The uvea is the part of the eye made up of the iris, the ciliary body and the choroid. The iris is the pigmented or colored membrane behind the cornea (clear outer surface of the eye). Thechoroid is the middle layer of the eye. It is located between the sclera, which is the fibrous protective outer coat (the white of the eye) and the retina, which is the light sensitive surface at the back of the eye. The ciliary bodyis a thickened extension of the choroid. The ciliary body connects the choroid and the iris.
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 contains the suspensory ligament and ciliary muscles which support the lens and control its shape and hence its ability to focus images. The iris and the ciliary body together form the anterior uveal tract.
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 iridocyclitis or anterior uveitis, while inflammation of only the choroid is choroiditis or posterior uveitis. If all three structures are involved, the condition is called pan-uveitis 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:
- Infection - viral, bacterial, parasitic or fungal
- Metabolic disease
- Diabetes mellitus
- High blood pressure
- 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, either primary or secondary
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 or blink spasmodically. Most cats will avoid bright lights.
"Uveitis is a painful condition..."
In most cases, the visible parts of the eye will be intensely red and the cat may have difficulty seeing. Usually there is a clear watery discharge from thee 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 into 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 (and 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 the pet 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. 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. In many cases, this treatment involves the use of a combination of oral medications and either eye drops or ointments applied topically. 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 a another generalized disease, the underlying disease will need to be treated.
"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, 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 that is the result of systemic illness with feline leukemia virus (Feleuk), feline immunodeficiency virus (FIV) or feline infectious peritonitis (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.