Eosinophilic keratoconjunctivitis in a horse.

An 11-year-old Quarter Horse gelding was evaluated because of a persistent, raised band of 1- to 2-mm subepithelial plaques of the left cornea. Cytologic examination of corneal scrapings revealed numerous eosinophils and segmented neutrophils, with few mast cells, plasma cells, and lymphocytes. Bacteriologic culture yielded sparse growth of alpha-hemolytic Streptococcus and Staphylococcus spp. Histologically, the plaques consisted of subepithelial foci of fragmented and degenerated collagen fibers infiltrated by eosinophils and neutrophils, with few lymphocytes, plasma cells, and macrophages. Plaques were surrounded by a layer of brightly eosinophilic, acellular, granular material. Distribution of inflammatory cells in the conjunctiva was similar to cells in the cornea. After reepithelialization of the cornea, corticosteroid ointment was administered topically. Twenty-eight days after treatment with corticosteroids, the plaques had completely resolved. Histologic and cytologic diagnoses in this horse were similar to reports of eosinophilic keratitis in cats.