Keratitis is a generic term indicating inflammation in the cornea. Inflammation can be a feature in a variety of eye conditions and is a non-specific term. Inflammatory cells can be of various types, and one must examine the tissue microscopically to determine which cells are present and better define the problem.

Eosinophils are one subset of inflammatory cells that are only seen under certain circumstances or in specific conditions. Eosinophilic Keratitis is one such condition that is seen in cats. It typically affects younger to middle-aged cats and can affect one or both eyes. Usually the condition only affects the cornea, though it can also affect the third eyelid and the conjunctiva.

Signs of Eosinophilic Keratitis

  • squinting or holding the eye closed
  • cloudy or chalky appearance to the cornea
  • pink to reddish discoloration or plaque formation in the cornea
  • mucus discharge 
  • corneal ulceration

The cause of this condition is not clearly understood. In some cats, there may be an underlying viral infection (Feline Herpes Virus) that initiates the disease. Eosinophilic Keratitis is believed to be an immune-mediated disorder in which there is an exaggerated response of the immune system (similar to an allergic response) to an antigenic (foreign protein) stimulus.


The condition may be suspected based on the examination findings, however the diagnosis is confirmed by taking a sample (swab or scraping) from the corneal surface and examining the cells under the microscope. In addition to the the cytologic exam, the cornea is also checked for the presence of concurrent ulceration.  


Treatment of this condition is directed at controlling the inflammatory response in the tissue. This usually involves the topical application of drops or ointments containing a steroid (corticosteroid) preparation. The selection of medication, however, is dependent on other factors including whether a virus (Feline Herpes Virus) is suspected and whether the eye shows evidence of a corneal ulceration.

*Steroids used in patients with a viral infection or corneal ulcer can make matters worse. Therefore, treatment of these cats becomes a bit more complicated and the selection of medications may include other types of anti-inflammatories or systemic medications. One systemic medication that has been used in such circumstances is megesterol acetate. Its use must be carefully considered as systemic side effects can be seen including causing cats to develop diabetes mellitus and mammary gland tumors.
Cats with suspected Feline Herpes Virus may be concurrently treated with topical and / or systemic antiviral medications.


In simple, uncomplicated cases receiving appropriate treatment, the prognosis is good and clarity can be restored to the cornea - usually within 2 to 4 weeks.

In cats with concurrent Feline Herpes Virus infection or corneal ulceration, the prognosis is still good, but the treatment course may be prolonged and complicated. Frequent follow ups may be required to monitor these cats and their healing response. Cats may wind up with varying degrees of scarring in their cornea depending on the extent of the lesions and these complicating factors.

Eosinophilic Keratitis can be a chronic, recurring condition in some cats. They may have periods of remission and experience relapses - particularly in times of stress.