by Diane Garrod

Created on: November 28, 2011

Exophthalmus describes a bulging of the eye from the socket in its simplest form.  In veterinary medicine the term eye socket refers to the orbital bone as well as the contents of the socket -the eye, nerves and other tissues. The anatomy of the eye socket varies across breeds of dogs, according to an article on Canine Eye Socket Diseases.

Exophthalmus causes the eyeball to move forward, meaning to cause the eyeball to protrude, or bulge from the orbit of the eye. It indicates the eyeball is in an abnormal position (orbit). The important detail to understand with exophthalmus is that the eye size is normal, it is the position of the eye that has changed. If the eye itself becomes enlarged it denotes a different malady.

This can occur in one or both of the eyes and is considered normal in many brachycephalic-nosed dogs, such as French Bulldogs, English Bulldogs and Boston Terriers. It can also occur in Pekingese, Pugs and Chihuahuas.

When this condition occurs in only one eye, or in dogs where it is not the breed norm, it is a symptom of another disorder, one of which may be hypothyroidism or Graves disease. In some cases, this bulging may create pressure on the nerves and arteries that are associated with the eye and lead to further complications, including blindness. This pressure may cause pain in the dog.

Eleven causes of exophthalmus in dogs are:

1 - The space occupying mass behind the eyeball simply increases.

2 - There is bleeding or hemorrhaging within or behind the eye. Trauma from blunt objects may cause bleeding behind the eye. Trauma is commonly seen in young dogs that are allowed to roam free. A rare condition is inability for a dog's blood to clot properly.

3 - Pus

4 - Bacterial or fungal inflammation

5 - The sac of mucous in the bone that surrounds the eye becomes inflamed or swollen

6 - Myositis or inflammation in the muscles surrounding the eye(s). Myositis involves the muscles of the eye and tend to occur in young large breed dogs. Myositis is treated with corticosteroids.

7 - Arteriovenous fistula (when arteries join with veins, and a new, abnormal passage is formed), again, rare.

8 - Cancer of the tissues behind or beneath the eye. Cancer behind the eye is one of the more common causes of exophthalmos in the older dog. There are numerous treatments for cancer behind the eye. Some forms of cancer, such as lymphosarcoma and mast cell tumor, may be treated with chemotherapy. Other tumors, such as those arising in the nose, may be treated

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