ABSTRACT
VITREOUS ANATOMY AND PHYSIOLOGY The vitreous is the largest of the ocular structures, occupying the space bounded anteriorly by the lens and zonules and peripherally by the ciliary body, retina, and optic nerve (14.1). The vitreous is a hydrogel consisting of 99% water. It is relatively lacking in cells with the normal cellular components being macrophages (hyalocytes) that originate from the blood1. Most of the hyalocytes are located in the peripheral vitreous near the ciliary body. Noncross-linked type II collagen fibers make up the framework and hydrated, negatively-
charged hyaluronic acid polymers fill the spaces2. Hyaluronic acid is responsible for the viscosity of the vitreous and the relative amounts of collagen and hyaluronic acid determine whether the vitreous is in a gel or fluid state. The negatively-charged hyaluronic molecules repulse each other, causing expansion of the gel. The addition of positively-charged ions causes the vitreous gel to collapse, due to the neutralization of the repulsive negative charges3. Hyaluronic acid is produced by the hyalocytes and is in highest concentration in the peripheral vitreous4. The percentage of vitreous that is fluid increases with age.
