Exophthalmos An overview of common causes and treatment

Dr Izak Venter BVSc MMedVet (Opthal)

Johannesburg Animal Eye Hospital

44 Kingfisher Drive, Fourways, 2067

Tel: 011 465 1237

The purpose of this article is to describe the more common causes of exophthalmos and their treatment. The authors did not aim to supply a complete differential diagnosis list and also do not discuss the less common causes.

The purpose of this article is to describe the more common causes of exophthalmos and their treatment. The authors did not aim to supply a complete differential diagnosis list and also do not discuss the less common causes.

There is very specific terminology used in ophthalmology which describes the position of the globe or size of the globe.

These include:

  • Buphthalmos: Enlargement of the eye due to glaucoma.
  • Enophthalmos: Abnormal recession of the eye into the orbit.
  • Exophthalmos: Abnormal protrusion of the eyeball.
  • Phthisis bulbi: Shrunken or fibrotic globe as a result of ciliary body damage following trauma or internal eye infection or inflammation.
  • Proptosis: Abnormal protrusion of the eyeball beyond the orbital rim. Usually associated with trauma.

When examining an animal with a prominent eye, there are a number of techniques/features which can be used to aid your diagnosis.

1. Measurement: Measure the corneal diameter and compare it to the opposite eye. This allows you to easily differentiate buphthalmos from exopothhalmos.

2. Retropulsion: In cases of exophthalmos there will be more resistance to retropulsion of the globe.

3. Protrusion of the third eyelid: This occurs due to pressure on the fat pad at the base of the third eyelid. This clinical signs is uncommon in cases of buphthalmos but occurs frequently in exophthalmos.

4. Observing the patient: View the head by looking directly down the snout as well as from a dorsal position so as to appreciate any asymmetry if it is present (Fig 1).

5. Examine the oral and nasal cavities: The mouth should be examined as extension of oral pathology can affect the orbital region. Both nares should be examined for discharges as nasal neoplasia or fungal infections may erode the medial orbit wall and cause secondary ocular pathology.

exopthalmos-fig-1

Figure 1: Asymmetry of the eyes as observed from above. The left eye is protruding

A complete and thorough history is imperative in cases of exophthalmos. Acute onset is usually related to retrobulbar abscess, trauma or foreign body whilst a slow progressive exophthalmos may be caused by cystic disease, proliferative disease or neoplasia. Orbital neoplasia is rare in animals less than 2 years of age.

Etiology of Exophthalmos

1. Physiological / anatomical exophthalmos

Brachycephalic breeds have a very shallow orbit which causes the globe to be more prominent. This condition is known as physiological exophthalmos. Due to this exophthalmos pigmentary keratitis and or corneal ulceration is commonly present in these patients. These breeds are also very susceptible to traumatic proptosis (Fig 2).

2. Traumatic exophthalmos

Traumatic exophthalmos can result from displacement of fractured bones and/or soft tissue swelling with haemorrhage. Most frequently this is a sequelae to blunt or penetrating trauma caused by motor vehicle accidents or collisions with stationary objects.

During the examination of the patient special emphasis should be placed on examination of the orbital margins. Fractures of the nasal and frontal sinuses can cause leakage of air causing orbital emphysema and exophthalmos. Radiology and ocular ultrasonography are valuable diagnostic tools for this form of exophthalmosis.

articletraumaticproptosisfigure2

Figure 2: Traumatic proptosis in a Pekingese dog.

Treatment:

One should approach patients with orbital trauma with the following principles:

  • Prevent additional swelling and haemorrhage.
  • Prevent exposure of the cornea and conjunctiva.
  • Prevent orbital infections

These principles can be implemented by:

  • keeping the animal confined and quiet.
  • using analgesics or tranquilizers if indicated.
  • applying cold packs to the orbital region.
  • performing a temporary tarsorrhaphy.
  • parenteral corticosteroids.
  • broad spectrum antibiotics.
  • Systemic hyperosmotic agents and nonsteroidal anti-inflammatory drugs should not be used. The latter can be used once haemorrhage or severe bruising has stabilised.

3. Inflammatory exophthalmos

Inflammatory orbital disease can be caused by bacteria, fungi, parasites and non infectious causes such as eosinophilic myositis. The process usually begins as orbital cellulitis, which localises and, at a later stage, organises to form an abscess.

Agents causing inflammation may gain entrance to the orbit via;

  • the haematogenous route
  • wounds due to external cranial trauma.
  • penetrating wounds from the oral cavity into the retrobulbar space.
  • infection in the adjacent paranasal sinuses and nasal cavity.
  • sialoadenitis or abcesses of the zygomatic salivary gland.
  • secondary rupture of the proximal nasolacrimal duct in cases of dacrocystorhinitis.
  • foreign bodies from the oral cavity or those penetrating the orbital adnexa or conjunctiva.

Clinical signs.

  • Acute, usually unilateral, exophthalmos.
  • Protrusion and congestion of the third eyelid.
  • Decreased globe mobility.
  • Serous to mucopurulent ocular discharge.
  • Periocular pain.
  • Severe pain on opening the mouth.
  • Lethargy and fever are common and assist in indicating an inflammatory cause.
  • An inflammatory leukogram may also be present.
  • A normotensive globe.
  • The classic history is an acute onset of signs and reluctance to eat.

Ocular ultrasonography is a cost effective method to differentiate cellulitis from a drainable retrobulbar abcess and to determine the presence of a foreign body.

Treatment:

Broadspectrum systemic antibiotics [amoxicillin and clavulanic acid] as well as systemic non steroidal inflammatory drugs should be used. Topical ophthalmic lubricants should be used to protect the cornea from exposure keratitis.

Orbital abcesses may require drainage of the orbital space into the mouth.This is done by incising only the buccal mucosa directly behind the last molar on the affected side with a scalpel blade and then placing a curved haemostat into the hole and gently pushing it up into the retrobulbar region and opening the forceps points. Exudate should drain from the oral wound. Remove the haemostat whilst keeping the points open. By opening and closing the jaw more exudate can be “pumped” out of the wound.

4. Eosinophilic myositis

This is an inflammatory disease of unknown cause. An autoimmune aetiology is suspected as autoantibodies to the 2M muscle myofibres of the muscles of mastication have been identified in affected dogs. The condition occurrs predominently in German Shepherd Dogs, Weimeraner, Samoyed and Dobermans but is also seen in other breeds.

extraocular_polymyositis1327539450401

Figure 3: A dog showing bilateral exopthalmus due to myositis of the ocular muscles

Clinically one sees recurrent signs of swelling of the masticatory muscles, protrusion of the third eyelid, dysphagia, enlarged mandibular lymphnodes and occassionally blindness (Fig 3). Concurrent fever and anorexia is common. This bilateral condition must be differentiated from orbital cellulitis or abscessation which is usually unilateral.

Diagnosis and treatment:

Diagnosis is based on biopsy and histologic examination 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

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 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.

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.

mri

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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