranian population was symmetrical and bell shaped. However, the CRF did not have a normal distribution. The mean CRF and CH were higher than those reported in almost all previous studies. (C) 2014 ASCRS and ESCRS