How to Medically Manage a Case of Equine Eosinophilic Keratoconjunctivitis

Equine eosinophilic keratitis or keratoconjunctivitis (EK) is an inflammatory disease of the conjunctiva and cornea. This disease has been described in other veterinary species, including cats, dogs, and rabbits; however, there is a dearth of information in the veterinary literature regarding this disease in horses. The disease appears to have a seasonal component, with the majority of cases occurring in summer and early fall. EK has been reported in the Quarter Horse, Thoroughbred, Arabian, Warmblood, Mustang, and Icelandic horse breeds and in one donkey. No definitive sex or breed predisposition has been identified. The exact etiology and pathogenesis of EK are still unknown, but EK is postulated to be the result of a hypersensitivity reaction to an unknown stimulus, a theory supported by the response to treatment with immunomodulating drugs in horses and other species. In horses, parasitic causes, such as Onchocerca, Thelazia, and Habronema infections, have been investigated and have not been found to play a role in the development of EK. Although a wide range of treatment approaches has been used in horses, including systemic and topical medications and surgical interventions, no treatment approach has been rigorously tested and shown to be superior to any other. Irrespective of treatment, the course of the disease is often extended, and it is not unusual for treatment to extend beyond 1 month. The exception is surgical intervention with a superficial keratectomy, which results in a relatively rapid resolution once performed. In one case series, Yamagata et al reported on seven horses diagnosed with EK in the Midwestern United States from 1976 to 1994. These horses were treated either medically or surgically. Time to resolution of clinical signs ranged widely, from 14 days for one horse that was treated with a superficial keratectomy, 90 days for one horse treated with topical antibiotics only, and between 45 and 106 days for five horses treated with a combination of topical medications, including antibiotics and corticosteroids. Secondary corneal bacterial or fungal infections were not identified in these cases. Although this is a small case series, it supports the hypothesis that topical corticosteroid treatment may increase the time to resolution, whereas surgical intervention with a superficial keratectomy may hasten resolution of EK. After this case series was reported, several case reports and case series have described EK in equids.