Long-Term Outcome of Corneal Collagen Crosslinking with Riboflavin and UV-A Irradiation for Keratoconus

Purpose: To evaluate long-term outcomes of corneal collagen crosslinking (CXL) using riboflavin and UV-A irradiation and to determine when to repeat CXL. Methods: In this retrospective consecutive interventional case series 131 eyes of 131 patients (95 male, 36 female, mean age 29.7 +/- 11.4 years) between 2006 and 2016 received standard CXL (Dresden protocol, epithelium-off) for progressive keratoconus. Corrected distance visual acuity (CDVA) and corneal tomography (K-1, K-2, K-max) were repeatedly recorded 1 year (n = 103 eyes) to 10 years (n = 44) postoperatively. Only one eye per patient was included. Paired t-test or Wilcoxon matched-pairs signed rank test was used for parametric and nonparametric data, respectively. Results: 1-3 years preoperatively, median K-2 significantly increased by 1.1 D (p < 0.001). Postoperatively, median K-2 increased by 0.1 D after 1 year, then decreased over the remaining postoperative period by 0.85 D (p = 0.021). K-max fluctuated without significant change. Median apical corneal thickness decreased by 16 mu m (p = 0.012) after 5 years and then returned to preoperative values. Mean CDVA showed a significant improvement (decrease in logMAR 0.08 after 10 years, p = 0.010). CXL non-responders, defined by a postoperative increase in K-max>2 D, increased from 16% after 5 to 33% after 10 years. Risk factors for non-response were young age, high astigmatism (>4.3 D), thin cornea (<480 mu m), poor initial visual acuity (CDVA >= 0.3 D), and atopic dermatitis. 4 eyes were re-treated 3-4 years after first CXL without complications and keratoconus stabilized thereafter. Conclusions: CXL can slow or stop keratoconus progression. However, as the number of responders declines after 5 years, especially patients with risk factors may require re-treatment.