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Diseases of the Orbit
by Noelle La Croix, DVM, Dip. ACVO

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Exophthalmos (bulging of the eye from the orbit) is often insufficient criteria for a diagnosis of orbital disease.  It can be difficult to define the "abnormal" displacement of  a veterinary patient's eye.  An eye may appear exophthalmic, but is in actuality "normal" in position compared with a contralateral enophthalmic or phthisical eye.  Buphthalmos (enlargement of the eye), unilateral pupillary dilation, facial nerve paralysis, and ptosis can also be mistaken for exophthalmos.  A systematic ophthalmic examination is therefore necessary to detect and identify true orbital disease.

The examination of a patient with suspected orbital disease begins with observations of the face taken from a distance of approximately two meters.  The examiner's and patient's eye levels should match during this gross examination.  Any subtle asymmetry, unilateral ptosis, buphthalmos, lagophthalmos, facial paralysis, orbital swelling, and/or anisocoria should be noted.  The patient's face should be viewed similarly from the top, front, and sides.  In cats and dogs, the oral cavity is then examined to observe for masses or swellings.  Opening the mouth also causes flexion/extension of the coronoid processes of the mandible.  This opening may be met with resistance and/or elicit pain in patients with an orbital mass.  A change in dietary habits may also therefore be indicative of an orbital mass.  Orbital masses may also arise as extensions of a nasal mass.  The flow of air flow from each nostril should be cotton wisp tested.  Other signs of underlying nasal disease include abnormal discharges, frequent sneezing, and/or nasal stridor.  The nasal sinuses should be palpated for swellings and any painful responses noted. In general an exophthalmic eye will be deviated away from the position of a mass (Figure 1).

It is also important to determine if the signs of orbital disease are acute or chronic.  Acute (and typically painful) orbital disease is likely to be caused by an infectious or inflammatory process within the orbit.  Chronic (and/or non-painful) orbital disease is more likely to be associated with a cancerous origin.

Dental radiographs can determine if orbital disease is associated with osteolysis at the apex of the roots of the caudal maxillary teeth.  This is often found associated with orbital abscesses and/or cellulitis.  Ocular ultrasonography can reveal purulent pockets within the orbit that require drainage.  Other forms of imaging (MRI and CT) can be used to reveal hard tissue masses and/or sinuses that are not visualized by ultrasonography.  Unfortunately, the most common ocular foreign body for both dogs and cats is plant material that will often not be easily revealed by any of these forms of imaging.

Acute exophthalmos that is not associated with either oral or nasal disease is typically conservatively treated for probable orbital cellulitis with antibiotics (amoxicillin/clavulanic acid).  Oral COX-2 inhibitor NSAIDs can also be used to reduce inflammation in patients with unremarkable bloodwork.  Corneal lubrication is prescribed to prevent ulceration in cases where exophthalmos precludes complete closure of the palpebral fissure.  Intraocular pressure (IOP) should be regularly monitored.  Severe orbital disease can elevate IOP (ocular hypertension) secondary to episcleral vessel hypertension due to venous obstruction.  Unusually high IOP can cause optic nerve damage necessitating the instillation of topical anti-glaucoma agents (e.g. dorzolamide) to preserve vision and promote comfort.

If acute exophthalmos does not resolve with these conservative treatments, then these cases should be referred to a veterinary ophthalmologist for further diagnostics.  Some of these cases will have cancerous etiologies.  In general, the prognoses for orbital cancers are guarded.  Canine orbital fibrosarcoma and feline squamous cell carcinoma have the poorest prognoses as they are typically resistant to radiotherapy.  However, some cancers associated with exophthalmos (e.g. multilobular tumor of the bone) do have relatively long survival times.  A team of specialists will be needed to explain treatment options and possible outcomes to clients.  Clients who choose not to pursue further diagnostics and/or treatments for their pet's orbital cancer should work with their primary veterinarian for palliative care.

If you have any further questions about orbital disease, please feel free to speak with your veterinary ophthalmologist.

Noelle La Croix, DVM, Dip. ACVO
Judy Seltzer, DVM, Dip. ACVD
The Veterinary Medical Center of Long Island
75 Sunrise Highway
West Islip, New York 11795
(631) 587-0800, fax (631) 587-2006
www.vmcli.com

Figure 1: In general an exophthalmic eye will be deviated away from the position of a mass.

In general an  exophthalmic eye will be deviated away from the position of a mass.

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