TARSAL PLATES

The tarsal plates are composed of dense connective tissue. Each plate, which is curved to conform with the shape of the globe, functions as an internal skeleton for the lid (169, 170).

The upper tarsus is approximately 10 mm (0.4 in) wide in the center of the eyelid and 25–29 mm (1–1.1 in) long at the margin. The superior part of the tarsal plate is domeshaped, and the inferior border is essentially straight when the eyelids are closed. This gives the tarsus of the upper lid the formation of the letter ‘D’ on its side. The thickness of the tarsus is approximately 1 mm (0.05 in). The posterior surface is covered by closely adherent conjunctiva. The anterior surface is covered by pretarsal orbicularis muscle in its lower half, and by the extension of the levator aponeurosis in its upper half. The palpebral muscle attaches to the central 10 mm of the superior tarsal border.

The lower tarsal plate is approximately 25–29 mm in length and 1 mm in thickness, but is only 3.5–4 mm (0.15 in) in width at its widest point.5 The posterior surface is covered by adherent conjunctiva. The anterior surface is covered by pretarsal orbicularis muscle. The tarsi are connected to the orbital margins via the medial and lateral canthal tendons.

Each tarsus contains numerous meibomian glands that are essentially sebaceous glands arranged in a single row. There are 30–40 in the upper lid and 20–30 in the lower lid. These glands open onto the lid margin and appear as a row of minute orifices on the inner side of the intermarginal sulcus (the gray line) (172). Their secretion is sebum, which is rich in fatty acids and cholesterol and, therefore, has a yellow appearance. This liquid secretion can often be seen at the opening of the glands along the lid margin.

The free margin of each eyelid is approximately 25–30 mm in length and 2 mm (0.1 in) in width. Approximately 6 mm (0.25 in) lateral to the medial canthal angle there is a small tubercle known as the lacrimal papilla, which contains the punctum (the orifice) of the lacrimal canaliculus (172). Medial to the lacrimal papilla, the lid margin is smooth and rounded and may be associated with occasional cilia. Lateral to the punctum, the lid margin is thickened and flattened. In the center of the lid margin is the intermarginal sulcus (the gray line), anterior to which are the eyelashes. The anterior part of the intermarginal sulcus is cutaneous up to the level of the meibomian orifices. Posterior to the orifices, the epithelium assumes the mucosal characteristics of the conjunctiva.

The cilia are short, stout hairs that are arranged in two or three regularly placed rows. In the upper lid, the cilia are 8–12 mm (0.3–0.5 in) in length and number 100–150. In the lower lid, the eyelashes are only 6–8 mm (0.25–0.3 in) in length and usually number 50–75.2

COMMENT

Careful attention to the lid margin is essential in the diagnosis, as well as the surgical treatment of eyelid tumors. Interruption of the normal pattern of cilia and/or of the meibomian orifices might be the earliest clue to an underlying malignancy. The re-approximation of the eyelid cilia and tarsal plate during eyelid reconstruction is important when attempting to obtain the best functional and cosmetic result.

The orbital septum is a thin membrane of connective and elastic tissue that is attached along the orbital rim to the arcus marginalis, a thickened line of periosteum that courses around the orbital margin. The septum is a circular structure that extends from the orbital margins toward the tarsal plates. The preseptal orbicularis muscle lies anterior to the orbital septum, and the preaponeurotic fat lies posterior to it (170). The inferior aspect of the orbital septum in the upper lid blends with the levator aponeurosis several millimeters above the superior border of the tarsus. In the lower lid, the superior aspect of the orbital septum blends with the capsulopalpebral fascia in the area of the inferior border of the tarsus. Laterally, the septum blends with fibers of the palpebral portion of the orbicularis muscle to form the lateral palpebral raphé. Medially, the septum attaches to the posterior lacrimal crest and the lacrimal fascia.

In children and adults into the fifth decade of life, the orbital septum is a relatively tough structure. However, in the sixth, seventh, and eighth decades of life, the septum becomes very delicate. This observation is of surgical importance since the tough orbital septum may be mistaken for the levator aponeurosis. The orbital septum functions as a barrier that separates the eyelids from the orbit itself. It tends to restrict the passage of fluid and inflammatory matter between these two spaces.

ORBITAL FAT

For surgical purposes, orbital fat should be considered one of the eyelid structures. Since it is usually in an anterior

6

172 Lacrimal system. 1 superior punctum; 2 inferior punctum;

3 superior canaliculus; 4 inferior canaliculus; 5 lacrimal sac;

6 nasolacrimal duct; 7 meibomian gland openings.

position, it may be involved with eyelid reconstruction (169, 170). In the upper lid, there is an anterior projection of the orbital fat which crosses forward between the orbital septum and the levator aponeurosis. This is often referred to as preaponeurotic fat. It is contained within a transparent capsule. If the capsule is ruptured and the fibers between fat pockets are interrupted, the fat globules will spread over the surgical field. However, if the fat capsule remains intact, the fat can be easily retracted during eyelid reconstruction. The medial fat layer of the upper lid projects beneath the trochlea. This fat tends to be whiter in color than the preaponeurotic fat, but it is also an extension of the orbital fat.

Orbital fat in the lower lid projects forward to the orbital septum. If the orbital septum is weak, the fat may cause bulging of the lower lid. When the orbicularis layer is retracted, the fat appears to be contained in three separate pockets. The lateral, central, and medial fat pockets are separated from one another by thin septa.

CONJUNCTIVA

The conjunctiva is a mucous membrane lining the posterior surface of the eyelids (170). At the lid margin, it is continuous with the skin. It is firmly adherent to the posterior aspect of the tarsal plates but more loosely adherent to the underside of Müller’s muscle. In the fornices, it reflects towards itself to cover Tenon’s capsule and the globe. It, therefore, forms the conjunctival sac, which opens externally through the palpebral fissure.

The conjunctiva may be divided into the palpebral conjunctiva, the conjunctiva of the fornix, the bulbar conjunctiva, and the plica semilunaris. The palpebral conjunctiva covers the posterior aspect of the eyelids. The bulbar conjunctiva covers the sclera and limbus. The conjunctiva of the fornix is the fold lining the cul-de-sac formed by the reflection of the mucous membrane of the inner surface of the lid to that lining the globe. It is thicker and more loosely attached than elsewhere, and allows free movement of the globe independently of the eyelids.

The suspensory ligament of the conjunctiva is composed of fibers that extend from the sheaths of the levator muscle and the superior rectus muscle to the conjunctival fornix (171). If this structure is interrupted during surgical dissection, the conjunctiva of the superior fornix may prolapse between the lids in front of the cornea.6 The conjunctiva is very glandular. It contains goblet cells, which are mucous glands, and the accessory lacrimal glands of Kraus and Wolfring.

The plica semilunaris, a vestigial structure, which consists of the crescent-shape fold of the conjunctiva in the area of the medial canthus, corresponds to the third eyelid or nictitating membrane of the lower vertebrate.

The caruncle is a small, fleshy structure that lies medial to the plica semilunaris. It is covered by stratified epithelium that does not undergo keratinization. In the caruncle are large sebaceous glands that form the beads of white secretion frequently seen at the inner canthus. There may also be small, colorless hairs on the caruncle.

Resection of the caruncle, which may have to be

Vascular Supply 69

sacrificed in order to excise malignancies, can usually be done with no significant complication.

The conjunctival vessels are numerous, allowing for excellent healing when the conjunctiva is injured or when it is used in reconstructive procedures.

COMMENT

An important feature of the conjunctiva is its ability to heal. If there is not conjunctiva to cover a certain area during eyelid reconstruction, the area of sclera or eyelid may be left free of conjunctiva. Within several days, these ‘bare’ areas will be covered with conjunctiva. Healing occurs by epithelial cells sliding into the defect, as well as rapid multiplication of these cells.

VASCULAR SUPPLY

The eyelids have a very abundant vascular supply with extensive collateral circulation, affording the advantage of excellent healing qualities after surgery or trauma. However, there is the disadvantage of significant bleeding during surgical procedures.

ARTERIES

The blood supply for the eyelids comes from the internal carotid artery via the ophthalmic artery and the infraorbital artery, and from the external carotid artery via the facial artery and the superficial temporal artery. The branches of these arteries anastomose in the eyelid area to give a large collateral circulation (173). The branches of the ophthalmic

173

173 Arteries of the eyelids. 1 frontal branch of the superficial temporal; 2 zygomatico–orbital; 3 lacrimal; 4 transverse facial; 5 superior orbital;

6 frontal branch of ophthalmic; 7 dorsal nasal; 8 superior medial palpebral; 9 inferior medial palpebral; 10 facial; 11 angular;

12 infraorbital; 13 inferior marginal; 14 superior marginal.

70 Surgical Anatomy

artery that supply the eyelids are the dorsal nasal artery, the frontal artery, supraorbital artery, and the lacrimal artery. The dorsal nasal artery leaves the orbit through the orbital septum between the trochlea and the medial canthal tendon and joins the angular artery, which is the terminal portion of the facial artery. The frontal artery emerges from the orbit at the upper medial corner. The supraorbital artery passes through the supraorbital notch to supply the forehead and the upper eyelid. The lacrimal artery passes through the lacrimal gland and then terminates in the lateral palpebral branches, which supply the lateral parts of both lids.

The superior and inferior medial palpebral arteries arise from the dorsal nasal artery before it leaves the orbit. These arteries pass downward giving branches to the lacrimal sac and the nasolacrimal duct. Each artery then divides into a marginal and a peripheral branch that run along each tarsal plate and join with the corresponding lateral palpebral branches. This circulation gives rise to the marginal arcade.

The marginal artery passes approximately 3 mm (0.1 in) from the free border of the lid immediately above the lash follicles between the tarsal plate and the orbicularis. The peripheral artery, which is smaller and less consistent, runs along the curved peripheral margin of each tarsus.

The infraorbital artery is a terminal branch of the internal maxillary artery and runs along the infraorbital sulcus and canal. It enters the lower lid via the inferior orbital foramen and supplies terminal branches to the medial aspect of the lower lid.

The facial artery branches directly from the external carotid artery in the neck. It passes over the mandible and travels up toward the side of the nose. When it reaches the medial canthal area, it becomes the angular artery which runs just beneath the skin and penetrates the orbital septum between the trochlea and the medial canthal tendon; there it meets the dorsal nasal branch of the ophthalmic artery. The facial artery anastomoses with the transverse facial and the infraorbital arteries, supplying the medial canthus, lacrimal sac, and the neighboring part of the lower lid.

The superficial temporal artery is the other main branch of the external carotid artery that supplies the eyelids. This artery courses in front of the ear and gives off

atransverse facial branch, zygomatico-orbital branch, and

afrontal branch, all of which supply the lateral aspect of the eyelids and associated orbital areas.2, 7–9

VEINS

The venous system of the eyelids themselves is composed of a superior palpebral arcade in the upper lid, and an inferior palpebral arcade in the lower lid (174). The superior palpebral vein and the inferior palpebral vein drain towards the angular vein, which lies in the medial canthus. The angular vein is formed by the junction of the frontal and supraorbital veins, and runs obliquely downward on the side of the root of the nose to become the anterior facial vein, which drains toward the internal jugular vein. The angular vein communicates with the superior ophthalmic vein through the nasal frontal vein, thereby forming an important anastomosis between the anterior facial vein and the cavernous sinus. The superficial temporal vein drains the lateral aspects of the eyelids toward the external jugular vein.9, 10

LYMPHATIC DRAINAGE

The lymphatics of the eyelids drain into the preauricular and the submaxillary nodes, which receive drainage from deep and superficial systems (175). The superficial plexus drains the skin and the orbicularis muscle. The deep system drains the regions of the tarsal plate and the conjunctiva. The medial aspects of the upper and lower lids and the central aspect of the lower lid drain into the submaxillary node. The majority of the upper lid and lateral aspect of the lower lid drain into the preauricular (parotid) node.2, 11

COMMENT

An understanding of the lymphatic system is important when evaluating potential metastases of tumors such as sebaceous cell carcinoma and malignant melanoma, which often metastasize to the appropriate lymph nodes.

NERVES OF THE EYELIDS

Two motor nerves are responsible for eyelid movement. The oculomotor (third) nerve regulates the levator palpebrae superioris, which is responsible for elevating the upper lid. The third nerve also innervates the inferior rectus muscle, whose power is responsible for depressing the lower lid in down-gaze via the capsulopalpebral fascia. The facial (seventh) nerve supplies the orbicularis muscle by way of the temporal and zygomatic branches.

The trigeminal (fifth) nerve is responsible for eyelid sensation (176). The upper lid is innervated by the ophthalmic (first) division. The main branches of the ophthalmic nerve are the lacrimal, supraorbital, supratrochlea, and infratrochlea. The lacrimal nerve supplies the lateral aspect of the upper lid. The supraorbital nerve exits the orbit via the supraorbital notch and supplies the center of the upper lid and the adjacent brow and forehead. The supratrochlea nerve leaves the orbit above the trochlea and supplies the medial aspect of the upper lid, brow, and the adjacent forehead. The infratrochlea nerve exits the orbit below the trochlea and supplies the medial aspect of the lower lid and the adjacent nose. The majority of the lower lid sensation travels via the infraorbital nerve, which exits the orbit through the infraorbital foramen.

COMMENT

An understanding of the distribution of the sensory nerves in the eyelids is important in tumor surgery. For instance, loss of sensation in the distribution of the supraorbital nerve might indicate that a tumor in the center of the eyelid had eroded deep to the periosteum or into the superior orbit. Similarly, patients should be warned that forehead anesthesia might occur after tumor resection if the lesion appears to be in the area of the supraorbital notch.

The lacrimal drainage apparatus is intimately associated with the eyelids and is, therefore, of significant importance when considering eyelid tumors and their treatment. The areas of the lacrimal apparatus that are of concern are the canaliculi and the lacrimal sac 172. The two canaliculi begin at the lacrimal papillae, each of which contains a 0.2–0.3 mm (0.01 in) diameter opening, the lacrimal punctum. The punctum opens into a lumen referred to as the ampulla. This is approximately 1.5–2.0 mm(0.1 in) in length and runs in a vertical direction from the eyelid margin. The canaliculus then curves at a right angle and runs from the ampulla in a medial direction toward the lacrimal sac. The horizontal part of the canaliculus is approximately 8 mm (0.3 in) in length. The canaliculi join together and, in most cases, open into the lacrimal sac via a common canaliculus. The lacrimal sac lies behind the lower part of the medial orbital rim in the lacrimal fossa. The canaliculi, therefore, have to course in a posterior, as well as a medial direction to reach the lacrimal sac.

In the middle of the lateral wall of the lacrimal sac is a diverticulum referred to as the sinus of Maier, into which the canaliculi empty. The body of the lacrimal sac lies directly posterior to the medial canthal tendon. The inferior part of the lacrimal sac continues as the nasolacrimal duct within the bone, forming the nasolacrimal canal.

1.Beard C, Quickert MH (1977). Anatomy of the Orbit, 2nd edn. Aesculapius, Birmingham.

2.Duke-Elder S, Wybar KC (1961). The Anatomy of the Visual System, Volume II. In: System of Ophthalmology. S. Duke-Edler (ed). Mosby, St. Louis, pp. 507–533.

3.Beard C (1981). Ptosis, 3rd edn. Mosby, St. Louis, p. 13.

4.Beard C (1981). Ptosis, 3rd edn. Mosby, St. Louis, p. 16.

5.Wesley RE, McCord CD Jr, Jones NA (1980). Height of the tarsus of the lower eyelid. Am. J. Ophthalmol., 90: 102–105.

6.Beard C, Quickert MH (1977). Anatomy of the Orbit, 2nd edn. Aesculapius, Birmingham, pp. 12–13.

7.Doxanas MT, Anderson RL (1984). Vascular supply of the orbit. In: Clinical Orbital Anatomy. Williams and Wilkins, Baltimore, pp. 153–170.

8.Gray H (1959). Anatomy of the Human Body, 27th edn. CM Gross (ed). Lea and Febiger, Philadelphia, pp. 619–641.

9.Jones LT, Wobig JL (1976). Surger y of the Eyelids and Lacrimal System. Aesculapius, Birmingham, pp. 51–56.

10.Gray H (1959). Anatomy of the Human Body, 27th edn. CM Gross (edn). Lea and Febiger, Philadelphia, pp. 725–730.

11.Doxanas MT, Anderson RL (1984). Clinical Orbital Anatomy. Williams and Wilkins, Baltimore, p. 169.