Comparison of Clinical and Biomechanical Outcomes of Small Incision Lenticule Extraction With 120- and 140-µm Cap Thickness.

Purpose: The purpose of this study was to compare the clinical outcomes and corneal biomechanical changes between 120-µm and 140-µm cap thickness after small incision lenticule extraction (SMILE). Methods: This prospective study included 150 eyes (150 patients: 91 eyes in the 120-µm group, and 59 eyes in the 140-µm group) who underwent SMILE. Enhanced correction nomograms were applied for patients according to cap thickness. Clinical outcomes, including visual acuity, refraction, and corneal wavefront aberrations, were compared between the two groups. Corneal biomechanics were evaluated using the Corvis ST (Oculus, Wetzlar, Germany). Results: The mean uncorrected-distance visual acuity, safety and efficacy indices, and refractive predictability were comparable in the 120-µm and 140-µm groups after SMILE. The postoperative total corneal root mean square higher-order aberrations (HOAs) and spherical aberrations was 0.48 ± 0.31 and 0.26 ± 0.10 in the 120-µm group, and 0.53 ± 0.16 and 0.34 ± 0.13 in the 140-µm group, which showed significant differences between the two groups (P = 0.027, and <0.001, respectively). Although corneal stiffness decreased after SMILE in both groups, the changes in the deformation amplitude ratio were significantly higher in the 140-µm group than in the 120-µm group (P = 0.022). Conclusions: SMILE with 120-µm and 140-µm cap thickness provided excellent predictable outcomes according to our enhanced correction nomogram. The amount of tissue removal required to achieve the same amount of refractive correction was greater in the thicker cap group. The induction of corneal HOAs and weakening of corneal biomechanics were less pronounced in the thin-cap group, which may be associated with the thinner cap, lesser lenticule thickness, or thicker residual stromal bed. Translational Relevance: Although SMILE with different cap thickness was effective, thicker lenticule thickness in the thick-cap group may be associated with induction of HOAs, and corneal stiffness changes.

Clinical outcomes of immediate transepithelial photorefractive keratectomy after suction loss during small-incision lenticule extraction.

PURPOSE: To investigate the surgical outcomes of immediate transepithelial photorefractive keratectomy (PRK) after suction loss during small-incision lenticule extraction (SMILE) and compare the outcomes with those of uneventful SMILE. SETTING: Eyereum Eye Clinic, Seoul, South Korea. DESIGN: Retrospective case series. METHODS: This study included 24 eyes of 12 patients who had uneventful SMILE in one eye and immediate transepithelial PRK after the development of suction loss during the lenticule cut in the contralateral eye. Visual acuity assessments, manifest refraction, and measurements of corneal wavefront aberrations were performed preoperatively and 6 months postoperatively. RESULTS: At 6 months, the mean uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), and spherical equivalent were -0.04 ± 0.05, -0.09 ± 0.05, and -0.02 ± 0.24 diopter (D), respectively, in the transepithelial PRK group and -0.10 ± 0.07, -0.06 ± 0.07, and -0.04 ± 0.17 D, respectively (P = .036, P = .109, and P = .671, respectively), in the uneventful SMILE group. The 6-month Snellen UDVA was better than 20/20 for 11 (92%) and 12 (100%) of eyes in the transepithelial PRK and uneventful SMILE groups, respectively. All 24 eyes showed unchanged or improved CDVA and a significant increase in the total corneal higher-order aberrations postoperatively. Corneal spherical aberrations exhibited a significant postoperative increase only in the transepithelial PRK group. CONCLUSIONS: Immediate transepithelial PRK after early suction loss during SMILE might be safe and effective, with refractive outcomes that are comparable with those after uneventful SMILE.

Comparison of clinical outcomes between vector planning and manifest refraction planning in SMILE for myopic astigmatism.

PURPOSE: To compare clinical outcomes of small-incision lenticule extraction (SMILE) between manifest refraction (MR) and vector planning for myopic astigmatism with high ocular residual astigmatism (ORA). SETTING: Yonsei University College of Medicine and Eyereum Eye Clinic, Seoul, South Korea. DESIGN: Prospective, randomized, comparative case series. METHODS: Patients with myopic astigmatism and ORA of 0.75 diopters (D) or greater were randomized into the MR or vector planning group and underwent SMILE without applying any nomogram for cylinder correction. Visual acuity, MR, corneal topography, and corneal aberration were measured preoperatively and postoperatively. Outcomes at 6 months postoperatively were compared between the groups. RESULTS: The study comprised 114 patients (114 eyes): 58 eyes in MR planning and 56 eyes in vector planning. The mean uncorrected and corrected distance visual acuity, safety and efficacy indices were comparable between the 2 groups. Postoperative refractive cylinder reached statistically significant differences between the groups (-0.22 ± 0.18 D and -0.14 ± 0.16 D in the MR and vector planning groups, respectively, P = .02). Postoperative corneal toricity and ORA reached statistically significant lower in the vector planning group. CONCLUSIONS: In myopic astigmatism with high ORA, MR and vector planning in SMILE were effective with comparable visual outcomes; vector planning showed statistically significant lower postoperative refractive and corneal astigmatism and ORA. Use of vector planning may improve refractive outcomes in SMILE cases with high ORA. However, the results may have been different had a nomogram adjustment been applied, as is often used for cylinder corrections with SMILE.

Decentration measurements using Placido corneal tangential curvature topography and Scheimpflug tomography pachymetry difference maps after small-incision lenticule extraction.

PURPOSE: To assess the agreement of decentration measurements between tangential curvature topography and tomography pachymetry difference maps after a small-incision lenticule extraction (SMILE) procedure. SETTING: Yonsei University College of Medicine and Eyereum Eye Clinic, Seoul, South Korea. DESIGN: Retrospective case series. METHODS: Decentrations and pupillary offset (angle κ) were analyzed and compared using two different methods. A difference map of the tangential curvature was generated with a Placido corneal topographer (Keratron Scout) and a pachymetry difference map was generated with a Scheimpflug tomographer (Pentacam) for each eye, using preoperative and 3-month postoperative scans. Decentrations were also compared using a vector difference plot for the two maps. RESULTS: The study comprised 155 eyes (155 patients). The magnitude of decentration was 0.27 mm ± 0.17 (SD) (range 0.02 to 0.88 mm) with the tangential curvature difference maps and 0.26 ± 0.20 mm (range 0.00 to 0.91 mm) with the pachymetry difference maps, showing no significant difference in the arithmetic values of decentration (P = .124). However, the vector difference in pupillary offset between preoperative and postoperative measurements from the pachymetry difference map significantly correlated with the magnitude of vector differences of decentration between the two maps (P = .007). The vector difference plot also showed a wide distribution spread to all 4 quadrants, demonstrating a lack of agreement. CONCLUSIONS: Although there was no significant difference between the scalar magnitude of decentration with the tangential topography difference maps and tomography pachymetry difference maps, the vector differences did not agree and increasing error was present with increasing differences in pupillary offset in the pachymetry difference maps.

Clinical outcomes of mechanical and transepithelial photorefractive keratectomy in low myopia with a large ablation zone.

PURPOSE: To evaluate the clinical outcomes, vector parameters, and aberrations between mechanical photorefractive keratectomy (PRK) and transepithelial PRK in eyes with low myopia. SETTING: Yonsei University College of Medicine and Eyereum Eye Clinic, Seoul, Korea. DESIGN: Retrospective, comparative case series. METHODS: Eighty-four eyes of 84 patients with low myopia (≤2.00 diopters) were treated with mechanical or transepithelial PRK (41 eyes and 43 eyes, respectively), with the application of a large optical zone (OZ). Visual acuity, manifest refraction, slitlamp evaluation, autokeratometry, corneal topography, and the evaluation of corneal wavefront aberrations were measured preoperatively and at 1, 3, and 6 months after surgery. The efficacy, predictability, vector parameters, corneal aberrations, and safety at 6 months after surgery were compared between the two treatment groups. RESULTS: The mean uncorrected distance visual acuity was comparable, at -0.13 ± 0.05 (SD) and -0.15 ± 0.05, in the mechanical and transepithelial PRK groups, respectively, at 6 months after surgery. The safety and efficacy indices, vector parameters, and aberrometric values were also comparable between the two groups. The OZ was large in both groups (7.09 ± 0.20 mm and 7.12 ± 0.27 mm in the mechanical PRK and transepithelial PRK groups, respectively), and showed no significant difference between groups. The corneal total root-mean-square higher-order aberrations and coma significantly reduced after treatment in both groups, and spherical aberrations significantly decreased after transepithelial PRK. CONCLUSIONS: Mechanical and transepithelial PRK with a large OZ provided effective and safe outcomes for the correction of low myopia without differences in visual acuity and refractive outcomes between procedures.

Adjustment of Spherical Equivalent Correction According to Cap Thickness for Myopic Small Incision Lenticule Extraction.

PURPOSE: To evaluate the amount of spherical equivalent correction for three different cap thicknesses (120, 130, and 140 µm) during myopic small incision lenticule extraction (SMILE) and determine the association between the amount of spherical equivalent correction and several variables in each cap thickness group. METHODS: In this retrospective, comparative, observational case series study, the authors compared refractive errors, keratometric values, laser setting (sphere correction, cylinder correction, spherical equivalent correction, optical zone, and cap diameter), and spherical aberration measured preoperatively and at 3 months postoperatively between three different cap thickness groups: 120 µm (n = 554), 130 µm (n = 377), and 140 µm (n = 90). Multiple linear regression analyses were used to determine the associations between the amount of spherical equivalent correction and several variables, including age, preoperative spherical equivalent, optical zone diameter, central corneal thickness, preoperative mean keratometric values, and preoperative corneal asphericity. RESULTS: According to cap thickness, attempted correction is adjusted to achieve the same refractive outcomes for different cap thicknesses. There were significant differences in the amount of sphere correction and spherical equivalent correction, as well as lenticule thickness, among subgroups. Changes in keratometric values, corneal asphericity, and spherical aberration were also significantly different among subgroups (all P < .001). Changes in keratometric values, corneal asphericity, and spherical aberration significantly increased as cap thickness increased. Preoperative spherical equivalent mainly influenced the amount of spherical equivalent correction in each group. CONCLUSIONS: Dioptric adjustment of spherical equivalent correction according to cap thickness is essential to obtain similar refractive outcomes in myopic SMILE procedures. [J Refract Surg. 2019;35(3):153-160.].