A diagnosis of anterior uveitis simply means there is inflammation inside the eye. Numerous diseases can manifest as uveitis, so it can be difficult to diagnose the underlying cause. Several diseases mentioned below may be confined to the eye. However, in other cases, the condition may affect multiple parts of the body and the eye is but one aspect of disease. A pet may have either predominately ocular signs (those pertaining to the eye) or other signs such as weakness, lethargy, decreased appetite, coughing, fever or other problems.
Infectious causes of anterior uveitis are numerous. Some common causes include: Viral diseases such as distemper and adenovirus in young unvaccinated dogs.
Fungal diseases, like blastomycosis, histoplasmosis, cryptococcosis, coccidiomycosis and candidiasis. Different fungi are more common in certain regions of the world. Fungal diseases more frequently involve the posterior (back) segment of the eye as well as the front.
Rickettsial diseases. These include ehrlichiosis and Rocky Mountain spotted fever, which are both transmitted by ticks.
Other causes of anterior uveitis include:
Many different strains of bacteria and different types of toxins. Bacterial infections that are important causes of uveitis in the dog include Lyme disease and leptospirosis. Bacterial infections in other locations in the body, such as a uterine or kidney infection can also lead to inflammation inside the eye.
Tumors can cause anterior uveitis. The appearance varies, but the clinical signs of inflammation (uveitis) are common.
Lymphoma – The iris is generally thickened and there may be yellowish, white or pink discoloration.
Melanoma – The iris is generally thickened and darker brown than usual.
Adenoma or adenocarcinoma – Thick fluffy white areas can be seen through the pupil and sometimes the iris.
Metastatic tumors – Various tumor types can start elsewhere in the body and then move to the anterior uvea, although spread to the posterior uvea is much more common.
Trauma. Any type of injury to the head or eye can cause a uveitis because the uvea is filled with blood vessels, so inflammation and "bruising" can occur.
Metabolic diseases. Because the uvea is an extension of the body's circulating blood system, many diseases that affect the body can have an impact on the eye. Examples include diabetes mellitus, hyperlipidemia, hypertension, and pancreatitis.
Lens-induced anterior uveitis can be caused when cataracts are present and are slowly leaking protein into the eye. This form of uveitis may be mild and chronic or can be more severe. The most severe form of acute lens-induced uveitis occurs when penetrating trauma to the eye disrupts the lens.
Uveitis can be associated with any of the following:
Immune-mediated diseases. In these diseases, the animal's immune system "attacks" itself. These diseases tend to be more common in the dog, and the reaction may be confined to just eye tissues. Immune-mediated uveitis most often affects large breed dogs.
Uveodermatologic syndrome, also known as VKH or Vogt-Koyanagi-Harada-like syndrome, is a rare disease of dogs in which melanin (pigment) is attacked and destroyed by the immune system. In addition to anterior uveitis, dogs can have whitening of hair and skin, especially around the eyes, mouth and feet. It is most commonly seen in the oriental and sled-dog breeds, such as the Akita, Siberian husky, Samoyed, chow chow and Shetland sheepdog.
Other immune-mediated diseases may involve tissues elsewhere in the body. These include thrombocytopenia, in which platelets are being attacked and destroyed by the immune system, and hemolytic anemia, in which red blood cells are being attacked and destroyed by the immune system.
Several odd forms of uveitis occur in specific breeds of dogs. A uveitis called "pigmentary uveitis" occurs in golden retrievers. The cause of this condition is unknown. It is often associated with iris cysts and secondary glaucoma.
Secondary diseases complicating anterior uveitis include glaucoma, blindness, and lens luxation.