The uvea (or the uveal tract) is the colored inside lining of the eye consisting of the iris, the ciliary body, and the choroid. The iris is the colored ring around the black pupil. The ciliary body is the set of muscles that contract and relax to allow the lens to focus on objects; it is also the source of aqueous humor, the clear fluid in the eye. The choroid is the inner lining of the eyeball. It extends from the ciliary muscles to the optic nerve at the back of the eye. The choroid also contains layers of blood vessels that nourish the inside parts of the eye, especially the retina (see Eye Disorders of Dogs: Disorders of the Anterior Uvea in Dogs).
Persistent membranes across the pupil, a weakening and shrinking in size (atrophy) of the iris, cysts of the iris, and inflammation of the iris and ciliary body (anterior uveitis or iridocyclitis) are all conditions that can affect the anterior uvea. In cats, cysts of the iris are frequently attached at the edge of the pupil. Therapy is rarely necessary, but removal or rupture of a cyst may occasionally be required.
Inflammation of the Anterior Uvea
Anterior uveitis, or inflammation of the front portion of the uvea, occurs frequently in cats. It may be seen in one eye (as a result of trauma or various types of cancers) or in both eyes (as a result of a whole-body infection or parasites). The effects of anterior uveitis may be destructive to the eye and can affect vision.
Common causes of inflammation of the uvea in both eyes of cats include immune-mediated diseases and infectious diseases such as feline infectious peritonitis and feline leukemia (both viral infections), feline immunodeficiency virus infection, toxoplasmosis (a disease caused by microscopic parasites), generalized fungal infection, and leptospirosis (a bacterial infection). Often, anterior uveitis is the only sign of these disorders, so it is very important to have your cat examined by a veterinarian if it shows signs such as a protruding third eyelid (nictitating membrane), abnormally red or bloodshot eyes, or pus or nodules in the eye.
Your veterinarian will want a thorough medical history of your pet to help in diagnosing this condition. Other diagnostic steps may include examination of the cornea for injuries, a physical examination, blood tests, and tests on fluid from your pet's eye. Reducing the eye inflammation requires treating the underlying primary disease with appropriate drugs. Cortico-steroids are sometimes prescribed to treat cloudiness, reduce the inflammation, and reduce the chance of developing glaucoma.
Last full review/revision July 2011 by Kirk N. Gelatt, VMD, DACVO; David G. Baker, DVM, MS, PhD, DACLAM; A. K. Eugster, DVM, PhD