Strabismus is one of the most relevant health problems of the world, and infantile esotropia is perhaps the most visually significant yet the least understood. Infantile esotropia is the inward deviation of the eyes noted before the patient reaches age 6 months. It is associated with maldevelopment of stereopsis, motion processing, and eye movements. Amblyopia is a frequent consequence of infantile esotropia. To date, its exact cause has yet to be identified, and an effective treatment strategy is yet to be formulated.
The exact cause of infantile esotropia remains unknown. While some opine that esotropia is due to excessive tonic convergence, few agree on what accounts for such conditions. Worth strongly believed that esotropia is an inborn and irreversible defect of fusion. As such, it is a primary dysfunction in the normal development of binocular sensitivity. This was countered by Chavasse who asserted that the neural components necessary for normal binocular vision are present in strabismic individuals at birth, but the development of fusion is eventually impeded by abnormalities of optical input (eg, monocular cataracts) or muscular output (eg, cranial nerve palsies).
The origins of infantile esotropia are just as undefined. A few authors have implicated practically everything from and between the extraocular muscles to the visual cortex in the causation of infantile esotropia.
Although understanding the mechanisms behind infantile esotropia has come a long way, there is still a lot of ground to cover to unearth and clearly understand such an elusive condition.
Strabismus is one of the most prevalent ocular problems among children, affecting 5 in every 100 US citizens, or some 12 million people in a population of 245 million. Infantile esotropia accounts for 28-54% of all esotropias. A population-based study from 1965 to 1994 reports the birth prevalence of infantile esotropia to be 25 per 10,000 or 1 in 403 live births.  It is thought to affect about 1% of full-term, healthy newborns and a much higher percentage of newborns with perinatal complications due to prematurity or hypoxic/ischemic encephalopathy.
In an attempt to determine whether esotropia is present at birth or develops later in infancy, Nixon et al observed 1,219 alert infants in a normal newborn nursery at a city hospital and noted that only 40 babies (3.2%) had esotropia (intermittent esotropia in 17 patients, with 14 patients varying between esotropia and exotropia, and 9 patients with variable esotropia). In addition, no infant displayed characteristic features of infantile esotropia.  As such, infantile esotropia is not believed to be connatal but rather develops in the first few weeks or months after birth.
Greenberg et al reported an annual age- and gender-adjusted childhood esotropia incidence of 111 per 100,000 patients younger than 19 years.  This rate corresponds to a cumulative prevalence of approximately 2% of all children younger than 6 years, with a significant decrease in older ages. The incidence of childhood esotropia from this population-based study is comparable to the prevalence rates among Western populations. Esotropia is most common during the first decade of life, with the accommodative and acquired nonaccommodative forms occurring most frequently.
Exotropia in infancy is believed to be associated with an increased prevalence of coexisting neurologic, ocular, and craniofacial abnormalities. To a lesser degree, infantile esotropia also has been associated with a high prevalence of systemic disorders, including prematurity, neurologic, and genetic disorders. Reports of coexisting brain lesions (eg, periventricular leukomalacia, enlargement of the lateral ventricles with hypoplasia of the corpus callosum, myelination delay at the anterior horn adjacent of the lateral ventricles) have been published.
By definition, infantile esotropia is seen in infants before age 6 months.
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