Episcleritis can occur in dogs and is an inflammation of the episcleral tissue lying adjacent to the eyeball. The deep white tissue that comprises the firm outer layer of the eye is called the sclera, and the tissue above the sclera and extending away from it is the episcleral tissue. Episcleritis may also involve the conjunctiva, which is the thin tissue on the surface of the eye, and usually involves the tissue immediately beneath the conjunctiva. It can be focal (limited to a small area) and marked with nodes, or diffuse (widespread) and involving the entire circumference of the eye. Episcleritis may affect one or both eyes in dogs.
Overview of Episcleritis in Dogs
Focal episcleritis appears as a small, pink, raised mass over the white of the eye, and is more common in collies, Shetland sheepdogs, and American cocker spaniels than in other breeds. Diffuse episcleritis is seen more often in the American cocker spaniel, Airedale terrier and rottweiler. Most affected dogs are young adults.
The causes of episcleritis are not well understood. It is believed that it is an immune-mediated disease, which means that the immune system reacts to something, and this reaction causes tissue inflammation. Rather than helping the inflammation to subside, subsequent immune responses make the inflammation worse and a vicious cycle of progressively worsening inflammation begins.
During the past 20 years this disease has been given several names, including episclerokeratitis, fibrous histiocytoma, and nodular granulomatous episcleritis. At this time episcleritis is the most common name used.
What to Watch For
Neither of these conditions are usually painful, but the dog may exhibit some tearing.
If the inflammation affects the nearby cornea, then a whitish discoloration of the cornea may also be noted.
Diagnosis of Episcleritis in Dogs
Medical history, clinical findings, and ocular examination are usually highly suggestive of episcleritis. Much of the time the diagnosis is made based on the clinical appearance of the eye lesion.
A complete ocular examination is indicated to rule out other causes of a red eye. This involves performing a Schirmer tear test, fluorescein staining of the cornea, tonometry to measure the pressure within the eye, and a detailed examination of both the front and back portions of the eye.
A thorough physical examination is also performed to determine if any other lesions or abnormalities are present.
A complete blood count, biochemical profile, and urinalysis are usually normal, but may be performed prior to the onset of therapy.
Biopsy and histopathologic examination of affected tissue are diagnostic, but are not always performed due to the classic appearance of the lesion.
Your veterinarian may elect to refer your dog to a veterinary ophthalmologist for a comprehensive eye examination, to confirm the diagnosis, and to obtain advice on the best treatment.
Treatment of Episcleritis in Dogs
Both nodular and diffuse episcleritis require long-term therapy to control the condition. Both can be difficult to treat in some animals and different cases may require different forms of therapy.
The nodular form is not a tumor, although it has a similar appearance. When the nodular form occurs in older dogs, it tends to grow faster and be more aggressive in its behavior than the nodular forms that occur in young dogs.
Because nodular episcleritis can be difficult to treat, other therapies have been developed for this condition. They include cryotherapy, which is freezing the nodule with a super cooling agent, and the use of systemic drugs that suppress the immune system. Such drugs include oral prednisone and azathioprine (Imuran®).