Comparison of corneal biomechanics after SMILE versus LASEK in moderate to high myopia with relatively thin corneas: a retrospective comparative study

This study aimed to compare the 2-year refractive outcomes and corneal biomechanical changes after Small Incision Lenticule Extraction (SMILE) versus Laser-Assisted Subepithelial Keratectomy (LASEK) in patients with moderate to high myopia (spherical equivalent [SE]: -2.00 to -6.75 D) and relatively thin corneas (central corneal thickness [CCT] ≤ 530 μm). In this retrospective, comparative, non-randomized study, 47 patients (47 eyes) were included, assigned to either SMILE (n = 24) or LASEK (n = 23). Corneal biomechanical parameters (Corvis ST II [CST]: biomechanically corrected intraocular pressure [bIOP], stiffness parameter at first applanation [SP-A1], integrated inverse radius [IntInv-Rad], deformation amplitude ratio at 2.0 mm [DAR 2.0 mm], Ambrosio relational thickness horizontal [ARTh]) and refractive outcomes (safety and efficacy indices) were evaluated preoperatively and 2 years postoperatively. Intergroup comparisons of changes (Δ) in these parameters and correlation analyses with potential predictors were analyzed. The safety indices were comparable between the two groups (SMILE: 0.90 ± 0.11 vs. LASEK: 0.87 ± 0.09; P = 0.24), but the efficacy index was statistically higher in the LASEK group (1.09 ± 0.18 vs. 0.98 ± 0.13; P = 0.02), although the clinical relevance of this difference is likely limited as both values are close to the ideal of 1.0. Preoperatively, the LASEK group had thinner CCT (492.78 ± 18.92 vs. 509.71 ± 9.47 μm; P < 0.01), lower cylinder (-0.80 ± 0.86 vs. -1.28 ± 0.78 D; P = 0.05), and lower SE (-3.73 ± 1.39 vs. -4.71 ± 1.13 D; P = 0.01). At 2 years, compared with SMILE, LASEK resulted in a significantly smaller reduction in ΔSP-A1 (-11.31 ± 23.72 vs. -28.99 ± 21.37; P = 0.01) and smaller increases in ΔIntInv-Rad (+ 0.98 ± 1.48 vs. +1.75 ± 0.89; P = 0.03) than SMILE. Postoperative CCT was positively correlated with ΔSP-A1 (SMILE: r = 0.50, P = 0.01; LASEK: r = 0.60, P < 0.01) and negatively with ΔIntInv-Rad (SMILE: r=-0.51, P = 0.01; LASEK: r=-0.45, P = 0.03). This study suggests that in patients with moderate to high myopia and relatively thin corneas, LASEK was associated with smaller alterations in certain corneal biomechanical parameters at 2 years postoperatively compared to SMILE, as indicated by better preservation of corneal stiffness (SP-A1) and less change in overall biomechanical response (IntInv-Rad). Postoperative CCT is a significant predictor of these biomechanical alterations. Both procedures demonstrated excellent and comparable safety profiles, with all patients achieving the primary clinical goal of refractive surgery.