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

2013-11-01

Drs. Gionfriddo and Aaroe provide an overview of common orbital diseases in dogs and the best approaches for diagnosis and treatment.

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

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

1. Exophthalmos due to a retrobulbar mass in a dog. Note the lateral deviation of the globe.

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.

2. Enophthalmos in a dog as a consequence of a retrobulbar mass.

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

Orbital cysts

Orbital cysts are relatively uncommon in dogs. Congenital epithelial cysts have been most frequently reported and are divided into categories based on the type of epithelium lining them: epidermoid, dermoid, conjunctival-dermoid, and neuroepithelial.10 Neuroepithelial cysts arise from developmental abnormalities in early ocular embryogenesis.10

Acquired cysts that have been reported are mucoceles and implantation cysts.10,13 These types of cysts often result from trauma to the orbital area that results in leakage of saliva from the zygomatic salivary gland. The saliva causes inflammation and, eventually, necrosis of the surrounding tissue. The cysts present as fluctuant, often nonpainful swellings in the conjunctiva, either dorsally or ventrally to the globe, and as exophthalmos.

Conjunctival dacryops were recently reported in two unrelated golden retrievers.14 This type of cyst develops from pockets of the lacrimal glandular tissue and can form wherever lacrimal gland tissue is located. If a cyst is in the main lacrimal gland ductules, it can cause exophthalmos and ocular irritation. These cysts are thought to develop with trauma, which leads to excessive secretion of tears and secondary ductal inflammation.14

Orbital neoplasms

Neoplasms should be suspected in all cases of exophthalmos in dogs but are more commonly seen in older animals. They can be either primary or secondary and can be benign, locally invasive, or metastatic.15,16

Any tissue in the orbit may give rise to a neoplasm, but the most common primary orbital tumor in dogs is a meningioma.10,15,16 This tumor generally surrounds the optic nerve and causes exophthalmos and vision loss due to pressure on the optic nerve. Although any primary malignant tumor has the capability to secondarily metastasize to the orbit, the most common is lymphoma. When this type of tumor is diagnosed, it should always be considered a manifestation of a systemic process.

Orbital neoplasms, in contrast to abscesses, are generally minimally painful and slowly progressive. They often cause exophthalmos, but tumors arising from the rostral portion of the orbit may produce enophthalmos and protrusion of the third eyelid. Retropulsion of the globe is restricted.

Other diseases

Parasites and systemic mycotic infections can enter the orbit hematogenously or by local extension from the sinuses, nasal cavity, brain, or globe. Cryptococcus neoformans, Blastomyces dermatitidis, Coccidioides immitis, Candida species, and Aspergillus species are mycoses that have been reported to invade the orbits of dogs and cats.10 Generally, animals with orbital mycoses have concurrent or preceding systemic clinical signs. On occasion, orbital biopsy specimens are needed to make a diagnosis.10

Ocular onchocerciasis cases are more commonly seen in Europe but are becoming more frequent in the western United States, particularly in California.10 Clinical signs consist of single or multiple red, raised lesions on the bulbar conjunctiva. Exophthalmos, protrusion of the third eyelid, corneal edema, and anterior uveitis may also be present.

Hematomas of the orbit are generally associated with a history of trauma. They are characterized by exophthalmos, pain, and other head and ocular injuries.

Myositis

Swelling of the muscles of mastication adjacent to the orbit will often lead to exophthalmos because of the absence of a lateral orbital wall causing pressure on the globe.17,18 Cases of eosinophilic myositis of the muscles of mastication present acutely and may be painful, making it difficult to differentiate these cases from retrobulbar abscesses.17,18 In addition, both of these conditions often occur in young, large-breed dogs. One distinguishing feature is that abscesses tend to be unilateral, while myositis tends to be bilateral.

Extraocular myositis may also cause exophthalmos.17,18 This disease is most common in young golden retrievers, and females are overrepresented. Characteristic clinical signs include bilateral exophthalmos, chemosis, and retraction of the eyelids without protrusion of the third eyelid.

Other less common inflammatory diseases of the canine orbit include immune-mediated orbital disease, involving tissue such as the periosteum, and zygomatic sialadenitis.10-14

Vascular anomalies

Both orbital varices and arteriovenous fistulas have been reported in dogs, but they are rare. They can be congenital or associated with trauma.19,20 Interestingly, cases of arteriovenous fistulas usually occur in young dogs and present with a nonpainful exophthalmos that may be intermittent. The eye may also pulsate along with the systemic pulse.19,20

In one case of a puppy with a swelling in the orbit below the globe, the swelling pulsated and changed size with the changing of the head position (Gionfriddo J, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO: Unpublished data, 2012; Figures 3 & 4).

3 & 4. A 5-month-old puppy with its head held downward. Notice the large swelling, an orbital varix, ventral to the globe. When the puppy’s head is held up, the varix shrinks in size.

DIAGNOSIS

Orbital diseases can be presumptively diagnosed based on history, signalment, and ocular and physical examinations. Abscesses, parasitic infections, cysts, and varices are more common in younger dogs, while neoplasms are more common in older dogs. Abscesses are often associated with fever and pain.

All dogs with suspected retrobulbar disease should have a thorough oral examination, especially in the space behind the last premolar tooth (Figure 5). Tooth root abscesses of the upper fourth premolar in dogs rarely cause retrobulbar disease. These abscesses generally drain anteriorly to the orbit at the level of the nasolacrimal sac. If a swelling is noted behind the last premolar, an aspirate of the retrobulbar area may be obtained by placing a 22- or 20-ga needle into the swelling and directing it behind the eye with the aid of ocular ultrasonography.22

5. Swelling behind the fourth premolar in a poodle.

In most cases, ultrasonography of the retrobulbar area should be performed early in the diagnostic work-up (Figure 6).22 This will help differentiate between fluid-filled structures and solid masses. If purulent material is obtained by means of an ultrasound-guided aspirate, then a retrobulbar abscess can be diagnosed, and culture and sensitivity testing of the material should be performed. If no diagnostic material is obtained, further retrobulbar imaging can be performed.

6. An ultrasonogram of a dog’s eye. The dog had clinical exophthalmos. The ultrasonogram shows a heterogeneous mass in the medial aspect of the retrobulbar space. An exploratory surgery demonstrated this to be a neoplasm.

Computed tomography (CT) or magnetic resonance imaging (MRI) are other methods commonly used to obtain images of the retrobulbar area (Figure 7).23-25 The method chosen depends on the availability of equipment, owner preference, and index of suspicion of the disease involved. Plain radiographs of the skull are not useful in orbital disease unless bony involvement or metallic foreign material is present.

7. An MRI of a dog with a retrobulbar mass (arrow). Note the soft tissue swelling around the globe and the apparent smaller globe size.

TREATMENT AND PROGNOSIS

Treatment of orbital disease varies depending on the diagnosis. The prognosis for saving vision in the affected eye depends on the cause.

If an abscess is diagnosed, orbital drainage and systemic antibiotic therapy is indicated.1 To establish drainage, make an incision with a surgical blade into the mucous membrane over the swollen area behind the fourth premolar tooth. Carefully introduce closed hemostats into this incision, and bluntly dissect and explore for an abscess (Figure 8).

8. When draining a retrobulbar abscess, the approach is from behind the fourth premolar tooth. An incision is made through the mucous membrane, and hemostats are used to bluntly dissect the soft tissue on the floor of the orbit. Ideally, saliva or purulent material can be removed via this route.

If purulent material is obtained, allow it to drain into the mouth, using caution not to let it go down the throat. A sample should be examined cytologically to determine if it is a bacterial or fungal infection and then submitted for culture and sensitivity testing. The wound should be left open to allow for further drainage.

Bacterial infections generally resolve well after this regimen. Sharp dissection (e.g. the use of a needle) is not recommended. Treat fungal infections with systemic antifungal drugs; the prognosis is more guarded.

Retrobulbar tumors may be benign or malignant and may be treated with surgical removal (often along with removal of the eye) and chemotherapeutic drugs.15 The prognosis is guarded depending on the type of tumor involved.15

Often it is difficult to retrieve a recognizable foreign object from the retrobulbar area. Biological material, such as splinters and grass awns, are sometimes in the process of being autolyzed at the time of drainage of the orbit.

Some foreign objects and neoplasms can be removed surgically without disturbing the eye, while others require enucleation to reach the depths of the orbit.8 Weigh the options carefully before removing an eye. A referral to an ophthalmologist is highly recommended if orbital surgery, with or without enucleation, is to be considered.

CASE OUTCOME

Further examination of the oral cavity of the dog mentioned at the beginning of this article showed a large swelling behind the last premolar tooth (Figure 5). The dog was anesthetized, and the swollen area was opened and drained. A grass awn and large quantities of purulent material were found. The dog recovered without incident.

Juliet R. Gionfriddo, DVM, MS, DACVO, Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523.

William C. Aaroe, DVM, Fisher's Peak Veterinary Clinic, 1617 Santa Fe Trail Drive, Trinidad, CO 81082.

To view the references for this article, visit dvm360.com/OrbitalRefs.