The Increase In Corneal Stiffness After Accelerated Corneal Cross-Linking In Progressive Keratoconus Using Different Methods Of Epithelial Debridement

To investigate the corneal stiffening effect after epithelium-off accelerated corneal cross-linking (A-CXL(9*10)) with mechanical epithelial debridement (Epi-off-mech), transepithelial phototherapeutic keratectomy (Epi-off-tPTK) and wavefront-guided (Epi-off-tPRK), correcting high order aberrations (HOA), in progressive keratoconus (KC).

Retrospective, interventional, non-randomized and observational study performed at the Department of Ophthalmology, University Hospital Carl Gustav Carus, TU Dresden, Germany.

KC Patients in whom A-CXL was indicated were treated with different types of epithelial debridements. In the Epi-off-mech group (n=45), the epithelium was removed using a hockey knife. For Epi-off-tPTK (n=39) and Epi-off-tPRK (n=17) epithelium thickness was measured and ablated using an excimer laser, whereas a correction of HOA were performed in the Epi-off-tPRK group. Corneal biomechanics, such as biomechanical corrected IOP (bIOP), integrated invers radius (IIR), and stress-strain index (SSI), and corneal tomography, such as thinnest corneal thickness (TCT) were assessed with Corvis ST and Pentracam HR before and one month after-CXL. For the analysis of the group comparisons, an ANOVA and a paired t-test were used.

Corneal tomography did not differ between the groups preoperatively (P>0.05). TCT decreased post-CXL statistically significantly by -12.38, -20.67, and -42.82µm in the Epi-off-mech, Epi-off-tPTK, and Epi-off-tPRK group, respectively. Nonetheless, corneal biomechanical stiffening was found in the Epi-off-mech and Epi-off-tPTK group indicated by an increased bIOP and SSI as well as a decreased IIR (all P<0.05). In the Epi-off-tPRK group, corneal stiffening was detected with the increased bIOP and decreased IIR (all P<0.05). Only in this group, the HOA improved statistically significantly (P<0.001). Between the groups, there were no significant differences in biomechanical parameters but TCT was significantly reduced after laser ablation.

Corneal stiffening occurs after A-CXL independently of the epithelium removal procedure. The increase of corneal stiffness was less pronounced in the Epi-off-tPRK due to the higher decrease in corneal thickness. However, the HOA decreased stronger, indicating a potential improvement in visual acuity.