Ocular Disease



Cat with Conjunctivits                   Ocular disease


A common symptom associated with feline herpesvirus-1 (FHV-1) is ocular disease.  In fact, it is the most frequent cause of conjunctivitis and keratitis in domestic cats.  Living with a cat with ocular disease can be difficult, frustrating, and expensive to diagnose and treat.  Sometimes the only sign a cat will show is eye problems or they can show a multitude of signs related to viral rhinotracheitis.  There are several forms of ocular disease caused by FHV-1 which will be explained shortly.  First, it is important to understand the anatomy and physiology of the eye.

The cornea is the transparent front part of the eye.  It is composed of 5 layers which are made up of epithelium, collagen, and endothelium with the epithelium being the outermost layer.  When the epithelium and some of of the collagen are missing, a corneal ulcer will form.  This can lead to pain due to unwanted nerve stimulation.  Eyes that have intact corneas are far less sensitive than those with ulcerated corneas.  Because FHV-1 attacks epithelial cells, corneal epithelium is at risk of getting damaged as the virus invades and replicates in those cells.

A current FVH-1 infection and viral replication along with a secondary bacterial infection will lead to conjunctivitis.  Conjunctivitis is commonly seen in both eyes in this type of infection and redness around the eye along with clear discharge is seen.  Most cats will recover from their first infection in 10-20 days, but if the infection is severe or the cat's immune system is suppressed, this may lead to recurrent or chronic conjunctivitis.

Keratitis, inflammation of the cornea, is only caused virally by FHV-1.  When this occurs, it is likely to be in an adult cat stemming from the reactivation of a latent infection.  When the layers of epithelium and collagen, in the stroma, are damaged, this leads to a corneal ulcer in which its outward signs depend on the depth of corneal infection and chronicity.  Keratitis can occur in one eye or both, often without any respiratory signs.

Stromal keratitis, infection and inflammation of the deeper corneal layer, is a less common disease of FHV-1 infection.  It does have importance however, due to the fact that it can potentially lead to vision-threatening clouding over and scarring of the corneal tissue.  This condition is not a manifestation of a primary FHV-1 infection, but is rather, an accumulation of ocular disease periods seen with chronic recurrent infections.