Uveitis refers to an inflammation (irritation) of the uvea or middle layer of the eye. The outer layer that encloses the eye is composed of the clear cornea and the white sclera. The innermost layer is the nerve layer or the retina. The middle layer (uvea or uveal tract) is the nutritional layer rich in blood vessels. It is made up of: the iris (colored portion in the front part of the eye), the ciliary body that produces the fluid in the eye and the choroid that provides nutrition to the retina inside the eye. Clinical signs of uveitis include cloudiness, redness, tearing, squinting, bleeding into the eye and loss of vision. Uveitis can result in several eye complications such as cataract formation, scar tissue, glaucoma and damage to the retina.
Although uveitis is a specific diagnosis, the diagnosis in itself does not indicate cause. Unfortunately, uveitis appears similar regardless of cause. That is why diagnostic tests are commonly recommended as part of the uveitis evaluation. In dogs, no cause will be found in about 70% of cases. This is true for about 60% of feline cases. Many of these so-called “idiopathic” uveitis cases are immune-mediated and can be chronic. This is especially true in cats. When the uveitis affects both eyes, the concern increases that the uveitis is due to systemic disease, which is found in about 30% of dogs and 40% of cats. Due to its rich blood supply, the uvea or uveal tract is a natural target for diseases originating in other parts of the body. Signs of these diseases may be seen first in the eye often before signs develop elsewhere in the body. Systemic causes include cancer and certain unusual types of infections. Infectious causes of concern in cats include Toxoplasmosis, feline infectious peritonitis (FIP, dry form of the disease), FeLV or FIV (“kitty AIDS”), and possibly Bartonella and herpes. Fungal infections can cause uveitis in dogs or cats, though these are usually animals that have lived or traveled outside the Northwest.
Infectious causes in dogs include ehrlichiosis, Rocky Mountain Spotted Fever, Lyme’s disease and brucellosis. Trauma and cataracts are other common causes of uveitis in either species.
Medical treatment of uveitis must be aggressive to prevent glaucoma, scarring of the structures inside the eye and to prevent possible blindness. Different medications are used to control the original cause of the uveitis, if known, and to minimize the inflammation itself. The treatment protocol will vary for each patient, but often includes a steroid eye medication to decrease the inflammation, atropine to alleviate the pain (people with uveitis get a tremendous headache!) and possibly medicine to control glaucoma. If caught early and treated diligently and aggressively, uveitis will often resolve without serious consequences.