Immune-mediated keratitis in horses: 19 cases (1998-2004)

OBJECTIVE: The purpose of this study is to describe clinical and histologic findings, treatment, and outcome of horses with suspected immune-mediated keratitis (IMMK). DESIGN: Retrospective study. ANIMALS: Nineteen horses that presented to NCSU-VTH from 1998 to 2004 with IMMK. Procedures Information retrieved from the medical records included signalment, duration of clinical signs, therapy prior to initial examination, ophthalmic abnormalities, diagnostics performed, therapy instituted, and long-term vision. RESULTS: Nineteen horses (22 eyes) were diagnosed with IMMK. Three distinct clinical groups were identified based on the depth of the lesion in the cornea: superficial stromal (n = 11 eyes), midstromal (n = 6 eyes), or endothelial (n = 5 eyes). Horses ranged from 5 to 19 years of age, with a mean age +/- SD of 11.9 +/- 3.6 years. Eleven horses had 12 months or greater duration of clinical signs of corneal disease prior to referral. Overall there was a mean duration of 11.8 +/- SD 8.3 months. Superficial stromal keratitis appeared as a superficial stromal cellular infiltrate with diffuse vascularization. Midstromal keratitis appeared as midstromal cellular infiltrate with mild, surrounding corneal edema and vascularization. Endothelial disease appeared as endothelial cellular infiltrate with diffuse corneal edema. In all types of IMMK, signs of uveitis or severe discomfort were not observed. CONCLUSIONS AND CLINICAL RELEVANCE: Horses with superficial IMMK responded to topical medical therapy, but responded best to surgical removal of the lesion. Horses with midstromal keratitis responded to topical cyclosporine therapy. Endothelial disease was the least amenable to therapy.