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 maintains the eye’s pressure. The ciliary body also contains ligaments and muscles which support the lens and control its ability to focus on images.
What is uveitis?
Uveitis is an inflammation of one or more of the structures making up the uvea. If all three structures are involved, the inflammation is called true uveitis or pan-uveitis. If only the ciliary body and the iris are inflamed it is called anterior uveitis, while inflammation of the choroid is called posterior 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 (rabies, distemper), bacterial (Lyme disease, leptospirosis), parasitic (toxoplasmosis, ehrlichiosis) or fungal (blastomycosis, histoplasmosis, cryptococcosis, coccidioidomycosis)
- metabolic disease (such as diabetes)
- high blood pressure
- toxins (typically chemicals or irritants getting onto the eye
- immune mediated; particularly autoimmune disease where the dog 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?
Signs of uveitis are severe pain with an intense reddening of the visible parts of the eye. The eye is usually kept shut (squinting or blepharospasm) and most dogs avoid bright lights (photophobia). Cloudiness of the eye may also be noticed. Sometimes there is bleeding into the eye and there may be excessive tearing.
The pupil can be constricted (very small), and the iris can show a bulging outward. Blood or pus may also be seen inside the eye. The sclera (white part of the eye) and conjunctiva may appear redder than normal. The cornea may also have a cloudy or bluish appearance. In chronic cases, cataracts, blindness, or lens luxation (displacement) can also be seen.
How is uveitis diagnosed?
Many of the signs of uveitis are similar to glaucoma, thus measurement of intraocular pressure (IOP) is often performed to differentiate between the two. With uveitis, IOP is low whereas with glaucoma it is high. This is a simple and painless procedure.
A complete and thorough physical examination of your dog must be performed since generalized illnesses can have uveitis as one of their signs. Often there is a color change of the iris, which may be permanent. Special diagnostic procedures such as ultrasound may be used to examine the eye. Other tests may be done in order to help rule out systemic illnesses including blood tests, urinalysis, or radiographs (X-rays). For infectious causes, it may be necessary to perform specialized blood tests or take tissue samples for diagnostic testing.
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®).
Treatment of uveitis due to trauma can involve repair of any corneal tears or removal of a foreign body in the eye. This may involve referral to a specialist. 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.
"One of the goals of treatment is to prevent secondary complications from developing."
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 dog frequently. The frequency of subsequent recheck examinations will depend on the severity of disease and your dog’s response to treatment.
What is the prognosis of uveitis?
When properly treated, most cases of uveitis begin to improve within twenty-four hours, but the ultimate outcome will depend on the underlying cause. 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. Severe uveitis can result in irreversible blindness. Early diagnosis and prompt treatment provides the best prognosis.