In a study on accelerated corneal collagen cross-linking, the effectiveness and safety of this surgical technique on halting the progression of keratoconus and steadiness of vision over a 24-month period was demonstrated [1]. We congratulate the authors for their remarkable paper and we would like to comment on some aspects concerning the execution of this study.

First, we really appreciated the use of Pentacam instead of ultrasound pachymetry to evaluate corneal thickness. Ultrasound pachymetry, currently considered the gold standard for these measurements, has indeed several limitations: the exact axial placement of the probe at the corneal center and the reproducibility of measurements are strongly associated with the examiner’s expertise and can be influenced by the use of different anesthetic drops during the follow-up examinations. In addition, ultrasound pachymetric measurements are influenced by the amount of corneal water, as in the case of corneal edema or corneal stiffness, because the sound speed is lower in the case of edematous tissues, making such measurements even larger, and higher in the case of stiff tissues, making them even smaller [2].

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