be seen adjacent to the head of the pterygium called Stocker's line. The location of the line can give an indication of the pattern of growth. The predominance of pterygia on the nasal side is possibly a result of peripheral light focusing, where the sun's rays passing laterally through the cornea, where they undergo refraction and become focused on the limbic area. Sunlight passes unobstructed from the lateral side of the eye, focusing on the medial limbus after passing through the cornea. On the contralateral (medial) side, however, the shadow of the nose medially reduces the intensity of sunlight focused on the lateral/temporal limbus. Some research also suggests a genetic predisposition due to an expression of vimentin, which indicates cellular migration by the keratoblasts embryological development, which are the cells that give rise to the layers of the cornea. Supporting this fact is the congenital pterygium, in which pterygium is seen in infants. These cells also exhibit an increased P53 expression likely due to a deficit in the tumor suppressor gene. These indications give the impression of a migrating limbus because the cellular origin of the pterygium is actually initiated by the limbal epithelium. The pterygium is composed of several segments: Fuchs' Patches (minute gray blemishes that disperse near the pterygium head) Stocker's Line (a brownish line composed of iron deposits) Hood (fibrous nonvascular portion of the pterygium) Head (apex of the pterygium, typically raised and highly vascular) Body (fleshy elevated portion congested with tortuous vessels) Superior Edge (upper edge of the triangular or wing-shaped portion of the pterygium) Inferior Edge (lower edge of the triangular or wing-shaped portion of the pterygium). Diagnosis Pterygium (conjunctiva) can be diagnosed without need for a specific exam, however corneal topography is a practical test (technique) as the condition worsens. Differential Diagnosis Pterygium should be differentiated from pinguecula, which is histologically and etiologically similar to pterygium. Unlike pterygium, pinguecula is seen only on the conjunctiva, it will not progress to limbus or cornea. Another condition which is similar to pterygium is inflammatory adhesion of conjunctiva to cornea known as pseudopterygium. Unlike pterygium, it may occur anywhere around cornea and the adhesion is usually limited to its apex. Prevention As it is associated with excessive sun or wind exposure, wearing protective sunglasses with side shields and/or wide brimmed hats and using artificial tears throughout the day may help prevent their formation or stop further growth.