The Underlying Anatomy of Vitreous and Its Role in Retinal Disease

V itreous is a remarkable structure. It is 98% water, but owing to the 2% structural macromolecules, vitreous maintains an exquisite gel structure. Those structural macromolecules are hyaluronan, which is a glycosaminoglycan of repeating disaccharide units, and collagen. Because hyaluronan is very hydrophilic and absorbs water, where it goes, water follows. Hylauronan is also organized within an entangled network that creates viscoelasticity, an important biophysical property. Collagen is the “skeleton” of the vitreous body. The most prevalent subtype of collagen that comprises the human vitreous is type II. The only other place in the human body that type II collagen is found abundantly is the articular cartridge in the joints. In both the joints and vitreous, there are many simultaneous manifestations of inborn congenital errors. An organization of collagen and hyaluronan exists within the vitreous, so that the collagen fibrils are spread apart by the hyaluronan molecules, maximizing the number of photons that penetrate the vitreous and access the retina, where vision begins.1