What is the uvea?
The uvea is the part of the eye made up of the iris (the thin, circular structure in the eye that gives the eye its color and controls the size of the pupil), the ciliary body (part of the wall of the eye that makes the fluid that fills the eye) and the choroid (middle layer of the eye).
The iris and the ciliary body together form the anterior uveal tract. The ciliary body produces a fluid called the aqueous humor that provides important nutrients to the eye and that maintains intraocular pressure (IOP). The ciliary body also contains the suspensory ligament and ciliary muscles which support the lens and control its shape and hence its ability to focus images.
What is uveitis?
Uveitis is an inflammation of one or more of the structures making up the uvea. If only the ciliary body and the iris are inflamed, the condition is called anterior uveitis, while inflammation of only the choroid is called posterior uveitis. If all three structures are involved, the condition is called panuveitis or true uveitis.
Uveitis may only involve one eye, or it may occur in both eyes at the same time.
What causes uveitis?
There are many potential causes of uveitis. Sometimes the true cause is never discovered. Common causes are:
- infections; including viral, including feline leukemia (FeLV), feline immunodeficiency virus (FIV), feline infectious peritonitis (FIP), bacterial, parasitic (toxoplasmosis, migrating larvae), or fungal (cryptococcosis, blastomycosis)
- metabolic disease (such as diabetes)
- high blood pressure
- toxins (typically chemicals or irritants getting onto the eye)
- immune mediated; particularly autoimmune disease where the cat produces antibodies against its own tissues
- trauma to the eye
- lens damage resulting in the leakage of lens protein
- eye tumors
What are the clinical signs of uveitis?
Uveitis is a painful condition, and some cats with uveitis will paw at the sore eye while others will avoid any touch. A cat with uveitis may keep the affected eye shut or may squint (blepharospasm) or blink spasmodically. Most cats will avoid bright lights (photophobia).
"In most cases, the visible parts of the eye will be intensely red, and your cat may have difficulty seeing."
In most cases, the visible parts of the eye will be intensely red, including the sclera (the white part of the eye) and the conjunctiva, and your cat may have difficulty seeing. Usually there is a clear watery discharge from the eye, but in some cases there may be mucus or pus. If the anterior uvea is involved in the inflammation, the eye may appear cloudy; the cloudiness may be due to fluid leaking into the cornea or to an accumulation of protein or cells in the anterior chamber of the eye. Sometimes there may be bleeding or pus in the front chamber of the eye. With posterior uveitis, there is a risk of retinal detachment.
Uveitis may occur suddenly (acute uveitis) or may develop more slowly (chronic uveitis). With acute uveitis, the pupil is usually constricted. With chronic uveitis, the pupil may be constricted or normal, the iris may change in color (the color change may be permanent), cataracts may develop on the affected eye, or the lens of the affected eye may become dislocated or luxated.
How is uveitis diagnosed?
Many of the signs of uveitis are similar to glaucoma. The main difference between these two conditions is that with uveitis, intraocular pressure (IOP) is reduced (low) whereas with glaucoma it is elevated (high). Measurement of IOP is often performed to differentiate between the two conditions and is a simple, painless procedure. A complete and thorough physical examination of your cat must be performed since uveitis is a symptom of many generalized illnesses.
"A complete and thorough physical examination of your cat must be performed since uveitis is a symptom of many generalized illnesses."
With generalized illnesses, diagnostic evaluations may include blood tests, urine analysis, or radiographs (X-rays). For infectious causes, it may be necessary to perform specialized blood tests or take tissue samples for diagnostic testing. Special diagnostic procedures such as ultrasound may be used to examine the eye, and your veterinarian may recommend a referral to a veterinary ophthalmologist.
What is the treatment of uveitis?
Treatment is initially aimed at reducing inflammation and providing pain relief primarily with topical eye medications such as corticosteroids (prednisolone, dexamethasone) or non-steroidal anti-inflammatory drugs, such as flurbiprofen (brand name Ocufen®). If the uveitis is the result of trauma, treatment may include repairing the traumatic injury. If the uveitis is due to an infectious agent, specific anti-infective therapy will be prescribed. If the uveitis is a symptom of another generalized disease, the underlying disease will need to be treated. Oral medications may be used once underlying causes have been ruled out. The best course of treatment will address the clinical signs but also any primary condition that the uveitis is a result of.
"Treatment is initially aimed at reducing inflammation and providing pain relief."
One of the goals of treatment is to prevent secondary complications from developing. These secondary complications may include glaucoma (an increase in IOP which is painful and can lead to blindness), retinal detachment, lens luxation, or synechia (development of adhesions or attachments between the iris and either the cornea or the lens). In order to assess the initial response to treatment, your veterinarian will need to examine your cat frequently, sometimes daily. The frequency of subsequent recheck examinations will depend on the severity of disease and your cat's response to treatment.
Is uveitis contagious?
Uveitis may be a symptom of certain infectious diseases that are contagious. A cat with uveitis resulting from a systemic illness with FeLV, FIV, FIP may be contagious to other cats. A cat with uveitis caused by toxoplasmosis may be infectious to other cats or to people.
What is the prognosis of uveitis?
When properly treated, most cases of uveitis begin to improve within twenty-four hours. If the eye is very cloudy or if hemorrhage has occurred, this may take a few more days to clear.
Complications are more common after very severe or recurrent cases of uveitis. If complications occur, your veterinarian may recommend referral to a veterinary ophthalmologist. Severe uveitis can result in irreversible blindness.