Topography

The eyelids extend from the eyebrow superiorly to the cheek inferiorly and can be divided into orbital and tarsal components. At the level of the tarsus, the eyelid consists of 4 main histologic layers, from anterior to posterior (Fig 13-1):

• skin

• orbicularis oculi muscle

• tarsus

• palpebral conjunctiva

There is a surgical plane of dissection into the eyelid that is accessed through an incision starting at the gray line, an isolated slip of orbicularis muscle known as the Riolanmuscle. This dissection plane functionally separates the eyelid into anterior and posterior lamellae. See also BCSC Section 7, Oculofacial Plastic and Orbital Surgery.

Figure 13-1 Cross section of a normal eyelid. Proceeding from left (posterior) to right (anterior) are the palpebral conjunctiva; the tarsus, containing the meibomian glands (between arrowheads); the orbicularis oculi muscle (bracket); and the dermis, underlying the epidermis. Arrows indicate the eyelid margin.

(Courtesy of Heather Potter, MD.)

The skin of the eyelids is thinner than that of most other body sites. The surface epidermis consists of keratinized stratified squamous epithelium, which contains melanocytes and antigen-presenting Langerhans cells. Deep to the epidermis is the dermis (stromal tissue), which is composed of loose collagenous connective tissue and contains the following:

• cilia, or eyelashes, and associated sebaceous glands (of Zeis; specialized pilosebaceous units)

• apocrine sweat glands (of Moll)

• eccrine sweat glands

• pilosebaceous units (vellus hairs)

Eyelid glands secrete their products in various ways. Sebaceous glands are holocrine glands, meaning that their secretion contains entire secreting cells. The secretion from apocrine sweat glands contains the apical part of the secreting cells (decapitation secretion). Eccrine sweat glands and lacrimal glands secrete sweat and tears, respectively, without loss of any part of the secreting cells.

Two muscles elevate the upper eyelid: the levator palpebrae superioris (a skeletal muscle), of which only the aponeurotic portion is present in the eyelid, and the Müller muscle (a smooth muscle). The orbicularis oculi (a striated skeletal muscle), whose fibers are arranged circumferentially around the eye, closes the eyelid. The tarsal plate—a thick plaque of dense, collagenous connective tissue—contains the meibomian glands (specialized sebaceous glands). Also present near the upper border of the superior tarsal plate (and less so along the lower border of the inferior tarsal plate) are the accessory lacrimal glands of Wolfring; the accessory lacrimal glands of Krause are located in the conjunctival fornices. The palpebral conjunctiva adheres tightly to the posterior surface of the tarsus.

Excerpted from BCSC 2020-2021 series: Section 4 - Ophthalmic Pathology and Intraocular Tumors. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.