CHAPTER 12

Clinical Approach to Depositions and Degenerations of the Conjunctiva, Cornea, and Sclera

Degeneration of a tissue refers to decomposition and deterioration of tissue elements and functions. Degenerations of the ocular surface may result from physiologic changes associated with aging, be related to a specific disease, or follow chronic environmental insults to the eye, such as exposure to ultraviolet (UV) light. They may be unilateral or bilateral; if bilateral, they may be asymmetric. They uncommonly exhibit an inheritance pattern. It is important to differentiate corneal degenerations from corneal dystrophies (Table 12-1).

Table 12-1

Degenerative Changes of the Conjunctiva

Age-Related (Involutional) Changes

As a result of aging, the conjunctiva loses transparency and becomes thinner. The substantia propria (stroma) becomes less elastic, causing conjunctival laxity. In older individuals, the conjunctival vessels can become more prominent. Saccular telangiectasias, fusiform dilatory changes, or tortuosities may appear in the vessels. These changes are not necessarily uniform; they tend to be more pronounced in the area of the interpalpebral fissure, corresponding to the area most commonly exposed to the environment.

Pinguecula

A pinguecula is a common conjunctival condition that occurs typically on the nasal side of the bulbar conjunctiva, adjacent to the limbus in the interpalpebral zone. It usually is bilateral, appears as a

yellow-white elevated mass (Fig 12-1), and occurs as a result of the effects of aging, UV-light exposure, and other environmental traumas such as dust and wind. It may enlarge gradually over long periods of time. Recurrent inflammation and ocular irritation may be observed. Pingueculae represent an elastotic degeneration (the material stains for elastin but is not broken down by elastase) of subepithelial collagen with hyalinized connective tissue. Lubricant therapy to alleviate ocular irritation is the mainstay of treatment. Excision is indicated only when pingueculae are cosmetically unacceptable or when they become chronically inflamed or interfere with successful contact lens wear. Judicious use of topical corticosteroids may be considered in patients with inflammation, but their use as a long-term therapy for pingueculae is strongly discouraged due to their adverse effects.

Figure 12-1 A pinguecula, seen, as is typical, on the nasal side of the bulbar conjunctiva. (Courtesy of Cornea Service, Paulista

School of Medicine, Federal University of São Paulo.)

Pterygium

A pterygium is a wing-shaped growth of conjunctiva and fibrovascular tissue on the superficial cornea (Fig 12-2). As with a pinguecula, the pathogenesis of a pterygium is strongly correlated with UV-light exposure, although environmental traumas such as exposure to dust, wind, or other irritants that cause chronic inflammation may also be factors. The predominance of pterygia on the nasal side in the interpalpebral zone is theorized to result from light passing medially through the cornea, focusing on the nasal limbus area, while the shadow of the nose reduces the intensity of light transmitted to the temporal limbus. The prevalence of pterygia increases steadily with proximity to the equator and is more common in men than women, in persons 20–30 years of age (the most common age of onset), and in people who work outdoors. The histopathology of pterygia is similar to that of pingueculae, only it involves subepithelial fibrovascular tissue. Further discussion of the histopathology of both pingueculae and pterygia can be found in BCSC Section 4, Ophthalmic Pathology and Intraocular Tumors.

Figure 12-2 A pterygium: a wing-shaped growth of conjunctiva and fibrovascular tissue on the superficial cornea. (Courtesy of

Cornea Service, Paulista School of Medicine, Federal University of São Paulo.)

Pterygia are nearly always preceded by pingueculae, although why some patients develop pterygia whereas others have only pingueculae is not known. Regular and irregular astigmatism, as well as corneal scarring, occurs in proportion to pterygium size. A pigmented iron line (called a Stocker line) may be seen at the central anterior edge of the pterygium on the cornea. A pterygium must be differentiated from a pseudopterygium, which may occur after trauma or secondary to inflammatory corneal disease. Treatment with artificial tears can alleviate associated irritation, but as with pingueculae, long-term use of topical corticosteroids is contraindicated. Excision is indicated if the pterygium approaches the visual axis, exhibits rapid growth, causes chronic irritation, or is cosmetically unacceptable. See Chapter 14 for discussion of the surgical treatment of pterygium.

Conjunctival Concretions

Concretions are small, yellow-white dots found in the palpebral conjunctiva of older patients or patients who have had chronic conjunctivitis. Concretions appear to be epithelial inclusion cysts filled with epithelial and keratin debris, as well as mucopolysaccharide and mucin. Concretions are almost always asymptomatic but may erode the overlying epithelium, causing foreign-body sensation. If symptomatic, concretions can be easily removed under topical anesthesia.

Conjunctival Inclusion Cysts

Inclusion cysts of the conjunctival epithelium are typically asymptomatic and are often an incidental finding during routine ophthalmic examination. Conjunctival inclusion cysts can be congenital or acquired. Most acquired cysts of the conjunctiva are derived from an inclusion of conjunctival epithelium into the substantia propria. The implanted cells proliferate to form a central fluid-filled cavity that is lined by nonkeratinized conjunctival epithelium. Conjunctival cysts may also form from ductal epithelium of the accessory lacrimal glands; these cysts are lined by a double layer of epithelium. Stimuli for cyst formation include chronic inflammation, trauma, and surgery.

Conjunctival inclusion cysts typically appear clear and can occur in either the bulbar conjunctiva or the conjunctival fornix (Fig 12-3). A corneal epithelial inclusion cyst is rare, but it can occur if trauma, surgery, or chronic inflammation results in conjunctival overgrowth onto the surface of the cornea. Dilated lymphatic channels may mimic an inclusion cyst of the bulbar conjunctiva.