PURPOSE: To compare small incision lenticule extraction (SMILE) and femtosecond laser–assisted in situ keratomileusis (FS-LASIK) in terms of the predictability of central stromal thickness reduction in eyes with high myopia. METHODS: In this prospective, randomized contralateral eye trial, 42 patients received SMILE in one eye and FS-LASIK (using the Amaris 750S excimer laser [SCHWIND eye-tech-solutions]) in the fellow eye for the correction of high myopia (manifest refraction spherical equivalent: < −6.00 diopters). Spectral-domain optical coherence tomography was used to measure the central corneal and epithelial thickness. Pre-operative and postoperative values were compared to determine the amount of central stromal reduction achieved. RESULTS: At the 6-month follow-up visit, the amount of central stromal reduction was overestimated by 20.05 ± 5.92 µm in the SMILE group ( P < .0001) and underestimated by 8.21 ± 8.14 µm in the FS-LASIK group ( P < .0001). The mean actual central stromal reduction achieved with SMILE was significantly less than that achieved with FS-LASIK (10.10 ± 18.01 µm, range: 1.90 to 18.29 µm, P < .001). The discrepancy between the planned and achieved central corneal stromal reduction was not associated with refractive overcorrection or undercorrection in either the SMILE group or the FS-LASIK group ( P = .9743 vs P = .0777). CONCLUSIONS: In patients with high myopia, the laser software platform may underestimate and overestimate the amount of actual corneal reduction in eyes treated with FS-LASIK and SMILE, respectively. SMILE required less corneal stroma compared to FS-LASIK in the studied cohort using the Amaris 750S excimer laser when correcting a similar spherical equivalent refraction. [ J Refract Surg . 2022;38(2):90–97.]

Purpose To compare the functional optical zone (FOZ) and visual quality after small-incision lenticule extraction (SMILE) and femtosecond laser–assisted laser in situ keratomileusis (FS-LASIK) in correcting high myopia. Methods Ninety-two eyes of 46 high myopic patients with the same programmed optical zone (POZ) received SMILE in one eye and FS-LASIK in the contralateral eye. FOZ was calculated using a refractive power method. The decentration, visual outcomes, wavefront aberrations, contrast sensitivity, and quality of vision (QoV) questionnaire were analyzed at 6 months postoperatively. Results The postoperative visual and refractive outcomes were comparable between SMILE and FS-LASIK. The FOZ for SMILE (5.62 ± 0.31 mm) was larger than for FS-LASIK (5.35 ± 0.28 mm; P < 0.001). Moreover, the total decentration for SMILE (0.29 ± 0.14 mm) was greater than in FS-LASIK (0.22 ± 0.11 mm; P < 0.001). The induced change in spherical aberration was less for SMILE than for FS-LASIK ( P < 0.001). There was better contrast sensitivity under the mesopic condition with glare for SMILE than for FS-LASIK ( P = 0.024). However, no significant difference was found in QoV scores between the two groups. Conclusions SMILE created a larger FOZ and greater decentration than FS-LASIK when the same POZ was designed in high myopia. Objective and subjective visual symptoms were comparable between SMILE and FS-LASIK. Translational Relevance The differences in FOZ and decentration between SMILE and FS-LASIK have little effect on vision outcomes. Surgeons should consider the FOZ and decentration in surgical options in high myopia.

Background: To compare the corneal biomechanical changes after small incision lenticule extraction (SMILE) and femtosecond laser-assisted in situ keratomileusis (FS-LASIK) with the same programmed optical zone (POZ) and similar refractive correction in patients with high myopia. Methods:In this prospective comparative study of the contralateral eye, 50 patients with high myopia with the same POZ and similar refractive correction who underwent SMILE in one eye and FS-LASIK in the other eye. Corneal biomechanical parameters and central corneal thickness (CCT) were measured using a Corvis ST II. All the patients were evaluated during follow-up visits beyond one year. Additionally, the corneal volume (CV) of the 10-mm diameter region was measured using a Pentacam.Results: Ambrosio relational thickness to the horizontal profile (ARTh) and stiffness parameter A1 (SP-A1) decreased significantly after SMILE and FS-LASIK, whereas deformation amplitude ratio 2.0 mm (DA ratio 2.0 mm) and integrated radius (IR) increased significantly in both groups. The ARTh and SP-A1 were greater after SMILE than those after FS-LASIK at all the follow-up visits. In addition, there were greater amounts of CCT and CV after SMILE compared with that after FS-LASIK. Moreover, a positive correlation was found between ARTh and SP-A1 and postoperative CCT, while a negative correlation was found between IR and DA ratio 2.0 mm and postoperative CCT. A moderate correlation was observed between SP-A1 and CV after both SMILE and FS-LASIK, whereas there were no relationships between CV and ARTh, IR, or DA ratio 2.0 mm. Conclusions: SMILE had greater CCT, CV, ARTh, and SP-A1 than FS-LASIK in high myopia with the same POZ and similar refractive correction. Our results demonstrated that SMILE had lesser effect on corneal biomechanics than FS-LASIK in high myopia.

Purpose: To compare the refractive outcomes and optical zone decentration between patients with symmetrical and asymmetrical high astigmatism after small incision lenticule extraction (SMILE). Methods: This was a prospective analysis of 89 patients (152 eyes) with myopia and astigmatism of more than 2.00 diopters (D) treated with the SMILE procedure. There were 69 eyes with asymmetrical topographies (asymmetrical astigmatism group) and 83 eyes with symmetrical topographies (symmetrical astigmatism group). Decentralization values were assessed using the tangential curvature difference map preoperatively and 6 months after surgery. Decentration, visual refractive outcomes, and induced changes in corneal wavefront aberrations were compared between the two groups 6 months postoperatively. Results: Both groups achieved favorable visual and refractive outcomes, with a mean postoperative cylinder of −0.22 ± 0.23 and −0.20 ± 0.21 D in the asymmetrical and symmetrical astigmatism groups, respectively. In addition, visual and refractive outcomes and induced changes in corneal aberrations were comparable between the asymmetrical and symmetrical astigmatism groups (all P > .05). However, the total and vertical decentration in the asymmetrical astigmatism group was greater than that in the symmetrical astigmatism group (all P < .05), whereas no significant differences were found in the values of horizontal decentration between the two groups ( P > .05). There was a weak positive correlation between induced total corneal higher order aberrations and total decentration ( r = 0.267, P = .026) in the asymmetrical astigmatism group but not in the symmetrical astigmatism group ( r = 0.210, P = .056). Conclusions: An asymmetrical corneal surface might affect treatment centration after SMILE. Subclinical decentration may be associated with the induction of total higher order aberrations, but it did not affect high astigmatic correction or induced corneal aberrations. [ J Refract Surg . 2023;39(4):273–280.]