The normal cornea is clear, and any alteration in clarity signifies pathology. Possible pathologic changes include corneal vessels, edema, pigment, lipid or calcium deposits, inflammatory cell infiltrates, destruction from degradative enzymes, and scarring. Such changes are usually non-specific and incited by numerous causes.
Ocular disease due to feline herpesvirus (FHV) is common. It is estimated that 80% of cats are latently infected with the virus, and approximately 40% of these cats will suffer recrudescent infection in later life. These estimates are based on data that is several decades old, and the actual percentages may be higher.