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Purpose To compare the corneal epithelial remodeling in eyes with high astigmatism that had small incision lenticule extraction (SMILE) and femtosecond laser–assisted laser in situ keratomileusis (FS-LASIK). Methods Seventy-four patients with myopic astigmatism of greater than −2.00 diopters (D) and little binocular difference in spherical equivalent were included in this contralateral comparative study. All patients received SMILE in one eye and FS-LASIK in the other eye randomly. The corneal epithelial remodeling pattern was mapped using the latest RTVue spectral-domain optical coherence tomographer (Optovue) by region. Results Satisfactory refractive correction was achieved in all enrolled eyes with either SMILE or FS-LASIK. The corneal epithelium gradually thickened following surgical cylinder correction, distributing mainly along the flat medium. The corneal epithelium proliferation is milder centrally but more pronounced in the mid-peripheral area after SMILE, compared with FS-LASIK. The flat-steep difference in corneal epithelial thickness (CET) is evident in the mid-peripheral and peripheral areas, which is more obvious in SMILE. Residual cylinder was positively correlated with CET in eyes that had FS-LASIK, but not SMILE. More importantly, these epithelial changes were positively correlated with the ablation depth and higher order aberrations following surgical refractive correction. Conclusions The postoperative CET map varied between SMILE and FS-LASIK. In eyes with high astigmatism, SMILE surgery is followed by milder and more stable corneal epithelial thickening. Moreover, the corneal epithelium is sensitive to stromal ablation and corneal remodeling is crucial to the postoperative visual quality. This study rigorously distinguished the CET difference between SMILE and FS-LASIK in astigmatic eyes and shed light on subsequent research. [J Refract Surg. 2024;40(10);e728–e741.]

Purpose: To compare differences in corneal densitometry (CD) and higher order aberrations (HOAs) in eyes that underwent small incision lenticule extraction (SMILE) and femtosecond laser–assisted laser in situ keratomileusis (FS-LASIK) for the treatment of myopia and myopic astigmatism at postoperative months 3, 6, and 12, and to evaluate their changes in a separate cohort of eyes after SMILE enhancement. Methods: In this prospective, randomized, paired-eye clinical trial, consecutive eligible participants were randomized to undergo SMILE or FS-LASIK in either eye. Main outcome measures were CD and HOAs preoperatively and at 3, 6, and 12 months postoperatively. A separate cohort of consecutive patients who had SMILE and underwent enhancement were also included for comparison. Results: For CD, no significant differences were found between SMILE and FS-LASIK up to month 12. For HOA measured by wavefront aberrometry, both SMILE and FS-LASIK had an increase in total root mean square (RMS) HOAs, spherical aberration (SA), and vertical coma up to month 12. SMILE had an additional increase in vertical quatrefoil, and FS-LASIK had an increase in horizontal coma at month 12. FS-LASIK had higher SA than SMILE, whereas SMILE had higher vertical quatrefoil than FS-LASIK at month 12. Central and posterior zone CD had significantly decreased after SMILE enhancement compared to after primary SMILE up to 2 years after enhancement. RMS HOAs, lower order aberrations, and SA were all increased after SMILE enhancement compared to after primary SMILE. Conclusions: SMILE induced lower SA but higher vertical quatrefoil than FS-LASIK at 1 year. Both SMILE and FS-LASIK had similar increases in RMS HOAs and vertical coma up to 1 year. There were no differences in CD between both groups. SMILE enhancement additionally had decreased central and posterior CD but greater RMS HOAs and SA compared to primary SMILE. [J Refract Surg. 2024;40(5):e291–e303.]

For ophthalmologists who are already using femtosecond lasers as well as those just starting out who are looking for the definitive reference manual, Femtosecond Lasers in Cornea and Lens Surgery is a comprehensive, cutting-edge guide to this technology that features a robust supplemental website with nearly 40 surgical videos.

To compare dry eye after small incision lenticule extraction (SMILE) and femtosecond laser-assisted LASIK (FS-LASIK) for correcting myopia. CENTRAL, Embase and PubMed were searched in November 2016. All randomized controlled trials (RCTs) and prospective cohorts that compared dry eye after SMILE with FS-LASIK were selected. Five cohorts and one RCT were identified for comparing dry eye after SMILE (291 eyes) and FS-LASIK (277 eyes). The pooled results revealed that the SMILE and FS-LASIK groups did not differ significantly in terms of Schirmer's I test (SIT) and tear film osmolarity (TFO) at any postoperative visits. By contrast, tear break up time (TBUT; p = 0.04 for one month, p < 0.001 for three months, and p = 0.02 for six months) and ocular surface disease index (OSDI; p < 0.001 for one month and three months, and p = 0.006 for six months) were significantly worse in the FS-LASIK group than in the SMILE group at follow-up. At six months postoperatively, TBUT and TFO values in both the SMILE and FS-LASIK groups and OSDI scores in the SMILE group returned to preoperative levels, but SIT values in both groups (p = 0.02 for the SMILE group and p < 0.001 for the FS-LASIK group) and OSDI in the FS-LASIK group (p < 0.001) were still statistically impaired. Dry eye after both SMILE and FS-LASIK usually occurs transiently. SMILE does not show obvious superiority over FS-LASIK by exhibiting similar and acceptable objective parameters, and SMILE may have milder subjective symptoms.

Purpose To investigate long-term corneal biomechanical changes in thin corneas after small incision lenticule extraction (SMILE). Methods Patients with indications for SMILE were enrolled in this study between November 2017 and March 2018. Patients were matched for age, spherical diopter, cylinder, spherical equivalent (SE), and lenticule thickness (LT), and then categorized into the thin cornea group (preoperative thinnest central corneal thickness [CCT] of 500 µm or less, 32 eyes) or normal cornea group (CCT of greater than 500 µm, 32 eyes). Corneal biomechanical properties were measured using the Corvis ST system. Data were collected at 1 day, 3 weeks, 3 months, and 3 years postoperatively. Results At 3 years postoperatively, the safety indexes were 1.06 ± 0.12 and 1.09 ± 0.12 (P = .23) in the thin cornea and normal groups, respectively; the respective effective indexes were 0.89 ± 0.23 and 0.98 ± 0.18 (P = .12). Recovery of overall corneal stiffness was observed in both groups. Comparative analysis of biomechanical parameters revealed that the change between preoperative and 3-year postoperative values was smaller in the thin cornea than in the normal group, without statistical significance. Correlation analysis showed that SE, LT, and CCT were the main parameters affecting changes in corneal biomechanical properties in the normal group. No significant correlations were found between the stress-strain index, Corvis biomechanical index for laser vision correction, and preoperative CCT or age. Conclusions With rigorous preoperative screening and appropriate surgical design, thin corneas are biomechanically stable in the long term after SMILE. Moreover, postoperative biomechanical strength increases over time. [J Refract Surg. 2025;41(1):e39–e49.]

Purpose To examine lenticule decentration and visual quality following small incision lenticule extraction (SMILE) using either the coaxially sighted corneal light reflex (CSCLR) or the tear film mark (TFM) centration method. Methods A total of 186 eyes from 93 patients were enrolled in this prospective, randomized, contralateral eye comparison study. Each patient had one eye randomly assigned to the CSCLR group (n = 93) and the contralateral eye to the TFM group (n = 93). Visual outcomes, optical zone decentration, contrast sensitivity, corneal higher order aberrations (HOAs), and the relationships between the magnitude of decentration and induced corneal HOAs were evaluated at 3 months postoperatively. Results The magnitudes of total decentration (CSCLR: 0.23 ± 0.13; TFM: 0.22 ± 0.13; P = .996), as well as horizontal and vertical decentration, were comparable between the two methods. However, in the angle kappa greater than 200 µm subgroup, a statistically significant smaller horizontal decentered displacement was observed in the CSCLR group (0.01 ± 0.16) compared to the TFM group (0.07 ± 0.18) (P = .024). The induced HOAs and contrast sensitivity were comparable between the two methods (all P > .05). Additionally, significant correlations were identified between total decentered displacement and induced HOAs, including RMS HOAs, RMS coma, vertical coma, and RMS spherical aberration, in both groups. Conclusions Both the CSCLR and TFM methods can yield accurate treatment centration and satisfactory visual quality. However, the CSCLR method may contribute to less horizontal decentration in patients with a large preoperative pupil offset. [J Refract Surg. 2025;41(2):e144–e154.]

Myopia is the most common refractive error. Surgical correction with laser is possible. LASIK and SMILE are the techniques currently most used. Aim of the study was to compare changes in corneal volume and thickness after the respective laser treatment. 104 eyes of 52 patients were matched based on refractive error into two equally sized groups, either treated with LASIK or SMILE. Measurements were obtained from the Scheimpflug camera (Pentacam) preoperatively and at 3 and 12 months postoperatively. 3 months postoperatively, the flapless SMILE procedure resulted in a significant overall greater loss of corneal volume (P < 0.01) and corneal thickness (P < 0.01) compared to LASIK. No significant difference was found when comparing the 3 to 12-months values in each group. Within the currently used ranges of refractive error correction, loss in central corneal thickness and corneal volume with SMILE is higher in comparison to LASIK. As greater loss in corneal volume and thickness might contribute to higher level of corneal instability maximum ranges of refractive error correction with SMILE should not supersede those set currently for LASIK until more long-term results on corneal ectasia are available for SMILE.

To investigate the changes of posterior corneal elevation after small incision lenticule extraction (SMILE) for moderate and high myopia. In this prospective study, fifty consecutive eyes of thirty patients (10 male, 20 female) who underwent SMILE for myopia and myopic astigmatism were included. Eyes were divided in two groups based on the preoperative spherical equivalent refraction: high myopia group (32 eyes, range -6.25D to -10.00D) and moderate myopia group (18 eyes, range -3.00D to -6.00D). Posterior corneal surfaces were measured by a Scheimpflug camera (Pentacam, Oculus Germany) preoperatively and 1 month, 3 months, 6 months and 12 months postoperatively. Posterior central elevation (PCE) and posterior mean elevation (PME) at 17 predetermined points in the central-4mm area above the best-fit sphere were analyzed. No significant difference in the amount of posterior corneal elevation changes in the high myopia group was noted over time (P = 0.23 and P = 0.94 for PCE and PME, respectively). Similarly, the changes in the moderate myopia group before and after SMILE were not significant either (P = 0.34 and P = 0.40 for PCE and PME). A statistically significant correlation was found between the residual bed thickness and the shift of the PCE in the high myopia group at 12 months postoperatively (r = 0.53, P = 0.01). The results of this study suggest that the posterior corneal surface remain stable within one year after SMILE for both moderate and high myopia. The changes of PCE correlate to the residual bed thickness for high myopia. Long-term changes of posterior corneal surface need further investigation.

To compare centration and functional optical zone (FOZ) after small incision lenticule extraction (SMILE) and femtosecond laser-assisted in situ keratomileusis (LASIK). In this prospective, randomized, single-masked, paired-eyed, clinical trial, 70 patients received SMILE in one eye and LASIK in the other eye for myopia and myopic astigmatism. FOZ was calculated using custom software on 3-month postoperative refractive power maps (Pentacam HR; Oculus Optikgeräte GmbH, Wetzlar, Germany). Programmed treatment area was defined as the total area of the programmed OZ plus the transition zone. Centration was evaluated by the linear distance between FOZ centroid and the pupil center and the corneal apex. The average preoperative spherical equivalent (-5.38 ± 1.65 vs -5.45 ± 1.61 diopters [D]), postoperative spherical equivalent (0.05 ± 0.39 vs 0.06 ± 0.39 D), uncorrected distance visual acuity (0.01 ± 0.13 vs 0.00 ± 0.08 logMAR), and corrected distance visual acuity (-0.07 ± 0.10 vs -0.07 ± 0.10 logMAR) were comparable in SMILE- and LASIK-treated eyes of the 60 patients with complete datasets (P > .419). Postoperative increase in spherical aberration was lower in SMILE than in LASIK (0.08 ± 0.16 vs 0.17 ± 0.18 µm, P = .002). The FOZ area was significantly larger in SMILE than in LASIK (30.25 ± 3.60 vs 29.21 ± 3.72 mm ), despite the smaller programmed OZ diameter (6.48 ± 0.08 vs 6.52 ± 0.11 mm) and smaller programmed treatment area (33.87 ± 0.81 vs 46.30 ± 2.61 mm , P < .037). Pupil centration (0.43 ± 0.21 vs 0.41 ± 0.22 mm) and apex centration (0.48 ± 0.24 vs 0.48 ± 0.22 mm) were comparable between SMILE and LASIK (P > .694). SMILE created a larger FOZ than LASIK, despite the smaller programmed OZ. This may be due to a difference in the biomechanical response between the two procedures. Visual outcome and centration were comparable between SMILE and LASIK. [J Refract Surg. 2019;35(4):230-237.].

AimTo compare the effect of the two femtosecond laser settings on visual performance after small-incision lenticule extraction (SMILE) for myopia and myopic astigmatism.MethodsForty-four eyes of 22 consecutive patients who underwent SMILE with an energy level of 140 nJ (spot distance 3.0 µm) in one eye, and with an energy level of 170 nJ (spot distance 4.5 µm) in the other eye, the eyes being randomly assigned. Preoperatively, 1 week, and 1 and 3 months postoperatively, the values of the modulation transfer function (MTF) cutoff frequency, Strehl ratio, objective scattering index (OSI) and Optical Quality Analysis System (OQAS) values (OVs) for these eyes were quantitatively assessed using an Optical Quality Analysis System (Visiometrics).ResultsNo significant differences were detected between the two groups in the visual and refractive outcomes, or in the MTF cutoff frequency, the Strehl ratio, the OSI, the OV 100%, the OV 20% or the OV 9% at any time point before or after surgery.ConclusionsSMILE with energy settings of 140 and 170 nJ was effective for the correction of myopia and myopic astigmatism. It is indicated that the differences in laser setting (140 nJ, spot distance 3.0 µm vs 170 nJ, spot distance 4.5 µm) did not significantly affect the optical quality including the intraocular scattering of eyes undergoing SMILE.Clinical trial numberThe protocol was registered with University Hospital Medical Information Network Clinical Trial Registry (UMIN000016241).