Summary
The presence of strabismus precludes normal visual development in infancy and early childhood, resulting in poor fusion and, in many cases, amblyopia. Quality of life can also be affected, especially as the child grows older. Refractive correction and amblyopia treatment may improve strabismus in some children, so that strabismus surgery is not needed. In other cases, strabismus may persist, worsen, or develop, despite nonsurgical treatments or due to other underlying etiologies. Children with constant or poorly controlled deviations larger than 10 to 12 prism diopters can benefit from strabismus surgery not only to improve the ocular alignment but also to improve the chances of developing or maintaining fusion. Diplopia rarely occurs in young children due to suppression of the deviating eye, while older children may report diplopia if the strabismus is worsening or is of new-onset.
The preoperative evaluation of a patient with strabismus includes a complete sensorimotor examination to determine a diagnosis with a clear plan for treatment, which may or may not include strabismus surgery. If strabismus surgery is planned, the goals and risks of surgery are discussed with the patient’s family and with the patient, if capable of giving assent. In the operating room, patient and surgeon positioning, coordination with the anesthesiologist, and availability of the proper equipment, instruments, and sutures are key factors to ensure as smooth a surgical experience as possible.
The chapters of this section cover the types of strabismus surgery that may be considered in the pediatric population. Overarching information on the goals, advantages, expectations, indications, contraindications, complications, and postoperative care for strabismus surgery is included in this chapter. Information specific to the type of strabismus surgery described is included in each respective chapter.
1 Preparation for Strabismus Surgery
1.1 Goals
The ideal outcome of strabismus surgery is orthophoria in all gaze positions while wearing the appropriate refractive correction to allow development and maintenance of fusion and normal stereoacuity; however, this may not be a realistic surgical outcome in all patients.
Therefore, the goal of strabismus surgery is an improvement of the ocular alignment, in some cases with a small residual deviation within monofixation range that can allow for development of gross fusion and stable long-term alignment.
In some cases, improvement of an anomalous head position is the primary goal of strabismus surgery.
Resolution of diplopia, if present.
1.2 Advantages
Strabismus surgery is a well-studied treatment for children who have persistent strabismus despite nonsurgical treatments, or for whom nonsurgical treatments are unlikely to improve the eye alignment.
Observation can be considered an alternative to strabismus surgery but it does not allow for development or maintenance of fusion in early visual development.
Unlike adults with diplopia due to strabismus, prism glasses are seldom prescribed for strabismus in young children due to suppression and absence of diplopia in most cases.
In most cases, strabismus surgery can result in stable, long-term improvement of alignment with a favorable risk-to-benefit ratio.
Compared to botulinum toxin injection, strabismus surgery is less dependent on the presence of or potential for fusion to achieve a good postoperative outcome; if strabismus recurs after botulinum toxin treatment, strabismus surgery is often considered as the next step. Botulinum toxin injection has its own advantages as an alternative to strabismus surgery and is addressed in Chapter 10.
1.3 Expectations
Safe and effective procedure.
Improvement of ocular alignment.
Improvement of stereoacuity in some patients.
Uncomplicated healing of the operative muscles and conjunctival wounds.
1.4 Key Principles
The extraocular muscles can be weakened, tightened, and transposed using various methods to improve ocular alignment.
Proper surgical technique minimizes bleeding and scarring to allow for uncomplicated wound healing and less complex reoperations, should they be needed.
1.5 Indications
The indications for strabismus surgery in the pediatric age range are:
Abnormal visual development due to strabismus, for which strabismus surgery is performed to increase the chance of normal visual development in early childhood by establishing or re-establishing binocular fusion and treating amblyopia 1 in some patients.
Strabismus affecting quality of life due to its effects on interpersonal relationships, communication, and self-esteem. 2
An anomalous head position due to ocular torticollis from Duane or other dysinnervation syndrome, nystagmus with a null point that is not in primary gaze, 3 or cranial nerve paresis.
Binocular diplopia.
1.6 Contraindications
Most patients can safely undergo multiple strabismus surgeries, keeping in mind the following risks:
Risk of anterior segment ischemia if two or more rectus muscles in one eye have been previously disinserted. Signs of anterior segment ischemia include conjunctival injection, corneal edema, iritis, iris atrophy, corectopia, posterior synechiae, and cataract formation.
Persistent significant misalignment despite multiple strabismus surgeries may indicate that the risks of additional surgery, though low, may actually outweigh the potential benefits, and other treatment options, including observation, may need to be offered. Orbital imaging may be useful in such cases. For example, restriction due to extensive scarring or dysinnervation syndromes with anomalous extraocular muscles may limit the improvement that can be achieved with additional strabismus surgery.
High general anesthesia risk, in which case the decision for surgery is a collaborative decision with the patient’s pediatrician, the anesthesiology team, and the patient’s family. If anesthesia is required for another procedure, an effort should be made to combine procedures to avoid multiple episodes of general anesthesia.
If the patient family’s postoperative expectations do not seem realistic, additional discussion is needed and a second opinion may be offered.
1.7 Preoperative Preparation
A detailed history of the presenting strabismus is obtained, including onset (infantile or acquired), frequency of deviation, fixation preference, and any significant anomalous head position. Older children and teenagers may complain of diplopia. A full past medical history, including the patient’s birth and developmental history, as well as family history of amblyopia and strabismus are obtained. The family may recall a relative with a “lazy eye,” which should be further elaborated.
A complete ophthalmologic examination is performed in the evaluation of strabismus with attention to the sensorimotor examination. The examination begins with testing of stereoacuity and fusion before any dissociation from occlusion during visual acuity and cover testing. Strabismus measurements and visual acuity testing are then performed. If visual acuity testing determines the presence of amblyopia, treatment with refractive correction and/or occlusion therapy may be indicated. In some cases, strabismus surgery that improves eye alignment may also aid in the treatment of amblyopia. 1
The overall appearance of the patient’s eye alignment is observed first. Strabismus measurements are then performed with simultaneous prism cover testing to determine the manifest strabismus, followed by alternate prism cover testing in all gaze positions at distance, and in primary gaze and/or slight downgaze at near. 4 Patterns such as V- or A-patterns may be noted during the measurements and may be correlated to oblique muscle overaction during evaluation of versions. Measurements in right and left head tilt are also performed if a cyclovertical strabismus is present. Additional latent strabismus may be revealed by prism adaptation testing or prolonged cover testing to maximally dissociate the patient. In poorly cooperative patients and young infants, cover testing in only primary gaze at near or corneal light reflex testing with or without prisms may be used to estimate the deviation. Conversely, older children with vertical strabismus and complaints of torsional diplopia, may undergo double Maddox rod testing or Lancaster red-green testing to evaluate torsion. In addition, in older children with possible anomalous retinal correspondence who are at risk of developing early postoperative diplopia, which typically resolves, a loose prism can be used during preoperative testing to demonstrate the type of diplopia they may experience in the early postoperative period to help set expectations.
Versions and ductions are then evaluated with attention to overaction or underaction of the horizontal and cyclovertical extraocular muscles and in more extreme gaze positions than may be examined during prism testing. Forced duction testing can be performed at the time of surgery under anesthesia to confirm suspected restriction as a cause of strabismus and, in some cases, for final surgical planning. During the office examination, the patient’s head position is also observed. An anomalous head position may be due to an incomitant strabismus resulting from Duane syndrome or other dysinnervation syndrome, cranial nerve paresis or palsy, nystagmus with a null point not in primary gaze, and even due to refractive error in some children. The examination then proceeds with dilation of the pupils and cycloplegia to measure the cycloplegic refraction and to perform a fundoscopic examination. If a significant refractive error is found, refractive correction may be warranted before proceeding with strabismus surgery.
Examination findings which indicate a possible systemic or neurologic cause of strabismus should be further investigated with imaging and possibly blood work in coordination with the patient’s pediatrician.
1.8 Surgical Planning
The planning for strabismus surgery and the surgery itself are embodiments of the art of medicine. While uncomplicated cases may have one straightforward approach for treatment, many cases have more than one option for a favorable outcome. The surgery that is performed depends on the preoperative and intraoperative examination findings, as well as the surgeon’s experience.
The subsequent chapters of this section will address in detail the various ways to weaken, tighten, or transpose the extraocular muscles. In some patients with prior ocular surgery or injury, surgery on the extraocular muscles may not always be required; rather, dissection and release of adhesions and scarring around the extraocular muscles may be sufficient to resolve restriction causing the strabismus.
1.9 Perioperative Tips and Pearls
1.9.1 Anesthesia
General anesthesia is required for strabismus surgery, including brief procedures, in pediatric patients. Communication should occur with the anesthesiology team regarding concerns about underlying medical problems including acute upper respiratory infections, a family history of malignant hyperthermia, and preferred preoperative fasting guidelines.5 Child life specialists are also a part of the multimodal approach to prepare the pediatric patient for surgery. Families may ask about concerns for neurotoxicity from anesthesia exposure in young children. At this time, they may be reassured that, while the effects of anesthesia on a child’s development remain unclear, the initial concern was based on animal studies using very high doses of anesthetic agents, and recent human studies are reassuring. 5 In addition, a short duration of anesthesia, which is sufficient for most strabismus surgeries, appears safer than long-duration or repetitive exposures.
A laryngeal mask airway (LMA) may be used in most patients. Some patients with chronic diseases and syndromes may be at increased risk of anesthesia related complications, including difficult airways, hemodynamic instability due congenital heart disease, and metabolic abnormalities, and endotracheal intubation with paralysis may be safer for these patients, 5 as well as for young infants. The distal end of the LMA or endotracheal tube should lie as flat as possible on the patient’s chin and chest, so that it does not tent the surgical drape and remains directed away from the surgical field, decreasing the risk of dislodgement. Propofol anesthesia has the advantage of causing less postoperative nausea, but strabismus surgery in itself increases the risk of nausea. Postoperative pain and nausea may be mitigated by the use of perioperative medications, including ketorolac, dexamethasone, ondansetron, and acetaminophen, in coordination with the anesthesiologist. During surgery, the surgeon should notify the anesthesiologist when traction is to be placed on an extraocular muscle, especially a rectus muscle, to be prepared for potential changes in the heart rate secondary to the oculocardiac reflex. Communication regarding signs that additional anesthesia is needed, based on observations of the patient’s Bell’s reflex or unexpected movement, or when the second eye surgery is about to begin, can also ensure efficiency in the operating room and patient safety.
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