Uveitis

The uvea (or uveal tract) comprises the iris, the ciliary body and the choroid within the eye. They form the middle layer of the eye and provide nutrition and a good blood supply to the eye. The choroid is found at the back of the eye, sandwiched between the sclera - the fibrous protective outer coat (the white of the eye) and the retina which is the light sensitive surface within the eye.

The iris and the ciliary body together form the anterior uveal tract. The iris is the pigmented membrane behind the cornea (clear part of the eye). It is responsible for the colour of the eye. The hole in the centre of the iris is the pupil and its size controls the amount of light entering the eye. The ciliary body is located between the choroid and the iris. It produces the aqueous humor important in nutrition of the eye and also in maintaining intraocular pressure (IOP). The ciliary body contains muscles and the suspensory ligament supporting the lens within the eye and changes in muscle tone alter the lens shape and assist with focusing.

Uveitis is inflammation within the eye. It has a variety of synonyms. If all three structures are involved (ciliary body, iris and choroid), it is true uveitis or panuveitis. If only the ciliary body and the iris are inflamed it is called anterior uveitis (or iridocyclitis), while inflammation of just the choroid is posterior uveitis. Anterior uveitis is the most common form.

What are the causes of uveitis?

There are many factors that can cause uveitis. Sometimes the true cause is never discovered. Common causes are infection, e.g. viral, bacterial, parasitic or fungal, metabolic disease such as diabetes mellitus, raised blood pressure, toxaemia, immune mediated (particularly autoimmune disease where the dog produces antibodies against its own tissue) trauma, lens damage resulting in the leakage of lens protein, and tumours.

"Common causes are infection, e.g. viral, bacterial, parasitic or fungal, metabolic disease such as diabetes mellitus, raised blood pressure, toxaemia, immune mediated (particularly autoimmune disease where the dog produces antibodies against its own tissue) trauma, lens damage resulting in the leakage of lens protein, and tumours."

What are the signs?

The usual signs are severe pain with an intense reddening of the visible parts of the eye. The eye is usually kept shut and bright lights avoided. Cloudiness of the cornea eye may be noticed. Sometimes there is bleeding into the eye. There may be excessive tearing. It is frequently sudden in onset and one or both eyes can be involved.

How is the condition diagnosed?

Careful examination of the eye using specialised instruments will be necessary. In many cases the pressure in the eye needs to be measured since many of the signs of uveitis are similar to those of glaucoma. With uveitis intraocular pressure (IOP) is reduced whereas with glaucoma it is raised.  Measurement of IOP is often employed to differentiate between the two conditions and is a simple, painless procedure. A thorough examination of the whole of the animal must be performed since generalised illnesses can have uveitis as one of their signs Additional tests such as blood tests might be required. Special procedures such as ultrasound may be used to examine the eye - particularly if the cornea is cloudy and direct examination is not possible.

What does the treatment involve?

Treatment is initially aimed at reducing inflammation and providing pain relief. A combination of drops or ointments plus tablets may be required. Frequent reassessment will be required to ensure that the treatment is effective. In simple cases treatment is only required for a few days, but some patients require long term medication.

If the uveitis is due to trauma then treatment might involve repair of any corneal tears or removal of a foreign body in the eye for example. This may involve referral to a specialist. 

Are there any complications?

Most cases of uveitis show response to treatment within 24 hours. If the eye is very cloudy or some haemorrhage has occurred this may take a few more days to clear. However the patient should be comfortable and vision will be normal once the inflammation has fully settled.

Complications can occur after very severe or repeated cases of uveitis. These can involve the development of adhesions within the eye and also secondary glaucoma (raised intraocular pressure). Both of these complications require specialist treatment. Severe uveitis can result in blindness.