The relationship of the trabecular meshwork and the Schlemm canal to other structures is complex because the outflow apparatus is composed of tissue derived from the cornea, sclera, iris, and ciliary body (see Figs 2-11, 2-13). The trabecular meshwork is a circular spongework of connective tissue lined by trabeculocytes. These cells have contractile properties, which may influence outflow resistance. They also have phagocytic properties. The meshwork is roughly triangular in cross section; the apex is at the Schwalbe line, and the base is formed by the scleral spur and the ciliary body.
The trabecular meshwork can be divided into 3 layers (see Fig 2-13):
The uveal portion and the corneoscleral meshwork can be divided by an imaginary line drawn from the Schwalbe line to the scleral spur. The uveal meshwork lies internal and the corneoscleral meshwork external to this line.
Aging changes to the trabecular meshwork include increased pigmentation, decreased number of trabecular cells, and thickening of the basement membrane beneath the trabecular cells. Trabecular sheets thicken two- to threefold. Endothelial cellularity is lost, connective tissue increases, debris accumulates in the meshwork, and glycosaminoglycans accumulate in the extracellular space. These changes can increase resistance to aqueous outflow. Such changes are exaggerated in chronic open-angle glaucoma. This subject is covered in greater depth in BCSC Section 10, Glaucoma.
Uveal Trabecular Meshwork
The uveal meshwork faces the anterior chamber. It is composed of cordlike trabeculae and has fewer elastic fibers than does the corneoscleral meshwork. The trabeculocytes usually contain pigment granules. The trabecular apertures are less circular and larger than those of the corneoscleral meshwork.
Excerpted from BCSC 2020-2021 series: Section 2 - Fundamentals and Principles of Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.