Uveitis is an inflammatory process involving the middle of the three layers in the eye. To understand uveitis it is important to know the basic anatomy of the eye. The outer layer enclosing 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 is the uveal tract, which is rich in blood vessels. It is composed of the iris in the front part of the eye, the ciliary body, which produces the fluid (aqueous humor) inside the eye, and the choroid which nourishes the retina in the back of the eye. Because of its rich blood supply, the uveal tract is a natural target for diseases originating in other parts of the body. When inflammation attacks specific segments of the uveal tract, the disease is further classified as iritis (inflammation of the iris), cyclitis (inflammation of the ciliary body) or choroiditis (inflammation of the choroid), depending on the affected structure. If all the structures are inflamed then it is called panuveitis (inflammation of all uveal structures of the eye).
Ocular pressure is maintained by the aqueous humor (fluid) produced by the ciliary body within the eye. Initially, if the ciliary body is inflamed, the fluid production slows down and the ocular pressure drops. The aqueous humor produced in the eye normally drains through the angle between the ciliary body and the iris. The inflammatory debris produced in uveitis can block the drainage angle and result in increased intraocular pressure (glaucoma) over time. Once uveitis resolves, glaucoma can remain if drainage structures were damaged by the inflammation. Recheck of the eyes following uveitis is important for this reason.
Additionally, disease processes such as uveitis can lead to lead to corneal ulcers (superficial to deep), ocular infections, corneal scarring, corneal vascularization, corneal mineralization, cataract, lens luxation, retinal detachment and keratoconjunctivitis sicca. Uveitis also can lead to secondary complications similar to those to which treatment for uveitis can give rise, as discussed under “Prognosis”.
Uveitis is associated with many different diseases. Examples in the dog include Ehrlichiosis and Coccidioidomycosis, two systemic diseases common to the southwestern United States. In the cat, uveitis can be a consequence of Feline Leukemia Virus, Feline Infectious Peritonitis or many other diseases. In any animal, penetrating injuries such as cactus spines or a cat scratch may produce uveitis. Inflammation of the uveal tract can occur when the lens capsule is breached (such as following surgery, trauma, or injury of the lens) or in the presence of cataracts where lens proteins leak out of the lens capsule into the eye. Other possible causes of uveitis are local bacterial infection, immune mediated diseases and parasitic diseases. Treatment can be more specific if the actual cause is known. It is important to test for some infectious diseases to make sure there is not an underlying cause for the inflammation, but unfortunately, in up to 75% of the cases the cause is never determined.
Uveitis must be treated aggressively in order to prevent glaucoma, scarring of the uveal structures, and possibly blindness. Different medications may be used to treat the underlying, original cause of the uveitis and to attempt to control the inflammation itself. Aspirin (not aspirin substitutes) and corticosteroids minimize the inflammatory process. Corticosteroids may be administered by injection under the lid of the eye, by drops in the eye, or as an oral medication, depending on the suspected cause of uveitis. Topical use must be postponed if damage to the corneal surface is present because the corticosteroids prevent healing of the ulcer. If certain systemic diseases are suspected, oral corticosteroids may be postponed until test results become available. Atropine dilates the pupil and helps prevent scarring of the iris. This medication may be contraindicated, however, if glaucoma is present as it may further decrease the drainage of aqueous humor from the eye. Oral and topical antibiotics are employed when a bacterial infection is present in the eye.
The treatment of uveitis requires therapy to halt the inflammation of the uveal tract along with a search for the original cause of the disease. Many tests may be needed to determine possible causes and the results are important for proper treatment.
Treatment for uveitis can involve life-long topical and/or oral medications. Life-long topical medications seldom give rise to complications, which occur in less than 5% of these cases. Nevertheless, potential complications include, but are not limited to, inflammation of the pink tissue (conjunctivitis); corneal ulcerations (superficial to deep); corneal scarring, vascularization, and mineralization; ocular rupture, secondary to ulceration; worsened inflammation inside the eye, secondary to infection or ulceration; high pressure within the eye (glaucoma), secondary to the uveitis; retinal detachment or degeneration, secondary to uveitis or infection; ocular or orbital pain, secondary to uveitis, glaucoma or infection; eyelid rubbing; bleeding inside the eye (hyphema), secondary to uveitis or infection; tearing (epiphora); and/or lens luxation, secondary to uveitis, glaucoma or infection. Some of these complications can lead to blindness. Some oral medications used to treat these disease processes may cause changes in behavior, gastrointestinal upset (diarrhea, vomiting, decrease/increase in appetite/thirst), panting, decreased white blood cell counts (such as leukopenia), and various changes in chemistry values (liver, kidney, potassium, to name a few).
Your awareness of your pet’s symptoms and compliance with recommendations for recheck examinations and periodic blood work help control these potential complications.
If you have any questions regarding canine uveitis, please call Eye Care for Animals.