Disorders of the Anterior Uvea in Cats
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. The anterior uvea refers to the uvea in the front of the eye: the iris, the ciliary body, and the anterior chamber angle; however, diseases that affect the anterior uvea often affect the choroid as well.
A weakening and shrinking in size (atrophy) of the iris can be seen in cats. It can involve the edge or the connective tissue of the pupil. Shrinkage of the edge of the pupil creates a scalloped border and a weakening of the sphincter muscle, which results in a dilated pupil or slowed reflexes of the pupil in response to light. Shrinkage of the connective tissue results in dramatic holes in the iris, and often, displacement of the pupil. Neither of these types of atrophy appears to affect vision. Animals lacking a functional sphincter muscle (which controls the opening and closing of the iris) may show increased sensitivity to bright light.
Inflammation of the front portion of the uvea (the iris and the ciliary body) is called anterior uveitis or iridocyclitis. It occurs frequently in cats. It may be seen in one eye (as a result of trauma, eye parasites, or various types of cancers) or in both eyes (as a result of a whole-body infection or immune-mediated diseases). The effects of anterior uveitis may be destructive to the eye and can affect vision.
Common infectious diseases that can cause anterior uveitis include 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 squinting of the eyelids, a protruding third eyelid (nictitating membrane), abnormally red or bloodshot eyes, or any other changes to 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. Antibiotics are necessary if there is a bacterial infection.
Bleeding inside the eyeball is called hyphema. It may appear as liquid or clotted blood. Causes include uveitis, traumatic injury, a tumor within the eye, detachment or tearing of the retina, high blood pressure, clotting disorders, birth defects, and glaucoma. Sudden, severe bleeding usually has a good outcome if the cause is identified and treated. Recurrent or longterm hyphema has an unknown or poor outlook because glaucoma or blindness is likely. Although no drugs are available to treat hyphema, certain medications may help.
Also see professional content regarding the anterior uvea.