Evaluating Keratoconus Progression prior to Crosslinking: Kmax versus the ABCD grading system.

Purpose To evaluate the correlation between changes in maximum keratometry (Kmax) and ABC values from the ABCD Progression Display (Pentacam (OCULUS; Wetzlar, Germany)) in progressive keratoconus (KC) and to evaluate whether the ABC changes were able to detect progression earlier than Kmax. Setting Humanitas Clinical and Research Center, Rozzano, Milan, Italy. Design Retrospective study. Methods Seventy-six eyes of 63 patients scheduled for Cross-linking (CXL) with documented progression (Kmax increase of >1 Dioptre) were included. Kmax, ABC values and thinnest point (ThCT) were recorded the day of CXL (T0) and previous follow-up (T-1). In patients without earlier progression in Kmax, follow-up exam (T-2) was used to determine whether any of the ABC parameters reached statistical significance for progression. Results There was a significant, albeit moderate, correlation between the change in Kmax between T0 and T-1 and the change in both A (rho=0.391) and B values (rho= 0.339). There was no significant correlation between the change in Kmax between T0 and T-1 and the change in either C or ThCT. In patients with T-2 exams, 51.6% (16/31) showed a statistically significant change on the ABCD progression display that was not detected with Kmax. Conclusions Our study showed a significant, but moderate, correlation between the change in Kmax and the change in A and B values in progressive KC. Moreover, more than half of the cases showed documented progression earlier with the ABCD progression display than detected by standard Kmax changes. This study suggests possible changes in progression criteria to allow for earlier intervention.