Tomography-Guided Customized CXL.

Tomography-Guided Customized CXL Cassagne et al. should be congratulated for their work on customized corneal cross-linking (CXL) in the May 2017 issue.1 This novel technique has the potential to replace the standard protocol, and that is why we need a clear and contradiction-free presentation of parameters and results. However, the study has some flaws that need to be discussed. First, the maximally used radiant exposure was 15 J/cm2, which clearly exceeds the official exposure limit of 1 J/cm2 as published by the International Commission on Non-Ionizing Radiation Protection.2 Even assuming an absorption of the ultraviolet light by riboflavin, which has been reported to be maximally 90%,3,4 the energy load for intraocular structures is still substantially too high. Second, this is by far not the first report of customized CXL. Our group presented nearly identical results already at the CXL Expert Meeting 2014 and the ESCRS 2015 meeting, and published in the American Journal of Ophthalmology in March 2016.5 Other groups have published similar results regarding customized CXL.6 Third, the presentation of the technique of ultraviolet application is contradictive: on page 291, it reads “superimposed concentric circular zones,” but Figure 1 presents sectorial areas. Which customization was really used? Finally, the title itself includes two misnomers: “topography-guided” and “collagen cross-linking.” Because the authors centered the treatment on the posterior elevation obtained by the Oculyzer, the technique presented would be better characterized as “tomography-guided.” Since 2013, we know that the CXL procedure established additional chemical bonds not only within the collagen molecules of the cornea but also well (and maybe even more important) in the interfibrillar space between proteoglycans forming bridges between the collagen fibers.7 When using the term “collagen cross-linking,” do the authors really refer only to the new chemical bonds within the collagen molecule or to the entire CXL process?