Confocal microscopy in corneal cross-linking

Conventional riboflavin ultraviolet A (UVA) corneal cross-linking (CXL) represents an evolving therapy for the conservative treatment of progressive keratoconus and secondary corneal ectasia. 1, 2 The physiochemical basis 3, 4 of conventional CXL lies in the photodynamic type I to II reactions induced by the interaction between 0.1% riboflavin molecules absorbed in corneal tissue and UVA rays delivered at a 5.4 J/cm2 energy dose for 30 minutes, releasing reactive oxygen species that mediate cross-link formation between and within collagen fibers, increasing biomechanical corneal resistance against ectasia and intrinsic anticollagenase activity. 5-7 Since 3mW/cm2 for 30 minutes conventional CXL procedure 8 requires a long time (about 50-60 minutes), 6 new high irradiance accelerated CXL (ACXL) treatment protocols based on the physical principles stated in Bunsen-Roscoe law of reciprocity have been recently investigated. According to the “equal-dose” principle stated in the Bunsen-Roscoe law, 10 mW/cm2 for 9 min, 18 mW/cm2 for 5 min, 30 mW/cm2 for 3 min or 45 mW/cm2 for 2 min at constant energy (E) dose of 5.4 J/cm2 may have the same photochemical impact as conventional CXL at 3 mW/cm2 for 30 minutes.