orbital septum. The lateral canthal tendon is a distinct entity, separate from the orbicularis muscle. It measure about 1 mm in thickness, 3 mm in width, and approximately 5–7 mm in length [27]. The insertion of these fibers extends posteriorly along the lateral orbital wall, where it blends with strands of the lateral check ligament from the sheath of the lateral rectus muscle. With age the tendon becomes lax, allowing the canthal angle to move several millimeters with up and down gaze [27].

and sweat glands. Just lateral to the caruncle, there is a vertical fold of conjunctiva, the plica semilunaris. The submucosa of this tissue contains adipose cells and smooth muscle fibers, resembling the nictitating membrane of lower vertebrates. This likely represents a vestigial structure that has been modified to allow enough horizontal slack at the shallow medial fornix for rotation of the globe.

The Conjunctiva

The conjunctiva is a mucous membrane that covers the posterior surface of the eyelids and the anterior surface of the globe, except for the cornea. The palpebral portion is closely applied to the posterior surface of the tarsal plate and the sympathetic tarsal muscle of Müller. It is continuous around the fornices above and below where it joins the bulbar conjunctiva. Small accessory lacrimal glands are located within the submucosal connective tissue.

At the medial canthal angle is a small mound of tissue called the caruncle. This consists of modified skin containing hairs, sebaceous glands,

Nerves to the Eyelids

The motor nerves to the orbicularis muscle derive from the facial nerve (N. VII) through its temporal and zygomatic branches (Fig. 3.6). The facial nerve divides into two divisions: an upper temporofacial division and a lower cervicofacial division [28]. The upper division further subdivides into the temporal and zygomatic branches that innervate the frontalis and orbicularis muscles. The lower cervicofacial division gives rise to the buccal, mandibular, and cervical branches, innervating muscles of the lower face and neck. There can be considerable variation in the branching pattern of these nerves, and in some individuals extensive anastomoses interconnect all of these peripheral branches.

The sensory nerves to the eyelids derive from the ophthalmic and maxillary divisions of the trigeminal nerve. Sensory input from the upper lid passes to the ophthalmic division through its main terminal branches, the supraorbital, supratrochlear, and lacrimal nerves. The infratrochlear nerve receives sensory information from the extreme medial portion of both the upper and lower eyelids. The zygomaticotemporal branch of the lacrimal nerve innervates the lateral portion of the upper eyelid and temple. These branches also innervate portions of the adjacent brow, forehead, and nasal bridge. The lower eyelid sends sensory impulses to the maxillary division via the infraorbital nerve. The zygomaticofacial branch from the lacrimal nerve innervates the lateral portion of the lower lid and part of the infratrochlear branch receives input from the medial lower lid.

Vascular Supply to the Eyelids

Vascular supply to the eyelids is extensive. The posterior eyelid lamellae receive blood through the palpebral arterial arcades (Fig. 3.7). In the upper eyelid, a marginal arcade runs about 2 mm above the eyelid margin and a peripheral arcade extends along the upper border of tarsus between the levator aponeurosis and Müller’s muscle. These vessels are supplied medially by the superior medial palpebral vessels from the terminal ophthalmic artery and laterally by the superior lateral palpebral vessel from the lacrimal artery. The lower lid arcade receives blood from the medial and lateral inferior palpebral vessels.

The venous drainage system is somewhat less well defined than the arterial system. Drainage is primarily into several large vessels of the facial system (Fig. 3.8). Lymphatic drainage from the