Changes in corneal biomechanics during small-incision lenticule extraction (SMILE) and femtosecond-assisted laser in situ keratomileusis (FS-LASIK)

Abstract

Observe the influence of femtosecond laser cutting on corneal biomechanics during small-incision lenticule extraction (SMILE) or femtosecond-assisted laser in situ keratomileusis (FS-LASIK) and assess the biomechanical changes following the operation. Prospective, non-randomized study. A total of 80 eyes from 80 patients were treated with either SMILE or FS-LASIK. Parameters of inverse concave radius, deformation amplitude ratio 2mm or 1mm (DA ratio 2mm or 1mm), highest concavity radius (HC radius), biomechanically corrected intraocular pressure (bIOP), and central corneal thickness (CCT) measured by Corvis ST II were recorded at 1day preoperatively, immediately after the lenticule or flap creation, during subsequent lenticule extraction or excimer laser ablation, and during follow-up at 1week, 1month and 3months postoperatively. After lenticule creation, the DA ratio 2mm or 1mm was bigger (p < 0.05), meanwhile, CCT was thicker (p < 0.05) than with flap creation. Partial parameters changed significantly after lenticule creation or flap creation, and all parameters changed significantly after tissue removal. All parameters showed no significant differences between the two groups (p > 0.05) after operation. The variations in bIOP (ΔbIOP) after operation were significantly less than those in Δnon-contact IOP (p < 0.001) in two groups. Femtosecond laser cutting during lenticule creation has a greater impact on corneal biomechanics than flap creation. Both the femtosecond laser cutting and removal of tissue degrade corneal biomechanics; however, these effects may be predominantly a result of tissue removal. SMILE and FS-LASIK have no differences in corneal biomechanics when the same CCT is consumed. bIOP is more reliable after the operation, but further study is essential.