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Editor,—Ingram et al 1 describe the effects of spectacles on changes of spherical hypermetropia in infants who did, and did not, have strabismus. The aim of the study was to explore why emmetropisation fails in children who have strabismus. It was found that mean spherical hypermetropia decreased in both eyes of non-squinters (consistent wearing of glasses impeded this process) whereas in the children with strabismus, there were no significant changes in either eye.
Could the difference between squinters and non-squinters not be explained by assuming that esotropia is more likely to occur in children who have increasing as opposed to decreasing hypermetropia, as suggested by us in 1992?2 If one reads early papers on the course of hypermetropia in childhood this seems so logical: papers reporting a decrease of hypermetropia during the first years of life3-5 concern cross sections of the general population, whereas papers that report an initial increase in hypermetropia6-10 originate from ophthalmological practices or strabismus departments. These contrasting findings could be reconciled when assuming a population bias: the children who are referred to an ophthalmologist will often have esotropia, and esotropia could well be more likely to occur when hypermetropia increases. Although hypermetropia decreases in most children, its change follows a change in distribution. In children who happen to have increasing hypermetropia with age, binocular vision develops and the relation between vergence and accommodation becomes fixed, so additional accommodation will be needed to overcome hypermetropia and they will consequently squint. Findings of other recent studies could be reconciled with this argument.11 12
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