Exophthalmos in Dogs
Overview of Canine Exophthalmos
Exophthalmos is the forward movement of the eyeball, so that it sits in an abnormal position in the eye socket (orbit). It is seen in both dogs and cats and, depending on the underlying cause, affects different ages and breeds.
Exophthalmos should not be confused with actual enlargement of the eye. With exophthalmos the size of the eye is normal, but its position has changed. When the eye itself becomes enlarged, the condition is called buphthalmos. When the eye becomes so exophthalmic that is it no longer in the socket and the eyelids roll behind the eye rather than in front of it, the condition is called a proptosis. Proptosis is discussed in another article.
General Causes of Exophthalmos in Dogs
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.
Abscess or infection of the soft tissues surrounding the eye (especially behind the eye) – Infection behind the eye is often caused by migration of foreign material from the mouth, or by extension of infection from the roots of the teeth in the upper part of the mouth. Occasionally, infections somewhere else in the body can spread to the tissues behind the eye. Infection behind the eye is a common cause of exophthalmos in the dog.
Bleeding or hemorrhage behind the eye – Trauma to the face from blunt objects, automobile or bicycle accidents may result in bleeding behind the eye. Trauma is a common cause of exophthalmos in young dogs that are allowed to roam free. A rare cause of bleeding behind the eye occurs in dogs that are unable to clot their blood properly.
Myositis or inflammation of muscle – Myositis may involve the muscles of the eye itself or the muscles of the head responsible for chewing. Both conditions tend to occur in young large breed dogs, and both may result in exophthalmos.
Zygomatic salivary gland disease – The zygomatic salivary gland sits on the floor of the orbit, just beneath the eye. If this gland becomes enlarged from infection, cyst formation or tumor growth, then it may push the eye forward. Diseases of the zygomatic salivary gland are uncommon in the dog.
Cyst formation – Cysts may arise from the zygomatic salivary gland or the lacrimal gland (which is the major tear gland in the orbit). Cysts that cause exophthalmos are also uncommon in the dog.
What to Watch For
Eyelid swelling and/or bruising
Swelling and drying of the conjunctiva
Abnormal forward position of the eye
Third eyelid protrusion
Decreased ability to close the eyelids over the eye
Secondary drying and ulceration of the cornea from an inability to blink properly
Possible pain while eating or upon opening the mouth
Possible visual impairment (partial to complete blindness)
Occasional fever, lethargy or other signs of illness
Diagnosis of Exophthalmos in Dogs
A complete eye examination and physical examination are indicated to confirm the presence of exophthalmos and to obtain information on potential causes. An oral examination is also an important part of the diagnostic work up. Additional tests may include:
Complete blood cell count (CBC)
Certain tests for fungal and other infections, depending upon the geographic area in which the dog resides
Computed tomography imaging (CT SCAN) or magnetic resonance imaging (MRI)
Fine needle aspirate or biopsy of the orbit for cytology and culture
Treatment of Exophthalmos in Dogs
Depending on the underlying cause, specific therapy may be indicated:
Intravenous fluid therapy and support may be indicated in dogs that are dehydrated or systemically ill.
Systemic and oral antibiotics are indicated for infections. If the area behind the eye is infected or abscessed, then surgical opening and drainage of that area is often required in addition to antibiotics.
Hot packing the eye and surrounding tissue may decrease swelling that accompanies trauma or infection.
Lubricant ointments or antibiotic ointments are used to protect the cornea and to treat corneal ulceration.
Following trauma, the eyelids may be sutured closed for a period of time in order to protect the cornea and to prevent a proptosis from developing.
Myositis is treated with corticosteroids.
Cysts and chronically enlarged zygomatic salivary glands must usually be surgically removed.
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 with radiation therapy. Some tumors behind the eye can only be surgically removed. In these cases the eye must usually be removed first (enucleation) in order to reach the tumor. Sometimes there are no good treatments for tumors behind the eye, or the tumors are too extensive to be treated, and in these cases euthanasia of the animal may be considered.