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 accumulation of protein and cells in the anterior chamber, low pressure within the eye, an abnormally high level of blood in the conjunctiva, swelling of the iris, photophobia (high sensitivity to light), mild-to-severe squinting, blinking, eyelid closure, and tearing. If left untreated, anterior uveitis may lead to glaucoma, cataracts, and retinal detachment. In small breeds, uveitis can develop secondary to lens luxation.
The uvea is the main bed of blood vessels in the eye, consisting of the iris, the ciliary body, and the choroid. It is divided into the anterior uvea, which includes iris and ciliary body, and posterior uvea, which includes 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 that 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.
Shiba inu breed is considered predisposed to uveodermatologic syndrome that is characterized by chronic and recurrent bilateral uveitis and skin depigmentation
Multiple factors have been implicated in the development of the anterior uveitis, including virus and bacteria, 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 species. 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 required.
The following microorganisms have been implicated in the development of uveitis:
- Canine adenovirus-1 (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 causes a fatal neonatal disease in puppies, with severe anterior uveitis and chorioretinitis. It is not a clinical problem in adult dogs.
- In general, canine distemper virus infection does not lead to blindness. However, the virus may also directly target the optic nerve, causing optic neuritis, which presents as sudden onset blindness. This may affect one or both eyee.
- Brucellosis is most commonly associated with abortion or stillbirth. However, it can infect other tissues, including the eye, where it may cause recurrent anterior uveitis.
- Borrelia burgdorferi causes Lyme disease in humans and dogs and has been associated with canine uveitis. All forms of Leptospira interrogans infection may cause uveitis.
- Ehrlichiosis is caused by Ehrlichia canis and E. platys and is often associated with eye disease. Acute E. canis or chronic infection may be accompanied by acute conjunctivitis, eye bleeding, anterior uveitis and retinal bleeding.
Fungal diseases are a cause of anterior or posterior uveitis in some parts of the world, including Cryptococcosis, histoplasmosis, blastomycosis, prototheca infection, and candidiasis. toxoplasmosis can cause either a generalized multisystemic disease or a neurological disease. Eye manifestations may include anterior uveitis, chorioretinitis and optic neuritis. Migrating parasites may gain access to the anterior or posterior segment of the eye and induce uveitis. Toxocara canis (dog roundworm) and Angiostrongylus vasorum (French heartworm) are possible causes. Abnormal migration of nasal bot fly larvae Oestrus ovis, warble fly larvae, and Dirofilaria immitis (dog heartworm) may also cause uveitis. 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.
Correct diagnosis of anterior uveitis is extremely important to prevent vision loss. Blood samples, cultures of aqueous humor and more sophisticated tests may be necessary. The aim of the therapy of the inflammatory processes of the uveal tract is based on preventing the development of the inflammation with steroid and non-steroid anti-inflammatory drugs. A large number of research studies have shown the use of antioxidants and their positive effects in the anti-inflammatory processes.
- Golden Retriever uveitis: 75 cases (1994-1999). Sapienza JS, Simó FJ, Prades-Sapienza A.
- BSAVA Manual of Canine and Feline Infectious Diseases. The Eye. David Gould
- Lester Mandelker, Peter Vajdovich. Studies on Veterinary Medicine