Changes in Corneal Biomechanics and Epithelial Thickness in High Myopia Over −8.00D with/without Myopic Regression After Femtosecond Laser-Assisted in Situ Keratomileusis

Purpose: To compare the changes in corneal biomechanics and epithelial thickness after femtosecond laser-assisted in situ keratomileusis (FS-LASIK) in high myopia over -8.00D patients with and without myopia regression.Methods: This retrospective case-control study included thirty-nine patients.Based on refractive status at one year after surgery, patients with a myopic shift 1.00 D were classified as the myopic regression group (R group, 33 eyes), while the remaining patients were classified as the normal group (N group, 42 eyes).Preoperative and postoperative visual outcomes, refraction, topography, corneal epithelial thickness, and corneal biomechanics were compared.Results: Ambrosio relational thickness to the horizontal profile (ARTh) at 3, 6, and 12 months postoperatively was significantly smaller in the R than in the N group, with mean differences of -9.75 (95% confidence interval (CI): -18.44 to -1.04), p= 0.029; -12.23 (95% CI: -20.02 to -4.42), p= 0.003; and -9.47 (95% CI: -16.86 to -2.08), p= 0.013, respectively.Meanwhile, the stiffness parameter A1 (SP-A1) at 6 and 12 months after surgery was smaller in the R than in the N group, with mean differences of -6.62 (95% CI: -12.85 to -0.37), p= 0.038 and -7.26 (95% CI: -13.79 to -0.71), p= 0.030, respectively.The postoperative changes in SP-A1 at 6 and 12 months were significantly larger in the R group than in the N group (6.47, 95% CI: 1.04 to 11.91, p= 0.020; and 5.96, 95% CI: 0.37 to 11.52, p= 0.037, respectively).In addition, corneal epithelial thickness (CET) in different zones showed a significant negative correlation with refractive error at 12 months after surgery, with correlation coefficients ranging from -0.55 to -0.32 (all p< 0.05, with the central zone showing p< 0.001).Conclusion: Ultra-high myopic patients with post-FS-LASIK regression have poorer corneal biomechanics and greater central epithelial thickening, highlighting these factors as key susceptibility features for refractive instability.Early assessment of these parameters may help identify at-risk patients and guide personalized management to improve long-term outcomes.