The chemical identification of collagens and proteoglykans adds to the knowledge of the fine structure of the cornea as seen in histological sections and with the electron microscope. Chemical properties of collagens and proteoglykans help to understand the microscopical appearance of the tissue and some special functions of the cornea, such as transparency, stromal hydration, cohesion, elasticity and shear force resistance. Understanding mechanical properties of the cornea may be valuable for corneal and especially refractive surgery. A review of recent literature on intrastromal implants to be used for optical correction of refractive errors showed, that the resulting problems of corneal nutrition and also those of hydration may be solved by the time. But presumably proteolytic processes around intrastromal implants still prevent longterm tolerance of such implants.