Effectiveness of corneal collagen crosslinking in vivo for corneal stiffening.

Additional references are provided by the authors to support their claims. However, the Hashemi and Mehravaran study reported results from only 23 subjects, which is likely underpowered to detect small changes in the posterior surface. Ciolini and Belin investigated a larger dataset but reported amean difference between preoperative andpostoperative changes in the posterior surface without a statistical analysis, so the differences in the posterior surface that weremeasured are difficult to interpret. Both references reported a statistically significant difference between the 2 devices used to make themeasurements. The authors also suggest that the statistically significant posterior surface steepening reported by Smadja et al., which occurred in proportion to the amount of anterior tissue disruption during myopic LASIK and regressed during the 1 to 3 month postoperative interval, is “minute and clinically irrelevant.”Wedisagreewith this characterization of the conclusions since the study demonstrates with yet another imaging technology the tendency of photoablative severing of stromal lamellae to produce peripheral corneal thickening and central posterior surface steepening in the early postoperative period. In conclusion, consistent changes to the posterior surface after refractive surgery have been reported with multiple tomographic devices, although the magnitude of the changes differs by device. These changes decrease over time and are associated with a normal postoperative outcome of a safe procedure. They are also consistent with our proposed biomechanical response to refractive surgery.dCynthia J. Roberts, PhD, William J. Dupps Jr, MD, PhD