In Vivo changes in corneal biomechanics after corneal collagen crosslinking in progressive keratoconus patients

Purpose: To investigate the effect of riboflavin/UV-A-assisted corneal collagen cross-linking therapy (CXL) on corneal biomechanics in patients with progressive keratoconus at least one year follow-up. Materials and Methods: This retrospective study included 31 eyes of 25 patients with progressive keratoconus who underwent CXL between June 2021 and January 2024 in the Cornea Unit of the Department of Ophthalmology at Çukurova University Faculty of Medicine (CUTF). The data from the preoperative ophthalmological examination, corneal topographic measurements obtained with the Pentacam® device, and biomechanical measurements obtained with the Corvis®ST device were recorded prior to the surgical procedure and at 1, 3, 6, and 12 months postoperatively. The demarcation line distance was recorded with corneal optical coherence tomography (Zeiss Cirrus®) at the postoperative third month. A correlation analysis was conducted to determine the relationship between keratoconus stages, as determined according to the Pentacam® Belin/Ambrosio keratoconus staging system, and corneal biomechanical data, as measured with the Corvis®ST device. Results: The study cohort comprised 25 patients, 15 males and 10 females, with a mean age of 17.8 ± 3.9 years (13–29 years). The statistical analysis of the data obtained from the Corvis®ST device in 22 eyes of 20 patients with a follow-up period of 12 months or more revealed a significant postoperative decrease in SSI, DA, ARTh, IR, CBiF, E-staging, and CCT parameters (p < 0.05). The analysis of the preoperative and postoperative 12-month change in Pentacam® data revealed a statistically significant decrease (p < 0.05) in K1, K2, Kmax, EIKK, ART-max, KI, and KISA values, as well as an increase (p < 0.05) in Rmin, BAD-D, and mean progression index values. A negative correlation was observed between keratoconus stage and corneal biomechanical markers, including A2 velocity, SSI, SPA1, ARTh, and CBiF values. Conversely, a positive correlation was noted between DA ratio, IR, and E-staging values. The postoperative biomechanical improvement was found to be less pronounced in keratoconus patients with topographically advanced keratoconus prior to CXL. The demarcation line distance, as measured at three months post-CXL, demonstrated a correlation with select biomechanical stiffness parameters, including A1 velocity, A2 velocity, SSI, DA ratio, and IR, as assessed with the Corvis®ST device. Conclusion: In our study, we observed that the change in biomechanical parameters in patients with keratoconus who underwent CXL was most pronounced in the early postoperative period, and that this change decreased over time in the subsequent period. We also observed that while the improvement effect of CXL on visual and topographic values was more pronounced and continuous, the biomechanical results were variable. Further clinical studies with larger case series and longer follow-up periods are required in order to gain a deeper understanding of this issue. Keywords: Keratoconus; Corneal cross-linking; Corneal biomechanics