W e appreciate Toprak’s interest in our work . The purpose of our study was to do our best to provide a real-life clinical scenario to determine the impact of corneal epithelial thickness maps on screening for refractive surgery candidacy. As stated numerous times throughout our manuscript, this process was by definition subjective because the process of screening for refractive surgery candidacy remains subjective. As clinicians, we are not only trying to screen out obvious ectatic disease but also eyes we deem to be at greater risk of postoperative ectasia. Due to the elective nature of refractive surgery, we try to err on the side of caution.
As stated in the text, the statistical analysis used was a simple calculation of percentages and two-tailed t tests. An assessment of intra-observer reliability was not applicable because the examiners did not perform the same test twice (their first evaluation did not include epithelial thickness maps, while their second evaluation did). Although both examiners used the same principles described in the text when interpreting imaging findings, refractive surgery screening remains subjective. Therefore, our aim was not to compare the examiners’ individual discrete decisions for each study subject, but rather to determine whether epithelial thickness maps had a similar impact on their decision-making. For this purpose, the use of t tests was adequate, without necessitating a more detailed evaluation of inter-observer reliability.
Regarding the impact of contact lens wear and cessation prior to refractive surgery evaluation, we agree that contact lens wear can impact epithelial patterns. Schallhorn and associates , nicely illustrated the different patterns that can occur between eyes with keratoconus and those with contact lens-induced warpage. However, the impact of contact lens warpage on the typical refractive surgical candidate is overstated by Toprak, as is the inaccurate claim that there is a definitive “widely accepted rule” regarding cessation of contact lens wear prior to evaluation that is well grounded in science. Among the specific studies cited to support Toprak’s statement regarding contact lens cessation, one found warpage in 30% of subjects but defined warpage as a change in manifest refraction or keratometry or corneal curvature on imaging, and did not define the number or percentage of patients who had any change in their imaging findings. A second study used Scheimpflug mapping and found no differences in axial curvature, which is the curvature representation we used in our study, after 2 weeks out of contact lenses. One of eight anterior curvature metrics studied (inferior tangential curvature) was significantly different, but this would not have influenced our decision-making since we did not utilize tangential curvature for patient evaluation in our study. Furthermore, the McKernan study compared measurements after 2 weeks of contact lens rest to initial measurements obtained less than 24 hours after contact lens removal. In our study, all patients had at least 3 days of contact lens rest. Given the lack of relevant curvature differences, even in a study design that exaggerates the potential differences in this way, Toprak errs in using this study as evidence in favor of a 2-week rest period and in applying the findings to our study. The third cited study found differences in epithelial thickness between patients who did vs those who did not wear contact lenses but did not evaluate the impact of contact lens removal on epithelial patterns. Thus, none of these studies addressed the impact of contact lens cessation on epithelial mapping, and their relevance to our study is unclear at best.
Toprak also voices concerns regarding our screening process for the patient shown in Figure 2 from our paper. We appreciate the detailed analysis regarding the “correct” way to locate a possible cone; however, this flow is simply as subjective as any other approach. We notice that Toprak did not provide any citation for the method employed or the relative value of metrics from the Enhanced Ectasia Display that is called “one of the most valuable screening tools.” We are also unaware of any citations to support these statements or their screening methodology. Inferior steepening has long been recognized and validated as a possible risk factor for developing postoperative ectasia. , There have, however, been numerous cases where LASIK has been performed in eyes with inferior steepening that did not develop ectasia. With the advent of epithelial mapping, we can now identify eyes with possibly concerning inferior steepness in which focal inferior epithelial hypertrophy is most likely producing the steep feature. This finding, along with the absence of a colocalized thinning of epithelium that is masking an underlying steep stromal feature, decreases the likelihood of an underlying ectatic process. This case nicely highlights the way we are using epithelial mapping for screening in our clinical practice, and we appreciate the opportunity to further highlight our approach.
Acknowledgements: All authors attest that they meet the current ICMJE criteria for authorship
References
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