Variation in Corneal Biomechanical Properties Following Continuous Cross-Linking Treatment

Background
This retrospective study aimed to evaluate the ecacy of transepithelial accelerated corneal cross-linking when applied separately (transEpi ACXL) 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 of follow-up. The following parameters were assessed preoperatively and 6 months postoperatively: biomechanically corrected intraocular pressure (bIOP), maximum and mean keratometry (Kmax and Km), minimum and central corneal thickness (MCT and CCT), corneal coma, best-
corrected visual acuity (BCVA), deformation amplitude ratio at the apex and 2 mm nasal/temporal (DAR2), integrated inverse radius (IIR), stiffness parameter at rst 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). Both groups exhibited significant reductions in IIR, and increases in SSIv1 and SSIv2 (all P < 0.05). The improvements in Kmax, 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 (SSIv2Rdif) exceeded those of other biomechanical parameters in both groups (transEpi ACXL: SSIv2Rdif > DAR2Rdif, IIRdif; transPTK ACXL: SSIv2Rdif > DAR2Rdif, IIRRdif, SP-A1Rdif, HCTRdif, and SSIv1Rdif, 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.