History
Infantile esotropia typically is not present at birth but rather develops in the early months of infancy. Often, the child manifests with chronic inward deviation (esodeviation) of the visual axes at age 2-4 months. This may be preceded by several weeks of transient episodes of misalignment, accounting for the often mentioned history of eyes crossing at birth.
Certain risk factors have been associated with infantile esotropia. Significant among these are prematurity, family history or secondary ocular history, perinatal or gestational complications, systemic disorders, use of supplemental oxygen as a neonate, use of systemic medications, and male sex. The added risks of perinatal complications (eg, prematurity, birth injury, low birth weight) to infantile esotropia have been investigated, yielding equivocal, if not contrary, results. Awareness of these risk factors can lead to early detection and management of esotropia.
Physical
Classic infantile esotropia is constant and involves a large angle of deviation exceeding 20 prism diopters (PD) on corneal light reflex measurement. As a rule, children with constant esotropia of greater than or equal to 40 PD in the first 2-4 months of life rarely resolve spontaneously to orthophoria. In addition, reduction of the angle of deviation below 40 PD is uncommon in these patients.
Children with initially smaller angles of deviation (< 40 PD) or variable angle esotropia have a slightly better chance of resolution to orthophoria. However, 3 cases with infantile esotropia whose angle of deviation decreased spontaneously to less than 10 PD over a minimum follow-up period of 37 months eventually were observed to develop late complications of infantile esotropia (eg, bilateral inferior oblique muscle overaction, latent nystagmus, dissociated vertical deviation).
According to Tychsen, infantile esotropes manifest with a constellation of ocular motor signs, as follows [4] :
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Esotropia, with or without strabismic amblyopia
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Pursuit asymmetry
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Latent fixation nystagmus
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Motion visual-evoked potential (VEP) asymmetry and motion perception abnormalities
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A face turn and abduction deficit
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Dissociated vertical deviation
Infantile esotropia may be associated with a spectrum of clinical presentations, including amblyopia, impaired binocularity, central scotomas, and incomitance.
Amblyopia is relatively common in patients with infantile esotropia. Weakley et al stated that amblyopia should be suspected strongly in patients with esotropia and asymmetric inferior oblique activity, specifically in the eye with more inferior oblique overaction. [5] It has been observed that motor skills are reduced in amblyopic children particularly those with strabismus. Manual dexterity tasks requiring speed and accuracy are affected the greatest. Most clinical evidence suggests that sensory and motor functions are nearly normal if alignment (within 10 PD of orthophoria) is attained within the first 2 years of life.
Virtually all patients with infantile esotropia fail to develop normal binocular vision and stereopsis.
Mohindra et al reported that children with infantile esotropia corrected with prisms equal in size to the deviation showed some degree of binocularity up to at least 2.5 years, as measured by a Polaroid bar stereogram procedure with 1800 seconds of arc disparity; however, all older patients (>6 y) with a history of infantile esotropia failed the test. [6]
On the other hand, studies have shown that compared to an age-matched population, monocular preferential-looking acuity in infantile esotropes was not significantly different during months 3-14 for the preferred eye and during months 3-8 in the nonpreferred eye. Stereopsis and monocular acuity were noted to be significantly lower in the older esotropic patients. These studies showed that deficits in preferential-looking acuity and subsequent amblyopia occur after the onset of fixation preference and that stereoscopic pathways are present and functional in at least some esotropic infants.
Central scotomas almost always are identifiable, even in patients with optimal motor alignment and with the highest levels of binocular vision. On the other hand, it had been stated that the inferonasal quadrant of the visual filed is constricted in patients with infantile esotropia as a result of dissociated vertical deviation. Haefliger et al subsequently refuted this statement. [7]
Incomitance also may be observed. The most common type is the V-pattern infantile esotropia, wherein esodeviation is greater in downgaze than in upgaze. V-pattern infantile esotropia is attributed largely to overaction of the inferior obliques. The reverse of this type, the A-pattern, also may be noted in infantile esotropes.
Causes
The exact cause of infantile esotropia has yet to be identified distinctively. While it strongly is believed that a genetic component exists, a solid basis for linkages among family members still needs to be established. However, several studies have made significant inroads toward establishing a genetic causation for infantile esotropia. Tychsen and Lisberger reported in 1986 that the strabismic patient who had the most severe pursuit/motion processing asymmetry had 2 siblings with infantile esotropia. Furthermore, large-scale investigations have shown that 20-30% of children born to a strabismic parent eventually will develop strabismus themselves. On the other hand, there is a suggested relationship of nonsyndromic infantile esotropia to the susceptibility loci on regions 3p26.3-26.2 and 6q24.2-25.1 and may share alleles that underlie Duane retraction syndrome. [8]
