Source: James W Bonz, MD, Emergency Medicine, Yale School of Medicine, New Haven, Connecticut, USA

Lateral canthotomy is a potentially eyesight-saving procedure when performed emergently for an orbital compartment syndrome. An orbital compartment syndrome results from a buildup of pressure behind the eye; as pressure mounts, both the optic nerve and its vascular supply are compressed, rapidly leading to nerve damage and blindness if the pressure is not quickly relieved.

The medial and lateral canthal tendons hold the eyelids firmly in place forming an anatomical compartment with limited space for the globe. In an orbital compartment syndrome, pressure rapidly increases as the globe is forced against the eyelids. Lateral canthotomy is the procedure by which the lateral canthal tendon is severed, thereby releasing the globe from its fixed position. Often, severing of the lateral canthal tendon alone is not enough to release the globe and the inferior portion (inferior crus) of the lateral canthal tendon also needs to be severed (inferior cantholysis). This increases precious space behind the eye by allowing the globe to become more proptotic, resulting in decompression. Most frequently, orbital compartment syndrome is the result of acute facial trauma, with the subsequent development of a retrobulbar hematoma.

Examination of the patient will reveal a proptotic globe as it strains from the pressure against the tendons anchoring it in place. Patients experience decreased visual acuity and severe eye pain. Patients may develop a relative afferent pupillary defect (RAFD), otherwise known as a Marcus Gunn pupil, and will have increased intraocular pressure (IOP).

1. Confirm need to perform emergent lateral canthotomy.

1. Confirm that an RAFD is present by performing the swinging flashlight test.
2. Swinging flashlight test:
   1. The practitioner first observes both pupils
   2. A light is then directed at the unaffected eye. When this occurs, both pupils (the unaffected and the affected) will constrict in response
   3. The light is then directed toward the affected eye. Both pupils will dilate from their previous constriction (neither pupil will

Orbital compartment syndrome with elevated IOP is associated with a very poor prognosis unless there is immediate intervention. If suspected, emergent decompressive surgery is indicated, as permanent vision loss can result within two hours from the onset of retinal ischemia.

Vision loss and/or change in visual acuity, coupled with elevated IOP, are paramount in making the diagnosis and deciding to act. A relative afferent pupillary defect may be demonstrated, but can occur in a multitude of un