Corneal collagen cross-linking is a technique which uses UV light and a photosensitizer to strengthen chemical bonds in the cornea. The goal of the treatment is to halt progressive and irregular changes in corneal shape known as ectasia. These ectatic changes are typically marked by corneal thinning and an increase in the anterior and/or posterior curvatures of the cornea, and often lead to high levels of myopia and astigmatism. The most common form of ectasia is keratoconus and less often ectasia is seen after laser vision correction such as LASIK.

Cross-linking of collagen refers to the ability of collagen fibrils to form strong chemical bonds with adjacent fibrils. In the cornea, collagen cross-linking occurs naturally with aging due to an oxidative deamination reaction that takes place within the end chains of the collagen. It has been hypothesized that this natural cross-linkage of collagen explains why keratoectasia (corneal ectasia) often progresses most rapidly in adolescence or early adulthood but tends to stabilize in patients after middle-age.

In addition to the cross-linking that occurs commonly with corneal maturation, there are several other pathways that can lead to crosslinkage. Glycation refers to a reaction seen predominantly in diabetics that can lead to the formation of additional bonds between collagen. In the pathway most relevant to this topic, oxidation has been shown to be able to trigger corneal crosslinkage through the release of oxygen free radicals.