Among the representatives of the class Aves ocular lesions may be a particularly strong indication of systemic disorders. A causative diagnosis of ocular lesions may be vital for the avian patient, not only as a basis for effective therapy of the primary disease, but also for saving the vision, as birds orientate themselves primarily by vision. The following paper presents a synopsis of important ocular disorders in avian patients that are either pathognomonic for certain disorders or, when considered in conjunction with other organic diseases, enable a specific diagnosis to be arrived at. In part 1 bacterial and parasitic etiologies will be described. Part 2 deals with viral infections and noninfectious etiologies.