OPTHALMOLOGY
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 .
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 .
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 haemorrahge . Most frequently this is a sequelae to blunt or penetrating trauma caused by motor vehicle accidents or collisions with stationary objects .
Issue 04 | AUGUST 2016 | 27