Comparison of the visual results after small incision lenticule extraction and femtosecond laser-assisted LASIK for myopia.

To the Editor: During the past 3 years, several studies have suggested that small incision lenticule extraction (SMILE) is a promising alternative to LASIK for the correction of myopia. For this reason, we have read with great interest the article by Lin et al.1 about the comparison of the visual results after SMILE and femtosecond laser-assisted LASIK (FS-LASIK) for the treatment of myopia. However, we have concerns about two facts of this study. First, when reading the preoperative demographics, we have observed that the preoperative cylinder was higher in the FS-LASIK group than in the SMILE group, with a surprising P value of 1.101 for the comparison of this parameter between both groups. We remark that the maximum possible P value is 1.0, which is an exceptional statistical situation that is only found when the parameter compared in two groups is exactly equal in both. Given the fact that the amount of preoperative astigmatism may be relevant in the refractive outcomes of the procedure, we invite the authors to revise this P value. Second, the authors conclude that both SMILE and FS-LASIK provide excellent outcomes in terms of safety, efficacy, and predictability. Given the fact that the authors included a small population (60 eyes in the SMILE group and only 51 eyes in the FS-LASIK group) and a short-term follow-up (only 3 months), we think that the evidence provided in this study is not enough to support that the visual results of SMILE are comparable to the well-known visual outcomes of FS-LASIK.2,3 Although SMILE seems to induce less dry eye4 and has less impact on corneal sensation4,5 than FS-LASIK, we think that further prospective studies with a larger number of cases and a longer follow-up are needed to ensure the real advantages and disadvantages of SMILE. Until these studies are available, we do believe that FS-LASIK should still be considered as the goal standard for the correction of myopia. REFERENCES 1. Lin F, Xu Y, Yang Y. Comparison of the visual results after SMILE and femtosecond laser-assisted LASIK for myopia. J Refract Surg. 2014;30:248-254.