Effects of customized corneal cross-linking on higher-order aberrations in progressive keratoconus and low-grade myopia

Objective: To evaluate the effects of customized corneal collagen cross-linking (CXL) on higher-order aberrations (HOAs) in keratoconus (KC): vertical coma (VC), horizontal coma (HC), spherical aberration (SA), trefoil (TF) and astigmatism, compared with the same effects in healthy eyes undergoing CXL for low-grade myopia.

Methods: This mixed-designed study included 38 eyes of 38 patients with KC, treated and followed prospectively, who received customized epi-on CXL in high oxygen, and a retrospective control group of 23 eyes from 23 patients who underwent central 4-mm CXL treatment for low-grade myopia. VC, HC, SA, TF and keratometry values were obtained from Pentacam HR® measurements at baseline and at 1, 6, 12 and 24 months post-treatment. Statistical analyses included paired T-tests for changes over time and Pearson correlation tests to assess relationships between aberrations, best spectacle-corrected and low-contrast visual acuities (BSCVA and LCVA, respectively) and CXL parameters.

Results: Reduced HOAs and improved visual acuities were observed in KC. A 20% reduction in VC was observed at 24 months (from -1.82 ± 1.15 μm to -1.46 ± 1.01 μm; 95% CI: [0.155, 0.629], p = 0.002), while a 17% reduction in HC was observed at 12 months (from -0.35 ± 0.56 μm to -0.29 ± 0.62 μm; 95% CI: [0.003, 0.096], p = 0.037). A positive correlation was found between baseline VC and the level of improvement in VC at 24 months (R² = 0.200, p = 0.015). SA increased by 126% at 24 months (from -0.21 ± 0.62 μm to 0.054 ± 0.52 μm; 95% CI: [0.143, 0.347], p ≤ 0.001). TF and astigmatism did not alter from the treatment. In myopia, the natural positive SA increased by 57% post-treatment (from 0.14 ± 0.061 μm to 0.22 ± 0.076 μm at 24 months; 95% CI: [0.067, 0.098], p ≤ 0.001), while changes in VC and HC were minor and BSCVA remained stable.

Conclusion: Customized CXL effectively reduces HOAs in KC. For VC the improvement is larger in cases with higher preoperative VC, indicating that the concept of customization has its intended effect. Accordingly, SA and visual acuities improve in KC whereas CXL for low-grade myopia tends to increase corneal SA unfavourably.