Lateral Orbital Canthotomy 

Orbital compartment syndrome is an ocular emergency whose prompt diagnosis and treatment are essential to prevent blindness. Because the orbit is a relatively closed compartment with limited ability to expand, orbital pressure can rise rapidly when an acute rise in orbital volume occurs. Untreated, orbital compartment syndrome results in ischemia of the optic nerve and retina. For more information, see eMedicine article Acute Orbital Compartment Syndrome.

The most common etiology of orbital compartment syndrome is retrobulbar hemorrhage from trauma, recent retrobulbar anesthesia, or eyelid surgery. Spontaneous retrobulbar hemorrhage due to venous anomalies, atherosclerosis, intraorbital aneurysm of the ophthalmic artery, hemophilia, leukemia, von Willebrand disease, and hypertension has also been described. Other less common causes of orbital compartment syndrome include orbital cellulitis, orbital abscess, tumors, orbital emphysema, and inflammation.

Patients with increased orbital pressure present with pain, decreased vision, diplopia, limited extraocular movements, proptosis, ecchymosis around the eye, bloody chemosis, increased intraocular pressure (IOP), resistance to retropulsion, and an afferent pupillary defect.

The lateral and medial canthal tendons attach the eyelids to the orbital rim and limit any anterior displacement of the globe.^[1] Orbital pressure can be relieved with an emergent lateral canthotomy and inferior cantholysis.^[2] Without decompression, irreversible vision loss due to increasing orbital pressure may occur in as little as 90-120 minutes.^{[3, 4]} Knowledge of this potentially sight-saving procedure is important for clinicians, especially those in remote areas where access to ophthalmologists is not readily available.^[5]

Absolute indications for lateral canthotomy include retrobulbar hemorrhage resulting in acute loss of visual acuity, increased IOP, and proptosis.^[6] In the unconscious or uncooperative patient, an IOP greater than 40 mm Hg is an indication for lateral canthotomy (normal IOP is 10-21 mm Hg).^[7]

Lateral canthotomy may also be considered in patients with retrobulbar hemorrhage along with any of the following: afferent pupillary defect, ophthalmoplegia, cherry-red macula, optic nerve head pallor, and severe eye pain. However, these findings are subjective, less reliable, and nonspecific. A CT scan of the orbit may help to clarify the diagnosis.^[8]

Suspected globe rupture is a contraindication to lateral orbital canthotomy. Signs of globe rupture include hyphema; a peaked, teardrop-shaped, or otherwise irregularly shaped pupil; exposed uveal tissue, which appears reddish-brown; and extraocular movement restriction that is greatest in the direction of the rupture. Subtle signs of globe rupture include subconjunctival hemorrhage, enophthalmos, or a conjunctival laceration. For more information, see eMedicine article Globe Rupture.

Local anesthesia (lidocaine 1-2% with epinephrine) is injected into the lateral canthus.

Equipment needed for the procedure includes the following:

• Sterile gloves, face shield, gown (if desired)
• Lidocaine 1-2% with epinephrine
• Syringe with 25-gauge needle
• Sterile drapes
• Normal saline for irrigation
• Straight hemostat
• Sterile iris or suture scissors
• Forceps

Although the head should be initially elevated to help decrease IOP, the patient must be moved into the supine position and must be able to fully cooperate during the procedure itself. Unexpected patient head movement can result in iatrogenic injury, including accidental globe puncture. To accomplish this, the patient may need to be restrained, undergo conscious sedation, or even be intubated and paralyzed, depending on the situation.

• Provide adequate anesthesia by injecting 1 mL of lidocaine 1-2% with epinephrine into the lateral canthus. Direct the needle tip toward the lateral orbital rim and begin injecting when the needle touches bone. The combination of lidocaine with epinephrine assists with hemostasis and local anesthesia.
• Confirm the affected eye and perform a repeat inspection, noting the typical findings of unilateral proptosis, an afferent pupillary defect, decreased visual acuity, and an intraocular pressure (IOP) of 40 mm Hg or higher.
• Irrigate the eye with normal saline to clear away debris that may enter the eye or interfere with the procedure.
• Use a straight hemostat to crimp the skin at the lateral corner of the patient's eye. Crimp the skin all the way down to the orbital rim for 1-2 minutes. This crimp functions to achieve hemostasis and to mark the location where the incision is to be made. See video below.

  Crimping the lateral orbital canthus to mark where to cut the skin.
• Use forceps to pick up the skin around the lateral orbit.
• Use the scissors to make a 1-2 cm incision beginning at the lateral corner of the eye and extending laterally outward. See video below.

  Cutting the lateral orbital canthus.
• This incision decreases some pressure but is often insufficient alone; therefore, proceed to cantholysis.
• Retract the inferior lid downward to visualize the lateral canthus tendon.
• With the scissors directed along the lateral orbital rim (pointing away from the globe), dissect the inferior crux of the lateral canthus tendon and cut it. See video below.

  Cutting the inferior canthal ligament.
• If this procedure is insufficient (ie, IOP remains >40 mm Hg), cut the superior portion of the lateral tendon by dissecting superiorly before cutting it. See video below.

  Verifying laxity of the lateral canthus and inferior canthal ligament after cutting.

A few key points to keep in mind include the following:

• Lateral retraction of the tissue by an assistant during manipulation decreases the chance of a globe injury.
• When cutting the canthal ligament, aim inferoposteriorly toward the lateral rim;^[9] this helps to avoid injury to the levator muscle, lacrimal gland, and lacrimal artery, which are located in the upper lid.^[6]
• Despite high intraorbital pressures, only a small amount of blood is usually expressed with the release of the hematoma.^[10]
• Successful inferior cantholysis results in the lower lid becoming completely mobile as it loses its attachment to the lateral orbital wall and is easily pulled away from the lid margin.^{[6, 11]}
• Tonometry and globe palpation are contraindicated in patients with an open globe injury.
• A successful procedure is marked by improved visual acuity, resolution of a previously detected afferent pupillary defect, and decrease in IOP to below 40 mm Hg.^[12]
• Always seek emergent consultation with an ophthalmologist when this procedure is performed.

The afferent pupillary defect, or Marcus Gunn pupil, is tested using the swinging flashlight test. The test is positive when the affected pupil dilates in response to light (the other normal pupil also dilates when light is shone in the affected eye). Both pupils constrict when the light is shone in the normal eye. The Marcus Gunn pupil results from injury to the afferent fibers of cranial nerve II of the defective eye, while the efferent signals from cranial nerve III of the normal eye are uninjured.

For more information, see eMedicine article Neuro-Ophthalmic Examination.

Complications include iatrogenic globe injury by forceps or scissor tips; ptosis due to damage to the levator aponeurosis which is located superiorly;^[13] and injury to the lacrimal gland and lacrimal artery, which also lie superiorly. Less common complications include bleeding and infection. Extensive cantholysis may result in ectropion.^[10] Irreversible vision loss can occur if retina ischemia time is greater than 90-120 minutes.