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David Ingvoldstad, MD · Scott E. Olitsky, MD
During the first month of life, ocular deviations are common and do not always indicate an abnormality. Oculomotor instability may impede adequate assessment of alignment. A more accurate assessment of motility becomes possible at approximately 3 months of age. During this time of instability, alignment may vary. A study by Nixon and coworkers1 revealed that of 1,219 infants in a nursery, 40% had straight eyes, 33% had exotropia, 3% had esotropia, and 7% showed variable alignment. The remainder could not be classified.
Pseudoesotropia
Pseudoesotropia is one of the most common reasons an ophthalmologist is asked to evaluate an infant.
Pseudoesotropia gives the false appearance of crossing, which is often due to a broad nasal bridge,
prominent epicanthal folds, or a narrow interpupillary distance. This appearance is accentuated when
a patient adducts the involved eye.
Pseudoesotropia can be differentiated from a true manifest deviation by observation of the corneal light reflex and the cover-uncover test. It may be useful to show the corneal light reflex to the parents to assist in reassurance. While most children will outgrow this appearance, parents and pediatricians should be made aware that a true esotropia may develop in a child with pseudoesotropia. Therefore, if the apparent deviation does not improve, then a patient should be re-examined.
Congenital Esotropia
Few children with congenital esotropia are born with this condition. Therefore, the term is confusing.
However, parents will often give a history of crossing since birth. Ophthalmologists, on the other
hand, have found that infants with esodeviations are rarely born with the condition. In one
prospective study, three of 3,324 infants developed congenital esotropia. All of them were orthotropic
or exotropic at birth.2 Some have advocated the term "infantile" or "congenital-infantile esotropia"
when referring to esotropia occurring before 6 months of age. Still, the term congenital esotropia is
widely accepted.
Epidemiology
Congenital esotropia is a common form of strabismus. Congenital esotropia occurs equally in boys and
girls. Some families transmit congenital esotropia as an irregular autosomal dominant trait, while
in other families congenital esotropia is recessive. Parents of affected patients may show reduced
binocular function and often have strabismus. Several conditions such as cerebral palsy,
hydrocephalus, and low birth weight have been linked to the development of esotropia.
Pathogenesis
Although the pathogenesis of congenital esotropia is largely unanswered, two popular theories have
surfaced. Worth3 developed the sensory concept in 1903 that presumed that congenital esotropia stemmed
from a congenitally defective fusion center in the brain. Restoration of binocularity was thus
considered hopeless.
In 1939, Chavasse3 suggested the motor theory. He postulated that normal binocular vision may be achieved by curing the mechanical deviation in early infancy. In the 1960s, several authors began to report favorable binocular vision in infants undergoing surgery between 6 months and 2 years of age. 4-7
It is now known that even early surgery usually leads to imperfect binocularity. Von Noorden5 stated that "subnormal binocular vision must be considered an optimal result." In 1969, the monofixation syndrome was defined by Parks6. This condition can be defined as peripheral fusion with a central suppression scotoma and deficient stereopsis. Alignment is usually within 10 prism diopters (PD).
The exact pathogenesis of congenital esotropia is unclear. Most likely combinations of sensory and motor factors contribute to the development of the disorder. As these mechanisms become clearer, it is conceivable that several distinct forms of congenital esotropia may be classified, each with surgical and prognostic implications.
Clinical Manifestations and Associations
Amblyopia is strongly associated with congenital esotropia. Several studies report an incidence
ranging from 40% to 72%.4, 7, 8
Alternating fixation and cross-fixation can give the appearance of a pseudoparesis of abduction. With alternating fixation, usually occurring without amblyopia, a patient will switch fixation to use the adducted, or crossed, eye to regard the opposite field of gaze. This will give the false appearance of a bilateral abduction paresis.
In a patient with cross-fixating, usually with amblyopia, the better seeing eye will cross-fixate. This gives the false appearance of unilateral abduction paresis of the amblyopic eye. A pseudoparesis can be differentiated from a true abducens palsy by using a doll's head maneuver or by patching one eye before testing rotations. This is clinically useful, as it avoids an unnecessary workup for a presumed sixth cranial nerve palsy and it also helps to diagnose amblyopia.
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Measurements should be taken using the prism cover test when possible. However, this may not be feasible in some infants and the Hirshchberg or Krimsky methods may be substituted. The distance and near measurements tend to be similar. Yet, the angle of deviation may be dynamic over time. An increase in the angle is seen more commonly than a decrease. Oblique muscle dysfunction and A and V patterns must also be noted, as these are not uncommon.
Patients with congenital esotropia tend to have refractive error similar to the age-matched general population.4 This is in contrast to the hyperopia seen in accommodative esotropia.
Dissociated vertical deviation (DVD) is common with congenital esotropia. A DVD can be thought of as a slow upward deviation of one eye. It is often bilateral and associated with excyclotorsion on upward drifting. DVD may be latent, seen only with a cover test, or manifest. Characteristically, no simultaneous hypotropia of the contralateral eye exists. Therefore, a DVD is easily differentiated from a true vertical deviation.
The incidence ranges from 46% to 90%, and the onset appears to be time dependent.10 Early surgical alignment of horizontal deviations has not been shown to reduce the incidence of DVD. 11, 12
Measurement of DVD may be difficult. One choice is to use either the Hirschberg or Krimsky method. The prism cover test may also be used, although this may be difficult. Many practitioners prefer to use a semi-quantitative grading scale.
Inferior oblique overaction (IOOA) is also commonly associated with congenital esotropia. The incidence may be as high as 70% to 80%, most often becoming apparent in the second to fourth years of life.10, As with DVD, an association between timing of strabismus surgery and development of IOOA is not evident.
Because IOOA may cause excessive elevation of one or both eyes in adduction, it is often confused with DVD. DVD may become manifest on adduction as the nose acts as a cover. As a rule, the vertical misalignment in DVD is equal in abduction, adduction, and primary gaze.
With IOOA, the affected eye will become hypertropic on adduction if it is the non-fixating eye. However, a contralateral hypotropia will occur if the affected eye is the fixating eye. This is not the case in DVD. To further complicate matters, DVD and IOOA may coexist in the same eye in as many as 59% of patients.10 IOOA is recorded as grade I to IV.
Nystagmus is frequently seen in children with congenital esotropia. Latent nystagmus may be found in up to 50% of patients with congenital esotropia. Latent nystagmus may have implications for the treatment of amblyopia in these patients.
Methods other than occlusion may be used. Another type of nystagmus, rotary nystagmus, may also occur with congenital esotropia. Hiles and co-workers13 found that 30% of their patients with congenital esotropia had rotary nystagmus.
Others argue that the incidence of rotary nystagmus is much less than 30% in these patients. Both forms of nystagmus diminish with time.
Table 1 Differential Diagnosis of Congenital Esotropia
Differential Diagnosis
Pseudoesotropia
Duane retraction syndrome
Möbius syndrome
Nystagmus blockage syndrome
Congenital sixth nerve palsy
Early-onset accommodative esotropia
Sensory esotropia
All infants presenting with esotropia require a complete ophthalmic examination, including a dilated
funduscopic examination. Congenital esotropia may be simulated by a number of conditions during the
first year of life (Table).
Generally, a small angle of deviation should raise doubt when making the diagnosis of congenital esotropia. Most cases of congenital esotropia demonstrate a relatively large angle of deviation.
Timing of Treatment
The primary goal in treatment of congenital esotropia is to reduce the deviation to orthotropia. This
not only allows for development of normal sight in each eye, but also promotes a rudimentary form of
sensory fusion. This sensory fusion aids in maintaining alignment. It is thought that earlier
intervention fosters the development of sensory fusion and binocularity. 14
A spectrum of sensory results define success in treatment of congenital esotropia. The most common sensory result in patients aligned before 2 years of age is the monofixation syndrome. In this situation, normal peripheral retinal correspondence occurs along with normal fusional vergence amplitudes.
These characteristics are vital to the maintenance of motor alignment.15 The type and degree of residual deviation after surgery also is predictive of long-term stability. Small angle esotropia tends to be less stable than orthophoria but more stable than small angle exotropia.
Considering the benefits of early surgery such as enhancing binocular performance and addressing the social stress placed on a parent of a child with congenital esotropia, most ophthalmologists advocate early surgery. Generally, children with congenital esotropia undergo surgery when an examination demonstrates an esotropia with alternating fixation and absence of an accommodative component. Typically, this is around 6 months of age.
Other surgeons encourage surgery earlier than 6 months of age in hopes of achieving perfect binocular vision. 16 Patients with a constant and stable esotropia of at least 40 PD who present between 2 to 4 months of age are unlikely to improve spontaneously, providing another argument for earlier surgery. 17
Other surgeons continue to express concerns over operating at an early age. These concerns include the documented spontaneous resolution of esotropia in some infants, anesthetic risks and an unproven influence on long-term horizontal alignment and the development of IOOA and DVD.
Amblyopia
Early and aggressive treatment of amblyopia is essential in the treatment of congenital esotropia.
Surgical treatment should generally be delayed until amblyopia is treated. Most clinicians prefer
nearly total daytime patching of the dominant eye. Patching is continued with monitoring of fixation
behavior or visual acuity measurements at intervals of 1 week per year of age.
A variety of occluding devices have been developed. It is important to use a device that makes it difficult for the child to "cheat" or allow use of the dominant eye. Cycloplegic agents, usually atropine, can also be used to penalize the dominant eye. Even when effective, atropine penalization usually takes longer than occlusion therapy to treat amblyopia.
Once the child demonstrates alternate fixation in the midline, patching is discontinued. At this point, it is assumed that no significant amblyopia remains. However, continued monitoring is needed. Some infants require part-time maintenance therapy if amblyopia recurs. Other children may require occlusion of the previously amblyopic eye if their fixation preference switches to that eye. If occlusion therapy is not successful after several months, then reexamination for organic disorders is required. Often times, noncompliance is the cause of failure.
Refractive Errors
Most children are hyperopic and it may be difficult to decide which children should be treated with
anti-accommodative therapy. Accommodative esotropia is uncommon in young infants, but it does occur.
In a patient with large angle esotropia with an early onset, correcting even moderate hyperopia would not be expected to correct the deviation. Spectacles may be fit in young infants if necessary and the deviation can be measured again.
Miotics have also been used, but they may be less reliable than glasses. Miotics are also associated with pupillary cysts and retinal detachment and cataract in adults. Miotics may also result in prolonged apnea after general anesthesia if succinylcholine is used.
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The hang-back technique provides excellent exposure for even large recessions. The recessions are graded with more millimeters of surgery for a larger deviation. For large deviations two-, three-, or four-muscle surgery may all be appropriate. It is important to note that large recessions have been shown to provide good results and do not cause a postoperative adduction or convergence deficit. 19, 20
Also, two-scale surgery is faster, simpler, and less traumatic than surgery involving more muscles. When a second procedure is required, then a bilateral lateral rectus resection or a recess-resect procedure in the fellow eye may be performed. Regardless of the type of surgery done initially, late under-corrections or over-corrections may occur. This may likely be due to an underlying defect in binocular function.
Botulinim toxin has been used by some surgeons to treat congenital esotropia. 21 It has not been shown to provide results that equal those using incisional surgery. 22
Over-correction and Under-correction
Successful alignment, even if performed early in life, does not ensure long-term stability. Therefore,
repeat observations during the first decade of life are imperative.10 Initially, a small over-correction
may be desirable in young patients. A large over-correction associated with an adduction weakness
immediately postoperatively may be due to a slipped muscle. This requires surgical exploration and
repair.
A consecutive exotropia greater than 15 PD 6 weeks postoperatively usually requires a second surgery. This is best accomplished by operating the previously unoperated muscle(s). If, however, an adduction deficit is present, then the previously recessed medial rectus muscle may be advanced or resected.
Under-corrections of greater than 10 PD should be treated. Initially, a trial of spectacle correction for hypermetropia greater than + 1.50 D is indicated. Secondary surgery should be considered in patients with greater than 15 PD of residual esotropia.
Accommodative Esotropia after Congenital Esotropia
Accommodative esotropia may be present in children treated surgically for congenital esotropia. Hiles and
colleagues13 reported that 65% of corrected congenital esotropes required spectacle correction of
hypermetropia to control esotropia at some time postoperatively. Generally, any hyperopia in excess
of + 1.50 D should be treated before considering further surgery.
Dissociated Vertical Deviation
Patients with DVD are often asymptomatic. DVD may improve with time, as it is found more often in children
than adults with strabismus. Others have disputed this notion. The surgical indication for DVD is usually
one of appearance. If the DVD is entirely latent, then surgery is not indicated.
The decision for surgery is driven by the size and frequency of the deviation. A unilateral DVD is more likely to occur in the non-dominant eye. Therefore, in children beyond the amblyogenic age with nearly equal vision, slight optical blurring or cylcloplegia of the dominant eye produce a change in fixation and masking of the DVD without surgery.
Classically, three choices for the surgical correction of DVD are available. The superior rectus muscle may be recessed. 23 Recession of the superior rectus muscle may be accompanied by a posterior fixation suture or the inferior rectus may be resected. 24, 25 Many surgeons now perform an anterior transposition of the inferior oblique to treat DVD in patients with congenital esotropia. This procedure will also correct IOOA.
Inferior Oblique Muscle Overaction
IOOA is also a problem of appearance and not one of symptoms. Patients will avoid the extreme lateral gaze
to avoid eliciting IOOA. They will instead turn the face to look laterally. The indications for and type
of surgery to correct IOOA depend largely on whether horizontal strabismus surgery is also being
considered.
A significant cosmetic defect should be present to justify operating on the inferior obliques. Objectively, a significant defect is present when there is an obvious elevation of the adducting eye at about 30º of lateral gaze. If horizontal strabismus surgery is being performed, then smaller grades of IOOA may be corrected simultaneously.
An overacting inferior oblique muscle may be effectively weakened by performing an inferior oblique recession, anterior transposition, disinsertion, myectomy or denervation, and extirpation. Inferior oblique recession is associated with low rates of complications and recurrences. This procedure may also be graded according to the amount of overaction.
Anterior transposition of the inferior oblique has the distinct advantage of treating inferior oblique overaction and DVD. The authors consider this the procedure of choice when motility disturbances are present. Anterior transposition is accomplished by placing the distal end of the inferior oblique near the lateral end of the inferior rectus muscle. This effectively eliminates IOOA and also limits elevation to some degree. This may become clinically significant in some unilateral cases. Bacal and Nelson26 showed that anterior transposition was effective in treating either DVD or IOOA or both when concurrently present.
Postoperative Amblyopia
The possibility of amblyopia occurring postoperatively must always be considered. Each postoperative visit
must include fixation preference testing. A 10 PD vertical prism may be placed in front of one eye to
produce a vertical deviation to uncover any fixation preference.27
If amblyopia occurs, then it should be treated promptly with occlusion therapy. Initially, full-time occlusion may be required. This may be followed by part-time (1 hour to 2 hours per day) maintenance therapy until visual maturity is reached. This generally occurs at 9 years of age.
