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How to perform a lateral canthotomy


On a cold, wet January evening, M.J., a 14-year-old boy, walks into the emergency department. Accompanied by his mum and sporting a black eye and facial abrasions, he tells me how he fell from his e-scooter while travelling at approximately 15kph without a helmet. He describes how he fell and struck his face off the ground. He denies any loss of consciousness, and apart from the apparent facial injuries, he denies any other injuries. He denies any headache, and there has been no vomiting. However, he is unable to open his left eye due to swelling.

He has multiple abrasions to the forehead and left temporal region. There is a small laceration in the left eyebrow with significant periorbital bruising. The rest of the examination is unremarkable. Due to significant swelling, examining the globe on the left isn’t easy, but he tells you that he can make out light.

A CT facial bones is performed revealing a left orbital floor fracture with herniation of the contents into the maxillary sinus. The radiologist reports a left retrobulbar haematoma with straightening of the left optic nerve and proptosis.  

After the scan, a relative afferent pupillary defect (RAPD) is noted. It wasn’t there before the scan. M.J. has ocular compartment syndrome and needs urgent intervention. Ophthalmology are contacted and suggest that he needs a lateral canthotomy, The problem, is they are on-call off-site, It’s going to be at least an hour till they can get there and that is one hour too long.

With some trepidation, one of the seniors performs a lateral canthotomy under local anaesthetic. M.J. tolerates the short procedure well, and by the time the ophthalmologist arrives two hours later, the RAPD has resolved, and intra-ocular pressures are normal. There has been no direct damage to the globe, and despite the orbital floor fracture, his eye movements are intact. Even with this injury and subsequent CT findings, there is no immediate threat to his sight, and he should recover fully.

Lateral canthotomy

A lateral canthotomy can be a sight-saving intervention. Although it’s a relatively simple procedure, it may be met with real apprehension. Most of us will be unfamiliar with the steps and may have never seen it performed.  A 2021 study of 45 emergency department physicians in the UK found that 86% of junior trainees had never performed a lateral canthotomy. The procedure is relatively straightforward, and the benefits far outweigh the risks.

What is a lateral canthotomy?

It is the release of the lateral canthal tendon to relieve pressure in the event of an ocular compartment syndrome. Most commonly, ocular compartment syndrome arises due to trauma and subsequent retrobulbar haematoma. These elevated pressures can compress the optic nerve and threaten the patient’s vision if not promptly relieved.

Indications for a lateral canthotomy

  • Proptosis
  • Raised intra-ocular pressure (IOP)
  • Visual loss
  • Relative afferent papillary defect
  • Retrobulbar haematoma

You can detect a RAPD by shining a light directly into each eye and checking the pupillary response. When you shine a light on the unaffected eye, both pupils constrict. However, when light is shone in the affected eye, there will be less constriction of both pupils, indicating a defect in the afferent fibres of that eye.

Special consideration should be given to the unconscious/intubated trauma patient. This cohort is unable to report a new visual loss. Subtle proptosis may be overlooked, and identifying a new RAPD may be challenging if serial examinations are not performed. The retrobulbar haematoma may take time to develop, so maintain a high level of suspicion even if you have normal findings on your initial exam.

Don’t panic if you can’t find the tonometer. You can get a rough impression of the intraocular pressure by gently pressing against the eyeball with a fingertip. One side will feel “wood hard” compared to the unaffected side.

Finally, if your patient has had a CT brain/facial bones performed, don’t forget to look at the orbits. You may be able to spot a retrobulbar haematoma or subtle proptosis.

Once you’ve recognised an ocular compartment syndrome, it is crucial to intervene promptly. It may be tempting to await a specialist ophthalmology review, but this should be avoided. Similarly, the procedure should not be delayed while awaiting imaging.

Performing the procedure

You will need:

  • Chlorhexidine/iodine/sterilizing solution
  • Lidocaine
  • Needle and syringe for injection
  • Mosquito forceps/heamostat
  • Iris scissors
  • Forceps

Note:  Procedural sedation must be used if it’s available.

  1. Clean the area thoroughly.
  2. Inject the lidocaine into the lateral canthus and the inferior orbital rim, aiming your needle away from the globe at all times, down towards the body.
  3. Slide your open forceps between the globe and the tissues at the lateral canthus. Clamping the forceps for one minute at this point will help to reduce bleeding.
  4. Release the forceps and remove them.
  5. Slide your iris scissors into the same location and cut through all the tissues.
  6. Pull the lower lid away using forceps to reveal the lateral canthus tendon. The tendon will look like a white fibrous band. If it cannot be visualized, you will feel its resistance, like a guitar string, with your iris scissors.
  7. Cut through the inferior crus of the lateral canthus tendon in its entirety.
  8. The lower lid should fall away freely.

At this point, reassess the IOP. In some circumstances, the IOP remains elevated; in these cases, you should proceed to cut through the superior crus of the lateral canthus tendon.

Post-procedure notes

Ophthalmology should be consulted for specialist review.

Vision typically returns/improves between 15 minutes and 6 hours post-procedure. The final incision is typically 1 to 2cm in length. Scarring post-procedure is minimal. As this may be a sight-saving intervention, the benefits far outweigh the risk of scarring.

Take home message

Lateral canthotomy is a sight-saving procedure.

The procedure is quick and simple. All necessary equipment can be found in the emergency department.

If an ocular compartment syndrome is diagnosed, do not delay the procedure for imaging or specialist ophthalmology review.


Justin Morgenstern, “Lateral Canthotomy – procedure guide”, First10EM blog, April 1, 2015. Available at:

Lim, Christina S; Malick, Huzaifa; Berry-Brincat, Antonella Emergency canthotomy and cantholysis – Factors affecting confidence among ophthalmic trainees in the United Kingdom, Indian Journal of Ophthalmology: September 2021 – Volume 69 – Issue 9 – p 2385-2388 doi: 10.4103/ijo.IJO_278_21

Max MacBarb, “an approach to lateral canthotomy”, The Moring Report Blog, December 23 2019. Available at:


  • Roy Mc Kenna is an emergency medicine trainee in Ireland with special interests in trauma care, pre-hospital care and human factors in the emergency department. Away from the hospital he spends his time walking his dog Connie, Dublins most adorable Boxer Dog. He/Him/His



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