Corneal collagens.

Cornea is a highly differentiated tissue rich in extracellular matrix (ECM) specifically distributed in space in order to insure its dual role--transparency and protection of inner eye-tissues. Corneal ECM is especially rich in collagens. Since the characterisation of a number of distinct collagen types it appeared that most of them are present in the cornea. Their synthesis follows a specific program of sequential expression of the different collagen types to be synthesised during the development and maturation of the cornea. The precise regulation of the diameter and orientation of fibers, and of the interfibrillar spaces is partially at least attributed to interactions between glycosaminoglycans and collagens. The 'program' of vectorial collagen synthesis and GAG-collagen interactions changes also with age and in several pathological conditions as corneal dystrophies and wound healing. The Maillard reaction, especially in diabetes, is one of these important factors involved in age-dependent modifications of corneal structure and function. Far from being inert, corneal collagens were shown to have relatively short half-lives. The biosynthesis of corneal collagens was studied also during wound healing. The refibrillation of wounded corneas does not follow the original 'program' of ECM-synthesis as shown by the comparative study of wound healing using biochemical and morphometric methods. This review recapitulates briefly previous and recent studies on corneal collagens in order to present to clinicians and scientists an overview of the state of the art of this important field at the intersection of eye research and matrix biology.