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Compendium February 2013 (Vol 35, No 2)

Clinical Snapshot: Corneal Edema in a Tennessee Walking Horse

by Sharon Tirosh-Levy, DVM, Ron Ofri, DVM, PhD, DECVO

    Case Presentation

    A 6-year-old Tennessee walking horse mare presented for ophthalmic evaluation at the Veterinary Teaching Hospital of the Koret School of Veterinary Medicine, Hebrew University of Jerusalem, Israel. Ten days before presentation, the owner noticed that the mare had bilateral, slowly progressive corneal edema. Physical examination revealed no nonophthalmologic abnormalities. On ophthalmic examination, the patient’s eyes were open, were not painful, and had minimal discharge. The menace response and the direct and consensual pupillary light reflexes were normal in both eyes. Both eyes had similar corneal lesions (FIGURE 1). The results of the rest of the ophthalmic examination, including ophthalmoscopic examination of the fundus, were unremarkable for both eyes. Corneal scrapings were taken from both eyes, and the cytologic findings are shown in FIGURE 2 .

    1. What is your diagnosis?

    2. What features of the ophthalmic and cytologic examination support your diagnosis?

    3. What are your treatment options?

    4. What prognosis would you give the owner?

    Answers and Explanations

    1. Based on the clinical and cytologic findings, a diagnosis of eosinophilic keratitis was made. Eosinophilic keratitis is immune mediated, and although the initial cause is undetermined, allergic or parasitic stimulation is suspected. Cytologically, the plaques consist predominantly of eosinophils and neutrophils, with smaller numbers of mast cells, lymphocytes, plasma cells, and macrophages (FIGURE 2).

    2. Typical findings of eosinophilic keratitis are perilimbal lesions, epithelial to superficial-stromal white plaques with surrounding corneal edema, and a bilateral presentation. In some cases, this condition may involve the conjunctiva and may induce some signs of pain, such as blepharospasm and epiphora. In our case, the lesions involved the entire perilimbal cornea and were characterized by deep vascularization, white-yellow plaques, and peripheral corneal edema. Our diagnosis was further supported by cytologic findings of a large number of inflammatory cells, with a predominance of intact and degranulated eosinophils and neutrophils.

    3. Most treatment options are directed at suppressing the inflammatory response and should be prolonged—up to several months. Topical corticosteroids may be used even when corneal ulceration is present, but only after infection has been carefully ruled out with cytology and cultures of the corneal lesion. Topical corticosteroid treatment may be combined with administration of topical antimicrobials (we use a preparation of chloramphenicol and polymyxin B) and atropine as well as a systemic NSAID. Cyclosporine and mast cell inhibitors may also be used topically. In some cases, superficial keratectomy is performed to remove the lesions.

    In this case, based on cytology, it was determined that infection was not present. The mare was initially treated systemically with an NSAID (phenylbutazone) and topically with a corticosteroid (dexamethasone), antimicrobials (chloramphenicol and polymyxin B), and atropine. After 5 days, when the superficial ulceration caused by the corneal scraping resolved, the systemic antiinflammatory agent, topical antimicrobials, and atropine were discontinued. Treatment with topical dexamethasone was continued, and topical cyclosporine was added. After 3 weeks of treatment, there was considerable improvement: the corneal edema improved, the vascularization was significantly reduced, and the number of plaques was reduced (FIGURE 3). Continued treatment with topical dexamethasone and cyclosporine was prescribed. Brief cessation of cyclosporine therapy after 6 weeks of treatment resulted in mild deterioration, which resolved when topical cyclosporine therapy was resumed.

    4. Although this condition may be self-limiting and responds well to treatment, some cases are chronic or may flare up periodically. Although the cause is unknown, recurrence may be due to seasonal allergic stimulation. Long-term treatment may be considered to decrease the probability of recurrence.

    Suggested Reading

    Brookes DE. Inflammatory stromal keratopathies: medical management of stromal keratomalacia, stromal abscesses, eosinophilic keratitis, and band keratopathy in the horse. Vet Clin Equine 2004;20:345-360.

    Gilger BC. Equine Ophthalmology. St. Louis, MO: Elsevier Saunders; 2011:196-197.

    Matthews A, Gilger BC. Equine immune-mediated keratopathies. Vet Ophthalmol 2009;12(Suppl 1):10-16.

    NEXT: Equine Laparoscopy: Gonadectomy


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