Eosinophilic keratitis or keratoconjunctivitis (EK) is a chronic inflammatory condition which affects the cornea of the horse's eye. It tends to have a sudden onset and the disease rapidly progresses. It usually occurs in horses during the summer in the Mid-Atlantic United States.

EK may affect one or both eyes of the horse and can recur in the same horse in one season or in subsequent years. Mini-outbreaks have occurred in some groups of horses. No cases have been reported in horses that wear fly masks all the time. Studies indicate that systemic but not topical corticosteroid treatment may decrease therapy duration and treatment with cetirizine may be associated with a decreased risk of recurrence.