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Nathan Hamaker, MD · Scott E. Olitsky, MD
Esotropia is a convergent (inward) deviation of the eyes. Accommodative esotropia is an inward deviation of the eyes due to an activation of the accommodation reflex, which controls ocular accommodation, convergence and miosis. An important adaptation for near work, the accommodation reflex allows clearer vision and binocular fusion of near objects. Patients with hyperopic refractive errors may also activate accommodation to provide clearer distance vision. However, when a patient has a significant hyperopic refractive error, the magnitude of accommodation activated for distance work may cause esotropia. Also, if the convergence reflex is excessively strong, a form of esotropia with near work may result.
Accommodative esotropia is subdivided into three categories: refractive, nonrefractive and mixed mechanism. Each has a somewhat unique presentation.
Refractive Accommodative Esotropia
Refractive esotropia occurs when patients have a hyperopic correction for distance vision. The pathogenesis of refractive accommodative esotropia involves three components - hyperopia, accommodative convergence and insufficient fusional divergence amplitudes - to maintain single binocular vision. In a patient with uncorrected hyperopia, the accommodative reflex is activated to minimize blur of the retinal image. While a sharper retinal image is produced, the convergence mechanism is stimulated. If the patient has enough fusional divergence to compensate for the stimulated accommodative convergence, then the eyes will remain straight. In some patients, however, the motor divergence to overcome these forces is insufficient and esotropia results. Other factors, such as sensory deprivation or anisometropia, may also interrupt motor divergence, leading to uncompensated accommodative convergence.
Refractive accommodative esotropia is most commonly seen in patients 2 to 3 years of age, although it has been reported in children between 4 months and 7 years of age.1,2 Hyperopic corrections average 4.5 D to 5 D, but may include lesser degrees of hyperopia, especially when the patient is anisometropic. The measured deviation is the same at both 20 feet and 14 inches and is approximately 20 ΔD.3,4
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Accommodative esotropia is a common cause of amblyopia, making identification and treatment of refractive accommodative esotropia important. A cycloplegic refraction should be performed at the initial clinic presentation for newly diagnosed esotropia. One study suggests that using atropine 1% drops may give more accurate results than cyclopentolate 1%, but using atropine requires a second visit because it takes several days to take full effect.5 In this study, it was demonstrated that 22% of children refracted with atropine were found to be 1 D more hyperopic than when they were refracted with cyclopentolate. In either case, glasses should be prescribed for the full hyperopic correction. If amblyopia is noted, it should be treated, although the ophthalmologist may wait to see whether the vision improves with spectacle correction alone. After undergoing a trial of glasses, the patient is brought back, usually 1 month later, to retest vision and alignment. Purely refractive esotropia will be corrected with full hyperopic correction. If patients have straight (or nearly straight) eyes with glasses, then they may be monitored. Slide 1 and Slide 2 demonstrate accommodative esotropia in a patient who has good alignment with spectacle correction.
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Many parents note that when a child removes glasses worn for hyperopic correction after some time, their eyes seem to deviate more than before the glasses were prescribed. This is a normal phenomenon due to increased accommodative effort (without glasses) after the child has experienced clear vision (with glasses). Most children do not remove their refractive correction for long due to blurry vision and/or asthenopia.
The prognosis for patients with accommodative esotropia is generally good. Patients must be monitored because a decompensation of their esotropia, even with glasses, may occur. Also, patients may experience a relapse of their amblyopia. Decompensation has been reported as high as 50% in some children, although recent reports suggest it may be much less if treated early.6 Also, hyperopia typically increases until age 5 or 6, and thus a child may need frequent changes in lenses to prevent esotropia as he or she ages. A child whose eyes have been well aligned with glasses who develops a recurrence of his or her esotropia should undergo a repeat cycloplegic refraction to rule out an increasing hyperopia. Also, by age 5 or 6, many children have developed stronger fusional amplitudes and their hyperopic correction may be reduced by giving a manifest refraction. This should be done with caution in this age group; the development of a small angle strabismus can lead to amblyopia. Patients with significant hyperopia are unlikely to be "weaned" out of their correction completely, and aggressive reduction in their prescription is probably not warranted in most cases.7
A discussion of surgical correction for decompensated refractive esotropia follows later in this tutorial.
Nonrefractive Accommodative Esotropia
Nonrefractive accommodative esotropia can occur with any refractive error, although it is typically seen with an average of +2 D to +2.5 D in children between 2 and 3 years of age. In this condition, the effort to accommodate for near work elicits an abnormally high convergence (known as a high accommodative convergence: accommodation, or AC:A, ratio). This is manifest as an esotropia that is greater in magnitude at near than at distance. Methods to measure the AC:A ratio include the heterophoria method and the fixation disparity method. In practice, most clinicians prefer to assess the ratio using the distance-near comparison, which allows the ratio to be evaluated easily and quickly because it employs conventional examination techniques and requires no calculations. The AC:A relationship is derived by comparing the distance and near deviation. If the near measurement in an esotropia patient is greater than 10 ΔD, the AC:A ratio is considered to be abnormally high.8
Treatment of nonrefractive accommodative esotropia can be multifaceted and controversial. If the distance deviation is small, then many ophthalmologists recommend the use of bifocals to reduce or eliminate the need to accommodate for near work; doing so allows the near deviation to be decreased to an amount that allows fusion. Flat-top executive-style bifocals that cross though the pupil margin are recommended. Data from one recent study conducted on the use of bifocals show that 37% of patients were able to reduce or eliminate their bifocals, while 47% remained dependent on bifocals and 17% of patients decompensated into nonaccommodative esotropia.9 The use of progressive bifocals has also been successful in children to treat high AC:A ratio esotropia.10
The efficacy of the use of bifocals in treating esotropia due to high AC:A ratio has been questioned. Data from one study of patients with excess esotropia at near show no difference in the natural reduction of esotropia in patients wearing bifocals vs. patients who had their bifocals discontinued.11 However, 12% of patients who discontinued use of bifocals demonstrated bifoveal fixation and no one complained of diplopia at near.
Because esotropia at near may not be noticeable to young children, some authors have questioned the use of (and the additional expense of) bifocals to treat this condition. One report reviewed the long-term sensory status in patients with excess esotropia at near, half of whom were treated with bifocals. The authors found no difference in sensory status or deterioration rates between patients treated with bifocals and patients who were not treated with bifocals.12 In addition, decompensation of accommodative esotropia appears to be related to the magnitude of the AC:A ratio and not the use of bifocals.13
Miotics have been noted to normalize the AC:A ratio by increasing available acetylcholine at the cilliary body, thus reducing the effort needed to accommodate. However, miotics have several side effects in children, including iris cysts and hypersensitivity to certain anesthetic agents like succinylcholine. Additionally, the AC:A ratio returns to pretreatment levels upon discontinuation. However, miotics may be a useful tool when the deviation is not too large.
Surgery may be indicated if bifocals are not helpful, if the distance deviation is too large for management by glasses or if miotics cannot be employed. Surgery has been shown to decrease the AC:A ratio and should be considered when residual distance deviation is greater than 10 ΔD.14
Two surgical approaches have been proposed for management of high AC:A ratios. Some surgeons believe that surgery for the full deviation at near should be performed even when little or no deviation exists at distance.15,16 However, other surgeons have been concerned that operating for the full near esotropia may lead to an overcorrection at distance. These surgeons may utilize the posterior fixation suture, or Faden procedure, to treat the deviation at both distance and near fixation. In this procedure, a medial rectus recession is performed for the distance deviation and then a nonabsorbable suture between the muscle and sclera is placed as posteriorly as possible to limit further deviation at near. Posterior fixation sutures are thought to work by moving the effective insertion of the muscle to the point of the suture, increasing the arc of contact between the muscle and sclera and reducing the lever arm, thus weakening the muscle in its field of action but not in primary position. Kushner has shown that operating for an augmented distance correction is more effective at aligning the eyes and eliminating bifocals than using posterior fixation sutures without a significant overcorrection rate, even 15 years after surgery.16 Other studies have demonstrated the efficacy of operating for the deviation that is present at near.15
Partial or Decompensated Accommodative Esotropia
Refractive and nonrefractive accommodative esotropias may not necessarily exist in pure forms. This is most commonly seen when a patient with refractive or nonrefractive accommodative esotropia is treated late in the disease process,17 although it is also seen when patients with high AC:A ratios decompensate.
Surgery may be indicated to eliminate residual esotropia not corrected by glasses. When residual esotropia is greater than 10 ΔD, surgery may be undertaken in an effort to establish some level of binocular vision. This may increase the chances that surgical correction will remain effective as the patient can invoke motor fusion to help keep the eyes aligned. Other surgeons choose to watch smaller residual deviations. The decision to surgically treat these patients is based upon the wishes of the patient and his or her family.
One proposed surgical approach is to operate for the full deviation measured without glasses to eliminate the need for glasses. Most surgeons do not use this approach unless the deviation and level of hyperopia is small. Others suggest operating only for the residual difference and keeping the patient in refractive correction. In any case, operating for the deviation found at distance (or near if there is a high AC:A ratio) with spectacle correction may produce an acceptable number of undercorrections. Therefore, if the surgeon wishes to keep the patient in glasses and not operate for the full deviation, two methods have been proposed. One method is to average the angle of deviation found with and without glasses and to operate for this amount.18 A second method is to intentionally overcorrect a patient and then decrease the hyperopic correction. When hyperopic correction is reduced after a planned surgical overcorrection, the patient is stimulated to use accommodative convergence to bring the eye back into alignment. This effect can be titrated over several office visits, if necessary. A recent study showed that this technique is effective only when the overall refraction is equal to or less than +2.5 D.19
Prior to surgery for partially accommodative esotropia, some ophthalmologists use prism adaptation to enhance their surgical outcomes. In prism adaptation, the patient is prescribed a Fresnel press-on base-out prism for the esotropia that remains after prescribing the full hyperopic correction. The patient will then return in 2 weeks and the deviation is measured again. If it has increased, then a larger base-out prism is given. The process continues until a stable measurement of residual esotropia is achieved. The Prism Adaptation Trial was a multicenter, prospective, randomized study on prism adaptation that found that standard surgery resulted in approximately a 75% success rate. Patients undergoing prism adaptation showed an 85% success rate.20 Although prism adaptation appears to increase surgical success, it has the disadvantages of being costlier and requiring more time. Some surgeons perform a "mini"-prism adaptation by prism adapting the patient in the office. It is unknown if this type of prism adaptation provides the same increase in surgical success as prism adaption according to the protocol of the Prism Adaptation Study.
Accommodative Esotropia Following Congenital Esotropia
Accommodative esotropia is often seen in patients who underwent surgical correction for congenital esotropia. The incidence of accommodative esotropia following congenital esotropia ranges between 28% and 51%, according to recent publications.21,22 In many of these patients, accommodative esotropia may occur with less hyperopia than might be expected; as little as +1.50 D have been reported in some cases. This is probably due to underlying poor binocular function in these patients.23 Given the high risk for recurrent esotropia in these patients, it is helpful to discuss this possibility with parents prior to surgery, especially if the child is significantly hyperopic. This will help eliminate confusion as to why surgery was used as a treatment initially, but glasses were used for the recurrent deviation.
