Collagens and proteoglycans of the cornea: importance in transparency and visual disorders

The cornearepresents the external part of the eye and consists of an epithelium, a stromaand an endothelium. Due to its curvature and transparency this structure makes up approximately 70 % of the total refractivepower of the eye. This function is partly made possible by the particular organization of the collagen extracellular matrix contained in the corneal stromathat allows a constant refractive power. The maintenance of such an organization involves other molecules such as type V collagen, FACITs (fibril-associated collagens with interrupted triple helices) and SLRPs (small leucine-rich proteoglycans). These components play crucial roles in the preservation of the correct organization and function of the corneasince their absence or modification leads to abnormalities such as corneal opacities. Thus, the aim of this review is to describe the different corneal collagens and proteoglycansby highlighting their importance in corneal transparency as well as their implication in corneal visual disorders.