Principle
Photopolymerization using UV-light was found to be the most promising technique to achieve cross-links in connective tissue. Photopolymerization is activated by means of a non-toxic and soluble photomediator and a wavelength which is absorbed strongly enough to protect deeper layers of the eye (riboflavin-UV-A technique).
UV-A radiation with concomitant administration of riboflavin/dextran solution as a photosensitizer generates singlet oxygen and superoxide free radicals. This process leads to physical cross-linking of the corneal collagen fibers.
Principle of cross-linking: Combination of riboflavin and UV-A light.
Intrahelical or interhelical cross-links can be formed within or between the tropocollagen units that comprise the individual collagen fibrills; and, intermicrofibrillar cross-links can be formed between adjacent collagen microfibrils that comprise the collagen lamellae.
Biomechanical reaction of the cross-linking process.
Thus, progressive corneal thinning is slowed down or even stopped. Biomechanical strength of corneal tissue is improved by a factor of up to 4.