Is Kmax a Reliable Endpoint for Evaluating Outcomes after CAIRS?

In ectatic corneas such as keratoconus, maximum keratometry (Kmax) is commonly used to identify the cone apex and monitor disease severity and progression. However, with the advent of tissue-additive corneal-reshaping surgical techniques such as corneal allogeneic intrastromal ring segments (CAIRS), Kmax may no longer reliably reflect the true geometric changes of the diseased cornea. Automatically generated Kmax can be influenced by localized peripheral steepening over the implanted segments, leading to misinterpretation of the actual keratometric effect. We argue that Kmax is therefore a potentially misleading outcome parameter after CAIRS. A better capture of the true regularizing effect of CAIRS may therefore be mean keratometry, keratometry measured at the preoperative Kmax location, or maximum flattening on the difference map. Standardized reporting of these metrics is needed to enhance comparability between studies.