Comparative Evaluation Of Corneal Biomechanics After Smile And Femto‑Lasik Using Corvis St

To compare postoperative corneal biomechanical behavior following Small Incision Lenticule Extraction (SMILE) and Femto-Laser Assisted In Situ Keratomileusis (Femto-LASIK) using dynamic Scheimpflug imaging (Corvis ST), and to assess the clinical relevance of these differences for refractive procedure selection

Hazem Yassin international cornea center

This prospective comparative study included 20 patients (40 eyes) undergoing corneal laser refractive surgery for myopia. Eyes were allocated to SMILE or Femto-LASIK. Corneal biomechanics were evaluated using the Corvis ST preoperatively and at 3 months by measuring deformation amplitude. Preoperative parameters were analyzed in relation to age and central corneal thickness. Postoperative biomechanical parameters were correlated with postoperative corneal thickness and surgical variables, including stromal ablation or lenticule depth. All procedures were performed with the VisuMax 500 femtosecond laser and excimer ablation using the ALLEGRETTO system. Statistical analysis included intra- and intergroup comparisons, with p < 0.05 considered.

Both SMILE and Femto-LASIK resulted in statistically significant postoperative changes in corneal biomechanical parameters, reflecting altered corneal response to air-puff deformation. Deformation amplitude increased significantly after both procedures; however, the magnitude of increase was significantly greater in the Femto-LASIK group compared with the SMILE group (p < 0.05). Across multiple Corvis ST parameters, SMILE demonstrated relatively better preservation of corneal biomechanical stability. These findings indicate greater biomechanical weakening following flap-based refractive surgery compared with the flapless SMILE technique.

SMILE induces significantly less postoperative corneal biomechanical alteration than Femto-LASIK as measured by Corvis ST, highlighting the biomechanical advantage of flapless refractive surgery and critical role of anterior stromal preservation in maintaining corneal stability. Preoperative Corvis ST assessment provides functional information beyond corneal thickness and topography, with dynamic deformation parameters reflecting intrinsic corneal resistance to intraocular pressure–related stress. More compliant corneas may represent a higher-risk profile for flap-based procedures. Integrating biomechanical analysis with tomographic and refractive data supports individualized procedure selection and promotes long-term biomechanical safety.