Assessment of corneal biomechanical properties using Corvis ST following LASIK, PRK, and CXL

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Abstract
To evaluate within-group corneal biomechanical changes induced by LASIK, photorefractive keratectomy (PRK), and corneal cross-linking (CXL) using Corvis ST, while accounting for differences in baseline corneal status between refractive surgery candidates and keratoconic eyes. This prospective comparative study included 150 eyes of 150 patients undergoing LASIK (n = 50), PRK (n = 50), or epithelium-off CXL for keratoconus (n = 50). Corneal biomechanical parameters were assessed preoperatively and at 6 months postoperatively using Corvis ST, including deformation amplitude (DA), stiffness parameter at first applanation (SP-A1), DA ratio at 2 mm, Ambrósio relational thickness horizontal (ARTh), corneal biomechanical index (CBI), and tomographic biomechanical index (TBI), the latter derived from combined Pentacam tomography and Corvis ST measurements. Within-group changes were analyzed using paired parametric or non-parametric tests as appropriate. Between-group comparisons were performed using ANCOVA or linear mixed-effects models adjusted for baseline values, age, central corneal thickness, and biomechanically corrected intraocular pressure. LASIK and PRK eyes demonstrated significant postoperative increases in DA, DA ratio at 2 mm, CBI, and TBI, along with significant reductions in SP-A1 and ARTh (all p < 0.001), indicating biomechanical weakening relative to their preoperative state. The magnitude of weakening was greater following LASIK than PRK after baseline adjustment. In contrast, keratoconic eyes treated with CXL showed significant reductions in DA, DA ratio, CBI, and TBI, and a significant increase in SP-A1 (p < 0.001), consistent with biomechanical stiffening. These changes occurred despite differing baseline biomechanical profiles between groups. LASIK and PRK are associated with measurable corneal biomechanical weakening, whereas CXL induces biomechanical stiffening in keratoconic corneas. These findings should be interpreted within the context of distinct baseline corneal conditions rather than as direct comparisons of procedural efficacy. Corvis ST provides a robust framework for quantifying procedure-specific biomechanical directionality within different clinical settings.
Funding Information
  • Misr University for Science & Technology

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