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Summary
Proptosis is the term used to describe the sudden protrusion of the eye (referred to as the globe) from its socket (referred to as its orbit). This is a very common ocular emergency and one that requires immediate attention.
When the globe is suddenly displaced forward in this way, the eyelids become trapped behind it, which leads to inflammation of the lids and swelling of the contents encased in the back side of the eye. The cornea - the clear, delicate covering of the eye - is also severely affected under these conditions. Severe corneal desiccation (dryness) and ulceration are common under these conditions.
By far the most common cause of proptosis is trauma. Blunt trauma to the side or back of the head or any sharp trauma in the vicinity of the eye may lead to its proptosis. So, too, may a milder trauma, such as when certain kinds of collars and restraint devices are used, or when tumors apply pressure to the back of the eye.
Proptosis is considered very common, particularly among brachycephalic (short-headed, snub-nosed) breeds of dogs. Their shallow orbits, prominent globes, and abnormal eyelid conformation create ideal conditions for proptosis.
While it is possible to preserve the eye’s structure and even the patient’s vision after proptosis, success depends on a wide variety of individual parameters.
Symptoms and Identification
Proptosis is readily identified by visual inspection as the globe of the eye is visibly protruding from its orbit in all cases.
The severity of the protrusion will vary. In some patients, the globe is entirely proptosed, the extraocular eye muscles are avulsed, and the optic nerve is visible. In others, the eye appears almost normal and is protruding only slightly.
The appearance of the cornea will also vary, typically depending on the amount of time lapsed between proptosis and treatment. A desiccated, possibly even ulcerated cornea is more likely when over an hour has lapsed.
Pupil size is yet another prognostic indicator. If the pupil is fixed and dilated, the prognosis is typically poor. From a positive prognostic perspective, a constricted pupil is the preferred response to trauma.
Affected Breeds
As described above, brachycephalic breeds are impressively predisposed to proptosis. Pugs and Pekinese, among others, are particularly prone, since these breeds are selectively bred for their bulging globes and the kind of abnormal eyelid conformation that makes proptosis more likely.
Treatment
Treatment of proptosis depends on the severity of the protrusion and the prognostic indicators described above. If the globe is deemed salvageable, the preferred means of treatment is to replace the globe in the orbit and suture it in place. This suturing procedure is referred to as a temporary tarsorrhaphy.
After the replacement, pets require topical and systemic drugs, frequent rechecks, and, ideally, evaluation by a board-certified ophthalmologist early on in the process.
Complications with globe retention post-proptosis may include an inability to close the eyelids fully, exposure keratitis, keratoconjunctivitis sicca (KCS), and corneal ulcerations. Other possible long-term sequela include blindness, strabismus, optic nerve degeneration, retinal detachment, retinal degeneration, uveitis/glaucoma and phthisis bulbi.
Sadly, many proptosis patients require enucleation (complete removal of the globe) as a means of treatment.
Veterinary Cost
The veterinary cost of proptosis depends on the severity of the protrusion and the prognostic indicators described above, as is the owners’ commitment to globe retention. That’s because enucleation is far less expensive than replacement and tarsorrhaphy.
Enucleation typically costs $500 to $2,000. Meanwhile, replacement and tarsorrhaphy, given all its attendant costs and follow-up expenses, may cost upwards of $4,000 in some cases.
Long-term complications of formerly proptosed eyes are common enough that long-term follow-up veterinary care is a near-certainty. These future expenses should not be ignored by owners.
Prevention
Prevention ideally involves breeding more diligently for traits that will minimize the risk of proptosis among specific brachycephalic breeds. In general, breeding for exaggerated traits related to bulging eyes, inadequate eyelids, and shallow orbits will increase the risk of proptosis.
References
Kennard G., Ocular emergencies: Presenting signs, initial exam and treatment (Proceedings) CVC Kansas City, 2009: http://veterinarycalendar.dvm360.com/avhc/article/articleDetail.jsp?id=648158&pageID=1&sk=&date=
Merck Veterinary Manual: http://www.merckmanuals.com/vet/emergency_medicine_and_critical_care/ophthalmic_emergencies/traumatic_proptosis.html