Repeatability and reproducibility of corneal biomechanical parameters derived from Corvis ST

The aim of this study was to evaluate repeatability and reproducibility of newly calculated biomechanical parameters of the cornea, developed by our research group.

One eye from each of the 23 healthy subjects was measured three times consecutively, three times at different daytimes and on three different days. The within-subject standard deviation and coefficient of variation, as well as the intraclass correlation coefficient, were calculated for every parameter in each group.

Excellent repeatability and reproducibility (coefficient of variation < 5%, intraclass correlation coefficient > 0.75) was found for corrected values measured at A1, HC, and A2 time points (2nd A2 Time, 2nd A1 Time, 2nd HC Time, 2nd HC Def Amp and 2nd A1 Def Amp). Corneal-specific stiffness parameters, which showed good repeatability and reliability, were DA_cor (coefficient of variation = 4.02%, intraclass correlation coefficient = 0.919), KcLinear (coefficient of variation = 4.03%, intraclass correlation coefficient = 0.895), areaForceCornea (coefficient of variation = 3.34%, intraclass correlation coefficient = 0.853) and E2 (coefficient of variation = 4.1%, intraclass correlation coefficient = 0.78). Overall, most parameters fell into the category of good reliability (high intraclass correlation coefficient) and poor reproducibility (low coefficient of variation), including all the parameters describing extraocular deformation (DA_ext, AEPvED, AUC EDef, areaForceExtra, Kg and μg). Comparing the coefficient of variation values for intrasession, intersession and daytime measurements, there were no indices for diurnal changes.

Most parameters showed good repeatability and reliability. The extraocular stiffness parameters showed poor reproducibility. KcLinear can serve as a very reliable and repeatable indicator of corneal stiffness.