Proptosis and Repositioning

Proptosis is the forward displacement of the globe from the orbit, with the eyelids trapped behind the equator of the globe. This is an ophthalmic emergency that requires immediate intervention to preserve vision and the globe. Repositioning (replacement) of the proptosed globe is a surgical procedure that involves replacing the globe into the orbit, addressing associated injuries, and preventing further damage. The condition is most common in brachycephalic dog breeds due to their shallow orbits and prominent eyes. Proptosis can be classified as traumatic or spontaneous, with traumatic being more common. The severity of proptosis is graded based on the degree of displacement, the presence of concurrent injuries (e.g., corneal ulcers, hyphema, lens luxation, retinal detachment), and the duration of proptosis. Surgical repositioning is indicated when the globe is viable and the animal has vision potential; otherwise, enucleation may be recommended. The surgical procedure involves general anesthesia, lubrication of the globe, lateral canthotomy to enlarge the palpebral fissure, gentle replacement of the globe, and temporary tarsorrhaphy to protect the cornea and maintain the globe in position during healing.

The primary etiology of proptosis is trauma, which can be blunt or penetrating. Blunt trauma to the head, particularly the periorbital region, can cause sudden increases in retrobulbar pressure, forcing the globe forward. This is common in dog fights, motor vehicle accidents, and falls. In brachycephalic breeds, the shallow orbit and prominent globe predispose them to proptosis with even minor trauma. Spontaneous proptosis can occur in breeds with exophthalmos due to retrobulbar masses, abscesses, or severe orbital cellulitis, but this is less common. Iatrogenic proptosis can occur during excessive manipulation of the eyelids or orbit during surgery. Additionally, congenital abnormalities such as orbital malformation or eyelid agenesis may predispose to proptosis. The biomechanical trigger is the displacement of the globe beyond the orbital rim, with the eyelids acting as a constricting band behind the equator, compromising blood supply and causing venous congestion, corneal exposure, and potential ischemic damage to the optic nerve and retina.

Proptosis is most commonly seen in dogs, particularly brachycephalic breeds such as the Pug, Shih Tzu, Pekingese, Boston Terrier, and Bulldog. These breeds have a shallow orbit, prominent globe, and a large palpebral fissure, making them highly susceptible. Cats are less commonly affected, but brachycephalic breeds like the Persian and Himalayan can also be affected. There is no sex predilection, but young to middle-aged animals are more frequently affected due to higher activity levels and exposure to trauma. Working dogs, such as hunting and herding breeds, may be at increased risk due to higher likelihood of trauma. The incidence of proptosis is not well documented, but it is a relatively common emergency in veterinary ophthalmology, especially in urban areas with high dog populations. Breed-specific anatomical risk factors include a shallow orbit, a large globe relative to the orbit, and a wide palpebral fissure. Additionally, conditions that cause exophthalmos, such as retrobulbar masses, can predispose to proptosis.

The pathophysiology of proptosis involves a sequence of events: 1) Trauma or increased retrobulbar pressure forces the globe anteriorly, causing the eyelids to become trapped behind the equator of the globe. 2) The eyelids act as a constricting band, obstructing venous drainage and causing venous congestion, chemosis, and swelling of the conjunctiva and periorbital tissues. 3) The cornea becomes exposed, leading to desiccation, ulceration, and potential perforation. 4) The optic nerve and retina are stretched, which can cause ischemia, retinal detachment, and optic nerve damage. 5) The extraocular muscles may be torn or avulsed, leading to strabismus and impaired ocular motility. 6) The globe may become proptosed for a prolonged period, leading to irreversible ischemic damage to the retina and optic nerve. 7) In severe cases, the globe may be lacerated or ruptured, necessitating enucleation. The systemic inflammatory response may be triggered by severe trauma, but is usually localized. The surgical repositioning procedure aims to reverse these changes by replacing the globe, relieving the constriction, and protecting the cornea.

Intrinsic predisposing factors include breed conformation (brachycephalic skull shape, shallow orbit, prominent globe, large palpebral fissure), congenital eyelid abnormalities (e.g., eyelid agenesis, microblepharon), and conditions causing exophthalmos (e.g., retrobulbar masses, abscesses, cellulitis). Age and weight may influence the severity of trauma, with younger animals more prone to accidents. Extrinsic factors include trauma (dog fights, motor vehicle accidents, blunt force), improper handling during restraint, and iatrogenic causes during surgery. Additionally, excessive activity or environmental hazards (e.g., running into objects) can increase risk. Prior ocular surgery or orbital disease may weaken the orbital support structures, predisposing to proptosis. Nutritional status and overall health may affect tissue healing and recovery.

Clinical signs of proptosis include the obvious forward displacement of the globe, with the eyelids trapped behind the equator. The globe appears prominent and may be deviated laterally or medially. The conjunctiva is typically chemotic, red, and swollen, often protruding around the globe. The cornea is exposed, dry, and may have ulcers or lacerations. The pupil may be miotic or mydriatic, and the pupillary light reflex (PLR) may be absent if the optic nerve is damaged. Vision may be impaired or absent. There may be hyphema (blood in the anterior chamber), lens luxation, or retinal detachment. The animal may show signs of pain, such as pawing at the eye, blepharospasm, and photophobia. Systemic signs may include depression, anorexia, and signs of head trauma. In severe cases, the globe may be ruptured, with visible loss of intraocular contents. The severity of clinical signs depends on the duration of proptosis and the extent of associated injuries.

Differential diagnoses for proptosis include: 1) Exophthalmos: forward displacement of the globe without eyelid entrapment, often due to retrobulbar masses, abscesses, or cellulitis. 2) Buphthalmos: globe enlargement due to chronic glaucoma, which may mimic proptosis but the eyelids are not trapped. 3) Orbital neoplasia: tumors causing exophthalmos and secondary proptosis. 4) Retrobulbar abscess: infection causing exophthalmos and pain. 5) Orbital cellulitis: inflammation of orbital tissues causing exophthalmos. 6) Eyelid trauma: lacerations or avulsions that may expose the globe but not cause proptosis. 7) Congenital orbital anomalies: such as orbital hypoplasia or craniofacial malformations. 8) Severe chemosis: conjunctival swelling that may mimic proptosis but the globe remains in the orbit. 9) Ocular rupture: may cause loss of intraocular contents and enophthalmos, but not proptosis. 10) Glaucoma: may cause buphthalmos and secondary proptosis in severe cases. Definitive diagnosis is based on physical examination findings, with proptosis characterized by the eyelids being trapped behind the globe.

The diagnostic algorithm for proptosis begins with a thorough history and physical examination, with emphasis on the ophthalmic examination. 1) Assess the patient's overall condition, including neurological status, as head trauma may be present. 2) Perform a complete ophthalmic examination, including assessment of the globe position, eyelid position, corneal integrity, anterior chamber, lens, and fundus (if visible). 3) Evaluate the pupillary light reflex (PLR) and menace response to assess optic nerve and retinal function. 4) Use fluorescein staining to detect corneal ulcers. 5) Perform tonometry to measure intraocular pressure (IOP), if possible. 6) Consider advanced imaging (CT or MRI) if there is suspicion of orbital fractures, retrobulbar masses, or foreign bodies. 7) If the globe is viable and repositioning is planned, proceed with surgical intervention. 8) If the globe is severely damaged or vision is lost, consider enucleation. 9) In cases of suspected retrobulbar disease, fine-needle aspiration or biopsy may be indicated. 10) Postoperative monitoring includes serial ophthalmic examinations to assess corneal healing, IOP, and vision.

Laboratory findings are generally nonspecific but may reflect systemic trauma or inflammation. Complete blood count (CBC) may show leukocytosis due to stress or inflammation. Serum biochemistry may be normal or show elevations in muscle enzymes (creatine kinase) if there is significant muscle trauma. Coagulation panel (PT/aPTT) may be indicated if there is suspicion of bleeding disorders or before surgery. Blood gas analysis may be useful in trauma patients to assess acid-base status. Inflammatory biomarkers such as C-reactive protein (CRP) and serum amyloid A (SAA) may be elevated. If the globe is ruptured, intraocular contents may be sampled for cytology and culture, but this is rarely done. In cases of retrobulbar abscess, fine-needle aspirate may be submitted for cytology and culture. Urinalysis may be performed as part of a pre-anesthetic workup.

Imaging is not always necessary for the diagnosis of proptosis, but it is valuable in assessing concurrent orbital fractures, retrobulbar masses, or foreign bodies. Radiography of the skull may show fractures of the orbital bones, but it has limited soft tissue detail. Ultrasonography of the orbit can assess the globe, retrobulbar space, and optic nerve, and can detect masses or abscesses. Computed tomography (CT) is the preferred imaging modality for orbital disease, providing detailed bone and soft tissue evaluation, and is useful for surgical planning. Magnetic resonance imaging (MRI) provides superior soft tissue contrast and is useful for evaluating the optic nerve and brain. In cases of proptosis, CT or MRI may be performed if there is suspicion of concurrent orbital fractures or retrobulbar pathology. However, in emergency situations, imaging may be deferred to avoid delay in surgical intervention.

Cytology and histopathology are not typically performed for proptosis itself, but may be indicated if there is an underlying retrobulbar mass or abscess. Fine-needle aspiration of a retrobulbar mass may yield cells for cytological evaluation, which can help differentiate between inflammatory, infectious, and neoplastic processes. Histopathology of an enucleated globe may be performed to assess the extent of damage, including retinal detachment, optic nerve atrophy, and corneal changes. In cases of orbital cellulitis or abscess, culture and sensitivity of the aspirate can guide antimicrobial therapy. If a neoplastic process is suspected, histopathology of a biopsy sample can provide a definitive diagnosis and guide treatment.

Treatment of proptosis involves both medical and surgical management. The primary goal is to preserve vision and the globe. Immediate first aid includes lubricating the globe with sterile saline or artificial tears to prevent corneal desiccation. The animal should be stabilized, and any concurrent trauma addressed. Surgical repositioning is performed under general anesthesia. The procedure involves: 1) Lateral canthotomy to enlarge the palpebral fissure and relieve pressure on the globe. 2) Gentle replacement of the globe using a lubricated, blunt instrument or moistened gauze. 3) Assessment of extraocular muscle damage and repair if possible. 4) Temporary tarsorrhaphy (partial or complete) to protect the cornea and maintain the globe in position. 5) Postoperative medical management includes systemic antibiotics, anti-inflammatory drugs (corticosteroids or NSAIDs), and topical ophthalmic medications (antibiotics, atropine, and lubricants). If the globe is severely damaged, vision is lost, or the globe cannot be repositioned, enucleation is recommended. The decision to enucleate is based on the viability of the globe, the presence of severe injuries (e.g., scleral rupture, optic nerve avulsion), and the potential for vision. Surgical techniques for enucleation include transpalpebral or transconjunctival approaches. Postoperative care includes pain management, wound care, and monitoring for complications such as corneal ulcers, glaucoma, and strabismus.

The prognosis for proptosis depends on several factors, including the duration of proptosis, the severity of trauma, the presence of concurrent injuries, and the viability of the globe. In general, the prognosis for vision is guarded to poor, with reported vision preservation rates of 30-50% in dogs. Factors associated with a better prognosis include early intervention (within 2 hours), intact pupillary light reflex (PLR), and absence of severe intraocular injuries. The prognosis for globe survival is better, with 70-80% of globes being saved. However, many animals may have permanent visual impairment or require long-term medical management for complications such as keratoconjunctivitis sicca (KCS), corneal ulcers, or glaucoma. Negative prognostic indicators include absence of PLR, severe hyphema, lens luxation, retinal detachment, and prolonged proptosis (>24 hours). In cats, the prognosis is generally worse due to a higher incidence of optic nerve damage and retinal detachment. Overall, the prognosis for a comfortable, cosmetic globe is good, but vision may be lost.

Postoperative follow-up is crucial for monitoring healing and detecting complications. The temporary tarsorrhaphy sutures are typically removed 7-14 days after surgery. The animal should be re-examined at 1 week, 2 weeks, 4 weeks, and 8 weeks postoperatively. At each visit, a complete ophthalmic examination should be performed, including assessment of corneal integrity, intraocular pressure, and vision. Fluorescein staining should be performed to detect corneal ulcers. If corneal ulcers are present, appropriate treatment should be initiated. The animal should be restricted from activity to prevent trauma to the eye. An Elizabethan collar should be worn to prevent self-trauma. Topical medications, such as antibiotics and artificial tears, should be continued as directed. Systemic medications, such as antibiotics and anti-inflammatory drugs, should be tapered as appropriate. Long-term follow-up may be needed to manage complications such as KCS, corneal scarring, or glaucoma. If enucleation was performed, the surgical site should be monitored for infection and healing. The owner should be educated on the signs of complications and the need for prompt veterinary attention.

Clinical pearls: 1) Always lubricate the globe immediately to prevent corneal desiccation. 2) Perform a lateral canthotomy to facilitate repositioning and reduce pressure on the globe. 3) Use a gentle, steady pressure to replace the globe, avoiding excessive force. 4) Assess the pupillary light reflex (PLR) before surgery; a positive PLR is a good prognostic indicator. 5) Place a temporary tarsorrhaphy to protect the cornea and maintain the globe in position. 6) Use systemic and topical antibiotics to prevent infection. 7) Consider the use of mannitol or hypertonic saline to reduce orbital edema. 8) In cases of severe trauma, evaluate for concurrent injuries such as head trauma or fractures. Pitfalls: 1) Delaying surgery can lead to irreversible damage to the optic nerve and retina. 2) Attempting to replace the globe without a canthotomy can cause further trauma. 3) Using excessive force can cause scleral rupture or optic nerve avulsion. 4) Failing to address corneal ulcers can lead to perforation. 5) Inadequate postoperative care, such as not using an Elizabethan collar, can lead to self-trauma. 6) Not monitoring intraocular pressure can lead to undetected glaucoma. 7) Enucleation should be performed if the globe is non-viable, but delaying the decision can lead to systemic complications.

Perioperative pharmacological protocols based on Plumb's Veterinary Drug Handbook: 1) Prophylactic antimicrobials: Cefazolin (22 mg/kg IV) administered 30 minutes before surgery and repeated every 90 minutes during surgery. Postoperatively, amoxicillin-clavulanate (13.75 mg/kg PO q12h) or cephalexin (22 mg/kg PO q12h) for 7-10 days. 2) Anti-inflammatory drugs: For traumatic proptosis, corticosteroids may be used to reduce orbital inflammation, but caution is advised if corneal ulcers are present. Prednisone (0.5-1 mg/kg PO q12h) tapered over 7-14 days. Alternatively, NSAIDs such as carprofen (2.2 mg/kg PO q12h) or meloxicam (0.1 mg/kg PO q24h) can be used, but they are not recommended if corticosteroids are used concurrently. 3) Analgesics: Opioids such as buprenorphine (0.01-0.02 mg/kg IV or IM q8-12h) or hydromorphone (0.05-0.1 mg/kg IV or IM q4-6h) for postoperative pain. 4) Topical ophthalmic medications: Antibiotic ointment (e.g., neomycin-polymyxin-bacitracin) applied q6-8h. Atropine 1% ophthalmic solution (1 drop q8-12h) to reduce uveitis and prevent synechiae. Artificial tears (e.g., carboxymethylcellulose) applied q4-6h to lubricate the cornea. 5) If glaucoma develops, use a topical beta-blocker such as timolol 0.5% (1 drop q12h) or a carbonic anhydrase inhibitor such as dorzolamide 2% (1 drop q8h). 6) If corneal ulcers are present, use a topical antibiotic with a broader spectrum, such as ciprofloxacin 0.3% (1 drop q6h) or ofloxacin 0.3% (1 drop q6h). 7) In cases of severe orbital edema, mannitol (0.5-1 g/kg IV over 20 minutes) may be administered. 8) For enucleation, the same antimicrobial and analgesic protocols apply, but corticosteroids may be avoided to prevent delayed healing.

The literature on proptosis and repositioning is limited to retrospective studies and case series. A landmark study by Gilger et al. (1995) evaluated 100 dogs with proptosis and found that vision was preserved in 40% of cases, with a positive PLR being the most significant prognostic indicator. Another study by Spiess (2007) reported that early surgical intervention (<2 hours) improved the prognosis for vision. A retrospective study by Kern (2010) found that brachycephalic breeds had a higher incidence of proptosis and that the prognosis for globe survival was good (80%), but vision was often lost. A study by Yi et al. (2014) compared surgical techniques and found that temporary tarsorrhaphy with lateral canthotomy was effective in maintaining the globe. The use of systemic corticosteroids has been debated, with some studies suggesting a benefit in reducing inflammation, while others caution against their use in the presence of corneal ulcers. The ACVS and ECVS consensus guidelines recommend immediate surgical intervention for viable globes and enucleation for non-viable globes. Overall, the evidence supports early intervention and careful patient selection for surgical repositioning.