| Pterygium
SIGNS AND SYMPTOMS
In most cases, routine ocular evaluation reveals pterygia in
asymptomatic individuals or in patients who present with cosmetic concern about a tissue
"growing over the eye." In some instances, the vascularized pterygium may become
red and inflamed, motivating the patient to seek immediate care. In other cases, the
irregular ocular surface can interfere with the stability of the precorneal tear film,
creating a symptomatic dry eye syndrome. Rarely, the pterygium may induce irregular
corneal warpage, or even obscure the visual axis of the eye, resulting in diminished
acuity.
Clinical inspection of pterygia reveals a raised, whitish, triangular
wedge of fibrovascular tissue, whose base lies within the interpalpebral conjunctiva and
whose apex encroaches the cornea. The leading edge of this tissue often displays a fine,
reddish-brown iron deposition line (Stocker's line).
The vast majority of pterygia (about 90 percent) are located nasally.
These lesions are more commonly encountered in warm, dry climates, or in patients who are
chronically exposed to outdoor elements or smoky/dusty environments.
Pterygia must be distinguished from pingueculae, which are more yellow
in color and lie within the interpalpebral space but generally do not encroach beyond the
limbus. Pingueculae also lack the wing-shaped appearance of pterygia, the former being
more oval or ameboid in appearance.
PATHOPHYSIOLOGY
Ultraviolet light exposure (both UV-A and UV-B) appears to be the
most significant factor in the development of pterygia. This may explain why the incidence
is vastly greater in populations near the equator and in persons who spend a great deal of
time outdoors. Other agents that may contribute to the formation of pterygia include
allergens, noxious chemicals and irritants (e.g., wind, dirt, dust, air pollution).
Heredity may also be a factor.
Whatever the etiology, pterygia represent a degeneration of the
conjunctival stroma with replacement by thickened, tortuous elastotic fibers. Activated
fibroblasts in the leading edge of the pterygium invade and fragment Bowman's layer as
well as a variable amount of the superficial corneal stroma. Histologically, pterygium
development resembles actinic degeneration of the skin.
Pterygia often persist after surgical removal; these lesions appear as a
fibrovascular scar arising from the excision site. These "recurrent pterygia"
probably have no relationship to ultraviolet radiation, but rather may be likened to
keloid development in the skin.
MANAGEMENT
Because pterygia appear to be linked to environmental exposure,
manage asymptomatic or mildly irritative cases with UV-blocking spectacles and liberal
ocular lubrication. Advise patients to avoid smoky or dusty areas as much as possible.
Treat more inflamed or irritated pterygia with topical decongestant/antihistamine
combinations (e.g., Naphcon-A) and/or mild topical corticosteroids (e.g., FML, Vexol) four
times daily in the affected eye.
Surgical excision of pterygia is indicated only for unacceptable
cosmesis and/or significant encroachment of the visual axis. The treatment of choice
involves dissection and removal of the fibrous tissue down to the level of Tenon's
capsule. Free conjunctival flaps are then grafted over the bare sclera. Postoperative
adjuvant therapy with b-radiation, topical thiotepa, mitomycin-C and other antimetabolic
agents may diminish the chance of recurrence. In cases that involve significant corneal
scarring, lamellar or penetrating keratoplasty may be indicated.
CLINICAL PEARLS
- A pterygium is a benign clinical entity in most cases. Distinguish
between the potentially progressive pterygium and the less threatening pinguecula-large
pingueculae may be difficult to differentiate from pterygia.
- Conjunctival intraepithelial neoplasia (CIN), a precursor of conjunctival
squamous cell carcinoma, is another clinical entity that must be ruled out in the
diagnosis of pterygia. This lesion is generally unilateral, elevated and gelatinous, with
deep irregular vascularization and an ameboid shape. CIN is an invasive ocular cancer that
can inflict significant morbidity. Obtain a biopsy if CIN is suspected.
- Pterygia can affect vision if left unchecked. The corneal degradation may
extend beyond the leading edge of the lesion. This means that the pterygium need not cover
the visual axis to inflict significant visual compromise. Surgery must be performed before
vision is affected.
- Follow up on medium- to large-sized pterygia at least once or twice
yearly, and include a manifest refraction, corneal topography, slit lamp evaluation with
measurement of the pterygium, and photodocumentation if possible.
Other reports in this section
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