What Is Strabismus? What Is Amblyopia?

Strabismus is the misalignment or deviation of the eyes. The prevalence in children ranges from 2% to 7%. This misalignment can be associated with diplopia, decreased vision, and headaches. Neonatal strabismus usually resolves by three months of age. Strabismus found in school age children is considered aberrant and usually warrants an evaluation. A general understanding of the more common diagnosis will facilitate this discussion. Esotropia is the inward deviation of the nonfixed eye. Exotropia is the outward deviation of the non-fixed eye. Hypertropia is an upward vertical deviation of the nonfixed eye while hypotropia is defined as the downward vertical deviation of the non-fixed eye.

Amblyopia or lazy eye is defined by decreased vision in an eye when it fails to work properly with the brain. It is commonly caused by strabismus and usually treated with patching or through the use of atropine eye drops, which blur vision in the stronger eye forcing a child to predominantly use the weaker eye.

Given the FDA’s Concerns with Neurodevelopment, Is It Imperative to Correct Strabismus at This Time or Could This Case Be Considered Elective and Be Performed When the Child Is Older?

While the FDA’s concerns on anesthetic neurotoxicity continue to be debated, it is imperative that this child receives treatment in the form of corrective lenses, pharmacologic aids, or surgical correction. Visual maturity usually occurs through age five and this must be weighed when deciding on corrective action. The primary reason for surgically correcting strabismus at an early age is to restore binocular vision to maintain visual acuity, to improve depth perception, and to eliminate double vision. Earlier correction may prevent amblyopia and visual loss given the higher risk children with strabismus pose. This is further supported by evidence that the duration of the misalignment is a major predictor of the outcome.

What Are Considerations Associated with the Preoperative Assessment in Children Presenting for Strabismus Repair?

Strabismus surgery remains quite common in pediatric ophthalmology practice. While most children with strabismus are healthy, the preoperative assessment should attempt to elucidate coexisting syndromes. This can include cerebral palsy, craniofacial syndromes, neurofibromatosis, and hydrocephalus. Outside of that, the risk of postoperative nausea and vomiting should also be discussed.

How Will You Secure the Airway in This Patient?

Several options are available for airway management during strabismus repair, including a supraglottic airway (SGA) or tracheal intubation. When using an SGA, it is most convenient for the surgeon if a flexible shaft is used, that can be secured to the chin. If tracheal intubation is chosen, an oral RAE tube should be used, when available, for the same reasons to facilitate the surgical approach.

How Will You Maintain General Anesthesia?

Inhaled anesthesia with volatile anesthetics, total intravenous anaesthesia (TIVA) with propofol, or a combination of both can be used for strabismus surgery. The use of propofol may decrease the risk of postoperative nausea and vomiting (PONV). Since these surgeries are at a relatively higher risk of OR fires because of the proximity to the airway, a low FIO₂ (<30%) should be maintained. PONV is discussed in detail in Chapter 5.

After Induction, the Surgeon Informs You that She Would Like to Perform a Forced Duction Test and Would Like Paralysis. What Is a Forced Duction Test and What Is Its Purpose? Is Succinylcholine an Appropriate Choice for This Patient?

The forced duction test (FDT) tests ocular muscle range of motion to differentiate between a mechanical or paralytic etiology for the strabismus. Surgeons may request nondepolarizing muscle relaxants to have the muscles completely relaxed, but this seems rare in practice. Use of succinylcholine should be avoided as it may result in erroneous information obtained during the FDT potentialy altering surgical management.

Is There a Malignant Hyperthermia (MH) Risk Associated with Strabismus Repair? What about Masseter Muscle Spasm?

By most accounts, the answer is that no correlation exists between malignant hyperthermia (MH) and patients undergoing strabismus repair. A review of MH susceptibility in over 2,500 patients revealed no association between MH and strabismus. When looking at masseter spasm, children with strabismus have traditionally had a fourfold higher incidence when compared to children without strabismus following a single exposure to succinylcholine. However, given the difficulty in diagnosing masseter muscle spasm and the lack of objective findings associated with this disorder, an association between strabismus and masseter spasm remains difficult.