When you have a ‘swollen eye’ and buphthalmos due to chronic glaucoma has been ruled out and exophthalmos due to expansion or orbital tissues has been ruled in (see previous blog), then you need to start narrowing down what is causing the orbital disease.  

Most cases of orbital tissue expansion fall into one of two categories, each or which usually follows a typical chronological and clinical pattern.

1. Inflammatory orbital disease, which is typically:
   • Acute onset
     

     Exophthalmic globe with nictitans elevation

   • Painful on globe palpation/retropulsion and mouth opening
   • Seen at any age, but often younger animals

Examples include orbital cellulitis/abscess, traumatic orbital haemorrhage, acute masticatory myositis, zygomatic adenitis

  2. Neoplastic orbital disease, which is typically:

• • Chronic, slow onset
  • Non-painful on globe palpation/retropulsion and mouth opening
  • Seen in older patients when neoplasia is more common

Examples include adenocarcinomas and sarcomas of orbital and adjacent (eg nasal, oral) glandular, mucosal and connective tissues, most of which are locally invasive with a very guarded prognosis.

Intraconal versus Extraconal orbital disease and its significance

The orbit comprises two main regions: the orbital cone comprising the extraocular muscles running from the globe in a cone shape to their boney insertions (and everything ‘inside’ that cone including the optic nerve); and the extraconal orbit comprising all other orbital tissue. 

Extraconal orbital disease makes up most cases and leans to prominent nictitans elevation.

Intraconal orbital disease is much less common and leads to more subtle exophthalmos without nictitans elevation.  The most common examples are extraocular polymyositis and optic nerve meningioma.

Young golden retriever with bilateral exophthalmos immune-mediated extraocular polymyositis