Options in Strabismus
Valerie M. Kattouf
Treatment of strabismus in the pediatric population requires a careful analysis of the diagnostic data. Consideration of the patient’s age at presentation, age of onset of strabismus, refractive error, magnitude of deviation, and fusional ability will aid in determining the best treatment option for the patient. Multiple options are available for treating strabismus in the pediatric population. This chapter reviews the most commonly used methods of treatment including surgical referrals, spectacle options, orthoptic treatment, and occlusion.
As with all diagnoses, it is important to determine the goal of the patient and parent in regard to treatment. When treating strabismus in the pediatric population, the greatest concern is often the improvement of the cosmetic nature of the strabismus. The cosmesis of a strabismic deviation has a very significant role in the psychological and motor development of a child. A literature review by Groffman (1) revealed that the face and eyes are the most important parts of the body in revealing personality. A strabismic deviation makes a child feel abnormal or different. The recognition of the strabismus by other children usually occurs around the age of 3 years. The negative attention often causes the child’s personality to adjust by either becoming shy and withdrawn or acting out to attract attention. A study by Fletcher and Silverman (2) revealed that, in strabismic patients, different personality characteristics and developmental issues arise at different stages of development. From 6 months to 5 years, behavioral problems and gross and fine motor delays are often evident. From 5 to 10 years of age, learning and attention issues often present. The cosmesis of a strabismus often causes a reaction in parents as well. Mothers often respond with an anxiety that may often be communicated to the child. For these reasons, we must address the cosmetic as well as the functional cure of strabismus at the appropriate age.
Treatment Options
Stabismus Surgery
Strabismus surgery is a medical treatment modality that often leaves optometrists fearful and suspicious. When the proper comanagement relationship is developed with a pediatric ophthalmologist, strabismus surgery is a valid and useful treatment option for young patients with the proper diagnostic and clinical characteristics. Strabismus surgery is often considered when the deviation is cosmetically apparent and not manageable by optical or orthoptic treatment. Strabismus surgery is also used if the patient is too immature for treatment with nonsurgical methods, or if the deviation is very large.
Strabismus surgery usually entails an extraocular muscle recession, resection, or a combination of procedures. The decision to perform the surgery unilaterally or bilaterally depends on the nature of the deviation and the
associated conditions. The three most common surgical procedures are extraocular muscle recessions, resections, and myectomies. A muscle recession weakens the muscle. This procedure disinserts the extraocular muscle and reattaches it further back on the globe. A resection strengthens the eye muscle. This procedure excises a portion of the distal end of the muscle and then reattaches it to the globe. A myectomy is also a weakening of the muscle. The procedure produces a weakening effect by excising a portion of the muscle belly. These terms are summarized in Table 21.1 (3). Common strabismic diagnoses and the most utilized surgical techniques for each are listed in Table 21.2 (2).
associated conditions. The three most common surgical procedures are extraocular muscle recessions, resections, and myectomies. A muscle recession weakens the muscle. This procedure disinserts the extraocular muscle and reattaches it further back on the globe. A resection strengthens the eye muscle. This procedure excises a portion of the distal end of the muscle and then reattaches it to the globe. A myectomy is also a weakening of the muscle. The procedure produces a weakening effect by excising a portion of the muscle belly. These terms are summarized in Table 21.1 (3). Common strabismic diagnoses and the most utilized surgical techniques for each are listed in Table 21.2 (2).
Table 21.1 Strabismus Surgery Key Words | ||||||
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Determination of which extraocular muscles are to be operated upon and the age at which the surgery is performed is made on a case-by-case basis. The two most common clinical characteristics of strabismus that require surgical correction are deviations with a large magnitude and high frequency. Caloroso and Rouse (4) developed guidelines regarding the need for surgical correction in strabismic patients. They determined that when a patient’s deviation measured with best correction is greater than 20 prism diopters of esotropia, 25 prism diopters of exotropia, and 10 prism diopters of vertical tropia, surgical treatment should be considered (Table 21.3). Associated conditions (e.g., amblyopia, central nervous system disorders) and previous treatment history all affect the decisions made by the referring optometrist and the operating ophthalmologist. Young patients are often excellent candidates for a surgical correction. The goal of strabismus surgery in an infant or toddler is to maximize the patient’s potential for sensory fusion development and to improve the motor fusion for a cosmetic cure.
Table 21.2 Strabismus Causes and Surgical Techniques | ||||||||||||||||||||
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When determining the success of a strabismus surgery, two different criteria are evaluated, the cosmetic versus the functional cure. Cosmetic cures can most easily be defined as a strabismus that is undetectable to the untrained eye. A recent study defined a strabismic angle evident to lay observers to be 8 to 12 prism diopters in exotropia and 12 to 15 prism diopters in esotropia (5). Determination of a functional cure
in strabismus varies throughout the literature. The most frequently used criteria include no strabismus at any distance by cover test, presence of motor fusion ranges at distance and near, and demonstration of sensory fusion (6). Table 21.4 contains a summary of cosmetic and functional cures.
in strabismus varies throughout the literature. The most frequently used criteria include no strabismus at any distance by cover test, presence of motor fusion ranges at distance and near, and demonstration of sensory fusion (6). Table 21.4 contains a summary of cosmetic and functional cures.
Table 21.3 Magnitude of Strabismus Deviation Necessary for Surgical Correction | ||||||||
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Table 21.4 Summary of Postsurgical Cures for Strabismus | |||||||||||||||
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In infantile strabismus, the practitioner and the parent must address specific goals to determine the need for a strabismus surgery. For example, a low percentage of infants with esotropia have a functional cure, whereas a high percentage will have a cosmetic cure (7). The longer the misalignment is left untreated, less is the chance for development of sensory fusion in a very young patient. In the infant and toddler population, surgical candidates fall into three main categories.
Patients with early onset, large-angle, constant deviations with a significant cosmesis that is not improved by refractive correction and may put the child at risk for amblyopia development.
Patients with large-angle, intermittent deviations with whom motor and sensory fusion is present when the patient is aligned. Surgical correction allows a higher frequency of fusion. These patients are excellent candidates for a surgical correction that can be followed with orthoptic training and prism correction as the child matures.
Patients whose parents have the sole goal of improving cosmesis.
The greatest concerns of a parent in regard to a child having strabismus surgery are the health risks. The highest level of concern in the pediatric population is that of the anesthesia risk. Although minimal, the risk in children under the age of 7 years is greater than in adults. The overall mortality rate of strabismus surgery is 1.4 per 10,000 (8). Other possible, but extremely rare, complications from strabismus surgery include vomiting, orbital cellulitis, suture abscess, transient changes in refractive error, and diplopia.
Relieving Prism Treatment
Relieving prism is a treatment option to consider for pediatric patients with strabismus. Successful use of prism involves selection of the patient with the proper diagnostic criteria. Patients who are the most successful with prism are those who are capable of central fusion. For example, a very early onset, constant strabismic deviation develops significant sensory anomalies that do not permit central fusion.These patients are not proper candidates for relieving prism treatment. Patients with intermittent deviations, adequate sensory fusion, and poor motor control are aided by relieving prism treatment. The goal of such treatment is to reduce, not to eliminate, the motor fusional demand. The residual deviation that a practitioner hopes to create when using relieving prism differs with the direction of the deviation. For an esotropia, it is 4 to 6Δ eso; for exotropia, 10 to 15Δ exo; and for vertical deviations, it is 2 to 4Δ hyper (9).
In a pediatric population, the examiner may have to make prism prescribing decisions without the aid of subjective testing. In addition to a lack of testing choices, a young patient may not be capable of maintaining fixation that can be held through multiple cover testing procedures. In these instances, the amount of relieving prism is chosen with the goal of decreasing the frequency of the deviation and improving motor control for the patient. For example, a patient 1 year of age presents with a history of an intermittent exotropia noted by the parents for the past 3 months. The parents claim the deviation is noticed 25% of the time and report that the frequency is increasing. Examination by Krimsky testing reveals a 25-prism diopter intermittent alternating exotropia present 50% of the time. Trial framing a prismatic correction of
5Δ base in the right eye (oculis dexter; OD), 5Δ base in left eye (oculis sinister; OS) revealed a decreased frequency of the exotropia. The patient is now responsible for only 15 prism diopters of convergence with the relieving prism versus the full 25 prism diopters. As stated, the goal of relieving prism is to reduce but not eliminate the motor fusional demand. This is an example of how a prism prescription aids in achieving that goal.
5Δ base in the right eye (oculis dexter; OD), 5Δ base in left eye (oculis sinister; OS) revealed a decreased frequency of the exotropia. The patient is now responsible for only 15 prism diopters of convergence with the relieving prism versus the full 25 prism diopters. As stated, the goal of relieving prism is to reduce but not eliminate the motor fusional demand. This is an example of how a prism prescription aids in achieving that goal.
Case Example
6-year-old patient
Distance cover test (CT): 10Δ exophoria
Near cover test: 15Δ intermittent alternating exotropia (30% frequency)
Near base-out (BO) ranges (prism bar):14/6 (break/recovery)
Interpretation
Convergence insufficiency type exotropia
Does not meet Sheard’s criteria (compensating vergence: 2 × phoria)
To meet Sheard’s criteria, BO vergence break point (14) would need to be ≥ 30 (15 × 2)
Prism prescription of 8Δ base-in (BI) (4Δ BI OD, 4Δ BI OS) will allow the patient to meet Sheard’s criteria
Decreases exo deviation to 7Δ and allows break point of 14Δ to meet Sheard’s criteria
If a pediatric patient can maintain fixation for cover testing and participate in fusion testing, then the prescribing of relieving prism may take into consideration Sheard’s criteria. Sheard’s criteria state that, to achieve visual comfort, the compensating fusional vergence should equal to twice the patient’s phoria. Below is a case example using Sheard’s criteria to prescribe prism for a patient with intermittent exotropia (10).
The prescribing of prism in the pediatric population is a useful tool in treating strabismus. It is often necessary for the practitioner to determine the amount of prism without relying on the more commonly used methods of testing (e.g., Maddox Rod, Worth 4-dot, fixation disparity). Relieving prism is also a superb treatment modality when used in conjunction with other strabismus treatment options. Prism often makes orthoptic treatment progress faster and result in higher rates of success; it can be used before and after surgery to maintain fusion in a strabismic patient.
Orthoptic Vision Therapy Treatment for Strabismus
The goal of orthoptic training for a strabismic patient varies according to the patient’s age and maturity level. In infants, the main goal is to preserve binocularity. The implementation of vision therapy in infants is typically home based. Use of occlusion techniques for amblyopia and strabismus will aid in improving acuity and avoiding the development of suppression. Gross vision therapy techniques can be used to improve motility, fixation, and vergence skills. Many orthoptic activities performed in infancy are done to avoid the development of anomalous sensory adaptations.
Use of large toys with varying amounts of contrast will encourage the infant to fixate and track an object that commands the child’s attention. Suggestions include using a face target (Mom’s face, baby doll face) to encourage fixation and tracking and using a toy to perform a near point of convergence push-up (11). Scheduling of these activities must avoid sleeping and feeding times for the infant. Parents are instructed to perform the suggested techniques daily for 5 to 10 minutes. Multiple vision therapy sessions can be done throughout the day.
In the toddler and preschool strabismic patient, the goal of orthoptic training is similar to that of an infant. Again, the techniques can be performed at home but with a bit more sophistication. The goals of vision therapy in this age range are to improve motility and depth perception; avoid the development of suppression; and to perform gross vergence activities (12). Motility and vergence activities can be done in free space with an age-appropriate target or can be computer based. Antisuppression activities with red-green anaglyphs and filters are often implemented for a preschool patient with strabismus. Depth perception activities often involve eye–hand coordination and visually directed reaching or pointing (e.g., placing stick in a straw).
As with all treatment options discussed, a weekly in-office vision therapy program is a viable option for the strabismic patient meeting the appropriate diagnostic and maturity criteria. Most children 5 or more years of age can be considered for structured orthoptic training. The orthoptic treatment of strabismus focuses on the motor vergence skills. Improving the compensating vergences of a strabismic patient can aid in increasing the frequency of fusion. Training the base-out (convergence) amplitudes for the exotrope and base-in (divergence) amplitudes for the esotropic patient aims to decrease how often the strabismic deviation manifests. In addition to vergence therapy, it is desirable to implement antisuppression tasks and normalize accommodative and ocular motor skills in all strabismic patients. The skills needed to perform orthoptic techniques require a certain level of cognitive ability and maturity. If the pediatric patient with strabismus is unable to perform the techniques, the practitioner may have to look to alternative methods of treatment to maintain fusion and consider vision therapy at a later time.
The orthoptic training of the motor vergence skills in a patient with a horizontal strabismus focuses on divergence (base-in) skills for an esotropic patient and convergence (base-out) skills for those who are exotropic. Motor training begins with smooth vergence activities (convergence only or divergence only) and eventually progress to jump vergence techniques (alternating between divergence and convergence in a step-by-step fashion). Motor vergence activities include techniques such as Brock string, vectograms, or computer orthoptic programs. As the patient’s motor vergences and fusional skills improve, the techniques progress to free space and utilize eccentric circle and lifesaver cards. Once motor vergences have reached the desired levels, the practitioner can begin techniques to integrate the vergence and accommodative systems (e.g., vectograms with ± 0.75 D flippers). A successful orthoptic program for a strabismic patient with fusion typically takes 12 to 24 sessions.
Treatment for Horizontal and Vertical Stabismus
Commonly encountered presentations of strabismic deviations in the pediatric population include infantile esotropia, accommodative esotropia, intermittent exotropia, and hypertropia. The practitioner is presented with the challenge of considering each treatment option available to the patient and parent. The most efficacious treatment decisions for these strabismic diagnoses are reviewed and summarized below.
Treatment of Infantile and Accommodative Esotropia
Infantile Esotropia
Treatment Options
Refractive error correction: if refractive error is out of age-appropriate range, if an accommodative component to the esotropia is suspected
Prism: rarely effective secondary to lack of sensorimotor fusion in most patients
Orthoptic training: rarely effective secondary to lack of fusion and immature age of many patients
Occlusion: for amblyopia as necessary
Surgery: most common treatment option
The clinical characteristics of infantile esotropia include an age of onset at 6 to 12 months, a constant deviation (13) of great magnitude, and a refractive
error that is typically within the age-appropriate range. If the cycloplegic refractive error is greater than + 2.00 to + 2.50 D, the examiner must rule out the possibility of an accommodative component to the esotropia. The most common differential diagnosis for infantile esotropia is accommodative esotropia. The onset of accommodative esotropia can be as early as 4 months of age. Other differential diagnoses include pseudostrabismus, cranial nerve VI palsy, Duane’s retraction syndrome, and an underlying organic cause (14).
error that is typically within the age-appropriate range. If the cycloplegic refractive error is greater than + 2.00 to + 2.50 D, the examiner must rule out the possibility of an accommodative component to the esotropia. The most common differential diagnosis for infantile esotropia is accommodative esotropia. The onset of accommodative esotropia can be as early as 4 months of age. Other differential diagnoses include pseudostrabismus, cranial nerve VI palsy, Duane’s retraction syndrome, and an underlying organic cause (14).
As with any strabismic deviation, the proper refractive error correction, when appropriate, is the starting point of the treatment plan. The early age of onset and the constant frequency of an infantile esotropia predispose the patient to the development of associated conditions, such as amblyopia (when the esotropia is constant and unilateral), cross-fixation, and anomalous correspondence (15). If the risk of amblyopia is present, the patient must be treated appropriately before further treatment is initiated or referral made. The presence of central fusion in infantile esotropia at any point in life is a very rare occurrence. The lack of central fusion development and limited existence of peripheral fusion predispose prism and orthoptics to be unsuccessful treatment choices.
The most common treatment for infantile esotropia is strabismus surgery. If the onset of the strabismus is before 6 months of age, clinically significant refractive error has been prescribed, amblyopia risk has been treated, nonsurgical treatment options have been unsuccessful, and the cosmesis of the deviation is unacceptable, then a surgical correction should be considered as a treatment option. The referring optometrist must educate the parents on success rates, risks, and complications of surgery, as well as at what age surgical intervention for infantile esotropia is most appropriate. Scheiman et al. (16) reviewed the literature to assess the success rates of surgical treatment in infantile esotropia. The results of the study revealed that surgery plays a large role in the cosmetic cure of infantile esotropia. Better results are typically achieved when the surgical procedure is performed before, rather than after, the child is 2 years of age. Table 21.5
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