Infantile esotropia is a form of ocular motility disorder where there is an inward turning of one or both eyes, commonly referred to as crossed eyes.
It occurs during the first 6 months of life in an otherwise healthy child. It can be associated with a systemic disease such as Down’s syndrome, albinism, cerebral palsy, or hydrocephaly.1-4
The etiology of infantile esotropia remains unknown. It is likely that there are multiple causes that lead to the development of the misalignment.1 Theories have been postulated regarding the pathogenesis of the disease.
An early theory by Worth2 suggested that there is congenital absence of fusion potential at the cortical level, where restoring binocularity is not probable. On the contrary, reports have shown favorable results in restoring binocular fusion and stereopsis by performing early surgery between the age of 6 months and 2 years.3-5
Another theory by Chavasse6 suggested a primary motor dysfunction, where the associated poor fusion and lack of high-grade stereopsis is probably a sensory adaptation to abnormal visual stimulation during early binocular development caused by the motor misalignment.
Tychsen et al have shown15 that naturally strabismic macaque monkeys lack vertical and horizontal connections in the ocular dominance columns that nonstrabismic monkeys have. They have also demonstrated that early surgery restores some of these pathways and allows for development of visual motion pathways in the cerebral cortex.15
Although only 30% of normal neonates have straight eyes, infantile esotropia occurs in only 1%-2% of the normal population.1 This is because eye alignment is a maturing process until 3-4 months of life when alignment should be straight when looking at objects ≥ 14 inches away. Infantile esotropia should not be confused with the common intermittent eye crossing seen in infants before they develop a higher level of accommodative and version control.
Genetic factors appear to play a small part in the development of infantile esotropia, with no sex predilection.
Environmental influences have been identified in approximately half of the affected children. Prematurity and perinatal hypoxia predispose to the development of the condition. Maternal smoking and alcohol consumption during pregnancy have also been associated.7
Detailed history taking regarding birth weight, complications of birth, the health of the child and developmental milestones may help in the management of the case. History of first presentation aided by photographs of the child in the first few months of life can assist in documenting the onset, detecting the stability of the condition and confirming the diagnosis. Family history may elicit the presence of a genetic factor/ familial inheritance.
Inspection of the infant through observation of the visual behavior, head posture and eye movements will establish a presumptive diagnosis. Penlight (Hirschberg corneal reflex test) held at 33 cm reveals large angle esotropia (inturning), where the corneal light reflex is temporally displaced. It is often helpful to place an accommodative fixation target next to the light source to maintain the child’s attention. The exam should be quick and performed in a fun atmosphere. Try to maintain the child’s attention at all times. This can be done by engaging the patient through the use of colorful toys, whistling and making noises. It is also advised to perform the exam without touching the child if possible. In addition, save the most intrusive parts of the exam for last.
Size of the devation
Esotropia is the most common type of strabismus occurring in infancy, characterized by a large angle manifest deviation that measures between 30 - 70 prism diopters.
Amblyopia occurs in approximately 40% - 50% of children with congenital esotropia.1 This can be elicited by showing a fixation preference for one eye.
Many infants may freely alternate their fixation. Others may cross fixate using alternate eyes in the opposite field of gaze, (i.e. looking to the left with the right eye and looking to the right with the left) and do not develop amblyopia.
Infantile esotropia with high refractive errors (hypermetropia more than +2.50 diopters) can easily be confused with accommodative esotropia, which may occur as early as 6 months of age. Accomodative esotropia manifests as eye inturning secondary to the increased work of focusing through significant hypermetropia.
Some infants may show some limitation of abduction upon initial examination of eye movements as a result of cross fixation. However by eliciting doll’s head maneuver where gentle spinning of the child stimulates a vestibular movement to the opposite direction of the spin and a refixation saccade in the same direction, full abduction can be elicited.
Dissociated vertical deviation (DVD) occurs in approximately 75% of patients with infantile esotropia. DVD is elevation of the non-fixing eye when covered or with visual inattention.
Inferior oblique overaction occurs in approximately 70% of patients with infantile esotropia. This is seen as over-elevation of the eye in supra-adduction.
Latent nystagmus occurs in approximately 50% of patients with infantile esotropia. It is a predominantly horizontal jerk nystagmus elicited by occluding either eye. The slow phase is toward the side of the occluded eye.8
Identification of the proper deviation in infancy without evidence of cranial nerve palsies or systemic disease to explain the deviation.
Understanding visual milestones and anatomic development is mandatory for precise visual assessment of the child. On average, by 2 months of age, the optic nerve completes myelinization. At 3 to 4 months, the fovea develops, and by 6 months iris pigmentation is approximately 90% complete. Methods to evaluate vision in infants include fixation and following visual behaviors, Visual evoked potential (VEP) testing, optokinetic response, preferential looking and optotype visual acuity depending on the child’s age and level of cooperation.8
Cover/uncover testing is used to detect and quantify eye misalignment. It is necessary to test the function of each extraocular muscle (ductions and versions) and the patient’s control over the deviation. Additional tests may include prism adaptation and diagnostic occlusion.10
Complete sensory evaluation in a preverbal child is difficult. Some signs may give a clue about the sensory development and the prognosis of the condition. Detection of fixation preference for one eye can be performed by the use of vertical prism test (10-prism diopter test)11. Optokinetic response to detect smooth pursuit and saccade eye movements will aid in the diagnosis of amblyopia.
• Accommodative esotropia
• Abducens palsy (Cranial Nerve IV)
• Nystagmus blockage syndrome
• Duane’s syndrome
• Esotropia secondary to central nervous system abnormalities
• Ciancia syndrome
• Congenital fibrosis syndrome
• Myasthenia gravis
Evaluation for an underlying disease process should be made when symptoms and signs lead in that direction. Medical therapy should be attempted. However, most cases of infantile esotropia will require surgical intervention.12 It should be noted that any eye disease which significantly decreases vision (i.e. corneal opacity, cataract, optic nerve disease, retinal disease) may compromise eye alignment and can lead to an esotropia. Life threatening conditions such as retinoblastoma must be ruled out when infantile strabismus is noted. Usually children with infantile esotropia that present after 6-9 months of age and those who show limited abduction require imaging.
Occasionally infants with small angle esotropia <30 PD may be corrected with hypermetropic spectacle correction.
The timing of amblyopia treatment in relation to eye muscle realignment surgery is debatable. Some surgeons treat amblyopia before performing surgery to create a stronger visual drive for straight eyes and thus better outcomes. Amblyopia occlusion treatment after the eyes are aligned can interfere with the exercise of binocularity. However, some surgeons may opt to surgically realign the eyes prior to amblyopia therapy if strabismic amblyopia is suspected. Early re-alignment has been shown to lead to improved sensory outcomes. 13
Stability of the esotropia angle is assessed prior to surgical intervention. Prism adaptation testing (PAT) may assist in this determination. Traditionally, PAT is used in acquired ET to determine the surgical angle and estimate fusion potential. According to the Prism Adaptation Study Research Group, “Prism adaptation is defined as the preoperative wearing of Fresnel prisms to offset the angle of esotropia with adjustment of prism power over time to accommodate buildup to larger angle of esotropia, until fusion is achieved or it is demonstrated that fusion cannot be attained.”14 Once a correction target angle of esotropia is determined surgery can be undertaken.
Theoretically, the earlier the surgery is performed the better the potential for binocular function. However technically the surgery is more difficult earlier in infancy because of the small size of an infant’s eye and orbit, in addition to the lack of stability of the deviation and the possibility of spontaneous resolution.12 Parents should be aware that the goal of treatment is to get the eyes aligned and encourage the best sensory development possible, which might take more than one surgical procedure. The standard approach for treatment is bilateral medial rectus recessions which weakens the medial recti (the muscles pulling the eyes inward). Alternately, a medial rectus recession with an ipsilateral lateral rectus resection can achieve the same effect. Botulinum toxin injection into the medial recti to weaken them has also been used, but studies have shown mixed sensorimotor outcomes when compared to traditional incisional surgery. If signs of inferior oblique overaction are noted, surgical weakening of the inferior oblique muscles is usually performed simultaneously. The other associated conditions of DVD and latent nystagmus usually appear later in life and may be addressed surgically at that point. Link to strabismus surgery entry.
Surgical follow up
After surgical realignment, patients are usually advised to return within 2 weeks following surgery to assess eye alignment and the ocular healing process. Intraocular infection is rare following strabismus surgery Patients should be followed closely for amblyopia, even if they achieve good motor alignment. Close follow up is required especially in cross fixating children as amblyopia in one eye usually presents after surgical alignment.7, 10
Undercorrection and overcorrection are the most commonly noted complications. Many of these are transient. Other less common complications include perforation of the sclera, lost or slipped muscles, infection, anterior segment ischemia, postoperative diplopia, conjunctival granulomas and cysts. Link to Horizontal Strabismus Surgery.
Untreated infantile esotropes can develop excellent vision in each eye, but bifoveal fixation with full binocular function will not be achieved. Therefore, they will have poor depth perception and atypical appearance. Poor visual acuity will occur in the face of amblyopia. When infants undergo early surgical intervention, they have a chance of better alignment and stereopsis outcomes. Multiple surgeries may be needed to correct large angle esotropia. The number of children requiring a second operation varies between 15-30%.7 Amblyopia, residual esotropia or consecutive persistent exotropia may develop and should be addressed early to get the best possible visual and fusion potential.
1. Wright KW. Esotropia. In: Wright KW. Pediatric ophthalmology and strabismus. St. Louis, MO: CV Mosby;1995.p.179-94.
2. Worth C. squint, its causes and treatment. London: Bailliere, Tindall, and Cox, 1903.
3. Costenbader FD. Infantile esotropia. Trans Am Ophthalmol Soc 1961;59:397-429.
4. Taylor DM. How early is early surgery in the management of strabismus? Arch Ophthalmol 1963;70:752-6.
5. Ing M, Costenbader FD, Parks MM, et al. Early surgery for congenital esotropia. Am J Ophthalmol 1966;62:1419-1427.
6. Chavasse FB. Worth’s squint on the binocular reflexes and the treatment of strabismus, 7th ed. Philadelphia: P.Blakiston’s Son & Co, 1939.
7. Elston J. Concomitant strabismus. In: Taylor D. Pediatric ophthalmology. 2nd ed. London: Blackwell science; 1997. p. 925-36.
8. Hiles DA, Watson A, Biglan AW. Characteristics of infantile esotropia following early bimedial rectus recession. Arch ophthalmol 1980;98:697-703.
9. Robbins SL et al, Vision testing in the pediatric population, Ophthalmol Clin N Am 16 (2003) 253-267.
10. Raab EL. Comitant esotropia. In: Wilson ME, Saunders RA, Trivedi RH. Pediatric ophthalmology: current thoughts and practicle guide. Leipzig. Springer;2009. p. 85-112.
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12. Pediatric Eye Disease Investigator Group. Spontaneous resolution of early-onset esotropia: experience of the Congenital Esotropia Observational Study. Am J Ophthalmol 2002;133:109-18.
13. Birch EE, Stager DR, Berry P, and Everett ME. Prospective assessment of acuity and stereopsis in amblyopic infantile esotropes following early surgery. Inv Ophthalmol and Vis Sci, 1990; 31:758-65.
14. Kutschke PJ, Scott WE. Prism adaptation in visually mature patients with esotropia of childhood onset. Ophthalmology. 2004 Jan; 111(1): 177-9.
15. Tychsen LT, Wong AF, Foeller P, Bradley D. Early versus delayed repair of strabismus in macaque monkeys: II. Effects on motion visually evoked responses. nvestigative Ophthalmology and Visual Science. 2004;45:821-827.