What are the key teaching points and step‑by‑step approach for identifying orbital compartment syndrome (OCS) using point‑of‑care ultrasound (POCUS) of the eye and performing a lateral canthotomy for retrobulbar hematoma in an ABEM oral board case?

Teaching ABEM Oral Board Case: Orbital Compartment Syndrome with Lateral Canthotomy

Immediate Recognition: Clinical Diagnosis of OCS

Orbital compartment syndrome is a clinical diagnosis that requires immediate surgical decompression—do not delay for imaging if definitive clinical criteria are present. 1, 2

Definitive Clinical Criteria (Any ONE warrants immediate canthotomy):

• Vision loss (decreased visual acuity from baseline)
• Relative afferent pupillary defect (RAPD)
• Intraocular pressure (IOP) >40 mmHg or >2 mmHg difference between eyes
• Proptosis with tense globe and resistance to retropulsion

Secondary Clinical Findings (Supportive but not definitive):

• Periorbital ecchymosis and edema
• Subconjunctival hemorrhage
• Ophthalmoplegia (restricted extraocular movements)
• Severe eye pain
• Cherry-red spot on fundoscopy (late finding)

Critical Pitfall: Do not wait for all signs to be present—vision loss alone in the setting of orbital trauma is sufficient to proceed. 1, 3

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POCUS Ocular Examination Protocol

Technique:

• Use high-frequency linear probe (7.5-10 MHz) with copious gel
• Place probe gently on closed eyelid—avoid pressure on globe
• Never perform if globe rupture suspected (check for penetrating injury, severe deformity, or positive Seidel test first)

Systematic Views:

1. Transverse view (probe horizontal across closed lid)
2. Sagittal view (probe vertical)
3. Scan through entire globe from limbus to optic nerve

Key POCUS Findings in OCS:

Retrobulbar Hematoma:

• Hyperechoic (bright) collection posterior to globe
• Intraconal location (within extraocular muscle cone) = worse prognosis 4
• Extraconal location (outside muscle cone) = more common

Secondary Signs:

• Optic nerve sheath diameter >5-6 mm (measured 3mm behind globe)
• Posterior globe flattening or tenting (loss of normal spherical contour)
• Lens dislocation (appears as echogenic structure in abnormal position)
• Vitreous hemorrhage (diffuse echoes in vitreous chamber)

Measurement for Prognosis:

• Calculate hematoma volume/orbital volume ratio—higher ratio predicts worse outcome 4

Common Diagnostic Errors on POCUS: 5

• Missing ocular masses (may mimic hematoma)
• Misinterpreting cataracts as pathology
• Failing to recognize subtle signs of raised ICP

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Imaging Considerations

CT Orbits without contrast is the gold standard for orbital trauma 6, 7

When to Image:

• NEVER delay canthotomy if definitive clinical criteria present 2
• Obtain CT after decompression if patient stable
• CT useful when clinical exam unreliable (obtunded patient, severe facial edema) 2
• Look for: orbital fractures (especially floor/medial wall), hematoma location, optic canal involvement, bone fragments

CT Findings Associated with Poor Outcome: 4

• Intraconal hematoma location
• Hematoma contacting optic nerve
• Orbital floor fracture
• High hematoma/orbital volume ratio

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Lateral Canthotomy and Cantholysis: Step-by-Step

Preparation (2-3 minutes):

• Call ophthalmology immediately—but do not delay procedure
• Obtain informed consent (document if patient unable to consent due to emergency)
• Position patient supine, head elevated 30°
• Assemble equipment:
  • Straight hemostats (or scissors)
  • Iris scissors (curved preferred)
  • Local anesthetic (1% lidocaine with epinephrine)
  • 4x4 gauze
  • Topical anesthetic drops (optional)

Procedure:

Step 1: Anesthesia

• Inject 1-2 mL lidocaine with epinephrine at lateral canthus
• Wait 30-60 seconds (don't wait longer—this is an emergency)

Step 2: Lateral Canthotomy

• Clamp lateral canthus with hemostat for 60 seconds (provides hemostasis)
• Using iris scissors, cut horizontally through full thickness of lateral canthus
• Cut should be 1-2 cm long, extending to lateral orbital rim
• You should see conjunctiva and orbital septum exposed

Step 3: Inferior Cantholysis (Critical Step)

• Identify inferior canthal tendon—pull lower lid away from globe and look for white fibrous band
• Completely divide inferior canthal tendon using iris scissors
• Cut should be perpendicular to lid margin, directed toward orbital floor
• Test adequacy: Lower lid should now be completely mobile and separate from globe

Common Pitfall: Incomplete division of inferior canthal tendon is the most frequent error—the lid must be completely free 1

Step 4: Confirm Decompression

• Globe should prolapse anteriorly (proptosis increases initially—this is expected)
• Recheck IOP immediately—should decrease by >10 mmHg
• Reassess vision—may take minutes to hours to improve

If Inadequate Decompression:

• Perform superior cantholysis (divide superior canthal tendon)
• Consider orbital septotomy (incise orbital septum to release additional pressure)
• Prepare for formal surgical orbital decompression in OR

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Time-Critical Management Algorithm

Time from injury to decompression predicts outcome: 3

• <6 hours: Best chance for visual recovery (72% in recovery group)
• 6-12 hours: Visual recovery still possible but decreased
• >12 hours: Poor prognosis (60% had persistent sequelae)

Management Timeline:

0-15 minutes (Initial Assessment):

• Check visual acuity (count fingers at 1 meter minimum)
• Assess for RAPD
• Measure IOP both eyes
• Exclude globe rupture (if suspected, shield eye and consult ophthalmology—do NOT perform canthotomy)
• Perform POCUS if immediately available

15-30 minutes (Decision Point):

• If definitive criteria present: Proceed immediately to canthotomy
• If secondary findings only: Obtain CT if available within 15 minutes
• Do not delay >30 minutes for imaging if high clinical suspicion

Post-Procedure:

• Recheck vision and IOP every 2 hours for 24 hours 3
• Monitor for delayed RBH (can occur up to 48 hours post-trauma) 4
• Ophthalmology follow-up for wound closure (typically 5-7 days)

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Documentation Essentials

Pre-Procedure: 1

• Exact visual acuity (not just "decreased")
• Pupil size and reactivity (document RAPD if present)
• IOP measurements (both eyes with values)
• Extraocular movements
• Time of injury and time of examination
• Anticoagulation status (aspirin use associated with worse outcomes) 4

Post-Procedure:

• Time procedure performed
• Immediate post-procedure IOP and vision
• Confirmation of complete canthal tendon division
• Ophthalmology consultation time

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High-Yield Teaching Points for Oral Boards

1. OCS is a clinical diagnosis—imaging should never delay treatment when definitive criteria present 2

2. Vision loss alone is sufficient to proceed with canthotomy in trauma setting 3

3. Complete inferior cantholysis is mandatory—partial division is inadequate 1

4. Globe rupture is the only absolute contraindication—must exclude before procedure 1

5. Time is vision: Decompress within 6 hours for best outcomes 3

6. Anticoagulation increases risk—elderly females on anticoagulants are high-risk population 4

7. Post-procedure monitoring is critical—delayed RBH can occur up to 48 hours 4

8. Intraconal hematomas have worse prognosis than extraconal 4