Is central corneal thickness a constant during air puff indentation with Corvis ST?

Abstract Purpose Corvis ST (Oculus Optikgeräte GmbH, Wetzlar, Germany) is the only commercial device that can capture corneal dynamic deformation in real time and provide a number of dynamic parameters, which include central corneal thickness (CCT). This study aimed to quantitatively analyse the change in CCT during air puff indentation using Corvis ST. Methods Sixty‐seven keratoconic eyes and 84 normal eyes were enrolled in this study. Dynamic videos were obtained from Corvis ST. An adaptive bilateral filtering method and a frame correlation method were used to remove noises. An adaptive threshold segmentation method was used to extract corneal boundary. The change in central corneal thickness, described as relative change rate of central corneal thickness (RCR CCT) and change speed of central corneal thickness (CS CCT ) were compared between keratoconus group and normal cornea group. Results It is shown that CCT would change and these two parameters were statistically significantly different between the keratoconus group and the normal cornea group RCR CCT , p = 0.014; CS CCT , p = 0.001. Conclusions The result of this study approved that CCT would change during air puff indentation. Further study is needed to develop more clinical applications based on these new findings, such as distinguishing keratoconus from normal cornea. image Fig. 1 Curves of changes in cornea and force over time. (A) Curve of corneal apex displacement and curve of air puff force; (B) A typical curve of the CCT changingover time. The red lineis the central corneal thickness‐time curve, the blue line is the force ‐time curve, and the green line is the fitting curveof force curve.