• By:

    Eric Pennock, MD

     

    Strabismus

    Establishing the diagnosis

    Etiology

    Acquired nonaccommodative comitant esotropia (ANAET) refers to a group of conditions not associated with accommodative effort. Onset can be acute, or it can result from deterioration of existing, previously controlled, esotropia. Once thought to be rare, ANAET has not been given very much attention in past discourses of childhood esotropia and is usually given only a few short paragraphs, if mentioned at all.1-3 With the new millennium came new information, and ANAET may not be as uncommon as previously thought. 

    Epidemiology

    In a 10-year retrospective cohort study of 627 cases of childhood strabismus, Mohney found ANAET to be the third most common type (10.2%) after accommodative esotropia (27.9%), and intermittent exotropia (16.9%).4 Congenital esotropia was fifth (4.8%). Of the 385 patients with esotropia, 36.4% had the accommodative form and 16.6% had the nonaccommodative form.5 The authors listed partially accommodative esotropia as a distinct entity that was reported in 10.1% of cases. Congenital esotropia was diagnosed in 8%. The distribution was similar in a three-year prospective study in Southern Appalachia, a region in the Eastern United States. Esotropia was diagnosed in 221 children, 23 (10.4%) of whom had ANAET and 12 (5.4%)6 of whom had congenital esotropia. Jacobs and colleagues proposed that ANAET was perhaps not as rare as it is thought to be. They retrospectively reviewed records of all patients aged 19 years and younger over a 30-year period. They identified 174 with ANAET, and determined that this number represented a prevalence of 1 in 287 live births.7 

    Pertinent history

    When childhood esotropia is mentioned, ophthalmologists first tend to think of infantile esotropia or accommodative esotropia. Classic infantile esotropia (also termed congenital esotropia) manifests before 6 months of age. There is no accommodative component, and surgical correction is required to achieve proper eye alignment. The age onset is what distinguishes classic infantile esotropia from other childhood esotropias. Accommodative esotropia, on the other hand, usually manifests between ages 1 and 3 years. In these children, proper eye alignment can be accomplished with spectacle correction. There are instances where a child may possess features of both classic infantile esotropia and accommodative esotropia.These conditions are discussed in separate chapters.

    Accommodative esotropia can be further classified as “full” and “partial.” Partially accommodative esotropia (PAET) has been defined as having a residual esotropia of 10 or more prism diopters (pd) after wearing spectacles for at least three to four weeks.4,8 A fully accommodative esotropia can at times decompensate into a condition that is no longer treatable with spectacle correction alone. In these children a nonaccommodative component develops for unclear reasons. Several risk factors have been suggested, including onset of esotropia before age 2 years,9,10 oblique dysfunction,9,11 and a greater esodeviation at near than at distance.9,10,12,13 In several studies the incidence of decompensation has been reported to occur in 13-19% of patients,2-4 though in some series it has been reported in as few as 2.4%14 and in as many as 50%.15 

    In some instances a very young child presents for the first time with both accommodative and nonaccommodative components. The mechanism is believed to be a primary infantile esotropia with an overlying accommodative component.10,15 A child may also present with an acquired esodeviation that is minimally responsive (defined as a decrease in the esotropia of less than 10 pd) to a 3-4 week trial of hyperopic spectacles.4,5 This last group is said to have a nonaccommodative esotropia. 

    In some instances the esodeviation manifests acutely. That is, there is no deterioration of a once-stable accommodative esotropia. Acute acquired comitant esotropia (AACE) classically is divided into three different subtypes.16,17 The Swan type (type I) occurs after a period of interrupted binocularity. It was first described in 1947 in 4 patients who developed esotropia after long periods of occlusion for treatment of amblyopia.18 Type II AACE, known as Burian-Franceschetti, is not associated with any known underlying etiology.19 Lastly, the Bielschowski type (type III) is associated with patients who are myopic.20 It was originally described in patients with 5 or less diopters of myopia but the definition has since been expanded to include myopia of higher magnitude. The mechanism of action of this subtype has been postulated to be convergence spasm.21

    Clinical Presentation

    The angle of esotropia in acquired comitant esotropia can be quite large, with a range from 16 to 50 pd at distance and 16 to 70 pd at near.8,9,22,23 Another characteristic feature is a relatively low hyperopic refractive error; however, cycloplegic refractive errors of over +5 diopters were reported in two series.14,13 The mean refractive error can range from +1.15 to +4 diopters.6,13,15,20 Acquired comitant esotropia has been observed in emmetropic19 and myopic18,19 patients as well. Patients with ANAET are generally thought to have good binocular potential.17,18,24

    Lastly, as the name implies, the esotropia associated with ANAET must be comitant in horizontal gazes. The presence of lateral incomitance would suggest cranial nerve VI palsy, type I or III, Duane retraction syndrome, aberrant regeneration of cranial nerve III, or myasthenia gravis.

    Many patients with AACE will present with complaints of diplopia or they will exhibit behaviors suggestive of diplopia, such as closing an eye or stumbling.13,15,19,20 When a patient complains of diplopia at distance only, it is more consistent with an AACE. At the outset these patients can maintain single vision in the near range. By comparison, diplopia due to decompensating esophoria is initially experienced only at near.19

    Evaluation and Management

    When a patient presents with esotropia it is important to obtain a careful history. An amblyopic patient undergoing occlusion therapy, or a patient with ptosis may have type I AACE. Prior strabismus surgeries must be considered. Did the esotropia occur suddenly or has it progressed slowly? Is there diplopia and was it initially worse at distance or at near? Is it worse when the patient looks in a certain direction?

    All of these patients should undergo a comprehensive ophthalmic examination. Ocular motility and ocular alignment must be carefully assessed. Alternate cover testing is the preferred method. In infants or very young or uncooperative children, the use of Krimsky testing or the Hirschberg estimate may be necessary. When possible, fusion and stereopsis should also be tested on all patients. Tests for assessing binocularity should be performed before an occluder is used, such as to check visual acuity.25 All patients, especially children, should have a cycloplegic refraction. Cyclopentolate 1% alone is typically sufficient to produce adequate cycloplegia. Patients with dark irides may require either a second dose of cyclopentolate, or a drop of either tropicamide or phenylephrine 2.5%.

    All patients with esotropia and a significant refractive error should be given a trial of spectacles. In the AAO Preferred Practice Pattern® the threshold is considered to be ≥ +2.50 d in infants, ≥ +2.00 d in 1-2 year-olds, and ≥ +1.50 d in children 2-3 years old.25 If the esotropia does not respond to spectacle correction, a second cycloplegic refraction, often with atropine 1%, is strongly recommended.

    If a residual esotropia of ≥ 10 pd persists after the initial 4 weeks of spectacle correction and, if necessary, a repeat refraction and new glasses, there is a nonaccommodative component. In some patients, the alignment and binocular status can be corrected with prismatic correction alone. In many cases; however, surgery is indicated. The exact procedure is often up to the discretion of the surgeon. If there is any underlying pathology it must be addressed.

    An intracranial tumor is among the most worrisome causes of a new-onset esodeviation. When the strabismus is clearly caused by uncorrected (or undercorrected) hyperopia, or by deterioration into a partly accommodative esotropia, neuroimaging is not immediately required. The same is true in otherwise healthy patients with acquired comitant nonaccommodative esotropia, such as the child who wore the full hyperopic refraction for 4 weeks with a less than 10 pd decrease in the esotropia. However, it is generally accepted that if the onset of esotropia is acute, and the child has an abduction deficit that accompanies the esotropia, then neuroimaging is warranted.

    The decision of whether to obtain imaging is not as clear if the esotropia is comitant. Part of the difficulty of managing patients with AACE stems from the fact that it is not a very common condition, and AACE caused by a tumor is even less common. In Jacobs’ report, 174 patients were followed for a mean of 10 years and there was not a single case of central nervous system (CNS) neoplasm.7 In a prospective study conducted over a 3.5 year period, Lyons and coworkers identified 10 patients with AACE and diplopia.15 In addition to a full ophthalmologic examination, all were examined by a pediatric neurologist and had a magnetic resonance imaging (MRI) and/or computed tomography (CT) scan. A CNS lesion was found in only one patient. Despite normal cerebellar function she had a large midline cerebellar astrocytoma. She started with an intermittent esotropia that became manifest after 6 weeks. Her refractive error was plano in both eyes, unlike the other 9 patients, who had at least 1.25 diopters of hyperopia. She also had a V-pattern. Kemmanu et al reported a series of five patients (over an unspecified amount of time) with AACE and diplopia.21 All had a low hyperopic refractive error. Though all had a comitant esotropia, 2 of the 5 demonstrated floating saccades and were found to have pontine gliomas. Another patient in this cohort had papilledema and was subsequently diagnosed with idiopathic intracranial hypertension. Simon and colleagues diagnosed ten patients with AACE over a 10-year period.24 Neuroimaging was obtained in 7 and all but 1 had normal findings. That patient had Arnold-Chiari type I malformation—and also presented with a downbeat nystagmus.

    In one of the earliest case series of AACE as a presenting sign of intracranial tumors, Williams and Hoyt describe 6 children who were diagnosed over a period of 9 years.26 None of these patients initially presented with anything other than an acute comitant esotropia. No patient in this cohort had divergence insufficiency, nor did any develop signs of abducens nerve dysfunction. Four were hyperopic and were given a trial of spectacles. One patient even had an improvement in the strabismus with hyperopic correction, as the angle decreased from 25 pd to 15 pd. There was no reason to suspect any sinister pathology. Neurologic examinations and imaging were obtained only after nystagmus developed in 3 patients, and facial paresis developed in another. The other two were scanned because of their parents’ insistence that they lacked motor coordination. Four of the patients were found to have cerebellar astrocytoma, including all 3 who developed nystagmus. A cerebellar medulloblastoma and pontine glioma were found in the other 2.

    Arnold-Chiari type I malformation has also been reported in patients who presented with AACE.23,27,28,30 These patients commonly develop nystagmus, an A-pattern, and/or other neurologic signs that prompt full neurologic examinations and imaging.

    Despite the definite association between AACE and CNS pathology, routine neurologic exam and neuroimaging are not routinely recommended.16,21,22,25,31 Others have suggested that it is better to err on the side of caution because though rare, a CNS lesion has potential for a devastating outcome.22 There are several factors that should raise suspicion and prompt further investigation. Some clinical signs such as severe headaches, gait disturbances, facial numbness or paresis, acquired nystagmus, floating saccades, or optic disc edema are obvious causes for concern. The patient’s history is important in determining if there are developmental delays, regression of development, or other systemic symptoms that may be attributed to a CNS lesion. The presence of a V-pattern should raise suspicion as well.16,32 Lastly, failure to regain stereopsis after prism adaptation or surgical correction is considered to be an important sign that there may be underlying CNS pathology.16,23,26,31

    In summary, nonaccommodative comitant esotropia may not be as uncommon in children as once thought. It has in fact been reported to occur almost twice as frequently as infantile esotropia. It is important for the ophthalmologist to distinguish between decompensating esodeviation and truly acute cases. Acute acquired comitant esotropia classically falls into 3 broad categories. In type I there is a history of temporary loss of fusion, and type III is associated with moderate to high myopia. In patients with type II there is no obvious cause. Comitance of the esotropia in horizontal gaze may provide some reassurance that an underlying CNS lesion is absent but by no means guarantees it. There is no definite algorithm to follow or series of boxes to check; therefore, the ophthalmologist must rely on his or her clinical acumen and the patient’s history to determine the need for neuroimaging.

    References

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