Riboflavin/Ultraviolet A Crosslinking of the Paracentral Cornea

Purpose: The depth of corneal crosslinking (CXL) does not seem homogeneous within the treatment area but shows a reduction toward the periphery of the cornea. This study was undertaken to investigate this reduction effect and to look for possible solutions. Methods: Ten corneas were investigated by means of an optical coherence tomography system (SS-100; Tomey, Nagoya, Japan) 1 month after standard CXL (epithelium off, 0.1% riboflavin for 30 minutes, ultraviolet A radiation 365 nm, 3 mW/cm(2)). The depth of the demarcation line was measured as a function of the radial distance from the apex. These curves were compared with a theoretical curve derived from a standard model of photopolymerization. Results: The CXL depth 3 mm away from the center decreases on average to 65% of the central depth (range: 52%-78%). Polymerization theory predicts this decay, however, underestimates the effect. Conclusions: The intended depth of CXL using current light sources is achieved only within the central area of the cornea. To provide CXL to the peripheral cornea, the ultraviolet beam either should have an improved intensity profile or may have to be decentered.