OPTHALMOLOGY
of normal orbital contents as primary tumours or
extend secondarily into the orbit from the adjacent
sinuses, nasal or cranial cavities as well as metastatically.
The most common primary malignant neoplasms in
dogs are osteosarcomas and optic nerve meningioma and the secondary neoplasms are adenocarcinomas and malignant melanoma. Secondary orbital
neoplasia in cats is more common than primary, with
lymphosarcoma, osteosarcoma and malignant melanoma being the most prevalent.
Figure 3: A dog showing bilateral exopthalmus due to myositis
of the ocular muscles
tion of the temporal muscles. Peripheral eosinophilia
is an inconsistent finding. Elevated creatine kinase
may be seen during the acute phase. Uncontrolled
myositis will eventually lead to atrophy of the affected
muscles.
Treatment.
This involves the administration of corticosteroids
[Prednisilone, 1-2mg/kg oid] for 7 days then gradually
tapering the dose for a total of 4-6 weeks. Without
treatment, inflammatory episodes run for 1-3 weeks.
5. Zygomatic mucocoeles / sialocoele:
The zygomatic salivary gland is situated in the rostral
portion of the pterygopalatine fossa with the duct entering the mouth lateral to the last upper molar tooth
behind the papilla of the parotid duct. Mucocoeles of
this gland are usually associated with trauma causing
leakage of saliva and secondary inflammation. Clinically these manifest themselves with exophthalmos,
exposure keratitis and secondary corneal ulceration
and swelling on temporal region of the orbit.
Diagnosis and treatment:
The clinical picture is of a slow, unilateral, progressive
exophthalmos with globe deviation. There is usually
no pain when opening the mouth. Many of the other
clinical signs of exophthalmos, mentioned before, will
assist to confirm the diagnosis. Specialised diagnostic
procedures can be used to make a definitive diagnosis. These include:
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Survey radiography
Ocular ultrasonography.
Ultrasound guided fine needle biopsy or aspiration for cytology.
Magnetic Resonance Imaging [MRI] (Fig4).
Computerized tomography [CT]
Exploratory orbitotomy.
In some cases remission can be achieved with combined application of surgery, radiation or chemotherapy. Generally the prognosis is poor as the average
survival time from diagnosis is less than 3 years. Exenteration or enucleation is the most widely performed
treatment.
Diagnosis and treatment
Diagnosis is based on:
• Retrograde sialography - The oral ostium of the
zygomatic salivary duct is located above the carnasial tooth. This is cannulated with a 24G Jelco
cannula and contrast media is injected up the
duct. Dorsoventral and lateral radiographs are
taken. The extent of the mucocoele will be demonstrated by the contrast study.
• Fine needle aspirate of the buccal swelling and
collection of a clear tenacious, golden fluid that
forms strands.
• Digital pressure on the globe may cause saliva to
ooze from the oral ostium of the duct.
Should the swelling persist the zygomatic salivary
gland can be surgically removed via the lateral or dorsal approaches which require an orbitotomy.
6. Orbital neoplasia
Orbital and retrobulbar neoplasia can arise from epithelial, vascular, neural, bone, and connective tissues
Figure 4: Mass behind the left globe causing the eye to bulge
Summary
Exopthalmos MUST be differentiated from buphthalmos. There are a number of possible causes and a
proper quick diagnostic work up is essential as this is
a sight threatening condition and in most cases vision
can be preserved if the correct diagnosis is made and
the appropriate treatment started.
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