Cantholysis is a surgical procedure performed after another surgical procedure (canthotomy) to treat ocular compartment syndrome (OCS). OCS is an emergent situation that must promptly be attended to since it can lead to rapid loss of vision if not well-diagnosed and imaging undertaken. OCS occurs in the context of retrobulbar hemorrhage (blood accumulating in the retrobulbar space) with proptosis (displacement of eye) leading to sudden loss of vision. OCS also manifests in afferent defects in the pupil (Marcus Gunn Pupil), severe eye pain, and intraocular pressure (IOP) greater than 40 mm Hg instead of normal IOP (10-21 mm Hg).
The eyelids are held firmly in place by the medial and lateral canthal tendons. The space created by this anatomical arrangement is limited for the globe so that when OCS occurs, elevated intraocular pressure results, forcing the globe against the eyelids. Sometimes canthotomy is not enough to release the globe from its fixed position to treat OCS. Therefore, cantholysis is performed by the severing of the inferior portion.
Speed is of utmost importance since OCS can lead to permanent vision loss within an hour or two of retinal and optic nerve ischemia (short oxygen supply due to restricted blood flow). With OCS, the extraocular muscles responsible for eye movement may be impaired. OCS is caused by retrobulbar hemorrhage from recent orbital trauma, eye surgery, eyelid surgery, and anesthetic injections. Though not common, other causes include spontaneous retrobulbar anesthetic caused by venous anomalies, leukemia, intraorbital aneurysm (excessive localized swelling of the ophthalmic artery), hypertension, von Willebrand disease (blood clot disease), haemophilia (blood collecting in the anterior chamber), and atherosclerosis (fat and cholesterol built-up in the walls of the artery).
Cantholysis can also be performed on patients with cherry-red macula, severe pain in the eye, ophthalmoplegia (eye muscle paralysis), and optic nerve head pallor (whiteness of optic disc and death of optic nerve axons). However, cantholysis should not be performed if the globe is raptured. Hyphema (collection of blood in the anterior chamber), an irregularly shaped pupil, extraocular movement restriction, and exposed uveal tissue are signs of globe rupture.
Preparation & Expectation Before Surgery
The doctor will need to confirm the diagnosis by performing the swinging flashlight test. Next is to establish elevated intraocular pressure using hand-held tonometry (a must). If the pressure exceeds 40 mm Hg, it is an indication that canthotomy and possibly cantholysis should be performed. If there is evidence of a penetrating globe injury, then plans to perform canthotomy and cantholysis must be abandoned. To obtain accurate measurements, IOP is measured several times consecutively.
Types, Purpose & Procedure
Topical anesthetics such as proparacaine and tetracaine are used to help with patient compliance. The anesthetic lidocaine 1% with epinephrine is used since epinephrine helps to constrict (narrow) blood vessels and keep the surgical site clean. The eye is irrigated with saline in case there is any debris to clear.
Once the globe cannot be released from its fixed position via canthotomy, the surgeon proceeds with cantholysis. After the lateral part of the inferior eyelid is lifted to expose the lateral canthal tendon, cantholysis follows. The lateral canthal tendon contains both a superior crus and an inferior crus. Cantholysis aims to cut the inferior crus to relieve intraocular pressure. The surgeon does this by loosening the inferior eyelid to allow the outward expansion of the globe. If need be, the superior crus is also cut to relieve intraocular pressure. Identifying the inferior crus of the lateral canthal tendon may prove to be a challenge. To feel for the inferior crus, the surgeon will use scissors to strum the area. The patient may feel tension meaning the tendon is intact and needs to be cut.
In cantholysis, the surgeon cuts inferoposteriorly toward the lateral rim. The purpose is to avoid injuring nearby structures superiorly like the lacrimal gland, lacrimal artery, and levator muscle. This action completely releases the lateral canthal tendon's inferior crus from its attachment to the lower lid. The lid should fall away from the margin of the lid, and if that doesn't happen, the procedure should be repeated until the tendon is properly released, and the lid has relaxed. If the IOP is still elevated, the surgeon may cut the superior crus to relieve intraorbital pressure further. S/he lifts and exposes the lateral upper eyelid's underside, followed by an incision superoposteriorly. During the incision, the surgeon ensures that the scissors are pointing away from the globe. The procedure provides laxity of the lower eyelid with increased orbital compartment space.
The surrounding tissue is not closed. Instead, the site is lightly covered by gently taping a sterile gauze pad loosely over the region. The area will only be closed when the acute retrobulbar hemorrhage has resolved.
The lateral tarsal strip may also require canthotomy and cantholysis. A new, shorter 'lateral canthal tendon' is created by tying up the tarsus to the orbital rim's periosteum after the lateral canthal tendon's release. This helps to tighten the lower lid and treat entropion and ectropion.
Risks, Side Effects & Complications
Infections, more elevated IOP, and bleeding or hemorrhage can result from the procedure.
One risk involves delay in closing the lower lid which can pose cosmetic challenges. This can later be addressed with minimal scarring. To minimize risks and complications, the surgery should be performed by highly skilled surgeons who have recognized the procedure's indications and contraindications. The right surgeon will avoid the deeper orbital contents and surrounding sensitive structures such as the lacrimal gland, lacrimal arteries, and the levator aponeurosis.
The procedure is performed infrequently and is relatively safe, with minimal risks if appropriately executed.
Complications following cantholysis may include:
- An incomplete cantholysis
- Loss of adequate lower lid suspension
- Ectropion due to extensive cantholysis
- Ptosis caused by a damaged levator aponeurosis (located superiorly)
- Irreversible loss of vision if the retinal ischemia time exceeds 90 minutes
- Iatrogenic globe injury (injury caused by medical examination or treatment)
- Mechanical eye or lid damage such as lacrimal gland, lacrimal artery (located superiorly)
After Care, Recovery & Outcome
Incisions made on the lateral canthus typically heal on their own and exhibit minimal scarring and therefore do not need suturing. The surgeon applies an antibiotic ointment like erythromycin 5% on the site because the patient cannot blink to lubricate the cornea following canthotomy. S/he covers the eye with a sterile dressing to ward off infection.
There may be pain and inflammation for several days after the procedure, and the patient is advised to use ice packs for relief. The patient should also desist from any form of eye strain.
Patients with severe injuries may be admitted to the hospital. Patients with progressive loss of vision may be given methylprednisolone for three days.
Should intraocular pressure remain, systemic and topical therapy can be considered. Topical therapy includes eye drops such as timolol 0.5%, dorzolamide 2%, and brimonidine 0.2%. Systemic therapy can consist of mannitol and acetazolamide.