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. Inside the eye, the innermost layer is the nerve layer or the retina. The middle layer of the eye (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 the part of the eye which produces the fluid inside the eye (aqueous humor) and the choroid that provides nutrition to the retina inside the eye. When inflammation develops within the uveal tract, the term is uveitis (-itis means 'inflammation of', so this is inflammation of the uvea). As specific segments of the uveal tract are affected, uveitis 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. These are doctor terms but are helpful for you to know. Due to its rich blood supply, the uveal tract is a natural target for diseases originating in other parts of the body. Because the cornea is normally clear, signs of disease may be seen inside 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), on the surface of the eye (such as corneal ulcer) and trauma.
Uveitis is not a disease just as a sprained ankle or a sore throat aren't diseases. It is a condition or syndrome which indicates inflammation within the eye. Uveitis may cause vague clinical signs that may include blinking, squinting, watery discharge from the eye, and/or fear of light (photophobia) without any obvious changes to the eye itself. The normally clear cornea may appear dull or hazy 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 (colored portion of the eye) becomes red or changes color. 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 certain diseases are 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. (This is not tears!) 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 or a membrane might develop over the iris and drainage angle and inhibit the outflow of the fluid causing elevated intraocular pressure (IOP). This is known as glaucoma. Alternatively, the iris may adhere to the lens and block fluid flow through and out of the eye resulting in glaucoma . Once uveitis resolves, glaucoma may persist if drainage structures were permanently damaged by the inflammation or the membrane. Alternatively, if the ciliary body has been severely damaged, fluid production may cease entirely and the eye will begin to shrink up. Recheck of the eyes following the resolution of uveitis is important for these reasons.
Uveitis may be caused by many different diseases. Diseases in the dog include lymphoma, bleeding disorders, 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 and/or other diseases. In any animal, a corneal ulcer or penetrating injury such as cactus spines, porcupine quills, pellets or b.b.'s or a scratch may result in uveitis. Blunt trauma can damage the eye severely and result in uveitis. Inflammation of the uveal tract can occur when the lens leaks some of its contents inside the eye. The lens may cause uveitis when injured, when a cataract is rapidly forming, when cataract is dissolving or following penetrating injury or certain types of surgery such as cataract 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 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) or Rimadyl® by mouth and indomethacin, Profenal®, Ocufen®, Voltaren® and corticosteroids (cortisone drugs) minimize the inflammatory process. Corticosteroids may be administered by injection under the conjunctiva (moveable white tissue of the eye), by eye drops or as an oral medication or a combination of these means 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. Rymadyl® is an oral non-steroidal antiinflammatory drug (NSAID) which can be given by mouth to dogs and by injection to dogs and cats. Indomethacin, Voltaren®, Ocufen® or Profenal® drops are topically applied NSAID's 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 often not used because bacterial infections are not commonly found as the cause of inflammation. Certain bacterial agents can cause uveitis in conjunction with the systemic infection. In these cases, such as Ehrlichia, Lyme's disease and Rocky Mt. Spotted Fever, antibiotic medication must be given to prevent worsening and recurrence of the uveitis.
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 lifelong. In other patients, uveitis is so severe that removal of the eye is necessary. Lastly, in occasional patients, uveitis is self-perpetuating (causes more uveitis). These patients are difficult to control.
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