Damaged eye

I work in shanty towns in Peru, where I see many people, both young and old, with one closed or blank eye, as a result of some disease.  How can this be prevented? Is the problem attributable mainly to Carrion's disease, Chagas' disease, dengue, all of the foregoing, or something else?  They all claim "they were born like that,"  or to have "lost an eye when very small."