How Modifications of Corneal Cross-Linking Protocols Influence Corneal Resistance to Enzymatic Digestion and Treatment Depth.

Abstract

The purpose of this study was to determine the effects of the Photoactivated Chromophore for Keratitis Corneal Cross-Linking (PACK-CXL) protocol modifications on corneal resistance to enzymatic digestion and treatment depth. Eight hundred one ex vivo porcine eyes were randomly divided into groups of 12 to 86 corneas, treated with various epi-off PACK-CXL modifications, including acceleration (30 > 2 minutes, 5.4J/cm2), increased fluence (5.4 > 32.4J/cm2), deuterium oxide (D2O) supplementation, different carrier types (dextran versus hydroxypropyl methylcellulose [HPMC]), increased riboflavin concentration (0.1 > 0.4%), and riboflavin replenishment during irradiation (yes/no). Control group eyes did not receive PACK-CXL. A pepsin digestion assay was used to determine corneal resistance to enzymatic digestion. A phalloidin fluorescent imaging assay was used to determine the PACK-CXL treatment effect depth. Differences between groups were evaluated using a linear model and a derivative method, respectively. PACK-CXL significantly increased corneal resistance to enzymatic digestion compared to no treatment (P < 0.03). When compared to a 10 minute, 5.4J/cm2 PACK-CXL protocol, fluences of 16.2J/cm2 and higher increased corneal resistance to enzymatic digestion by 1.5- to 2-fold (P < 0.001). Other protocol modifications did not significantly change corneal resistance. A 16.2J/cm2 fluence also increased collagen compaction in the anterior stroma, whereas omitting riboflavin replenishment during irradiation increased PACK-CXL treatment depth. Increasing fluence will likely optimize PACK-CXL treatment effectiveness. Treatment acceleration reduces treatment duration without compromising effectiveness. The generated data help to optimize clinical PACK-CXL settings and direct future research efforts.