The cornea, like most tissues, manifests only a limited number of responses to the wide variety of diseases and insults that assault it. To facilitate a systematic understanding of these responses, we have divided the cornea into four zones: the epithelium; the epithelial basement membrane, Bowman's layer and anterior stroma; the stroma; and the endothelium and Descemet's membrane. We describe six pathologic processes or responses in each zone: defects; fibrosis and vascularization; edema and cysts; inflammation and immune response; deposits; and proliferation. We illustrate this paradigm with a chart that contains examples of each pathologic process in each zone.