Biomechanical Effects of tPRK, FS-LASIK, and SMILE on the Cornea

Abstract

Purpose: The objective of this study is to evaluate the in vivo corneal biomechanical response to three laser refractive surgeries.Methods: Two hundred and twenty-seven patients who submitted to transepithelial photorefractive keratectomy (tPRK), femtosecond laser-assisted in-situ keratomileusis (FS-LASIK), or small-incision lenticule extraction (SMILE) were included in this study. All cases were examined with the Corvis ST preoperatively (up to 3 months) and postoperatively at 1, 3, and 6 months, and the differences in the main device parameters were assessed. The three groups were matched in age, gender ratio, corneal thickness, refractive error corrections, optical zone diameter, and intraocular pressure. They were also matched in the preoperative biomechanical metrics provided by the Corvis ST including stiffness parameter at first applanation (SP-A1), integrated inverse radius (IIR), deformation amplitude (DA), and deformation amplitude 2 mm away from apex and the apical deformation (DARatio2mm).Results: The results demonstrated a significant decrease post-operation in SP-A1 and significant increases in IIR, DA, and DARatio2mm (p < 0.05), all of which indicated reductions in overall corneal stiffness. Inter-procedure comparisons provided evidence that the smallest overall stiffness reduction was in the tPRK group, followed by the SMILE, and then the FS-LASIK group (p < 0.05). These results remained valid after correction for the change in CCT between pre and 6 months post-operation and for the percentage tissue altered. In all three surgery groups, higher degrees of refractive correction resulted in larger overall stiffness losses based on most of the biomechanical metrics.Conclusion: The corneal biomechanical response to the three surgery procedures varied significantly. With similar corneal thickness loss, the reductions in overall corneal stiffness were the highest in FS-LASIK and the lowest in tPRK.

Corneal Biomechanics After SMILE, Femtosecond-Assisted LASIK, and Photorefractive Keratectomy: A Matched Comparison Study

“…Our results indicated that the decreases in DCRs with SMILE were greater than those observed with FS-LASIK in a matched comparison study. Unlike our results, Xin et al 20 showed a greater decrease in stiffness with FS-LASIK than SMILE in low to moderate myopia at 6 months after surgery. This difference can be related to different follow-up times.…”

Predictive models for IOPs measured with NCT, GAT, and ORA among patients undergoing SMILE

“…In our opinion, there is room for improvement in the predictive models. Although only preoperative IOP NCT and IOP GAT played a significant role in the predictive models, it seems that there should be more parameters involved, such as corneal biomechanics ( Xin et al, 2022 ).…”

“…There are many studies on IOP among patients undergoing laser-assisted in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) ( Chang and Stulting, 2005 ; Kohlhaas et al, 2006 ; Yang et al, 2006 ; Pepose et al, 2007 ; Johannesson et al, 2012 ; Han et al, 2013 ; Schallhorn et al, 2015 ; Sales-Sanz et al, 2016 ), while limited literature reports exist on predictive models of IOP changes after small incision lenticule extraction (SMILE) ( Li et al, 2016 ; Shen et al, 2016 ). As a flapless procedure utilizing a small incision, SMILE preserves the integrity of the corneal tissue (including Bowman’s layer) and serves a better corneal biomechanics than LASIK ( Wang et al, 2022 ), although it does not preserve suspect corneas before iatrogenic ectasia ( Bao et al, 2022 ; Xin et al, 2022 ). The impact of SMILE on the corneal structure prompts changes in the IOP that might differ from other refractive surgeries.…”

The role of corneal biomechanical properties assessment in laser vision correction – the introduction

“…Many studies report that LVC compromise the biomechanical strength of the cornea [1][2][3][4][5][6]. However, the change in corneal biomechanics is strongly related to the refractive surgery technique and ablation profile.…”