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Basics ⬇

Basics

Definition

  • Abnormal position of the globe.
  • Exophthalmos-anterior displacement of the globe.
  • Enophthalmos-posterior displacement of the globe.
  • Strabismus-deviation of the globe from the correct position of fixation, which the patient cannot correct.

Pathophysiology

  • Orbit cannot be examined directly; orbital disease manifested by signs that alter the position, appearance, or function of the globe and adnexa.
  • Malpositioned globe-caused by changes in volume (loss or gain) of the orbital contents or abnormal extraocular muscle function.
  • Exophthalmos-caused by space-occupying lesions posterior to the equator of the globe.
  • Enophthalmos-caused by loss of orbital volume or space-occupying lesions anterior to the equator of the globe.
  • Strabismus-usually caused by an imbalance of extraocular muscle tone or lesions that restrict extraocular muscle mobility.

Systems Affected

  • Ophthalmic.
  • Respiratory-because of the close proximity, the nasal cavity and frontal and maxillary sinuses may be involved.

Signalment

  • Dog and cat.
  • Orbital abscess or cellulitis and myositis-more common in young adult dogs.
  • Myositis-predisposed breeds: German shepherd, golden retriever, Weimaraner.
  • Orbital neoplasia-more common in middle-aged to old dogs.

Signs

Exophthalmos

  • Secondary signs of space-occupying orbital disease.
  • Difficulty in retropulsing the globe.
  • Serous to mucopurulent ocular discharge.
  • Chemosis.
  • Eyelid swelling.
  • Lagophthalmos-inability to close the eyelids over the cornea adequately during blinking.
  • Exposure keratitis-with or without ulceration.
  • Pain on opening the mouth.
  • Third eyelid protrusion is due to extraconal mass or late in progression of intraconal mass.
  • Visual impairment caused by optic neuropathy.
  • Fundic abnormalities, including retinal detachment.
  • Retinal vascular congestion.
  • Focal inward deviation of the posterior globe.
  • Optic disk swelling.
  • Neurotropic keratitis after damage to the ophthalmic branch of cranial nerve V.
  • Fever and malaise-with orbital abscess or cellulitis.
  • IOP-rarely high.

Enophthalmos

  • Ptosis
  • Third eyelid protrusion
  • Extraocular muscle atrophy
  • Entropion-with severe disease

Strabismus

  • Deviation of one or both eyes from the normal position
  • May note exophthalmos or enophthalmos

Causes

Exophthalmos

  • Neoplasm-primary or secondary.
  • Abscess or cellulitis-bacterial or fungal; fungal more likely in cats; look for foreign bodies.
  • Zygomatic mucocele-not described in cats.
  • Myositis-muscles of mastication or extraocular muscles (eosinophilic or extraocular polymyositis).
  • Orbital hemorrhage secondary to trauma.
  • Arteriovenous fistula or varix-rare.

Enophthalmos

  • Ocular pain.
  • Microphthalmia.
  • Phthisis bulbi.
  • Collapsed globe.
  • Horner's syndrome.
  • Dehydration.
  • Loss of orbital fat or muscle.
  • Conformational enophthalmos in dolichocephalic breeds.
  • Neoplasia-especially those originating from rostral orbit.

Strabimus

  • Abnormal innervation of extraocular muscle.
  • Restriction of extraocular muscle mobility by scar tissue from previous trauma or inflammation.
  • Destruction of extraocular muscle attachments after proptosis.
  • Convergent strabismus-congenital; results from abnormal crossing of visual fibers in the CNS (Siamese cats).
  • Shar-Pei strabismus.

Risk Factors

Proptosis-more readily occurs in brachycephalic dogs with shallow orbits.

Diagnosis ⬆ ⬇

Diagnosis

Differential Diagnosis

Similar Signs

  • Buphthalmic globe-may simulate a space-occupying mass and cause the eye to be displaced anteriorly owing to its size in relationship to the orbital volume; IOP usually high; corneal diameter is greater than normal, corneal edema, mydriatic pupil, optic nerve cupping (i.e., signs of glaucoma), blindness.
  • Episcleritis-may cause severe diffuse or focal thickening of the fibrous tunic, often imitating a buphthalmic globe; corneal edema; normal or low IOP; aqueous flare.

Causes

  • Acute onset of exophthalmos-often inflammatory orbital disease. Pain, especially on opening the mouth, is more likely due to inflammatory orbital disease than orbital neoplasia.
  • Mucoceles-more variable in speed of onset and degree of patient discomfort.
  • Extraocular or eosinophilic myositis-bilateral diseases; Neospora caninum has caused extraocular polymyositis in a litter of German shorthaired pointers.
  • Neoplasia-usually slowly progressive, not painful, unilateral exophthalmos.

CBC/Biochemistry/Urinalysis

  • Usually normal.
  • Leukogram-may show inflammation with abscess or cellulitis or myositis.
  • Peripheral eosinophilia-occasionally seen in dogs with eosinophilic (masticatory muscle) myositis.

Imaging

  • Orbital ultrasonography, CT, and MRI-extremely helpful in defining the extent of the lesion(s) and distinguishing between types of myositis.
  • Skull radiographs (especially of the frontal sinuses and nasal cavity).
  • Thoracic radiographs-may help identify metastatic disease.

Diagnostic Procedures

  • Lack of globe retropulsion-confirms a space-occupying mass.
  • Oral examination, ocular ultrasound, and fine-needle aspiration of the orbit-may be completed after anesthetizing the patient.
  • Fine-needle aspiration (18- to 20-gauge)-submit samples for aerobic and anaerobic bacterial and fungal cultures, gram staining, and cytologic examination.
  • Cytology-often diagnostic for abscess or cellulitis, zygomatic salivary gland mucocele, and neoplasia.
  • Biopsy-indicated if needle aspiration is non-diagnostic. Biopsy of masseter, temporal, or extraocular muscle if myositis suspected; assays for type 2M fibers may be helpful.
  • Forced duction of the globe (strabismus)-grasp the conjunctiva with a fine pair of forceps following topical anesthesia; differentiates neurologic disease (in which the globe moves freely) from restrictive condition (in which the globe cannot be moved manually).

Treatment ⬆ ⬇

Treatment

Proptosis

See Proptosis.

Orbital Abscess Or Cellulitis

  • Drainage is seen in less than half of patients, usually because the lesion is at the cellulitis stage and a true abscess has not yet formed.
  • If an obvious swelling of the oral mucosa behind the last molar is not present and an ultrasound does not show an abscess, it is best to avoid incising the oral mucosa and treat with systemic antibiotics and anti-inflammatory medications; the affected globe should also be kept moist with topical lubricants q6h.
  • Severe cases may require intravenous fluids to maintain hydration and replace fluid deficits until patient is able to eat.
  • If a swelling of the oral mucosa behind the last molar is evident, establish ventral orbital drainage while the patient is anesthetized.
  • Incise the surgically prepared mucosa approximately 1 cm behind the last molar.
  • Push a blunt-tipped forceps (e.g., Kelly or Carmalt) into the orbital space and open; in general, advance the forceps until the abscess drains, to the level of the box lock, or until movement of the eye occurs with forceps opening.
  • Take care to minimize retrobulbar trauma and optic nerve damage; use only blunt dissection; never cut or crush tissue.
  • Complications that can occur with aggressive dissection include damage to the optic nerve and ciliary nerves.
  • Collect samples for bacterial culture and cytologic examination through this port.
  • Feed soft food until globe is back in normal position and pain appears resolved.
  • Hot packing-q6h; helps decrease swelling and cleans discharge.

Orbital Neoplasms

  • Usually primary and malignant.
  • Early exenteration or orbital exploratory surgery and debulking of the mass via a lateral approach to the orbit to save the globe are rational therapeutic choices.
  • Adjunctive chemotherapy or radiotherapy-depending on neoplasm type and extent of the lesion.
  • Without adjunct therapy-survival is weeks to months if malignant because the patient is usually examined late in the course of disease.
  • Consultation with an oncologist is recommended once the diagnosis is made.

Zygomatic Mucocele

May resolve with antibiotic and corticosteroid administration; if not, surgical excision of the cyst and associated gland is usually curative.

Strabismus

  • Neurologic-best treated by identifying the underlying cause and addressing that, if possible.
  • Restrictive or post-traumatic-may be treated surgically; repositioning or excising the attachments of the extraocular muscles; relieving excessive tension on those muscles; usually a very difficult procedure.

Medications ⬆ ⬇

Medications

Drug(s) Of Choice

  • Exophthalmos (all patients)-lubricate cornea (e.g., artificial tear ointment or gel q6h) to prevent desiccation and ulceration.
  • Ulceration-topical antibiotic (e.g., bacitracin, neomycin, polymyxin q8h) and cycloplegic (e.g., 1% atropine q12–24h), to prevent infection and reduce ciliary spasm, respectively.

Orbital Abscess or Cellulitis

  • Oral or intravenous antibiotics-sodium ampicillin (20 mg/kg q6–8h) or drugs with an anaerobic spectrum (amoxicillin with clavulanic acid or metronidazole) should be considered while awaiting results of bacterial culture and cytologic examination or if client declines diagnostic testing.
  • Bacterial orbital infections-may be mixed; Pasteurella multocida and Enterobacteriaceae common.
  • Most patients recover within approximately 2–3 weeks of treatment.
  • Fluconazole (2.5 mg/kg q12h or 5 mg/kg q24h) or posaconazole (5 mg/kg q12h) may be considered for orbital aspergillosis.
  • Prednisone-1 mg/kg SC or IM q24h, once or twice; minimize optic neuritis and reduce orbital swelling and globe exposure.
  • Alternatively, systemic NSAIDs (e.g., carprofen or meloxicam) can be used in place of prednisone but should be administered for several weeks.

Acute Myositis

  • Difficult prehension-systemic corticosteroids (prednisone 2 mg/kg SC or IM); then oral corticosteroids for the following 4–6 weeks (prednisone 2 mg/kg q24h) until the swelling subsides; then taper.
  • Azathioprine 1–2 mg/kg PO q24h for 3–7 days; then q48h and taper; with or without corticosteroids, may be used chronically to manage recurrent disease.

Precautions

  • Systemic corticosteroids-use with extreme caution with deep fungal orbital disease.
  • Azathioprine-may be hepatotoxic and cause myelosuppression. Follow CBC platelet count and liver enzymes every 1–2 weeks for 8 weeks, then periodically thereafter.

Follow-Up ⬆ ⬇

Follow-Up

Patient Monitoring

  • Inflammatory orbital disease-examine at least weekly until clinical signs abate.
  • Advise client to watch for recurrence of signs, especially if an orbital foreign body is likely.
  • Treat fungal infections for 60 days after signs cease.

Possible Complications

  • Vision loss
  • Loss of the eye
  • Permanent malposition of the globe
  • Death

Miscellaneous ⬆

Miscellaneous

Age-Related Factors

Give a course of antibiotic therapy first prior to attempting ventral orbital drainage.

Pregnancy/Fertility/Breeding

Avoid systemic corticosteroids, antifungal medications, and azathioprine in pregnant animals.

Abbreviations

  • CNS = central nervous system
  • CT = computed tomography
  • IOP = intraocular pressure
  • MRI = magnetic resonance imaging
  • NSAID = nonsteroidal anti-inflammatory drug

Author Kathern E. Myrna

Consulting Editor Paul E. Miller

Acknowledgment The author and editors acknowledge the prior contribution of Carmen M.H. Colitz.

Suggested Reading

Dubey JP, Oestner A, Piper RC. Repeated transplacental transmission of Neospora caninum in dogs. J Am Vet Med Assoc 1990, 197:857–860.

Miller PE, Orbit. In: Maggs DJ, Miller PE, Ofri R eds., Slatter's Fundamentals of Veterinary Ophthalmology, 5th ed. St. Louis, MO: Elsevier, 2013, pp. 352–373.

Speiss BM, Pot SADiseases and surgery of the canine orbit. In: Gelatt KN, Gilger BC, Kern TJ, eds., Veterinary Ophthalmology, 5th ed. Ames, IA: John Wiley, 2013.