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Uveitis
Inflammation of the Eye

 

Written by Dr. Dennis Hacker
Edited by Dr. Michael Zigler

To understand what uveitis is and how serious it is, it is helpful to know basic anatomy 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 inside the eye (aqueous humor) and the choroid that provides nutrition to the retina inside the eye. When inflammation attacks specific segments of the uveal tract the disease is further classified depending on the affected structure. Iritis is inflammation of the iris. Cyclitis is inflammation of the ciliary body. Anterior uveitis or iridocyclitis is inflammation of both the iris and ciliary body. Choroiditis or posterior uveitis is inflammation of the choroid. If all three structures (iris, ciliary body and choroid) are inflamed then it is called panuveitis. Uveitis

Due to its rich blood supply, the uvea or uveal tract is a natural target for diseases originating in other parts of the body. Because the cornea is normally clear, signs of these diseases may be seen first in the eye often before signs develop elsewhere in the body. Additionally, uveitis may have causes within the eye such as cataract or changes in the lens.

Diagnosis of Uveitis

Uveitis may cause vague clinical signs that can include blinking, squinting, watery discharge, and fear of light (photophobia) without any obvious changes to the eye itself. The normally clear cornea may appear dull or very blue due to uveitis. In other cases, the cornea becomes cloudy due to white blood cells accumulating on the inside of the cornea. The conjunctiva (white of the eye) becomes red and swollen. In some cases of uveitis, the iris (coloured portion of the eye) becomes red or changes colour. Uveitis is usually diagnosed by an examination of structures of the eye using instruments that magnify and illuminate. In more advanced cases, changes are visible without special instruments. Once uveitis is diagnosed, a general evaluation of the patient should be performed if uveitis is suspected to be a sign of internal disease. Blood profiles or other tests may be necessary if a certain disease is suspected or to find the cause of the uveitis. An ophthalmic examination consists of a visual inspection of the external and internal portions of the eye and the measurement of ocular pressure.

Ocular pressure is maintained by fluid (aqueous humor) which is continually produced by the ciliary body and drains from the eye. If the ciliary body is inflamed fluid production should slow down and the ocular pressure should drop. The aqueous humor produced in the eye flows through the pupil then drains into an 'angle' between the iris and the cornea where it leaves the eye. Cellular debris produced in uveitis can block this drainage angle. Alternatively, the iris may adhere to the lens and block fluid flow and result in increased ocular pressure - glaucoma. Once uveitis resolves, glaucoma may persist if drainage structures were permanently damaged by the inflammation. Recheck of the eyes following the resolution of uveitis is important for this reason.

Causes of Uveitis

Uveitis may be caused by many different diseases. Diseases in the dog include ehrlichiosis, Rocky Mountain Spotted fever, Lyme's disease and brucellosis. In the cat, uveitis can be a consequence of Feline Leukemia Virus (FELV), Feline Infectious Peritonitis (FIP), Feline Immunodeficiency Virus or Feline AIDS (FIV), toxoplasmosis or other diseases. In any animal, penetrating injuries such as cactus spines, porcupine quills, pellets or b.b.'s or a scratch may result in uveitis. Inflammation of the uveal tract can occur when the lens leaks some of its contents into the eye. The lens may cause uveitis when injured, when a cataract is rapidly forming, when cataract is dissolving or following certain types of surgery. Further possible causes are local bacterial infection, immune mediated (autoimmune) diseases, cancer and parasitic diseases. Treatment can be more specific if the actual cause of uveitis is known. Unfortunately, in up to 75% of the cases the cause of uveitis is never determined.

Medical Treatment

Medical treatment of uveitis must be aggressive to prevent glaucoma, to prevent 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.

Aspirin (not aspirin substitutes), indomethacin, Profenal(R) and corticosteroids (cortisone drugs) minimize the inflammatory process. Corticosteroids may be administered by injection under the conjunctiva (movable white tissue of the eye), by eye drops, or as an oral medication depending on the location of uveitis. Eye drops are most often used for anterior uveitis. Injections and oral medication are used for posterior uveitis or panuveitis. Drops in the eye must be postponed if damage to the corneal surface is present (ulcer) because the corticosteroids prevent healing of the ulcer or lead to a worsening of the ulcer. If certain systemic diseases are suspected, oral corticosteroids may be postponed until laboratory test results become available. Aspirin can be used in dogs and cats by mouth and helps reduce inflammation. Indomethacin or Profenal(R) drops are a non-steroidal anti-inflammatory agent that will help reduce the inflammation of the eye.

Dilating drops or ointments widen the pupil and relax the muscles within the eye. These two actions result in fewer adhesions and less pain for the patient. This medication may not be used if glaucoma is present as it may further decrease the fluid drainage from inside the eye and lead to increased pressure.

Oral and topical antibiotics are only given when a bacterial infection is present within the eye. Antibiotics are not often used as bacterial infections are not commonly found as the cause of inflammation.

Prognosis

The treatment of uveitis requires therapy to halt the inflammation of the uveal tract along with a search for the cause of the condition. Diagnostic tests may be needed to determine possible causes. The results of these tests are very important for proper treatment to be given. Follow-up examinations ensure optimal therapy is being given and guard against possible complications. Uveitis, if caught early and treated diligently and aggressively, will often resolve without serious consequences. Unfortunately, in certain individual patients the cause of uveitis is never determined and treatment may be life-long. In other patients, the uveitis is so severe that removal of the eye is necessary.