The cause of eosinophilic keratitis is not known for certain. The cause of EGC is likewise unknown. Pathology results reveal an infiltration of inflammatory cells including lymphocytes, mast cells, plasma cells, eosinophils and histiocytes into the area of biopsy. Over the years, we have noticed several cats with simultaneous infections with herpesvirus and eosinophilic keratitis. Diagnosis of eosinophilic keratitis is by cytological examination of a scraping of the cornea and conjunctiva.
Examination reveals eosinophils, neutrophils, lymphocytes and corneal epithelium.
Deeper corneal scrapings or pathology sections, obtained by performing surgery, often reveal plasma cells and lymphocytes, with mast cells, eosinophils and histiocytes. In some patients, the scrapings are devoid of eosinophils. As was stated above, some patients with eosinophilic keratitis also have herpesvirus. It is highly recommended that when collecting a corneal scraping for cytology, that a sample also be collected for a herpesvirus PCR and IFA test. When performed concurrently, these tests are very sensitive indicators of the presence of feline herpesvirus.