Corneal Stability of LASIK and SMILE When Combined With Collagen Cross-Linking

We investigate whether small incision lenticule extraction (SMILE) is associated with less ectasia than laser-assisted in-situ keratomileusis (LASIK) and whether concomitant collagen cross-linking (CXL) is protective in SMILE Xtra and LASIK Xtra. Using an established LASIK rabbit ectasia model, we performed -5 diopter (D) LASIK on six eyes and -5 D SMILE on six eyes; five eyes had -5 D LASIK Xtra, five eyes -5 D SMILE Xtra. Anterior segment optical coherence tomography and corneal topography were performed preoperatively and 2, 4, and 6 weeks postoperatively. Mean (standard deviation [SD]) values of postoperative keratometry (K), maximum posterior elevation (MPE) and minimum corneal thickness (CT) were compared to preoperatively and among the surgical groups (paired -test, analysis of variance). Mean (SD) K values decreased significantly following SMILE, SMILE Xtra, LASIK, and LASIK Xtra. The MPE increased significantly ( < 0.05) following LASIK, SMILE, and SMILE Xtra, but not following LASIK Xtra ( = 0.12). The MPE was less following SMILE than LASIK, but not statistically significant (week 2, 17.73 [5.77] vs. 22.75 [5.05] μm; = 0.13); post-LASIK Xtra MPE was less than that following LASIK (week 2. 13.39 [3.05] vs. 22.75 [5.05] μm; < 0.001). CT decreased significantly in all surgical groups; no differences were detected among the groups. SMILE may have less potential than LASIK to induce ectasia. LASIK Xtra and SMILE Xtra showed the smallest increase in MPE. Concomitant CXL may be protective following keratorefractive surgery and may reduce further the risk of ectasia.