lid is by the infratrochlear branch of the ophthalmic nerve and the infraorbital nerve, a branch of the maxillary division (Figure 9-21). Motor control of the orbicularis muscle is through the temporal and zygomatic branches of the facial nerve, and that of the levator muscle is through the superior division of the oculomotor nerve. The tarsal smooth muscles are innervated by sympathetic fibers from the superior cervical ganglion.

BLOOD SUPPLY OF EYELIDS

The blood vessels are located in a series of arcades or arches in each eyelid. The marginal palpebral arcade lies near the lid margin, and the peripheral palpebral arcade lies near the orbital edge of the tarsal plate (Figure 9-22). The vessels forming these arcades are branches from the medial and lateral palpebral arteries. The medial and lateral palpebral arteries are branches of the ophthalmic and lacrimal arteries, respectively. Normal variations occur in the blood supply, and the most common variation is a lack of the peripheral arcade in the lower lid.

FIGURE 9-20

Painless chalazion. (From Kanski JJ, Nischal KK: Ophthalmology: clinical signs and differential diagnosis, St Louis, 1999, Mosby.)

Lacrimal

nerve

Zygomatico

facial nerve

C O N J U N C T I V A

The conjunctiva is a thin, translucent mucous membrane that runs from the limbus over the anterior sclera, forms a cul-de-sac at the superior and inferior fornices, and turns anteriorly to line the eyelids. It ensures smooth movement of the eyelids over the globe. The conjunctiva can be divided into three sections that are continuous with one another: (1) the tissue lining the eyelids is the palpebral conjunctiva, or tarsal conjunctiva; (2) the bulbar conjunctiva covers the sclera; and (3) the conjunctival fornix is the cul-de-sac connecting palpebral and bulbar sections (Figure 9-23). Conjunctival stem cells are scattered in the basal layer throughout the conjunctiva, but are more numerous in the fornix region.68,69

Supraorbital

nerve

Supratrochlear nerve

Infratrochlear nerve

At the mucocutaneous junction of the lid margin (see Figure 9-15), the nonkeratinized squamous palpebral conjunctival epithelium is continuous with the keratinized squamous epithelium of the epidermis of the eyelid. The conjunctiva forming the fornices is attached loosely to the fascial extensions of the levator, tarsal, and extraocular muscles, providing coordination of conjunctival movement with movement of the globe and lids. The fornices are present superiorly, inferiorly, and laterally, easing

movement of the globe without creating undue stretching of the conjunctiva. The lateral fornix is the deepest and extends posterior to the equator of the globe.

The bulbar conjunctiva is translucent, allowing the sclera to show through, and is colorless except when its blood vessels are engorged. Bulbar conjunctiva is loosely adherent to the underlying tissue up to within 3 mm of the cornea, where it becomes tightly adherent and merges with the underlying Tenon’s capsule and sclera.

Supraorbital

artery

Lacrimal artery

Superior peripheral arcade

Superior marginal arcade

Superior lateral palpebral artery

Inferior lateral palpebral artery

Inferior peripheral arcade

Inferior marginal arcade

Supratrochlear artery

Superior medial palpebral artery

Inferior medial palpebral atery

Infraorbital

artery

Fornix

Bulbar conjunctiva

Palpebral conjunctiva

FIGURE 9-23

Three partitions of conjunctiva.

PLICA SEMILUNARIS

The plica semilunaris is a crescent-shaped fold of conjunctiva located at the medial canthus (see Figure 9-3). (It might be a remnant of the nictitating membrane seen in lower vertebrates.) The epithelium is 8 to 10 cells thick and contains numerous goblet cells, and the stroma is highly vascularized, containing smooth muscle fibers and adipose tissue.70 Because there is no deep fornix at the medial side as there is at the lateral side, the evident function of the plica is to allow full lateral movement of the eye without tissue stretching.

CARUNCLE

The function of the caruncle, a mound of tissue that overlies the medial edge of the plica semilunaris (see Figure 9-3), is poorly understood. The caruncle is similar to conjunctiva in that it contains nonkeratinized epithelium and accessory lacrimal glands, but it also has

skin elements: hair follicles and sebaceous and sweat glands.70,71 The sebaceous glands are a likely source for the occasional accumulation of matter in the medial canthus of the healthy eye.

CONJUNCTIVAL BLOOD VESSELS

The palpebral conjunctiva receives its blood supply from the palpebral arcades. Branches from the arcades anastomose on both sides of the tarsal plate; vessels from the posterior network supply the palpebral conjunctiva in both upper and lower lids.

The fornices are supplied by branches from the peripheral arcades, which then branch again and enter the bulbar conjunctiva, forming a plexus of vessels, the posterior conjunctival arteries. These anastomose with the plexus of anterior conjunctival arteries formed by branches from the anterior ciliary arteries. Conjunctival veins parallel the arteries but are more numerous. They drain into the palpebral and ophthalmic veins.

CONJUNCTIVAL LYMPHATICS

The conjunctival lymphatic vessels are arranged in superficial and deep networks within the submucosa. These vessels drain into the lymphatics of the eyelids; those from the lateral aspect empty into the parotid lymph node, and those from the medial aspect empty into the submandibular lymph node (see Figure 11-14).

CONJUNCTIVAL INNERVATION

Sensory innervation of the bulbar conjunctiva is through the long ciliary nerves. Sensory innervation of the superior palpebral conjunctiva is provided by the frontal and lacrimal branches of the ophthalmic nerve. Innervation of the inferior palpebral conjunctiva is provided by the lacrimal nerve and the infraorbital branch of the maxillary nerve. All sensory information is carried in the trigeminal nerve.

Clinical Comment: Biomicroscopic

Examination

The normal bulbar conjunctiva is clear and displays a fine network of blood vessels. The blood flow in an individual­

vessel may be seen under high magnification. The conjunctival­ surface is not as smooth as the cornea, and thus a small amount of fluorescein pooling might be evident in the normal eye. The palpebral conjunctiva is examined by everting the eyelids and should appear bright pink in color. The blood vessel network is evident, and arteries can be seen that run at right angles to the lid margins. The meibomian­

gland ducts, if seen, will appear as fine yellow lines.

Clinical Comment: Conjunctivitis

CONJUNCTIVITIS  is any inflammation of the conjunctiva and can be caused by a variety of factors. Among the ­common causative agents are bacterial or viral invasion and allergic reaction. In inflammatory conditions, fluids often accumulate in the loose stromal tissue; this ­conjunctival edema is called chemosis. Dilation and engorgement of the conjunctival blood vessels also occur with inflammation and irritation; this vascular change is known as conjunctival

injection. Both chemosis and injection are present to ­varying degrees in diseases and irritations of the conjunctiva. In viral conjunctivitis the preauricular lymph node often is ­prominent on the involved side.

Clinical Comment: Giant Papillary

Conjunctivitis

GIANT PAPILLARY CONJUNCTIVITIS  (GPC) is a  common complication often seen in the contact lens wearer. The patient has hyperemic palpebral conjunctiva with large papilla, so large they are described as “cobblestone.”

The cause is thought to be an allergic reaction either to substances in the lens material, in the cleaning solutions, or to buildup of material on the lens surface. Treatment might include changing lens material, changing solution, or perhaps discontinuation of wear temporarily.

firm attachment to the corneal surface. ­Fibrovascular tissue with the same abnormal characteristics seen in pingueculae underlie the epithelium of a ­pterygium.74-76 An extensive network of blood vessels is evident.72

Pingueculae and pterygia show many of the same ­connective tissue changes but are different diseases. If mutational changes occur in the limbal epithelium at the corneal edge of a pinguecula, it may become a pterygium.76 Exposure to irritants­ such as wind and dust might initiate hyperplasia and be a precursor of both these degenerative changes. Molecular damage produced by chronic solar radiation, particularly­ high-energy ultraviolet rays, is the primary causal factor in pterygium, with irritants being predisposing factors­ .74,77-79 Biochemical studies have shown that oxidative stress can result in biochemical cellular changes that cause cellular proliferation,­ vascularization, and the adhesion to the corneal­ surface that occurs in pterygium.80-82

Pingueculae rarely are treated unless inflamed. Pterygia are surgically removed (1) when the apex approaches the visual axis, (2) if significant corneal astigmatism is induced, or (3) for cosmetic concerns. Complete removal is difficult because the altered cells appear as normal cornea, and the ­abnormal cell can only be discerned histologically.75 Thus pterygia often recur. Patients with either condition should be advised of the relationship of these conditions to irritants and sun exposure, and ultraviolet-filtering protective lenses should be prescribed, as well as artificial tears and ocular lubricants as needed.

Clinical Comment: Pingueculae

and Pterygia

A PINGUECULA  consists of an opaque, slightly elevated mass of modified conjunctival tissue in the interpalpebral­

area, usually at the 3-o’clock or 9-o’clock position. Pingueculae­ may vary considerably in size and appearance­

but usually are round or oval and yellowish (Figure 9-24). Two histologic changes occur in the submucosal layers, whereas the epithelial layers remain unchanged. The first submucosal change is hyalinization, which occurs in a zone just below the epithelium. This zone contains ­degenerating collagen and a granular material that probably results from the breakdown of connective tissue­ components­ .72,73 The second submucosal change in development­ of pinguecula is the formation of abnormal elastic fibers. Precursors of elastic fibers and abnormally immature forms of newly synthesized elastic fibers are found beneath the zone of

hyalinization. These fibers degenerate, and elastic myofibrils are greatly reduced, which prevents normal assembly of elastic fibers.72,73 ­Fibroblasts in these regions show extensive alteration.

A pterygium is a fibrovascular overgrowth of bulbar conjunctiva­ onto cornea and is usually progressive. As with pinguecula, pterygium occurs in the 3-o’clock or 9-o’clock position of the interpalpebral area (Figure 9-25). The triangular­ pterygium may be gray in appearance, and its apex (often called the head) invades the cornea. This leading­ edge is composed of a zone of limbal epithelial tissue arising from altered basal stem cells. A zone of cells follows the

head, migrates along the corneal basement membrane, and dissolves Bowman’s layer.72,74 The head is the only site of

FIGURE 9-24

Pinguecula. (From Krachmer JH, Palay DA: Cornea color atlas, St Louis, 1995, Mosby.)

T E N O N ’ S C A P S U L E

Below the conjunctival stroma is a thin, fibrous sheet called Tenon’s capsule (fascia bulbi). Tenon’s capsule serves as a fascial cavity within which the globe can move. It protects and supports the globe and attaches it to the orbital connective tissue.