Retrobulbar Disease A prominent eye that is unable to be retropulsed back into the orbit is likely to have retrobulbar disease. Associated clinical s

Retrobulbar Disease

A prominent eye that is unable to be retropulsed back into the orbit is likely to have retrobulbar disease. Associated clinical signs may include prominence of the third eyelid and chemosis/swelling of the conjunctiva. In most cases the PLR—pupillary light response, and the IOP-intraocular pressure are normal. Animals exhibiting pain when the mouth is opened are more likely to have a retrobulbar abscess/cellulitis.

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Different causes of retrobulbar disease in dogs include:
* Abscess or cellulitis e.g. tooth root or foreign body
* Neoplasia
* Inflammation behind the eye e.g. extraocular muscle myositis
* Zygomatic salivary gland cyst (mucocoele)
* Haematoma e.g. following trauma or dental treatment
* Vascular anomaly (very rare)

Retrobulbar disease in cats is most often caused by and abscess or neoplasia.

It is very difficult to diagnose the cause of the problem just by examination only. Diagnostic aids are often required. These may include

1. Tonometry to rule out glaucoma
2. Ultrasound examination with either fine needle aspirate or biopsy
3. X-rays of the skull
4. CT Scan
5. MRI Scan
6. Exploratory Surgery

The most common underlying cause for a retrobulbar problem in a young dog or an older cat is infection. If an infections is suspected then antibiotics are indicated. At Animal Eye Care we generally use amoxicillin/clavulanic acid and clindamycin antibiotics. Many cases will also benefit from oral anti-inflammatory therapy such as carprofen. If there is no response within 2-3 days, further tests should be carried out. In many cases we may progress straight to a CT or MRI scan as ultrasounds and radiographs often do not yield as useful information. When a good response to therapy is achieved, and the signs resolve, the antibiotics should be continued for a minimum of 2 weeks. If there is recurrence following a the 2 week course of antibiotics, they can be recommenced and continued for a longer period such as 4 to 6 weeks.

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Neoplasia

Retrobulbar neoplasia can be primary i.e. arising in the orbit such as an optic nerve meningioma, or secondary to extension from the sinuses or the nasal cavity. They are usually slowly progressive may or may not be painful on palpation.

If neoplasia is present, a scan can determine the extent and likelihood of cure with resection. Orbitectomy is a major operation and we refer our cases to a specialist surgeon. Some tumours such as lymphoma will be treated with chemotherapy.

Meningiomas of the optic nerve can often be completely resected at the time of enucleation as long as they are not extending through the back of the orbit. Otherwise orbitectomy will be required to reach this area.

Myositis

Extraocular myositis is more commonly seen in younger dogs such as Labradors and Golden Retrievers. Most cases have bilateral prominent eyes and are of sudden onset. Treatment involves the use of oral cortisone. In the literature books, prognosis is poor and recurrence rates are noted to be high, however this is not our experience.

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Sialoceles, Mucoceles

Zygomatic salivary gland cysts can often be diagnosed by FNA of fluctuant swellings around the orbit. These are generally non painful on palpation. Thick zygomatic saliva is withdrawn. Treatment involves excision of this gland by a specialist surgeon.

Trauma

Haematomas can occur following dental procedures and usually resolve with supportive therapy. When such trauma occurs however, it is possible that the optic nerve has become damaged and the eye will be blind.

BEWARE EXPOSURE KERATITIS

When an eye is prominent there is a risk that the cornea could dry out and result in corneal ulceration. Owners can be advised to monitor their pet’s ability to blink. If this is reduced, lubricating ointments may be used (such as Tricin eye ointment). Alternatively, a temporary tarsorrhaphy suture can be placed under a short general anaesthetic to close the eyelids together and prevent desiccation. If an animal is anaesthetised to examine, place a TT suture—it can always be removed once it is no longer needed.

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