Strabismus is recommended for surgery when it does not improve with glasses, eye patches, prisms, or vision therapy. Strabismus surgery is a very safe and effective procedure. However, complications can occur with any surgical procedure.
The risk of serious vision-threatening complications is particularly low. 1) The estimated incidence of serious complications (scleral perforation, severe infection, muscle slip/loss, scleritis) is 1 in 400, of which poor prognosis is reported in 1 in 2,400. 2) Most complications are minor and resolve spontaneously or with topical medication. 1)
The reoperation rate varies by disease but is generally reported to be 20-30%.
Complications are broadly classified into the following three categories based on the time of occurrence.
Intraoperative complications: scleral perforation, oculocardiac reflex, lost or slipped muscle, wrong-site surgery, etc.
Early postoperative complications: postoperative infection, corneal dellen, anterior segment ischemia, allergic reaction, etc.
Late postoperative complications: overcorrection/undercorrection, pyogenic granuloma, conjunctival inclusion cyst, surgically induced necrotizing scleritis, etc.
QHow often do complications of strabismus surgery occur?
A
The estimated incidence of serious complications (scleral perforation, severe infection, slipped/lost muscle, scleritis) is 1 in 400, and among these, poor prognosis occurs in 1 in 2,400. 2) Many complications are minor and resolve spontaneously or can be managed with local treatment. 1)
Oculocardiac reflex: Sinus bradycardia is most common. Hypotension, arrhythmia, and asystole may also occur. 6) Can be prevented with atropine or glycopyrrolate.
Lost muscle: The medial rectus has no connections to other muscles and is easily retracted deep into the orbit. Incidence in adults 1/14,000. 2)
Causative organisms of postoperative infection: Staphylococcus aureus (MRSA/MSSA), Group A Streptococcus, coagulase-negative staphylococci.
Signs: Increased discharge after postoperative day 2, conjunctival edema, eyelid swelling, pain.
Findings of anterior segment ischemia: Corneal edema, Descemet membrane folds, moderate mydriasis. Can occur even with two rectus muscle surgery in elderly patients or those with vascular disorders.
Muscle slippage/stretched scar: May develop several years after surgery.
Retinal detachment: Adults are at higher risk than children due to liquefied vitreous.
Adherence syndrome: Orbital fat prolapse and restrictive strabismus due to Tenon capsule damage.
Eyelid deformity: Lower eyelid deformity after inferior rectus or inferior oblique surgery. 2)
Summarize the incidence of major complications.
Complication
Incidence
Postoperative infection (cellulitis)
1/1,100 to 1/1,900
Lost muscle
1/4,500 (adults)
Anterior segment ischemia
1/6,000
Endophthalmitis
1/30,000 to 1/185,000
QWhat happens when the oculocardiac reflex occurs?
A
Vagal nerve stimulation from extraocular muscle traction causes bradycardia and hypotension. The incidence is as high as 67.9%, but it usually resolves when the manipulation is stopped. 6) Cardiac arrest occurs in only 0.11%. 7) If it occurs frequently, intravenous atropine is administered.
The main risk factors for each complication are listed.
Scleral perforation: high myopia (scleral staphyloma), reoperation, posterior fixation suture. When the sclera is thin due to high myopia, multiple surgeries, or after retinal detachment surgery.
Lost or slipped muscle: The medial rectus and inferior rectus have short arcs of contact. Muscle stiffness or shortening (thyroid eye disease) also increases risk.
Postoperative infection: Young patients (especially with developmental delay), history of skin or ear infections.
Anterior segment ischemia: Simultaneous surgery on three or more muscles, elderly, vascular disorders, limbal incision. 2) It is recommended to avoid operating on three or more rectus muscles simultaneously.
Corneal dellen: Reoperation or transposition surgery, abnormal tear secretion. 3)4)
Oculocardiac reflex: Incidence tends to decrease with age.
Allergic reaction: History of hypersensitivity, systemic allergies, asthma.
Patients on anticoagulants: Many surgeons do not routinely discontinue them, but there is a risk of bleeding.
QDoes the risk increase with strabismus reoperation?
A
In reoperation, the risks of conjunctival scarring, scleral perforation, and corneal dellen increase. 3)4) There are reports that muscle slippage was observed in 10.6% of revision surgeries. The reoperation rate is generally 20–30%, and explanation before the initial surgery is important.
Postoperative infection: Suspect based on conjunctival injection, eyelid erythema/swelling, discharge, eye pain, fever, photophobia. Use MRI/CT to differentiate preseptal cellulitis from orbital cellulitis.
Anterior segment ischemia: Diagnose by findings of corneal edema, Descemet membrane folds, and moderate mydriasis.
Overcorrection/Undercorrection: Evaluate with postoperative ocular alignment testing. May occur at multiple stages including errors in strabismus angle measurement, intraoperative quantification, and suture placement.
Fundus examination under dilated pupil → If retinal tear is present, perform laser photocoagulation.
In children, no treatment is often necessary. In adults, laser photocoagulation is performed.
Retinal cryopexy is not recommended.
In cases with thin sclera, the hang-loose technique is chosen.
Oculocardiac reflex: Stop the maneuver → usually recovers. If frequent, administer intravenous atropine sulfate.
Lost muscle:
Attempt retrieval promptly during the same surgery.
If under local anesthesia, switch to general anesthesia for the procedure.
Search with the eye in adduction.
The lateral rectus and inferior rectus can be found by following their connective tissue attachments to adjacent muscles. The medial rectus is difficult to secure.
If retrieval is impossible, perform a muscle transposition procedure.
Slipped muscle: Trace the fascia posteriorly, locate the muscle, and reattach it.
Corneal dellen: Resolves within a few days with corneal surface protection using eye ointment.
Pyogenic granuloma: Topical steroid administration → if no response, perform surgical excision.
Conjunctival inclusion cyst: Surgical removal is required. Drainage alone leads to recurrence.
Allergic reaction: Change antibiotic eye drops and use topical steroids and antihistamines.
Overcorrection/Undercorrection: Managed with additional strabismus surgery. 2)
Eyelid deformity: If persistent, perform eyelid surgery. 2)
QWhat should be done if a muscle is lost during surgery?
A
Attempt to retrieve it promptly during the same surgery. If the surgery is under local anesthesia, switch to general anesthesia for management. The medial rectus muscle is prone to being pulled deep into the orbit due to lack of connective tissue with other muscles, making retrieval difficult. If retrieval is impossible, choose a muscle transposition procedure.
The mechanisms of each complication are described below.
Mechanism of scleral perforation: The suture needle penetrates the sclera, forming a chorioretinal scar.
Mechanism of oculocardiac reflex: Traction on extraocular muscles → trigeminal nerve stimulation → vagus nerve → bradycardia/cardiac arrest. 6)
Mechanism of lost muscle: The muscle tendon slips off the suture or instrument and retracts posteriorly into the orbit.
Mechanism of muscle slippage: Only the superficial fascia is fixated → the muscle belly retracts during contraction → presents as clinical muscle weakness.
Mechanism of anterior segment ischemia: Because the anterior ciliary arteries run within the rectus muscles, simultaneous surgery on multiple rectus muscles can cause blood flow impairment.
Iatrogenic Brown syndrome: After superior oblique tuck surgery, limitation of elevation in adduction may occur. This can be prevented by performing an intraoperative superior oblique traction test to determine the amount of tuck. If improvement is not seen, reoperation to loosen the superior oblique tuck is necessary. Elevation deficit may also occur after inferior oblique surgery, caused by adhesions from orbital fat exposure during inferior oblique manipulation or excessive anterior displacement of the inferior oblique muscle.
Mechanism of fat adherence syndrome: Tenon’s capsule injury → orbital fat prolapse → restrictive strabismus.
Mechanism of conjunctival inclusion cyst: During surgery, conjunctival epithelium becomes buried under the conjunctiva and forms a cyst.
Mechanism of corneal dellen: Postoperative irregularity of the ocular surface → abnormal tear film distribution → corneal thinning.
Mechanism of stretched scar: The suture site stretches → the muscle belly moves posteriorly → muscle action weakens.
7. Latest Research and Future Perspectives (Investigational Reports)
A 2025 retrospective study reported that prescribing postoperative antibiotic eye drops did not reduce infection rates. Further investigation is needed regarding the necessity of antibiotic eye drops for postoperative infection prevention.
It has been reported that using ketamine as the main anesthetic reduces the oculocardiac reflex, postoperative nausea and vomiting, and postoperative agitation. Improved anesthesia management is expected to reduce the risk of complications.
In some cases, chemical denervation by botulinum toxin injection has been reported to be effective for strabismus correction. Research is progressing as an alternative to surgical procedures.
