Vet360 Vol 3 Issue 04 August 2016 - Page 29

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: • • • • • • 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. Issue 04 | AUGUST 2016 | 29 VET360 AUGUST 2016 working.indd 29 2016/07/25 11:04 PM