Anterior Uveitis
The uvea of the eye is divided into the anterior uvea (iris and ciliary body) and posterior uvea (choroid). The uvea is the colored inside lining of the eye consisting of the iris, the ciliary body, and the choroid. The iris is the colored ring around the black pupil. The ciliary body is the set of muscles that contract and relax to allow the lens to focus on the objects; it is also the major source of aqueous humor, the clear fluid within the eye. The choroid is the inner lining of the eyeball and extends from the ciliary muscles to the optic nerve at the back of the eye. The choroid also contains layers of blood vessels that nourish the inside parts of the eye, especially the retina.
Anterior uveitis is an inflammatory condition of the iris and ciliary body. When severe, it results in a contraction of the pupil of the eye, increased protein and cells in the anterior chamber, low pressure within the eye (hypotony), an abnormally high level of blood in the conjunctiva, swelling of the iris, high sensitivity to light (photophobia, and mild-to-severe squinting, blinking, eyelid closure and tearing. If left untreated, anterior uveitis may lead to glaucoma, cataracts, or retinal detachments. In small breeds, uveitis can develop secondary to lens luxation.
Causes of Infectious Uveitis in Dogs
Infectious uveitis in dogs can be caused by a wide variety of bacteria and viruses.
Adenovirus-1 Infection
 <== Acute Anterior Uveitis caused by canine adenovirus-1 infection (CAV-1) Courtesy of Dr Sheila Crispin
CAV-1 causes acute anterior uveitis with corneal swelling, which is usually self-resolving over a period of weeks. CAV-1 is now uncommon owing to widespread vaccination. Live attenuated CAV-1 vaccines caused acute uveitis in some cases therefore live CAV-2 vaccines (which confer protection against both species) are now used.
Canine Herpesvirus
Canine herpesvirus causes a fatal neonatal disease in litters of puppies, with severe anterior uveitis and chorioretinitis in addition to systemic signs. It is not a clinical problem in adult dogs.
Canine Distemper Virus
The lesions are not usually severe enough to cause blindness. The virus may also directly target the optic nerve, causing optic neuritis, which presents as sudden onset blindness. This may affect one or both eyes.
Bacterial Disease
A wide range of bacterial species can cause anterior
uveitis if they gain access to the anterior segment. The most common site of entry is through the cornea after a penetrating injury. Cat scratch injuries most commonly inoculate Pasteurella spp. Treatment consists of topical antibacterials, with symptomatic treatment for anterior uveitis. A broad-spectrum topical agent that is able to penetrate the cornea and reach therapeutic levels in the anterior chamber is needed, such as chloramphenicol solution. Systemic antibacterials may also be used.
Brucellosis
Brucellosis is most commonly associated with abortion or stillbirth in bitches. However, it can infect other tissues, including the eye, where it may cause recurrent anterior uveitis.
Borreliosis
Borrelia burgdorferi is a spirochaete that causes Lyme disease in humans and dogs. It has been associated with canine uveitis. See Chapter 14 for further details on borreliosis.
Leptospirosis
Leptospirosis in humans and dogs is caused by Leptospira interrogans is a spirochaete. Clinical signs vary from acute infection, which may be fatal, to chronic or no signs. All forms of the disease may show uveitis.
Chronic Ehrlichiosis
 <== Chronic ehrlichiosis in a Labrador Retriever.
Ehrlichiosis is caused by Ehrlichia canis and E. platys which is often associated with eye disease. Acute E. canis infection may be accompanied by acute conjunctivitis, eye bleeding, anterior uveitis and retinal bleeding. E. canis can also cause chronic disease.
Rickettsia Infections
Signs of acute Rocky Mountain spotted fever are similar to those in acute Ehrlichia canis infection. Unlike ehrlichiosis, chronic disease does not occur. Salmon poisoning disease (caused by Neorickettsia helminthoeca) occurs on the western coast of the
USA. It is an acute disease characterized by fever, depression, loss of appetite, pus-filled eye discharge and serous nasal discharge. It is responsive to tetracycline.
Fungal Diseases
Fungal diseases are a cause of anterior or posterior uveitis in some parts of the world. Cryptococcosis, histoplasmosis, blastomycosis and candidiasis have been reported.
Leishmaniasis and Protozoal Diseases
Toxoplasmosis can
occur in intermediate or definitive hosts, when the microorganisms invade tissues and organs. In the dog, toxoplasmosis can cause either a generalized multisystemic disease or present primarily as a neurological disease. Eye manifestations may include anterior uveitis, chorioretinitis and optic neuritis.
Parasitic Disease
Migrating parasites may gain access to the anterior or
posterior segment of the eye and induce uveitis. Toxocara canis and Angiostrongylus vasorum are possible causes. Abnormal migration of nasal bot fly larvae (Oestrus ovis) and warble fly larvae may also cause uveitis. Dirofilaria immitis may be encountered in dogs. If the parasite is in the anterior chamber it may be directly visible. Since a dead larva within the anterior segment of the eye often provokes a more severe inflammatory response than a living one, management relies on surgical removal of the parasite rather than the use of
antiparasiticides.
Ocular signs and the clinical course of Golden Retriever dogs with a progressive anterior uveitis, are often associated with the iridociliary cysts. The overall prognosis for this progressive uveitis in Golden Retriever dogs is guarded, with 46% of the eyes becoming blind due to glaucoma. Iridociliary cysts in Golden Retriever dogs may lead to the development of glaucoma in this breed.
Diagnosis of Anterior Uveitis
Correct diagnosis of this condition is extremely important to prevent vision loss. Blood samples, cultures of aqueous humor and more sophisticated tests may be necessary. Uveitis can be caused by internal or external sources, and may be the result of infections (bacteria, viruses, fungi, parasites) or cancers. Bartonella infection has been associated with balateral uveitis in dogs.
Treatment of Anterior Uveitis
Successful treatment to preserve vision requires high levels of topical and systemic corticosteroids.
References:
REF FILE #DH-128-67
|