The Vitreous

The vitreous is a transparent gel composed principally of water, collagen, and hyaluronic acid; it occupies 80% of the volume of the eye. The vitreous body is divided into 2 main topographic areas: the central, or core, and the peripheral, or cortical, vitreous. The vitreous gel is made up of collagen fibrils separated by hydrated hyaluronic acid molecules, which act as fillers and separators between adjacent collagen fibrils.

The anterior surface of the vitreous body is called the anterior cortical gel, made up of a condensation of collagenous fibers that attach to the posterior lens capsule, forming the ligament of Wieger (Fig 1-1). The retrolental indentation of the anterior vitreous is called the patellar fossa. The potential space between the peripheral posterior lens and the anterior cortical gel bordered by the Wieger ligament is called the Berger space. In the vitreous base, the collagen fibers are particularly dense; they are firmly attached to the anterior retina and posterior pars plana, creating a ringlike area that extends approximately 2 mm anterior and 3–4 mm posterior to the ora serrata. The vitreous is not only attached at its base; it is also firmly attached to the lens capsule, retinal vessels, optic nerve, and macula. The densely packed collagen fibrils in the cortical vitreous form the cortical gel. Posteriorly, fibers course in a direction roughly parallel to the inner surface of the retina, forming the preretinal tract. The vitreous attaches to the retinal surface, specifically the internal limiting membrane, via the adhesion molecules fibronectin and laminin. There is no basement membrane between the vitreous base and lens, an area called the annular gap, which is a ringlike zone important for diffusion between the aqueous and vitreous compartments. The space known as the premacular bursa, or the precortical vitreous pocket (see Fig 1-1), which is anterior to the posterior attachment of the vitreous to the macula, is believed to decrease the tractional forces generated during ocular motion by the inertial movement of the vitreous relative to the macula. The vitreous inserts on the edges of the optic nerve head, creating a funnel-shaped void of vitreous. This void is the opening of the Cloquet canal and is referred to as the area of Martegiani. The anatomy of the vitreous is difficult to delineate in vivo; however, the vitreous appears to contain interconnected cisterns and canals, most notably the ciliobursal canal that connects the ciliary body and macula. The vitreous also contains hyalocytes, which arise from bone marrow–derived stem cells. Oxygen is derived from diffusion from choroidal and retinal circulation. Hyalocytes consume most of this, limiting the amount of oxygen that reaches the lens and anterior segment. The vitreous has high ascorbate levels, which protects against oxidative damage (eg, to the lens).

Figure 1-1 Cross section of vitreous anatomy. A, Cross section diagram of the eye with emphasis on the anatomical features of the vitreous. The vitreous is most firmly attached to the retina at the vitreous base, and it also has adhesions at the optic nerve, along vessels, at the fovea, and to the posterior lens capsule. A prominent area of liquefaction of the premacular vitreous gel is called the premacular bursa, or precortical vitreous pocket. B, Swept-source optical coherence tomography (SS-OCT) image of posterior vitreous and macula region demonstrates the signal void in the vitreous cavity in front of the macula that represents the premacular bursa (arrowheads). Note also the very thick macular choroid and photoreceptor disruption in the central macula, extending nasally.

(Part A illustration by Mark M. Miller, part B courtesy of SriniVas Sadda, MD.)

Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.