Residency · Residency · Ophthalmology

Orbital Compartment Syndrome: Diagnosis and Lateral Canthotomy

Introduction

Orbital compartment syndrome (OCS) is an ophthalmic emergency in which rapidly increasing pressure within the orbit compromises blood flow to the optic nerve and retina. Without intervention, irreversible vision loss can occur within 60-120 minutes. The definitive emergency treatment is lateral canthotomy and inferior cantholysis, a procedure that every ophthalmologist and emergency physician must be able to perform.

Anatomy

The Orbit as a Compartment

The orbit is a rigid, cone-shaped bony structure closed anteriorly by the orbital septum. The orbital septum is a fibrous extension of the periosteum, inserting into the tarsal plates. This creates a closed compartment; any rapid increase in volume raises intraorbital pressure. The optic nerve, central retinal artery, and short posterior ciliary arteries are vulnerable to compression.

Lateral Canthal Anatomy

The lateral canthal tendon has superior and inferior crura. The inferior crus of the lateral canthal tendon inserts on Whitnall tubercle on the inner aspect of the lateral orbital rim. Division of the inferior crus (cantholysis) releases the lower lid from the orbital rim, decompressing the anterior orbit. The lateral canthal artery (branch of the lacrimal artery) courses nearby.

Etiology

Traumatic Causes (Most Common)

Retrobulbar hemorrhage: most frequent cause; often from orbital fracture or midface trauma. Post-surgical hemorrhage (blepharoplasty, orbital surgery, sinus surgery) Orbital foreign body with hemorrhage.

Non-Traumatic Causes

Spontaneous retrobulbar hemorrhage (anticoagulation, bleeding diathesis, Valsalva) Orbital emphysema (nose blowing after orbital floor fracture) Orbital cellulitis with abscess and edema. Rapidly expanding orbital mass. Aggressive fluid resuscitation in burn or trauma patients (orbital edema)

Clinical Presentation

Symptoms

Severe, acute orbital pain. Rapidly progressive vision loss. Diplopia.

Signs

Proptosis: tense, firm globe displacement. Elevated IOP: often > 40 mmHg (may be the earliest objective sign) Relative afferent pupillary defect (RAPD): indicates optic nerve compromise. Resistance to retropulsion of the globe. Decreased extraocular motility (restricted by increased orbital pressure) Eyelid edema and ecchymosis (may or may not be present)

Tight, tense orbit on palpation. Decreased visual acuity (may range from blurred vision to no light perception) Cherry-red spot or pallid disc on fundoscopy (late findings)

Diagnosis

Clinical Diagnosis

OCS is a clinical diagnosis; do NOT delay treatment for imaging. The combination of acute proptosis, elevated IOP, decreased vision, and RAPD is sufficient. High clinical suspicion in the setting of orbital trauma, recent surgery, or anticoagulation.

Imaging (If Time Permits)

CT orbit without contrast: retrobulbar hemorrhage appears as a hyperdense collection; tenting of the posterior globe ("guitar pick" sign) indicates severe pressure. CT also identifies fractures, foreign bodies, and the source of hemorrhage. Never delay intervention for imaging if the diagnosis is clinically apparent.

Differential Diagnosis

Orbital cellulitis (subacute, fever, leukocytosis) Carotid-cavernous fistula (pulsatile proptosis, bruit) Thyroid eye disease exacerbation (usually bilateral, subacute) Orbital tumor (progressive, not acute)

Emergency Management: Lateral Canthotomy and Inferior Cantholysis

Indications

Clinical diagnosis of OCS with any evidence of visual compromise. Elevated IOP with proptosis and RAPD, even with normal vision (impending OCS) Should be performed within 60 minutes of diagnosis.

Equipment

Lidocaine 2% with epinephrine (local anesthesia and hemostasis) Hemostat (straight) Iris scissors or sharp straight scissors. Toothed forceps. Antiseptic (povidone-iodine or chlorhexidine)

Procedure

Step 1: Preparation

Consent if possible; if not possible due to urgency, document as emergency procedure. Inject 1-2 mL of lidocaine with epinephrine at the lateral canthus. Cleanse the lateral canthal area with antiseptic.

Step 2: Lateral Canthotomy

Clamp the lateral canthus with a hemostat for 1-2 minutes (compresses vessels, reduces bleeding) Using scissors, make a 1-2 cm horizontal incision from the lateral canthus toward the lateral orbital rim. Cut through skin, orbicularis muscle, and the lateral canthal tendon. This step alone is often insufficient for decompression.

Step 3: Inferior Cantholysis

Grasp the cut edge of the lower lid with toothed forceps. Pull the lower lid away from the globe. Identify and strum the inferior crus of the lateral canthal tendon (a taut band extending from the lower tarsus to the orbital rim) Using scissors directed toward the orbital floor (cutting inferiorly and posteriorly), divide the inferior crus. Successful cantholysis is confirmed when the lower lid falls away freely from the globe. If inadequate decompression, perform superior cantholysis (divide the superior crus)

Step 4: Post-Procedure Assessment

Reassess IOP, pupil, vision, and globe position immediately. Target IOP reduction to < 40 mmHg. If IOP remains elevated, consider superior cantholysis or urgent orbital surgical exploration.

Post-Procedure Care

Topical antibiotic ointment to the wound. Ice packs to reduce swelling. Monitor vision, IOP, and pupillary function every 1-2 hours for 24 hours. Definitive surgical repair or canthal reconstruction can be performed once the patient is stable (usually within 5-7 days) Address underlying cause (evacuate hematoma surgically if re-accumulation occurs)

Complications of Canthotomy

Hemorrhage (usually minor; controlled with direct pressure) Infection (rare; antibiotic prophylaxis) Lower lid malposition (ectropion, lateral canthal dystopia); repaired during secondary reconstruction. Inadequate decompression requiring additional procedures.

Adjunctive Medical Measures

Timolol 0.5% topical: reduce aqueous production and lower IOP. Mannitol 20% IV (1-2 g/kg): osmotic agent to reduce intraocular volume (temporary measure) Acetazolamide 500 mg IV: reduce aqueous humor production. Head elevation to 30-45 degrees. Reverse anticoagulation if appropriate (vitamin K, FFP, prothrombin complex concentrate) These measures are adjuncts, not substitutes, for canthotomy/cantholysis.

Key Clinical Pearls

Orbital compartment syndrome is a clinical diagnosis; never delay treatment for imaging when vision is threatened. Lateral canthotomy and inferior cantholysis must be performed within 60 minutes; irreversible vision loss can occur within 90-120 minutes. The inferior crus of the lateral canthal tendon is the key structure to divide; canthotomy alone is usually insufficient. If IOP remains elevated after inferior cantholysis, proceed to superior cantholysis before considering surgical exploration.

References

1. Lima V, Burt B, Leibovitch I, et al. Orbital compartment syndrome: the ophthalmic surgical emergency. Surv Ophthalmol. 2009;54(4):441-449.
2. Rowh AD, Ufberg JW, Chan TC, et al. Lateral canthotomy and cantholysis: emergency management of orbital compartment syndrome. J Emerg Med. 2015;48(3):325-330.
3. Ballard SR, Enzenauer RW, O'Donnell T, et al. Emergency lateral canthotomy and cantholysis: a simple procedure to preserve vision from an orbital compartment syndrome. J Spec Oper Med. 2009;9(3):26-32.
4. McCallum E, Keren S, Gelman R. Lateral canthotomy and cantholysis: an evidence-based review. Eye (Lond). 2019;33(12):1869-1874.

Read this lecture as Markdown