HALO Procedures Manual: Lateral Canthotomy and Cantholysis

1. Introduction

Orbital compartment syndrome (OCS) is a time-critical, vision-threatening emergency caused by rapidly rising intra-orbital pressure. Without urgent decompression, ischemia of the optic nerve and retina may result in irreversible blindness.

OCS represents the ophthalmic equivalent of limb compartment syndrome: pressure rises within a closed anatomical space, perfusion falls, and tissue injury becomes permanent within a narrow therapeutic window. Irreversible optic nerve injury may occur within 90–120 minutes.

Lateral canthotomy with cantholysis (LC/LOC) is the definitive emergency intervention. It is a low-morbidity, bedside procedure that emergency physicians must be prepared to perform without delay when indicated 

Lateral canthotomy

In HALO terms, lateral canthotomy is:

  • High Acuity – failure leads to blindness
  • Low Occurrence – infrequently performed
  • Time Critical – delays worsen outcomes possibly permanent vision loss
  • Skill Dependent – requires anatomical precision

2. Learning Objectives

After completing this chapter, participants should be able to:

  1. Recognize orbital compartment syndrome clinically.
  2. Identify clear indications and contraindications for lateral canthotomy.
  3. Describe relevant orbital anatomy.
  4. Perform lateral canthotomy and inferior cantholysis safely and efficiently (target: <2 minutes).
  5. Recognize and manage complications.
  6. Integrate decision-making into trauma and emergency workflows.

Pathophysiology of Orbital Compartment Syndrome

The orbit is a rigid, pyramid-shaped bony cavity with a volume of approximately 30 mL. The globe occupies ~7 mL and is tethered posteriorly by the optic nerve and vascular structures. Anteriorly, eyelid structures and canthal tendons form a functional barrier.

When haemorrhage, oedema, or emphysema increases orbital volume, intra-orbital pressure rises. Because the orbit is fixed:

  • Venous outflow is compromised
  • Arterial perfusion pressure falls
  • Optic nerve ischemia develops
  • Retinal perfusion ceases

Mechanisms include:

  • Retrobulbar haemorrhage (trauma, surgery)
  • Iatrogenic injection (retrobulbar/peribulbar anaesthesia)
  • Massive fluid resuscitation
  • Burns
  • Orbital cellulitis
  • Tumour-related bleeding 

Even modest increases in pressure can impair vision. While many sources cite IOP ≥ 40 mmHg as a threshold, visual compromise may occur at lower pressures 

4. Clinical Recognition

Classic Clinical Features

  • Proptosis
  • Decreased visual acuity
  • Relative afferent pupillary defect (RAPD)
  • Ophthalmoplegia
  • Tense orbit
  • Elevated intraocular pressure

In trauma patients, especially those sedated or intubated, diagnosis must be proactive. The closed, swollen eye in a severely injured patient is at risk of missed OCS 

Key principle: OCS is a clinical diagnosis. Do not delay intervention for CT imaging if suspicion is high 

CT Findings (if obtained rapidly)

  • Retrobulbar haemorrhage
  • Optic nerve stretching
  • Globe tenting
  • Marked proptosis 

5. Indications

Lateral canthotomy should be performed in patients with suspected OCS and:

  • Blunt orbital trauma with visual compromise
  • IOP ≥ 40 mmHg (soft threshold) 
  • RAPD
  • Proptosis with decreased visual acuity
  • Unconscious trauma patient with concerning orbital findings 

When in doubt and clinical suspicion is reasonable, decompression should proceed. Delay worsens outcome.

6. Contraindications

Absolute

  • Confirmed globe rupture 

Relative

  • Suspected globe rupture

However, overlap exists between OCS and globe rupture signs. If vision is threatened and diagnosis is uncertain, lateral canthotomy may still be required — performed carefully, avoiding pressure on the globe 

7. Equipment

Standard laceration tray equipment is sufficient 

  • 5 mL syringe + 25G needle
  • Lidocaine 1–2% with adrenaline
  • Tetracaine drops (or any anaesthetic eye drops)
  • Straight haemostat
  • Iris scissors (preferred) but straight scissors from a standard suturing kit will suffice in emeregncy
  • Tissue forceps ×2
  • Saline for irrigation
  • Sterile gloves, mask, eye protection

A pre-prepared lateral canthotomy kit improves procedural efficiency but a standard suturing set will also suffice in emergency.

8. Preparation

  • Position: Supine
  • Provide local anaesthesia
  • Clean and irrigate
  • Ensure adequate lighting
  • Assign assistant if available

Consent:

  • Verbal if patient has capacity
  • Not required if emergency and vision threatened 

9. Technique

Step 1: Anaesthesia

Instill Tertracaine drops.
Infiltrate 1–2 mL lidocaine with adrenaline into lateral canthus, needle directed away from globe 

Step 2: Irrigation

Flush debris with saline.

Step 3: Haemostat Crimp

Crimp lateral canthus to orbital rim for ~1 minute.
This defines incision line and reduces bleeding 

Step 4: Lateral Canthotomy

Make 1–2 cm horizontal incision from lateral canthus toward orbital rim 

Step 5: Inferior Cantholysis

Retract inferior eyelid

Identify inferior crus of lateral canthal tendon visually and by gently strumming it with forceps. It is a slightly taut structure compared to the rest of the tissue around it.

Cut tendon infero-posteriorly

Confirm eyelid laxity 

Step 6: Reassess

Check IOP

Reassess vision and RAPD

If inadequate decompression, divide superior crus in addition

Immediate reduction in pressure is expected, evident by digital tonometry (or instrumental if available)

10. Post-Procedure Care

  • Moist sterile dressing
  • Analgesia
  • Urgent ophthalmology referral
  • Reassess vision and IOP at 30 minutes 
  • Document findings and response

11. Complications

  • Incomplete cantholysis (most common) 
  • Iatrogenic globe injury 
  • Lateral canthotomy
  • Eyelid malposition
  • Lacrimal artery injury
  • Bleeding
  • Infection 
  • Failure to recognise inadequate decompression is a major preventable error.

12. Clinical Outcomes and Evidence

Case literature demonstrates dramatic improvement when decompression occurs early 

Lateral canthotomy

Visual acuity may improve within minutes if ischemia has not become irreversible.

Studies show:

  • Improved outcomes when performed within 2 hours 
  • Emergency physicians frequently delay for CT despite clinical diagnosis 
  • Training gaps contribute to preventable blindness. HALO training directly addresses this gap.

13. HALO Decision Algorithm

Suspected OCS → Assess vision + IOP → High suspicion? → Perform immediately.

Do not wait for:

  • CT imaging
  • Ophthalmology arrival
  • Operating theatre

This is a bedside, vision-saving intervention.

14. Simulation and Training Standards

Simulation objectives:

  • Time to decompression <2 minutes
  • Correct identification of inferior crus
  • Avoid globe injury
  • Appropriate reassessment

15. Key HALO Principles

  • Rare but catastrophic
  • Clinical diagnosis
  • No imaging delay
  • Low morbidity procedure
  • Time equals retina

17. Summary

Lateral canthotomy and cantholysis is a simple, rapid, sight-saving procedure. Orbital compartment syndrome must be diagnosed clinically and treated without delay. The greatest threat to vision is hesitation.

In the HALO framework, mastery of this procedure prevents permanent disability from a rare but devastating emergency.

References

  1. Tintinalli JE et al. Emergency Medicine.
  2. Roberts & Hedges. Clinical Procedures in Emergency Medicine.
  3. ATLS Manual.
  4. Rosen’s Emergency Medicine.
  5. NCBI StatPearls: Lateral Orbital Canthotomy