Compared to dogs, cats don't get many eye diseases. However, one of the most common eye problems in cats is uveitis, and it is usually chronic and can cause blindness and ocular pain. In fact, the three most common reasons for a cat's eye to be surgically removed (this is called "enucleation") is ocular trauma (such as a severe cat claw injury to the eye), glaucoma (increased intraocular pressure) secondary to chronic uveitis, and cancer (diffuse iris melanoma). Uveitis in cats can be caused by serious or life-threatening generalized disease in the cat's body. Therefore, feline uveitis is an important disease to diagnose and treat correctly, to decrease the chances of the eye being blinded and possibly removed, or even of the cat dying from the disease that caused the uveitis.

What is Uveitis?

Normal Cat Eye

Uveitis is inflammation of the uveal tract, which is the pigmented, vascular part of the eye. This includes the iris (this is the colored part of the eye that forms the pupil), ciliary body, and choroid. The uveal tract (or "uvea") is all in one piece, and is shaped like a hollow ball with a large slit in it, that fits inside the eyeball. The slit is the cat's pupil, and the rest of the ball is the iris, ciliary body, and choroid which all "blend" together as a vascular cup. Therefore, if the iris is inflamed, it is likely that the ciliary body and choroid are involved too, either slightly or severely.

What does Uveitis look like?

Severe Anterior Uveitis.

Uveitis can have many clinical signs. Here is a list of common ones, that can be mixed and matched in a variety of combinations: squinting, sensitivity to light, third eyelid protrusion, tearing, redness to the white part of the eye, abnormal pupil shape or size, an altered iris color (usually a "muddy" or reddened color compared to the normal color), cloudiness, cataract, and/or enlarged eye if glaucoma is present. Blindness may be apparent, but this is often not noticeable, especially if the fellow eye is visual.

The photo to the left shows severe anterior uveitis. The tannish cloudy area covering the pupil is a clot of inflammatory debris (fibrin) in the anterior chamber.

What are the causes of Uveitis?

In approximately 6 out of every 10 cats with uveitis, the cause cannot be identified, even with extensive diagnostic tests. However, when the cause can be identified, it is usually trauma, an infectious disease, or cancer. The most common infectious diseases that can cause uveitis in cats are: Toxoplasma gondii, feline infectious peritonitis (FIP), Bartonella henselae, feline immunodeficiency virus (FIV), feline herpesvirus-1 (FHV-1) and feline leukemia virus (FeLV). The two most common types of cancer that can cause uveitis in cats are lymphoma and also diffuse iris melanoma (DIM). Discussing these various diseases is beyond the scope of this handout. It is important to know that all of these diseases can be life-threatening, with perhaps the exception of feline herpes virus.