CXL is a procedure which uses UV light to strengthen 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.


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Cross Linking Background

Cross-linking of collagen refers to the ability of collagen fibrils to form strong chemical bonds, aka cross-links 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.

The bases for the corneal collagen cross-linking procedures were developed in Europe by researchers at the University of Dresden in the late 1990’s. Clinical trials have been in course since the same year. 

UV light was used to induce collagen cross-linking in soaked porcine and rabbit corneas via the oxidation pathway. The resultant corneas were shown to be stiffer and more resistant to enzymatic digestion. Investigation also proved that the treated corneas contained higher molecular weight polymers of collagen due to fibril cross-linking. Safety studies showed that the endothelium was not damaged by the treatment if proper UV irradiance was maintained and if the corneal thickness exceeded 400 microns.

Corneal collagen cross-linking is FDA approved in the United States. 


Indications for Cross-Linking

  • Corneal Ectasia

  • Keratokonus 

  • Iatrogenic Ectasia

  • Pellucid Marginal Degeneration (PMD)

  • Infectious keratitis



  • Corneal thickness of less than 400 microns is a contraindication to the standard treatment protocol

  • Prior herpectic infection is a contraindication because it may result in viral reactivation

  • Concurrent infection

  • Severe corneal scarring or opacification

  • History of poor epithelial wound healing

  • Severe ocular surface disease (ex. dry eye)

  • Autoimmune disorders