An eye on canine orbital disease: Causes, diagnostics, and treatment

An eye on canine orbital disease: Causes, diagnostics, and treatment

A variety of disorders can cause orbital disease, and because the clinical signs can be similar for each, it's critical to have a clear understanding of what to look for and how to treat it in order to achieve the most successful outcome in your veterinary patients.
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Nov 01, 2013

An 8-year-old spayed female miniature poodle was presented to a veterinary clinic in Colorado with the complaint of a swollen right eye, which had been present for several days. The dog's pulse and respiration rate were normal, but its temperature was slightly above normal at 102.6 F (39.2 C). The physical examination findings were normal except that the right eye was exophthalmic and the third eyelid was protruding halfway across the cornea. Additionally, the dog cried out in pain when its mouth was manually opened.

The clinical signs exhibited by this dog could be grouped together into one etiology—orbital disease. There are many causes of orbital diseases, including a retrobulbar, space-occupying mass (orbital abscess, cellulitis, cyst, or neoplasm); myositis; or an orbital vascular anomaly.1-20

CANINE ORBITAL DISEASE OVERVIEW


1. Exophthalmos due to a retrobulbar mass in a dog. Note the lateral deviation of the globe.
Orbital diseases are relatively common in dogs because of the anatomy of the orbit. Dogs have an incomplete orbit, and the floor is partially formed by the sphenoid and palatine bones; the remainder is muscle and connective tissue.2,21 This anatomy allows dogs to open their jaws widely to ingest prey but decreases their orbital protection.21 It also predisposes dogs to orbital invasion by foreign objects coming through the roof of the mouth, lodging in the orbit, and leading to retrobulbar cellulitis and abscesses.2


2. Enophthalmos in a dog as a consequence of a retrobulbar mass.
The orbit is a relatively confined space, so space-occupying masses or swellings most commonly result in exophthalmos of the globe (Figure 1). However, occasionally enophthalmos can result if the space-occupying mass is anteriorly located in the orbit so that it pushes the globe posteriorly (Figure 2).1 There also may be loss of ocular motility, strabismus, congestion of blood vessels, protrusion of the third eyelid, and blindness. Pain can be severe or absent depending on the etiology and extent of the orbital disease.

Foreign bodies and abscesses

Foreign bodies may enter the orbit through the conjunctiva or the roof of the mouth. Many types of orbital foreign bodies have been reported, including grass awns, porcupine quills, gunshot pellets, and wood slivers and chunks.4-8

Foreign bodies can cause cellulitis and abscessation.4-8 Dogs with orbital foreign bodies may present with some degree of exophthalmos, protrusion of the third eyelid, and severe pain on opening of the mouth.2 Purulent to mucopurulent ocular discharge and conjunctival and episcleral injection may be present, although the globe itself, if not penetrated by the foreign body, is often normal. The dog may be febrile if an abscess is present. Younger dogs are more commonly affected as they have a greater likelihood of chewing foreign objects.

In a retrospective study of 34 dogs and seven cats with orbital abscesses, the most common route by which bacteria entered the orbits was through extension from adjacent infected structures, foreign bodies, and penetrating trauma.3

Of the 34 dogs, about 60% had positive bacterial culture results. The most frequently cultured bacteria were of the genera Staphylococcus, Clostridium, Escherichia, Bacteroides, and Pasturella. Most of the aerobic organisms were susceptible (in vitro) to many antibiotics, including amikacin, ceftiofur, gentamicin, imipenem, ticarcillin, and trimethoprim-sulfamethoxazole.3