Strabismus surgery is a procedure to adjust the position of the extraocular muscles. Because traction on the extraocular muscles causes significant discomfort and the surgery is lengthy, it is generally performed under general anesthesia.
In adults at high risk for general anesthesia, local anesthesia may be chosen. Retrobulbar anesthesia, sub-Tenon’s anesthesia, and topical anesthesia are alternatives. For unilateral surgery in adults, retrobulbar or peribulbar anesthesia with sedation, or even topical anesthesia alone, may be feasible1). However, general anesthesia is recommended for reoperations, complex cases, bilateral surgery, and prolonged procedures1).
The choice of anesthesia method should consider the patient’s age, general condition, surgical complexity, duration, and whether the surgery is unilateral or bilateral.
This section describes symptoms and findings that appear as complications of anesthesia related to strabismus surgery.
The main symptoms that patients may experience related to anesthesia are as follows.
Risk factors for anesthesia complications in strabismus surgery vary depending on the anesthesia method.
The following risk factors have been reported for secondary strabismus after retrobulbar or peribulbar block1).
Malignant hyperthermia was previously considered a contraindication for general anesthesia in strabismus surgery. However, with appropriate preoperative planning, general anesthesia is now feasible. Measures such as avoiding trigger agents (succinylcholine, inhalational anesthetics) are necessary.
This section describes preoperative evaluation related to the choice of anesthesia. “Diagnosis” includes identification of anesthetic complications.
Many strabismus surgeons perform surgery without discontinuing anticoagulants 1). However, in some cases, temporary discontinuation may help reduce bleeding. The decision to discontinue should be made in consultation with the prescribing physician, and bridging therapy may be considered if necessary 1).
This section describes the indications, procedures, and precautions for each anesthesia method.
This is the standard anesthesia method for children and adults who can tolerate the risks of general anesthesia.
Contraindications and precautions for inhalation anesthetics are as follows:
| Drug | Contraindication/Precaution |
|---|---|
| Halothane | History of unexplained liver disorder |
| Isoflurane | Severe asthma/bronchospasm |
| Sevoflurane | Renal impairment |
This is a useful local anesthesia method as an alternative to retrobulbar block in strabismus surgery.
This is an option for adult monocular surgery when general anesthesia is difficult, but it is rarely used in strabismus surgery. The main concern is anesthetic myotoxicity due to accidental injection into the extraocular muscles. It can cause segmental fibrosis and muscle hypertrophy, leading to postoperative diplopia and strabismus1)2).
Retrobulbar block solution is usually a mixture of 2% lidocaine and 0.75% bupivacaine. Adding hyaluronidase increases the success rate of akinesia and reduces the need for additional injections.
Complications include retrobulbar hemorrhage, globe perforation, optic nerve injury, extraocular muscle injury, and anesthetic spread to the central nervous system2). Compared with peribulbar block, there is no difference in efficacy, but conjunctival edema is more common with peribulbar block, and eyelid hematoma is more common with retrobulbar block2).
General Anesthesia
Indications: Children, adults with poor cooperation, reoperations, complex cases, bilateral surgery
Advantages: Reliable immobilization and pain control
Cautions: Postoperative nausea and vomiting, complications of tracheal intubation
Sub-Tenon's Anesthesia
Indications: Cooperative adult cases
Advantages: Low risk of perforation and bleeding, reduces oculocardiac reflex
Cautions: Chemosis, rarely orbital hemorrhage
Topical Anesthesia
Indications: Simple cases in adults, when intraoperative eye position assessment is needed
Advantages: Minimally invasive, no risk of retrobulbar hemorrhage
Cautions: No akinesia, patient cooperation essential
General anesthesia is standard for children because cooperation during surgery is difficult. Both local and general anesthetics can be safely used in children with weight-based dosing and careful monitoring.
Local anesthetics used in retrobulbar and peribulbar anesthesia (especially bupivacaine) can cause myotoxicity if accidentally injected into the extraocular muscles.
Bupivacaine inhibits NMDA receptors and sodium channels, while lidocaine blocks sodium channels to prevent nerve depolarization. Direct contact of these drugs with extraocular muscles leads to progressive segmental fibrosis and muscle hypertrophy1).
The clinical course is biphasic. Initially, transient muscle paralysis occurs, followed by progressive deviation of the eye in the direction of action of the affected extraocular muscle1). The superior and inferior rectus muscles are most commonly injured during retrobulbar and peribulbar blocks, but the superior and inferior oblique muscles can also be affected1).
Traction on the extraocular muscles stimulates the ophthalmic branch of the trigeminal nerve (V1) as the afferent pathway, forming a reflex arc with the vagus nerve as the efferent pathway. This results in bradycardia, arrhythmias, and rarely cardiac arrest. Sub-Tenon’s injection of bupivacaine has been reported to reduce the incidence of the oculocardiac reflex compared to saline.
Inhalational anesthetics induce neural inhibition by enhancing signaling at GABA receptors and potassium channels. The exact mechanism is not fully understood and is still under investigation.
Induction agents (propofol, thiopental, etomidate) and volatile anesthetics (halothane, desflurane, sevoflurane) lower intraocular pressure. In patients with chronic hypotony, the choice of anesthesia may affect intraoperative and postoperative outcomes.
Injection of bupivacaine into the extraocular muscles is being studied as a pharmacological approach to treat strabismus by utilizing its myotoxicity. This is an attempt to intentionally use myotoxicity, previously recognized as a complication, to achieve selective weakening of the extraocular muscles.
In adult strabismus surgery, the use of adjustable sutures is becoming more widespread 1). Under topical anesthesia or sub-Tenon’s anesthesia, the suture position can be fine-tuned while evaluating eye alignment during and after surgery, so research is progressing on optimizing the combination of anesthesia and surgical technique.
