Pterygium most often refers to a benign growth of the conjunctiva. A pterygium commonly grows from the nasal side of the sclera.It is associated with and thought to be caused by ultraviolet-light exposure (e.g., sunlight), low humidity, and dust. Growth has been known to be preceded with scleral trauma around the Palpebral comissure. The predominance of pterygia on the nasal side is possibly a result of the sun’s rays passing laterally through the cornea, where it undergoes refraction and becomes 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
