13 Infantile esotropia

Background

Infantile esotropia is the term used to describe a large angle comitant convergent squint with an onset between three and six months of age, commonly associated with hypermetropia, cross fixation, inferior oblique overaction, dissociated vertical deviation, latent nystagmus and asymmetry of monocular OKN.1,2 It has a prevalence of 1% and accounts for up to 54% of all esotropias in industrialised countries.3–5

Once refractive errors and amblyopia have been treated, the main goal of surgical treatment of infantile esotropia is to achieve some degree of binocular single vision (BSV). To obtain full, normal BSV is rare,6–8 and subnormal or gross stereopsis is generally considered an acceptable result.9,10 Gross stereopsis is reported to be achievable in up to 50% of cases.11–14

Cosmesis is also an important outcome, as squint can have psychosocial implications for the affected child and parents,15 particularly if it remains uncorrected into adulthood.16

Von Noorden et al.17 have proposed the following taxonomy:

●“subnormal binocular vision” being the optimal result

●“microtropia” being a desirable result

●a “residual small angle eso/exotropia” as a cosmetically acceptable result

●a large angle eso/exotropia as a cosmetically unacceptable result.

The issues

Currently two major issues in the management of infantile esotropia are the optimal timing for surgical correction18 and the emerging use of botulinum toxin A (BTXA) as an adjunct or alternative to surgical alignment.

Over the past two decades, injection of botulinum toxin has become established as an important adjunct to surgery and as the primary treatment for some types of squints. It has recently been increasingly used in young children.19–21

Question

In children with infantile esotropia does early alignment (six months or under), compared with alignment at two years, result in better binocular single vision, better cosmesis and better long-term alignment?

The evidence

We found no randomised controlled trials that address this question. The Early Surgery for Congenital Esotropia Trial (ESCET) is an United States National Institute of Health funded multi-centre, randomised prospective study, which is currently underway and results are anticipated in 2004.22,23 This trial will compare the outcome of children operated on between the ages of 11 to 18 weeks with those operated on between the ages of 28 to 32 weeks. The primary outcome is stereoacuity, and secondary outcomes are motor alignment, fusion, dissociated deviations and re-operations.

Comment

Observational clinical and laboratory studies suggest that accurate alignment before the age of two years may be more beneficial than later surgery in terms of achieving binocularity.4,9,24 In a retrospective study of 40 children with infantile esotropia, all of whom had surgery aged 22 months or less and achieved alignment at a mean of 24 months (range 7 to 48 months), Rowe25 reported that 22·5% achieved binocular vision and 60% achieved a small angle (<20 prism dioptres) esotropia postoperatively. Nevertheless, surgical alignment after the age of two years does not preclude the attainment of subnormal binocular vision or microtropia.26

It has been demonstrated that normal infants show an abrupt onset of stereopsis in the time period of three to five months of age.27 As this would require motor alignment, it is increasingly argued that children with infantile esotropia should undergo surgery as soon as possible. However, observational data regarding the additional benefits of very early treatment in the first year of life are inconsistent.8,22,26,28–30 In an

analysis of 16 patients, Ing found that those who underwent surgery at five months or younger did not have significantly better binocularity at seven years compared with those undergoing surgery at older ages.31 Helveston et al.32 achieved measurable stereopsis in 40% of infantile esotropes who were aligned at a mean of 4·4 months. This group also demonstrated that very early alignment (age two to four months) did not increase the chance of achieving “fine” stereoacuity (i.e. 50 seconds of arc).

Question

In children with infantile esotropia does primary treatment with using botulinum toxin, compared with conventional primary surgical alignment, result in better binocular single vision, better cosmesis and better long-term alignment?

The evidence

We found no trials comparing alignment using botulinum toxin with surgery as the primary procedure.

Comment

To date, only observational clinical studies suggest that botulinum toxin may have a role as the primary approach in some children with infantile esotropia.33 Findings of a recent trial in children with residual squint following a primary surgical procedure suggest that botulinum toxin A confers greater benefits than a second surgical procedure, as it is a more rapid and less invasive procedure but with a similar outcome.34

Implications for practice

The issue of when to operate remains contentious. Whether very early surgery in the first year of life confers benefit needs to be established through ongoing and future trials. The results of the ESCET trial should provide information that is currently lacking. Observational and laboratory evidence suggests a benefit of surgical alignment at age two years or under. Equally, the increasing interest in botulinum toxin as an alternative or adjunct to surgery requires investigation through trials.

Implications for research

For both questions, long-term alignment and patientbased, subjective measures of outcome should be addressed.

References

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2.Norcia AM. Abnormal motion processing and binocularity; infantile esotropia as a model system for effects of early interruptions of binocularity. Eye 1996;10:259–65.

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21.Tucker MG, NcNeer KW, Spencer RF. The incidence of latent nystagmus in infantile esotropia patients treated early with bimedial botulinum toxin A. Invest Ophthalmol Vis Sci 1997;38:S112.

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32.Helveston EM, Neely DF, Stidham DB, Wallace DK, Plager DA, Spru. Results of early alignment of congenital esotropia. Ophthalmology 1999;106:1716–26.

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34.Tejedor J, Rodriguez JM. Early retreatment of infantile esotropia: comparison of reoperation and botulinum toxin. Br J Ophthalmol 1999;83:783–7.