Collagen-elastic eye frame and its role in homeostasis and pathology

Abstract

The concept of a unifi ed fi bro-elastic eye frame, including Descemet’s membrane, Dua’s membrane, trabecular tissue, Bruch’s membrane and the posterior borderline membrane of the optic nerve disc, makes it possible to consider a number of pathological processes aff ecting these structures within the framework of a single etiopathogenetic mechanism. Basement membranes are fi brous acellular structures, usually of type IV collagen, and separating the inner or outer surfaces of epithelial or endothelial formations from the underlying connective tissue. The ultrastructure organization of the basement membranes in various tissues of the body is similar: it distinguishes between the internal collagen part – the basal plate, and the underlying layer of reticular and elastic fi bers. Despite their extracellular location, the basement membranes are not part of the extracellular matrix and do not belong to connective tissue, although they have macromolecules in common with it. As you know, the most common functional role of basement membranes is manifested in the structural addition of epithelial formations histogenetically related to them and in the delimitation of the latter from the underlying connective tissue. The basement membranes maintain the unity of the structural and functional complex, providing adhesion between the epithelial monolayer on the one hand and the underlying stroma on the other. The general plan of this organization is the unity of collagen and elastic plates, which are formed from both the epithelium and the stroma, including the adjacent vascular component, the participation of which, in particular, has long been noticed in Bruch’s membrane. Violation of this unity triggers the pathogenetic mechanism of many pathological processes, which are clearly manifested in the eye. Thus, the eyeball can become part of a systemic pathological process caused by genetic defects in collagens and age-related degenerative processes. Among such common diseases, one should fi rst of all pay attention to open-angle glaucoma and endothelial corneal dystrophy. In these pathological processes, with all their clinical diff erences, one can see a unifying factor associated with the most vulnerable link that triggers the pathogenic mechanism. Despite certain molecular-biochemical nuances, collagen-elastic membranes have a universal structural design, and with a variety of pathological onditions in which it is involved, two etiopathogenetic mechanisms can be distinguished. These mechanisms appear as changes of a dystrophic or degenerative nature. In particular, in the trabecular tissue, the age-related decrease in the number of endothelial cells lining the trabeculae leads to a loss of the ability to retain intraocular fl uid and initiates a process similar to what occurs in bullous keratopathy in the corneal stroma. Swelling of the collagen fi bers of the trabecula leads to a narrowing of the lumen of the intertrabecular fi ssures and an increase in resistance to the outfl ow of intraocular fl uid. So, using the example of eye pathology, we can understand the special functional role of collagen-elastic membranes. To the same extent, this concept contributes to a deeper nderstanding of a number of diseases and pathological processes, in the etiopathogenesis of which Bruch’s membrane plays an important role. Among these diseases is age-related macular degeneration. Thus, the hypothesis presented by us and its theoretical justifi cation for the inner collagen capsule of the eye allows us to consider the pathogenesis of eye diseases in a new way and outline the practical steps of their treatment.