Repeatability of corneal biomechanical measurements in children wearing spectacles and orthokeratology lenses

Purpose: To determine the repeatability of corneal hysteresis (CH) and corneal resistance factor (CRF) measurements in children wearing spectacles and children under orthokeratology (ortho-k) therapy using the Ocular Response Analyzer (ORA). Methods: CH and CRF were measured twice at a 10-min interval using ORA on the same day in both eyes of 25 children (mean age=10.6±1.2years) wearing spectacles and 34 children (mean age=10.9±1.0years) wearing ortho-k lenses. Four measurements were obtained from each eye in each set of measurements. Only data from the right eyes were analyzed. Results: No significant between-measurement differences in CH and CRF were found in either group of subjects (paired t-tests, p>0.05) and no correlations were found between the mean differences and their means (Pearson's correlations, -0.09<r<0.21, 0.24<p<0.85). The 95% limits of agreement (LA) were -1.87mmHg to +2.59mmHg and -1.53mmHg to +1.41mmHg for CH and -1.86mmHg to +2.22mmHg and -1.45mmHg to +1.57mmHg for CRF in the spectacle and ortho-k groups, respectively. A significant between-group difference in CRF was found (unpaired t-tests, p=0.02). Conclusions: Repeatability of CH and CRF measurements using the ORA is within ±2mmHg in children wearing spectacles or ortho-k lenses. We suggest that the ORA can be used to monitor long-term corneal biomechanical changes during ortho-k treatment.