Purpose: To investigate and compare corneal biomechanical changes in the form of corneal hysteresis (CH) and corneal resistance factor (CRF) after small-incision lenticule extraction (SMILE) and laser-assisted subepithelial keratectomy (LASEK).
Methods: In this retrospective observational study, patients who underwent either SMILE (36 eyes, 21 patients) or LASEK (35 eyes, 19 patients) were included. Data were collected preoperatively and at 1 and 3 months postoperatively, which included corneal topography and Ocular Response Analyzer values of CH, CRF, and intraocular pressure (IOP). Differences between both surgical groups and the relationships between variables were evaluated.
Results: CH, CRF, Goldmann IOP, and corneal compensated IOP after surgery were significantly lower than the preoperative values (P < 0.05) in both surgical groups. Lenticule thickness (LT) correlated with ΔCRF (Δ = postoperative - preoperative value) in the SMILE group (r = -0.513, P = 0.001), but the ablation depth (AD) and ΔCRF showed no correlation in the LASEK group (r = -0.297, P = 0.083). In the SMILE group, ΔCRF/LT (-0.036 ± 0.01) and ΔCH/LT (-0.021 ± 0.01) values were significantly lower than ΔCRF/AD (-0.048 ± 0.02) and ΔCH/AD (-0.026 ± 0.02) values in the LASEK group (P < 0.05).
Conclusions: Both SMILE and LASEK alter corneal biomechanical strength. However, the changes induced by SMILE are more predictable than those induced by LASEK. In terms of per unit tissue removed, SMILE seems to have less effect on corneal biomechanics than LASEK, which may be due to preservation of the stiffer anterior stroma.