Case Presentation
Figure A. The patient’s right eye showing multifocal, superficial, light pink corneal nodules.
An 18-year-old Welsh pony mare presented in late August for superficial corneal opacities. On ocular examination, multifocal, light pink nodules extended from the dorsotemporal limbus to the paraxial cornea of both eyes. Corneal edema, pigmentation, and vascularization surrounded the lesions (FIGURE A). Bilateral blepharospasm, chemosis, epiphora, and conjunctival hyperemia were also noted. Fluorescein staining did not result in uptake in either eye.
1. What is the differential diagnosis?
2. What diagnostic test(s) should be performed to obtain a diagnosis?
Answers and Explanations
1. The differential diagnosis includes squamous cell carcinoma, keratitis induced by infection with Onchocerca cervicalis or Habronema spp, traumatic keratitis with associated granulation tissue, bacterial or mycotic keratitis, and eosinophilic keratitis.
2. A corneal scraping or superficial biopsy should be performed next, depending on the clinical findings. In this case, corneal scraping revealed numerous eosinophils and nondegenerative neutrophils with a few red blood cells, lymphocytes, and plasma cells (FIGURE B). The corneal scraping sample tested negative for fungal hyphae and bacteria. The clinical and cytologic profile was compatible with a diagnosis of eosinophilic keratitis—an idiopathic disease seen in the central to eastern United States. Lesions appear as raised, subepithelial necrotic plaques involving the superficial cornea. The disease is more prevalent in the summer and fall and may be associated with an environmental allergen or fomite. Topical corticosteroids are the treatment of choice, although topical mast cell stabilizers may be selected in environments in which fungal keratitis is a high risk. Superficial keratectomy to remove a portion of the plaques may also be beneficial. After treatment with anthelmintics, dying parasitic microfilaria of O. cervicalis and Habronema spp may cause similar eosinophilic reactions in the cornea and conjunctiva. Diagnosis is based on the timing of anthelmintic treatment and the presence of microfilaria in corneal scrapings or conjunctival biopsy samples.
Figure B. Corneal scraping of the right eye showing numerous eosinophils and nondegenerative neutrophils with a few red blood cells, lymphocytes, and plasma cells.
Suggested Reading
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Brooks DE. Inflammatory stromal keratopathies, medical management of stromal keratomalacia, stromal abscesses, eosinophilic keratitis, and band keratopathy in the horse. Vet Clin North Am Equine Pract 2004;20:345-360.
Cutler TJ. Corneal epithelial disease. Vet Clin North Am Equine Pract 2004;20:319-343.
Giuliano EA, Moore CP. Eyes and ocular adnexa. In: Cowell RL, Tyler RD, eds. Diagnostic Cytology and Hematology of the Horse. St. Louis, MO: Mosby; 2002:60.
Martin CL. Cornea and sclera. Ophthalmic Disease in Veterinary Medicine. London: Manson Publishing; 2005:258-259.
Matthews AG. Cornea. In: Barnett KC, Crispin SM, Lavach JD, Matthews AG, eds. Equine Ophthalmology. Hong Kong, China: Elsevier Limited; 2004:268.
McMullen RJ. Equine keratitis and the possible involvement of equine adenovirus type 1 and type 2. Vet Ophthalmol 2004;7(6):425-435.
Ramsey DT, Whitely HE, Gerding PA, Valdez RA. Eosinophilic keratoconjunctivitis in a horse. J Am Vet Med Assoc 1994;205(9):1308-1311.
Yamagata M, Wilkie DA, Gilger BC. Eosinophilic keratoconjunctivitis in seven horses. J Am Vet Med Assoc 1996;209(7):1283-1285.
