retina. The main portion of the vitreous body is a homogeneous gel containing approximately 99% water (the vitreous humor), collagen, glycosaminoglycans (principally hyaluronan), and a small population of cells called hyalocytes. These cells are believed to be responsible for synthesis of collagen fibrils and glycosaminoglycans. Hyalocytes in routine hematoxylin and eosin (H&E) preparation are difficult to visualize. Often, they exhibit a well-developed rER and Golgi apparatus. Fibroblasts and tissue macrophages are sometimes seen in the periphery of the vitreous body. The hyaloid canal (or Cloquet’s canal), which is not always visible, runs through the center of the vitreous body from the optic disc to the posterior lens capsule. It is the remnant of the pathway of the hyaloid artery of the developing eye.
Accessory Structures of the Eye
The conjunctiva lines the space between the inner surface of the eyelids and the anterior surface of the eye lateral to the cornea.
The conjunctiva is a thin, transparent mucous membrane that extends from the corneoscleral limbus located on the peripheral margin of the cornea across the sclera (bulbar conjunctiva) and covers the internal surface of the eyelids (palpebral conjunctiva). It consists of a stratified columnar epithelium containing numerous goblet cells and rests on a lamina propria composed of loose connective tissue. The goblet cell secretion is a component of the tears that bathe the eye.
Conjunctivitis, an infammation of the conjunctiva that is commonly called pinkeye, is characterized by redness, irritation, and watering of the eyes. For more clinical information, see Folder 24.4.
The primary function of the eyelids is to protect the eye.
The skin of the eyelids is loose and elastic to accommodate their movement. Within each eyelid is a flexible support, the tarsal plate, consisting of dense fibrous and elastic tissue. Its lower free margin extends to the lid margin, and its superior border serves for the attachment of smooth muscle fibers of the superior tarsal muscle (of Mler). The undersurface of the tarsal plate is covered by the conjunctiva (Fig. 24.16). The orbicularis oculi muscle, a facial expression muscle, forms a thin oval sheet of circularly oriented skeletal muscle fibers overlying the tarsal plate. In addition, the connective tissue of the eyelid contains tendon fibers of the levator palpebrae superioris muscle that open the eyelid (see Fig. 24.16).
In addition to eccrine sweat glands, which discharge their secretions directly onto the skin, the eyelid contains four other major types of glands (see Fig. 24.16):  The tarsal glands (Meibomian glands), long seba ceous glands embedded in the tarsal plates, appear as ver tical yellow streaks in the tissue deep in the conjunctiva.
 FOLDER 24.4
Clinical Correlation: Conjunctivitis