Corneal Collagen Cross-Linking in the Stabilization of Keratoconus

Background: Keratoconus is a slowly progressive ectatic deformity of the cornea with a prevalence of 200 to 400 cases per 100 000 persons. The cornea is thinner than normal and irregularly warped; irregular astigmatism and myopia result. Riboflavin-UVA crosslinking (collagen cross-linking) makes corneal tissue more rigid through a photochemical effect and can stop the progression of the disease. Methods: This review is based on relevant publications retrieved by a selective search in Medline, as well as on meta-analyses, Cochrane Reviews, and reports of national and international health care institutions. Results: Pertinent randomized controlled trials (RCTs) have shown that cross-linking prevents the progression of keratoconus to a statistically significant extent, as determined by measurement of topographic parameters. In the largest RCT to date (follow-up of 100 eyes for three years), the maximal corneal refractive power increased by 1.75 +/- 0.38 diopters in the control group and decreased by -1.03 +/- 0.19 diopters in the cross-linking group (p < 0.001). This was also the only trial in which data were reported on the patient-relevant endpoint of uncorrected visual acuity, which mildly improved in the cross-linking group (-0.15 +/- 0.06 logMAR, p = 0.009). Serious complications of cross-linking are known to date only from a few reports of individual cases. Cohort studies with follow-up times of up to ten years have shown that the condition can continue to progress after cross-linking, especially in younger patients. Conclusion: Cross-linking is the first available treatment for keratoconus that can improve the natural course of the disease.