Intraocular Inflammation
What is uveitis or intraocular inflammation?
Uveitis is the term used for inflammation of the uveal tract of the eye (the iris, ciliary body, and choroid). In order to understand uveitis, it helps to first understand the basic anatomy of the eye. The eye is made up of three primary layers of tissue. The outer layer enclosing the eye is made up of the cornea (the clear part at the front of the eye) and the sclera (the white of the eye). The inner layer is the retina, which primarily consists of nerve tissue. The middle layer is called the uveal tract, and it is rich in blood vessels, which makes it very susceptible to diseases present in other parts of the body. The uveal tract is composed of the iris (the colored part of the eye), the ciliary body (a structure which produces the fluid inside the eye), and the choroid, which nourishes the retina in the back of the eye.
How would I know if my pet has uveitis?
Animals with uveitis can show a number of different signs, including blinking, squinting, watery discharge, light sensitivity, cloudiness or redness of the eye, or visual deficits. These signs can also be present in other eye diseases, such as glaucoma, corneal ulcer, etc., so it is very important for your pet to be examined by a veterinary ophthalmologist to determine the exact nature of the eye problem. A veterinary ophthalmologist will use a number of different instruments to illuminate and magnify the structures of the eye in order to make a diagnosis of uveitis.
What causes this disease?
Many different conditions can cause uveitis in dogs and cats. In general, they can be categorized into four large groups: infection, neoplasia (cancer), trauma, and immune-mediated. Infection would include bacterial, viral and fungal infections. Neoplasia includes many types of cancers, but lymphoma is most common. Trauma includes either blunt trauma (blow to the head) or penetrating trauma (for example, a cat scratch to the eye). Immune-mediated diseases are those where the body reacts to some of its own tissues as if they were foreign substances. In horses, immune-mediated uveitis is the most common type and Appaloosas are over-represented. In all cases of uveitis, it is important to try to determine the underlying cause, so that it may be appropriately treated. Unfortunately, in about 50% of uveitis cases the cause is never determined.
How is uveitis treated?
Uveitis must be treated aggressively in order to prevent permanent damage to the eye. The inflammation present within the eye causes cells to accumulate within the aqueous humor. These cells can block the drainage outlet of the eye, and cause the pressure within the eye to increase, causing glaucoma. Even after the uveitis has resolved, the glaucoma may persist if the drainage structures were permanently damaged. Different medications are used to control the underlying cause of the uveitis and to minimize the inflammation itself. Anti-inflammatory medications can be given orally and in the form of eye drops. Atropine, an eye drop that dilates the eye, may also be given to alleviate pain. Oral and topical antibiotics may be given if the cause of the uveitis is an infection.
Uveitis will often resolve with no complications if it is caught and treated early. As has been mentioned previously, it is very important to also determine and treat any underlying cause of the uveitis. Many tests may be needed to make this determination, including bloodwork and possibly radiographs. Unfortunately, in some patients the cause of the uveitis is never found, and treatment may be lifelong. In other patients uveitis is so severe that it may be necessary to remove the eye.
Without treatment, uveitis can cause devastating complications. Not only is the inflammation itself painful, it can lead to permanent cloudiness in the cornea including corneal edema and scarring, adhesions of the iris to the lens, cataracts, lens luxation, vitreal degeneration, retinal detachment, and glaucoma. Most of these changes impair vision and/or lead to blindness, and many are irreversible. In fact, in horses uveitis is the leading cause of blindness. Additionally, the underlying cause of uveitis can make your pet very sick and in some cases the causative disease is life-threatening.
