Corneal Changes After Collagen Cross-linking ; Clinical and Oct Study

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 keratectasia (corneal ectasia) often progresses most rapidly in adolescence or early adulthood but tends to stabilize in patients after middle-age.

Human studies of UV-induced corneal cross-linking began in 2003 in Dresden, and early results were promising. The initial pilot study enrolled 16 patients with rapidly progressing keratoconus and all of the patients stopped progressing after treatment. Additionally, 70% had flattening of their steep anterior corneal curvatures (decreases in average and maximum keratometric values), and 65% had an improvement in visual acuity. There were no reported complications.

Per the typical cross-linking protocol, 0.1% riboflavin solution with 20% dextran is added to the de-epithelialized cornea and then photoactivated with UV-A light at 365 nm with irradiance of 3 mW/cm2 for 30 minutes. The cornea is de-epithelialized to allow adequate penetration of riboflavin into the corneal stroma. Riboflavin acts as photosensitizer; it creates free radicals, forms new molecular crosslinks, and ultimately increases the cornea's mechanical strength.

Collagen cross-linking experienced a rapid transition from laboratory procedure to clinical intervention because of the method's apparent safety and broad array of potential applications. One such clinical application is the treatment of keratoconus which is a degenerative disorder of the eye associated with thinning and subsequent bulging of the cornea, causing poor vision. Collagen cross-linking stops the progression of keratoconus in patients with mild disease, presumably by strengthening the cornea and preventing further bulging.

Collagen cross-linking has also been used successfully in the treatment of pellucid marginal degeneration and to treat iatrogenic (postoperative) ectasia. Studies have shown that CXL causes a reduction in corneal edema and thickness with improvement in visual acuity in patients with bullous keratopathy due to different causes. However, these changes last for only about six months and due to this transient effect, CXL may only have a palliative role, if at all, for now.