• Definition: exophthalmos is defined as ocular protrusion due to increase in orbital volume. It is different from buphthalmos that is described as ocular protrusion due to an increase in the size of the eye globe.
• Cause: increase in orbital (commonly retrobulbar) volume. This can be due to retrobulbar vascular anomalies, zygomatic salivary mucoceles, retrobulbar inflammatory lesions – in particular, retrobulbar neoplasia and trauma.
• Signs: uni- or bilateral anterior displacement of the globe, with or without rotation. Concurrent ipsilateral conjunctival chemosis and edema, periocular swelling, episcleral congestion, keratopathy, corneal ulceration, and globe desiccation may be present. Swelling of the caudal maxillary oral mucosa or hard palate may also be noted. Depending on the underlying etiology, signs consistent with dental disease may also be present. Anorexia and lethargy may be noted.
• Diagnosis: full ophthalmic examination, bloodwork (including coagulation testing if indicated), diagnostic imaging (skull CT or MRI considered most sensitive), retrobulbar tissue biopsy for cytology, histopathology and/or microbial culture and sensitivity testing.
• Treatment: protect affected globe to minimize further trauma and desiccation, and offer supportive care (analgesia, nutritional support if indicated). Address underlying etiology. This may include marsupialization of the salivary mucocele, creating a draining sinus for a retrobulbar abscess, exenteration in retrobulbar neoplasia.
• Prognosis: varies depending on underlying etiology and duration of clinical signs prior to diagnosis and treatment. Delayed intervention regardless of etiology may result in irreversible damage to the globe and vision loss. A good to fair prognosis is associated with zygomatic salivary mucoceles in ferrets. Retrobulbar neoplasia carries a guarded to poor prognosis.

• Uni- or bilateral protrusion of the globe.
• Ipsilateral palpebral/periorbital swelling.
• Ipsilateral red and weepy eye: conjunctival hyperemia, chemosis, episcleral congestion.
• Ipsilateral corneal opacities: exposure keratopathy, corneal ulceration.
• Signs consistent with dental disease Periodontal disease and/or oro-dental pain, eg dysrexia, dysphagia, ptyalism Ptyalism, halitosis, pawing at the mouth.
• Anorexia Anorexia, lethargy.

• Sudden onset of the above signs.
• Early increase in orbital (retrobulbar) volume may only result in subtle exophthalmos that may not be readily detectable. Exophthalmos may therefore only become apparent and thus present acutely once anterior displacement of the globe is sufficiently marked to result in significant periorbital edema and inflammation.

• Neoplasia occurs more commonly in older animals.
• Lymphoma Ocular lymphoma Lymphoma overview can affect ferrets of any age, although multicentric lymphoma may be more frequently identified in adults.

• No sex predilection has been reported.

• The underlying etiology of exophthalmos can often be suspected based on clinical examination and basic diagnostic investigations such as hematology Hematology, serum biochemistry and radiography Radiography: digital.
• A definitive diagnosis usually requires more advanced diagnostics such as computed tomographic (CT) imaging studies and tissue biopsies Biopsy overview for cytology, histopathology, and/or microbial culture and sensitivity testing. Costs of diagnostic investigations can therefore accumulate.
• Some oncological treatments, particularly chemotherapy and radiation therapy, can be costly, and may only be available at tertiary veterinary centers. Advanced imaging studies may also be required for ongoing monitoring.

• Exophthalmos predisposes the eye globe to exposure and trauma, which if untreated, can result in irreversible damage, desiccation, and vision loss.
• Risk of eye globe injury may be exacerbated under sedation or general anesthesia, when the palpebral reflex becomes obtunded or absent.

• Uni- or bilateral anterior displacement (with or without rotation) of the globe occurs due to increased orbital (commonly retrobulbar) volume. This can occur due to:
  • Vascular anomalies:
    • Systemic hypertension or abnormalities of the retrobulbar vascular plexus, eg hemorrhage, can result in exophthalmos.
  • Salivary mucocele:
    • The zygomatic salivary gland is medial to the zygomatic bone in the periocular area, ventral and rostrolateral to the globe.
    • Zygomatic salivary mucocele are thought to be caused by trauma and have been associated with ipsilateral exophthalmos.
  • Inflammatory lesions:
    • Dental disease Periodontal disease: tooth root abscess associated with the caudal maxillary premolars and/or molar.
    • Retrobulbar foreign body.
  • Retrobulbar neoplasia:
    • Disseminated lymphoma Ocular lymphoma Lymphoma overview affecting the retrobulbar tissue has been reported.
    • Retrobulbar adenocarcinoma has been reported in a ferret.
  • Retrobulbar trauma; hemorrhage and/or hematoma formation in the retrobulbar tissues.

General

• Inappropriate diets are proposed to contribute to dental disease Periodontal disease in ferrets.
• Neoplasia occurs more commonly in older animals. Lymphoma Ocular lymphoma Lymphoma overview can affect ferrets of any age, although multicentric lymphoma may be more frequently identified in adults.

Specific

• Skull and/or orodental trauma can result in hemorrhage and/or hematoma formation in the retrobulbar tissues.
• Odontogenic disease and infection of the caudal maxillary premolars and molars.

• Increased orbital volume results in anterior displacement of the globe ipsilaterally. Focal lesions outside the muscle cone behind the globe can also result in rotation of the globe off-axis into a direction opposite the mass lesion.
• The third eyelid (nictitating membrane) may also be anteriorly displaced and protrude.
• Ipsilateral epiphora and tear staining may be evident due to disruption of the lacrimal lake and occlusion of the lacrimal punctum by globe displacement.
• Increased orbital volume may result in ipsilateral swelling at the roof of the mouth near the fauces. Oro-dental lesions, eg tooth fracture, tooth instability, tooth loss, gingivitis Gingivitis, periodontitis Periodontal disease may also be noted, and may be the cause of inflammatory lesions within the retrobulbar space.
• Inflammatory changes in the orbital tissues cause tissue edema, which can additionally result in conjunctival chemosis and periocular swelling.
• Episcleral vessels can become congested due to decreased venous return caused by increased orbital tissue.
• Significant exophthalmos can lead to lagophthalmos with a decreased ability to close the eyelids. This can result in exposure keratitis, corneal ulceration, and globe desiccation.
• Vision loss may be present if the optic nerve is affected with the underlying etiology.

• Varies with etiology.
• Unless caused by trauma, exophthalmos typically develops over days to weeks. However, early, subtle changes may not be readily detected by the owner/carer.

• Neoplasia in general occurs more commonly in older animals. Lymphoma Ocular lymphoma Lymphoma overview can affect ferrets of any age, although multicentric lymphoma may be more frequently identified in adults.

Refereed papers

• Recent references from PubMed and VetMedResource.
• Parker L A & Ganjei J (2023) Partial caudal zygomatectomy for zygomatic sialoadenectomy in a ferret. Vet Rec Case Reports 11 (1), e510 ResGate.
• McBride M, Mosunic C, Barron G et al (2009) Successful treatment of a retrobulbar adenocarcinoma in a ferret (Mustela putorius furo). Vet Rec 165 (7), 206-208 PubMed.
• Good K L (2002) Ocular disorders of pet ferrets. Vet Clin North Am Exot Anim Pract 5 (2), 325-339 PubMed.

Other sources of information

• van der Woerdt A (2020) Ophthalmic Diseases of Small Mammals. In: Ferrets, Rabbits and Rodents: Clinical Medicine and Surgery. 4th edn. Eds: Quesenberry K, Mans C, Orcutt C & Carpenter J W. 4th edn. Elsevier, USA. pp 583-594.
• Pizzirani S, Penninck D & Spaulding K (2015) Eye and Orbit. In: Atlas of Small Animal Ultrasonography. 2nd edn. Eds: Dominique P & Marc-André D A. Wiley-Blackwell, USA. pp 19-54.
• Speiss B M & Plot S A (2013) Diseases and Surgery of the Canine Orbit. In: Veterinary Ophthalmology. 5th edn. Eds: Gelatt K N, Gilger B C & Kern J. Wiley, USA.