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.
- Confirm that an RAFD is present by performing the swinging flashlight test.
- Swinging flashlight test:
- The practitioner first observes both pupils
- A light is then directed at the unaffected eye. When this occurs, both pupils (the unaffected and the affected) will constrict in response
- The light is then directed toward the affected eye. Both pupils will dilate from their previous constriction (neither pupil will constrict).
- The light is then redirected toward the unaffected eye, and constriction is again confirmed in both pupils.
- Confirm elevated IOP by tonometry. IOP ~40mm Hg is a clear indication for lateral canthotomy
- In the trauma patient, IOP must be measured with a hand-held tonometer. Do not perform this assessment if there is suspicion of a penetrating globe injury.
- Most hand-held devices operate in a similar fashion. They are easy to use and work by pressing the tip of the device against the patient's cornea.
- In the awake patient, topical anesthetic (tetracaine, proparacaine) should be used to help ensure patient compliance. Anesthetic will not alter the accuracy of IOP measurements.
- The tip of the hand-held tonometer is then covered with a protective and disposable cover.
- Hold the unit as a pencil. Brace the heel of your hand against the patient's cheek to maintain stability.
- Approach the cornea perpendicularly, and touch the cornea lightly and briefly.
- Successful measurement is confirmed with a "chirp," and the reading is displayed.
- IOP should be measured several times consecutively to ensure accuracy.
- Once the decision to go forward with surgical intervention is made, it is time to gather supplies.
- Supplies needed: toothed forceps, straight hemostat, iris scissors, anesthetic (lidocaine 1% with epinephrine 1:100,000 is best, as the epinephrine will aid in constricting blood vessels and keep your surgical field clean), small-gauge needle (25 or 27 gauge), syringe, sterile saline, and gauze.
- In order to successfully address an orbital compartment syndrome with surgical intervention, it is important to have a basic understanding of the eye anatomy-specifically, the extraocular anatomy.
- The orbit is the bony, cone-shaped cavity in which the globe rests. It is approximately 4.5 cm deep and is composed of 7 fused bones. Foramina and fissures within this bony architecture allow nerves and blood vessels to supply the globe and its surrounding structures.
- There are 6 extraocular muscles that control the movement of the eye within the orbit. These muscles tether the eye to the orbit, but there is a certain degree of laxity that would permit outward movement of the entire globe if other certain structures were compromised.
- The eyelids (upper and lower) provide protection and nourishing lubrication to the cornea of the eye.
- The upper and lower lid of the eye are held in position medially by the medial canthal tendon, and laterally by the lateral canthal tendon.
- The lateral canthal tendon splits into an inferior and a superior portion (inferior crus and superior crus, respectively) as it moves from lateral to medial
- As with most truly emergent procedures, full sterile precautions are generally not observed. Care should be taken to perform the procedure "cleanly."
- Quickly cleanse the lids and lateral canthus area with gauze soaked with sterile saline. Chlorhexidine should be avoided because of the risk of ocular exposure.
- Draw up 2 mL of lidocaine 1% with epinephrine 1:100,000 in a syringe with a small needle (25 or 27 gauge) attached
- Anesthetize the lateral canthus and overlying skin by injecting the anesthetic with the needle directed away from the globe of the eye.
- The needle will enter the skin at the lateral canthus and just superficial to the epidermis. Inject anesthetic slowly, and advance the needle laterally (still in a superficial plane). As the needle advances, continue to inject anesthetic until the needle tip has advanced approximately 1.5-2 cm laterally.
- Retract the needle back toward the point at which it entered the tissue (lateral canthus), and redirect the needle 45° inferiorly, still keeping the needle in a superficial plane.
- Again advance the needle slowly while injecting more anesthetic. Advance the needle approximately 1.5-2 cm.
- Slide the hemostat over the lateral canthus with one prong deep to the skin and superficial to the orbit and the other over the skin. The tissue is thin at this point, and there is only one plane that the hemostats will dissect as they are advanced.
- Advance the hemostat so that approximately 2 cm of tissue is between the prongs.
- Crush the skin within the hemostat's grasp. This tissue should remain compressed for 1-2 minutes. This helps to minimizing bleeding and leaves a blanched imprint on the tissue where it was crushed by the hemostat. This imprint is used as a guide for cutting in the next step.
- Cut along the compressed tissue, through all layers, from the lateral canthus to the orbital rim.
- This should sever the lateral canthal tendon. Verify this by pulling the upper lid away from the incision; if the tendon is not severed completely, it will be seen and can then be completely cut. The tendon has a shiny white appearance.
- Pull the lower lid away with the forceps.
- Identify the inferior crus of the lateral canthal tendon. It will be identified by its shiny white appearance and anatomical position. Cut with the scissors directed inferiorly (at a 90° angle to the first incision).
- Check the IOP.
- If the IOP remains elevated, then the superior crus may be released as well
- If the superior crus is to be cut, this is completed in much the same manner as above. Use the toothed forceps to pull the upper lid away from the globe and superiorly.
- Superior crus should be visible and identified. Use the Iris scissors to cut through superior crus and completely release the globe.
Lateral canthotomy and inferior cantholysis is a potentially eyesight saving procedure, which is performed to relieve orbital compartment syndrome.
An orbital compartment syndrome, or OCS, results from a buildup of pressure behind the eye - most commonly caused by retrobulbar hematoma. As the pressure rises, both the optic nerve and its vascular supply are compressed, which may rapidly lead to nerve damage and blindness if the pressure is not decreased quickly. In such cases, the emergent procedure of lateral canthotomy-- which involves severing the lateral canthal tendon, and inferior cantholysis -- which is cutting the inferior crus, relieves the elevated pressure by allowing the globe to protrude further and thereby decompressing the retrobulbar space.
In this video, we will review the extraocular anatomy of the eye, the signs, symptoms and diagnosis of OCS, and the indications for lateral canthotomy and inferior cantholysis. We will then present the steps of the procedure and possible complications that one might encounter.
Understanding the extraocular anatomy of the eye is crucial to the diagnosis and treatment of OCS. The globe rests within the orbit , which is a bony, cone-shaped cavity, approximately 4.5 cm deep, and comprised of 7 fused bones. The nerves and blood vessels of the eye pass through the small foramina and fissures in the orbital wall. The six extra-ocular muscles control the movements of the eye. These muscles tether the eyeball to the orbit, but have some inherent laxity.nThe upper and lower eyelids, which protect and lubricate the cornea, are held firmly in position by the lateral and medial canthal tendons. The lateral canthal tendon splits into two limbs known as the inferior and the superior crura. These anterior attachments along with the bony orbit create an anatomical compartment with just enough space for the globe.
Therefore, increased pressure in the retro orbital space, which happens in an OCS, forces the globe anteriorly against the eyelids. And this condition requires immediate treatment, as it can quickly lead to complete vision loss.
Patients with OCS present with these signs and symptoms: severe eye pain, a proptotic - or protruding - globe, decreased visual acuity, Relative Afferent Pupillary Defect, otherwise known as a Marcus Gunn pupil, and an increased intraocular pressure.
The Marcus Gunn Pupil is demonstrated by the Swinging Flashlight Test. To perform this test, first direct the light at the unaffected eye and then at the affected eye, while looking for pupil constriction in both eyes. In the presence of the syndrome, light directed at the unaffected eye will cause both pupils to constrict - the consensual response. But when light is directed towards the affected eye neither pupil will constrict. This phenomenon occurs in diseases or injuries to the optic nerve or retina, where the afferent fibers to the brain are affected. However, the signal for the pupils to constrict is transmitted from the brain through the oculomotor nerve, which is unaffected by these conditions, so the consensual response remains intact. In addition, OCS is confirmed by measuring the intraocular pressure with a hand held tonometer, but this should not be performed if there is suspicion of a penetrating globe injury.
To perform tonometry in an awake patient, first anesthetize the cornea with a topical anesthetic such as tetracaine or proparacaine. This will not affect the pressure measurement and helps to ensure patient comfort and compliance. Next, place a disposable cover over the tip of the tonometer. Then, hold the device like a pencil, and brace the heel of the hand against the patient's skin. Now press the tip of the tonometer lightly and briefly against the cornea until the device chirps and a reading is displayed. Several consecutive measurements greater than 40 mm Hg confirms OCS.
Once diagnosed, the treatment of OCS via lateral canthotomy and inferior cantholysis is an emergency procedure. The first step is to gather the necessary supplies including: sterile gauze, sterile saline, 1% Lidocaine with 1:100,000 epinephrine - to help constrict the blood vessels and keep the surgical field clean, a small syringe with a 25- or 27-gauge needle, toothed forceps, a straight hemostat and iris scissors.
Because of the emergency nature of the situation, the procedure is performed cleanly, but full sterile precautions are generally not observed. Prepare the patient by cleansing the lids and the lateral canthus with gauze soaked with sterile saline. Avoid the use of chlorhexadine because of the risk of ocular exposure.
Next, draw up 2mL of the local anesthetic solution in a syringe and attach a 25 or 27 gauge needle to it.nInject the anesthetic slowly, and gradually advance the needle laterally approximately 1.5 - 2 cm. Then retract the needle to the entrance point and redirect the tip 45° inferiorly. Staying in a superficial plane, again advance the needle about 1.5 - 2 cm while injecting continuously.
Once the patient is anesthetized, slide a hemostat over the lateral canthus with one prong between the skin and the orbit, and the other prong superficial to the skin. Advance the hemostat until there is approximately 2cm of tissue between the prongs. Next, compress the skin with the hemostat for approximately 1-2 minutes to minimize bleeding and to create a blanched imprint on the tissue, which will be used as a cutting guide in the next step. Now pull the skin away from the orbit with the toothed forceps. Then, using the iris scissors, cut through all of the layers along the compressed tissue, from the lateral canthus to the orbital rim. This maneuver should sever the lateral canthal tendon, which can be verified by pulling the upper lid away from the incision. If the tendon, which has a shiny white appearance, is not completely severed, finish the incision under direct visualization.
Next, use forceps to retract the lower lid to visualize the inferior crus of the lateral canthal tendon, which also has a shiny white appearance. Now perform the inferior cantholysis procedure. With iris scissors directed inferiorly at a 90° angle to the first incision, cut the inferior crus. At this point, repeat the measurement of the intraocular pressure. If it is still greater than 40 mm Hg, then the superior crus of the lateral canthal ligament should also be released. To do this, retract the upper lid, identify the superior crus and incise it with the help of iris scissors. Finally, measure the intraocular pressure again to analyze the success of the procedure.
"Potential complications from emergency lateral canthotomy include: bleeding, infection and injury to the surrounding tissue. Globe puncture is possible, but rare. Most importantly, all of these risks are small compared to the risk of possible permanent vision loss from untreated orbital compartment syndrome."
"Following emergent decompression by a non-ophthalmologist, an ophthalmologist should be consulted for follow-up care."
You have just watched JoVE's video on how to perform a lateral canthotomy and inferior cantholysis for the emergency treatment of orbital compartment syndrome. The presentation reviewed the extraocular anatomy of the eye, the diagnosis of this condition, the description of the treatment technique and the possible complications. As always, thanks for watching!
Applications and Summary
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 unilateral diseases of the retina and optic nerve.
The swinging flashlight test works because the retina is compromised (from ischemia) and the afferent fibers within the optic nerve are compressed in an orbital compartment syndrome. The injured eye does not react to the light because the afferent fibers are unable to carry the signal away from the eye toward the brain. When the light is directed into the uninjured eye, however, the afferent fibers carry the signal away from the eye to the brain, which directs the motor response of constriction to both eyes (consensual response); this response is conducted through efferent fibers within the oculomotor nerve.
If an orbital compartment syndrome is decompressed by the non-ophthalmologic practitioner in emergent conditions, an ophthalmologist should be consulted. Complications from performing an emergent lateral canthotomy include bleeding, infection, and injury to the surrounding tissue. Globe puncture is a rare but potential complication. All of these risks are considered small in the face of imminent and permanent vision loss from an untreated orbital compartment syndrome.