[Morpho-physiological features of the human eye sclera as the key unit in the level of intraocular pressure under normal conditions and in glaucoma].

The results of sclera investigations from the positions of morphology, physiology, biomechanics and control-system theory, are summarized. The morphological evidence was obtained supporting the physiological hypothesis stating that the specific anatomical organization and spatial displacement of elastic fiber-containing scleral layers against one another, are the key elements in formation of the individual level of intraocular pressure (IOP) in man both under normal and pathological conditions. It was shown that the elastic fibers outlined the collagen lamallae in of scleral internal layers. External scleral layer lacked elastic fibers. Scleral elastic fibers are necessary for the functioning of the mechanism of sclera microfluctuations associated with the intraocular fluid accumulation and removal, they are also important for dampening the sudden changes of IOP. Under normal conditions, age-related increase in scleral rigidity is primarily associated with the process of accelerated aging of its superficial non-elastic layers, resulting in the physiological response of the current IOP level elevation. As IOP becomes elevated under normal conditions, the internal elastic fiber-containing scleral layers are increasingly pressed against more rigid external layer. This limits the displacement capacity of internal layers against each other, resulting in the decline of the efficiency of elastic fiber work in dampening the sudden changes of IOP. In the healthy eyes, the process of scleral aging brings to a natural development of ophthalmohypertension, when IOP elevation is physiologically required for the maintenance of the volume microfluctuation mechanism ("scleral respiration"). In glaucoma, the pathological rearrangement of the scleral fibrous structures is observed, resulting in an additional abrupt increase of its rigidity, with the reciprocal significant elevation of the current level of IOP and the amplitude of its jumps. Pathophysiological mechanism of these significant changes in glaucoma remains currently unknown, however, morphological evidence indicates that it is associated with the changes in the metabolic processes in sclera.