Variation in corneal biomechanical properties following continuous cross-linking treatment

Background: This retrospective study aimed to evaluate the efficacy of transepithelial accelerated corneal cross-linking (transEpi ACXL) when applied separately or combined with phototherapeutic keratectomy (transPTK ACXL) in keratoconic eyes using biomechanical parameters. Methods: The study included eyes with progressive keratoconus treated with either continuous transEpi ACXL or transPTK ACXL with 6 months follow-up. The following parameters were assessed preoperatively and 6 months postoperatively: biomechanically corrected intraocular pressure (bIOP), maximum and mean keratometry (K _max and K _m), minimum and central corneal thickness (MCT and CCT), corneal coma, best-corrected visual acuity (BCVA), deformation amplitude ratio at 2 mm nasal/temporal (DAR2), integrated inverse radius (IIR), stiffness parameter at first applanation (SP-A1), highest concavity time (HCT) and two versions of stress–strain index (SSIv1 and SSIv2). Results: A total of 75 eyes from 72 patients were included (31 in the transEpi ACXL group and 44 in the transPTK ACXL group). The two groups were comparable in age (23.0 ± 5.0 vs. 21.3 ± 5.2 years) and TKC grade distribution (grades 1–4), with no statistically significant between-group differences (P = 0.321 and 0.766, respectively). Both groups exhibited significant reductions in IIR, and increases in SSIv1 and SSIv2 (all P < 0.05). The improvements in K _max, coma, and SSIv2 were greater in the transPTK ACXL group than in the transEpi ACXL group (all P < 0.05). The relative difference in SSIv2 (SSIv2 _Rdif) exceeded those of other biomechanical parameters in both groups (transEpi ACXL: SSIv2 _Rdif > DAR2 _Rdif, IIR _dif; transPTK ACXL: SSIv2 _Rdif > DAR2 _Rdif, IIR _Rdif, SP-A1 _Rdif, HCT _Rdif, and SSIv1 _Rdif, all P < 0.05). Conclusions: TransPTK ACXL resulted in better biomechanical and visual benefits in comparison with transEpi ACXL 6 months after treatment. SSIv2 demonstrated superior performance in assessing the efficacy of corneal cross-linking.