Pterygium is a wing-shaped ocular surface lesion traditionally described as encroachment of fibrovascular tissue from the bulbar conjunctiva onto the cornea. Despite advances to understand the pathogenesis of pterygium, it remains a matter of debate whether it is a degenerative elastotic lesion or it represents a proliferative disorder due to an abnormal wound healing response. 1 The association of pterygia with other sun-related disorders such as cataracts, pinguecula, and ocular surface squamous neoplasia (OSSN) and their higher incidence in latitudes close to the equator suggest a major role for ultraviolet (UV) radiation in their pathogenesis. 2 Pterygia only present in humans and not in nonhuman primates or other animals, possibly due to the unique ocular morphology of humans. 3 They do have a predilection for the nasal limbus that may be explained by the phenomenon of peripheral light focusing, whereby incidental light passes through the anterior chamber and focuses at the nasal limbus, thus damaging the limbal stem cells in that area. 4 Clinically, pterygia typically present as a triangular fleshy tissue that comes from the bulbar conjunctiva and grows onto the cornea within the interpalpebral fissure. The apex of the triangular tissue (or head of the pterygium) is found on the cornea, and the base of the triangle (or body of the pterygium) is on the bulbar conjunctiva. In the vast majority of cases, the diagnosis can be easily made upon slit-lamp examination. A characteristic straightening of the vessels in the direction of the advancing head of the pterygium on the corneal surface is also seen (▶ Fig. 2.1). A pterygium may be like a thin translucent membrane or significantly thickened with an elevated mound of gelatinous material (▶ Fig. 2.2). Depending on its vascularity, it may be white, pink, or red. Fig. 2.1 (a) Typical pterygium with characteristic straightening of the vessels toward the advancing head. (b) Close-up view of the same lesion shows that the underlying episcleral vessels are not obscured by the body of the lesion (Grade T1). Fig. 2.2 An elevated mound of gelatinous material is seen at the head of this pterygium. In its early stages, a pterygium is a fine transparent tissue with minimal elevation, few vessels, and very little corneal involvement. As the lesion advances, it becomes a thick opaque vascular tissue that may extend even up to the visual axis (▶ Fig. 2.3). The presence of an epithelial iron line, called Stocker’s line, in front of the pterygium head suggests chronicity of the lesion. Other sun-related lesions, such as pinguecula, are present in the ipsilateral or contralateral eye. It is very unusual for pterygia to present in locations other than the 3 or 9 o’clock positions within the palpebral fissure. In fact, pterygium-looking lesions in other locations should immediately raise suspicion for alternate diagnosis. Fig. 2.3 A double-headed pterygium. The nasal lesion is fleshy, red, and progressive (Grade T3), while the temporal one appears less aggressive (Grade T2).
2.2 Clinical Signs
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