PTERYGIUM

Pterygium (L. Pterygion = a wing) is a wing-shaped fold of conjunctiva encroaching upon the cornea from either side within the interpalpebral fissure.
Etiology. Etiology of pterygium is not definitely known. But the disease is more common in people living in hot climates. Therefore, the most accepted
view is that it is a response to prolonged effect of environmental factors such as exposure to sun (ultraviolet rays), dry heat, high wind and abundance of dust.

Pathology. Pathologically pterygium is a degenerative and hyperplastic condition of conjunctiva. The subconjunctival tissue undergoes elastotic degeneration and
proliferates as vascularised granulation tissue under the epithelium, which ultimately encroaches the cornea. The corneal epithelium, Bowman's layer and superficial stroma are destroyed.

Clinical features. Pterygium is more common in elderly males doing outdoor work. It may be unilateral or bilateral. It presents as a triangular fold of conjunctiva encroaching the cornea in the area of palpebral aperture, usually on the nasal side (Fig.1),

Fig. 1. Pterygium

but may also occur on the temporal side. Deposition of
iron seen sometimes in corneal epithelium anterior to
advancing head of pterygium is called stocker's line.

Parts. A fully developed pterygium consists of three
parts (Fig.1):
i. Head (apical part present on the cornea),
ii. Neck (limbal part), and
iii. Body (scleral part) extending between limbus and
the canthus.

Types. Depending upon the progression it may be
progressive or regressive pterygium.

• Progressive pterygium is thick, fleshy and vascular with a few infiltrates in the cornea, infront of the head of the pterygium (called cap of pterygium).
• Regressive pterygium is thin, atrophic, attenuated with very little vascularity. There is no cap. Ultimately it becomes membranous but never disappears.

Symptoms. Pterygium is an asymptomatic condition
in the early stages, except for cosmetic intolerance.
Visual disturbances occur when it encroaches the
pupillary area or due to corneal astigmatism induced
due to fibrosis in the regressive stage. Occasionally
diplopia may occur due to limitation of ocular
movements.

Complications like cystic degeneration and infection
are infrequent. Rarely, neoplastic change to
epithelioma, fibrosarcoma or malignant melanoma,
may occur.

Differential diagnosis. Pterygium must be
differentiated from pseudopterygium. Pseudopterygium
is a fold of bulbar conjunctiva attached to
the cornea. It is formed due to adhesions of chemosed
bulbar conjunctiva to the marginal corneal ulcer. It
usually occurs following chemical burns of the eye.
Differences between pterygium and pseudopterygium
are given in Table 1.1 (below)

Table 1.1. Differences between pterygium and
pseudopterygium