[Etiopathogenic aspects in development and evolution of pterigyum]

Pterygium is an epithelial hyperplasia accompanied by a fibrovascular growth originating at the corneo-conjunctival junction, from where the modified limbic cells migrate and surpass the cornea. The studies reviewed show that it is an active process associated with cell growth, remodelling of the connective tissue, angiogenesis and inflammation. Despite the lack of knowledge regarding the pathogenesis of pterygia, epidemiologic evidence suggests that exposure to UV-irradiation may be an initial trigger in the development of this lesion. Other theories include changes of the apoptotic pathway the presence of some active angiogenetic factors or involvement of the MMPs, cytokines and growths factors. UV light could be the initial trigger that activates epithelial cells at or near the limbus to produce cytokines such as IL-6 and IL-8 and growth factors. These multifactorial proteins set up a cascade of events that include inflammation, proliferation, angiogenesis and antiapoptosis. Cytokines are able to induce the expression of MMPs and their tissue inhibitors (TIMPs) making it likely that they would also affect the rate of tissue remodeling, such as destruction of Bowman's membrane and the invasion of pterygium. In the etiology of pterygium abnormalities in tear functions have also been emphasized.