Corneal flattening following collagen crosslinking for keratoconus: Findings at 5-year follow-up.

CXL effect on cornea can be cumulative overtime and delayed flattening occurs in some cases. ΔKmax is positively correlated with preoperative Kmax and no association was found between ΔKmax and DDL. Therefore, DDL may not be a valid measure for the efficacy of CXL.