Corneal collagen cross-linking with riboflavin and UVA light (CXL) is the only method designed to arrest the progression of keratoconus. In recent years, it is a preferred method for targeting the stromal instability. It is popular treatment worldwide and is offered at various centers offering this option. The single most important outcome with CXL is the expected reduction in the need for donor keratoplasty. Our own study and several other studies have reported results up to 12 months after performing CXL. The studies with long-term data have been performed with the corneal epithelium scraped off and thus, this discussion is restricted to studies performed with the epithelium-off method.
In an uncontrolled retrospective study, Raiskup-Wolf et al. showed that the flattening process continues over a period of years: They followed a large cohort of patients (480 eyes of 272 patients) for up to 6 years and reported arrested keratoconus progression and significant improvements in visual acuity. The long-term stabilization of keratoconic corneas without significant side-effects has also been demonstrated in 44 eyes for up to 48 months after CXL, also accompanied by a reduction in the mean K value by 2 diopters and gradually increasing improvements in uncorrected visual acuity (UCVA) and best corrected visual acuity (BCVA) during the observation period. The statistical significance of these values was maintained after 36 and 48 months of follow up. In the Melbourne study, which was conducted in 49 patients, statistically significant differences were observed between control and treatment groups in terms of BCVA and K values for up to 12 months after CXL. More recently, another group has published an RCT reporting on one-year results after CXL for the treatment of keratoconus and corneal ectasia.
The procedure is reported to be safe and without any severe complications. Infectious keratitis and corneal melt have been reported. However, it is likely that the contact with the microbial agents causing infection or melt can occur during the epithelial healing phase and may not be directly attributable to the procedure itself.
In the light of currently available data, we can thus say that CXL is a safe procedure that is successful in arresting keratoconus. It is advisable to perform this procedure in patients with progressive keratoconus. Younger patients tend to have a more aggressive course, and thus should be offered this procedure too. It should no longer be considered as an elective procedure.