Corneal biomechanical properties comparison after laser-assisted in situ keratomileusis and refractive lenticular extraction

Background: Corneal biomechanical properties are a measure of corneal structural integrity and stiffness. Corneal refractive surgery can cause substantial changes in these properties and the extent of the effect is determined by the type of technique used. Objective: To compare the change in the biomechanics of the cornea after Laser-Assisted in Situ Keratomileusis (LASIK) and Small Incision Lenticule Extraction (SMILE). Methodology: The study was a prospective cohort study carried out at AL Yamama Eye Center, Baghdad, Iraq. Sixty patients with myopia and myopic astigmatism (mean age 26.6±7.3 years) were randomly recruited and stratified into two groups: LASIK group (mean spherical equivalent -3.1+2.3 D) and SMILE group (mean spherical equivalent -3.5+1.0 D). Every patient was subjected to complete corneal biomechanical analysis with the Corvis ST (Scheimpflug Technology) before operation and at 2 weeks and 2 months after operation. The main outcomes measures were deformation amplitude at 2 mm above the apex (DA 2mm), integrated radius (IR), and stiffness parameter at first applanation (SP-A1). Results: Surgical groups showed significant Decrease of corneal biomechanical properties at 2 weeks and 2 months after surgery by reducing central corneal thickness, stiffness parameter at initial applanation, increasing deformation amplitude at 2 mm, and increasing integrated radius (all p<0.05). The results of intergroup comparison showed that there was no significant difference in the corneal stiffness at 2 weeks after the operation (p > 0.05). At 2 months follow-up, however, the LASIK group had considerably more corneal stiffness reduction than the SMILE group (p<0.05). Conclusion: Both LASIK and SMILE operations result in the significant change of corneal biomechanical properties, though LASIK showed a higher level of corneal stiffness change than SMILE. These results indicate that SMILE can provide a better maintenance of corneal biomechanical integrity in the correction of myopia and myopic astigmatism.