A pterygium is described as an ingrowth of subconjunctival tissue whose stimulus to growth is ultraviolet light. Ultrviolet radiation at the wavelength of 320-286 nm has been identified as a primary causative factor. Contributing processes to pterygium formation are dry eyes and inflammation. Contributing factors include thermal and chemical irritants, mechanical eye rubbing, recurrent infections, allergies and trauma. A pingueculum transforms into a pterygium with the addition of an inflammatory process. A pathogenesis pathway is introduced and discussed.