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| British Journal of Ophthalmology
2006;90:357-361; doi:10.1136/bjo.2005.078105 Copyright © 2006 by the BMJ Publishing Group Ltd.
Longitudinal changes in the spherical equivalent refractive error of children with accommodative esotropiaS R Lambert1, M J Lynn2
1 Emory Eye Center, Pediatric Ophthalmology,
Atlanta, GA, USA
Correspondence to: Accepted 17 October 2005
Aim: To assess the longitudinal changes in the spherical equivalent (SE) refractive errors of children with accommodative esotropia as a function of the age when glasses were prescribed. Methods: Refractive errors were followed longitudinally for 126 children with accommodative esotropia for a mean of 4.4 (SD 2.5) years. Cycloplegic refractions were performed using an autorefractor for older children and retinoscopy for younger children. The refractive data were analysed for three groups of children based on their age at the time spectacles were prescribed. Results: The initial SE refractive error was age dependent (<2 years, 5.1 (1.9) D; 2<4 years, 4.2 (1.9) D; 48 years, 3.8 (1.7) D). Children in all age groups had an initial increase in their SE refractive error, followed by a later decrease; however, the greatest decrease occurred in the patients in the oldest age group. The SE refractive error peaked 1 year after spectacles were prescribed for the children 48 years of age versus 6 years after spectacles were prescribed for the children less than 2 years of age. Conclusion: Longitudinal changes in SE refractive error for children with accommodative esotropia vary as a function of their age when spectacle wear is initiated.
Keywords: emmetropisation; accommodative esotropia; spheroequivalent refractive error; amblyopia; autorefraction; children Accommodative esotropia has its onset during childhood and is associated with varying degrees of hyperopia. The initial treatment is optical correction of the full hyperopic refractive error. Several studies have followed longitudinally the spherical equivalent (SE) refractive errors of children with accommodative esotropia.13 In most cases, there is an increase in the SE refractive error during the first 7 years of life, followed by a myopic shift extending into adulthood. Usually the myopic shift is not large enough to allow spectacle wear to be discontinued. Animal models have demonstrated that wearing either plus or minus lenses can alter the normal process of emmetropisation in immature eyes. Lens induced changes in refractive errors are generally compensatory, with plus lenses inducing a hyperopic shift and minus lenses a myopic shift.4,5 Smith and Hung6 noted that fully correcting the hyperopic refractive errors of juvenile monkeys induced a hyperopic shift. The goal of this study was to evaluate the longitudinal changes in the SE refractive errors of children with accommodative esotropia as a function of their age when they were prescribed spectacles. Unlike other longitudinal studies of children with accommodative esotropia, we studied the longitudinal changes in refractive errors as a function of age when spectacles were prescribed rather than chronological age alone.
After obtaining approval from the institutional review board, data were collected from a consecutive series of patients with accommodative esotropia. The patients were identified by creating a printout of all patients in a database coded with ICD-9 378.35 (accommodative component in esotropia), who were examined by the author between 1998 and 2001. The charts were then reviewed retrospectively and patients with 0.75 dioptre or more of hyperopia and an esotropia that decreased by 10 prism dioptres or more when the patient wore their full hyperopic correction were considered for inclusion in the study. Also included were patients who had been treated by another ophthalmologist before being examined by the author provided that all the inclusion criteria were met and provided that the date they were prescribed glasses and the refractive correction prescribed could be ascertained from their medical record. Patients were excluded from the study if they had a neurological disorder, other ocular disorders associated with reduced visual acuity, visual acuity not correctable to 20/30 or better in at least one eye, spectacle use before the onset of their esotropia, or a follow up interval of less than 6 months. All patients who were examined prospectively between January 2002 and April 2004 who met the inclusion and exclusion criteria were also included in the study. A general information data form was completed on each patient including the date of birth, the date of the first ocular examination, the date the esotropia was first noted, the date spectacles were prescribed, and the dates strabismus surgeries were performed. A visit data form was then completed to record each time the patient underwent a cycloplegic refraction using retinoscopy or autorefraction. Included on this data form was date of the visit, refractive error (sphere, cylinder, and axis), technique used to assess refractive error, best spectacle corrected visual acuity (BSCVA), power of the correction worn, angle of stereopsis, angle of esotropia with and without correction, and type of amblyopia treatment prescribed. All patients were then assigned a study ID number and the data forms were then faxed to a biostatistician for analysis. When possible visual acuity was obtained using Snellen letters.
In younger children, Allen letters and the HOTV test were used.
Amblyopia was defined as an interocular difference in visual
acuity of two lines or more. Ocular alignment was assessed
using the simultaneous prism cover test in older children and
the Krimsky or Hirschberg light reflex test in younger
children. Cycloplegia was obtained with 1% cyclopentolate.
Refractions were performed 3060 minutes later after the
patients were fully cyclopleged. Beginning in December 1997, a
Nidek ARK-700A (Nidek, Hiroishi, Japan) autorefractor was used
to ascertain the refractive error of all cooperative
children. The Nidek ARK 700A autorefractor has a red hot air
balloon as a fixation target and eye tracking capabilities
which make it possible to autorefract most children who are 3
years of age or older. Before 1997 and in uncooperative
children, the refractive error was ascertained using
retinoscopy with hand held lenses or a phoropter. Cycloplegic
refractions were generally performed once each year. They were
performed more often if there was a reduction in visual acuity
or a deterioration in ocular alignment. Anisometropia was
defined as an interocular difference in the SE refractive error
Spectacles were prescribed that corrected the entire cycloplegic refractive error when spectacle treatment was initiated. In older children with fully accommodative esotropia, an attempt was made to gradually reduce their hyperopic correction to the lowest power that would maintain orthotropia without causing asthenopia. No attempt was made to wean children with partially accommodative esotropia from spectacles correcting their cycloplegic refractive error. The full astigmatic refractive error was prescribed for patients at all ages. The SE refractive error was defined as the sum of the sphere and one half of the cylinder power. Cylinder powers were measured and recorded using plus nomenclature. Only five patients had more than 10 years of follow up, so data were only analysed for the first 10 years of follow up. Two patients were excluded from the analysis because the date of onset of esotropia could not be ascertained. Stereopsis was assessed using the TNO test (Lanιris Ootech, Groenekan, Netherlands). The stereopsis measurement that was taken closest to the age of 6 years was chosen for analysis. Statistical
analysis The statistical analysis relating the longitudinal values of refractive error and cylinder power to the time after spectacles were prescribed and the age of the patient was done using a general linear mixed model.7 The general linear mixed models were estimated using Proc Mixed from the Statistical Analysis System (SAS) (SAS Institute, Inc, Carey, NC, USA).
A total of 126 patients met the inclusion criteria for the study. The mean age of onset of the esotropia was 2.6 (1.8) years (range 08.0 years) and the mean age that spectacles were prescribed was 3.2 (1.7) years (range 0.38.2 years). The mean length of follow up was 4.4 (2.5) years (range 0.59.7 years). Sixteen (13%) of the patients received patching therapy, three (2%) received atropine penalisation, and two (2%) received both. At the last follow up examination, the BSCVA was 20/30 or better in 109 (90%) right eyes and 107 (88%) left eyes and the worst BSCVA was 20/50 in a right eye and 20/60 in a left eye. Stereopsis was assessed at a mean age of 6.7 (2.2) years. Ten (12%) patients had 1560 seconds of arc of stereopsis and 15 (18%) had 120480 seconds of arc. The remaining 58 patients (70%) only had gross stereopsis (<480 seconds of arc) or no stereopsis. High grade stereopsis (15%60 seconds of arc) was found to correlate with an older age when the esotropia was noted (p = 0.008) and an older age when spectacles were prescribed (p = 0.0167). Thirty eight patients (30%) underwent one or more strabismus operations. Change in spherical
equivalent refractive error
Linear mixed model To evaluate the statistical significance of the effect of age when spectacles were prescribed and time after spectacles were prescribed on the change in the mean SE refractive error, a linear mixed model was employed (table 3  ). The final model included a linear term for age,
a linear and quadratic term for time after spectacles were
prescribed, and an interaction term for age and time. The
quadratic term for time after spectacles were prescribed
(p<0.0001) and the interaction of age and time after
spectacles were prescribed (p<0.0001) were both highly
significant. Following the hierarchical principle, the linear
terms for both time after spectacles were prescribed
(p<0.0001) and age (p = 0.03) were also included in the
model. The model suggested that there was a significant effect
of age and time after spectacles were prescribed on the SE
refractive error. The SE refractive error changed in a
non-linear manner with time according to the age of the child
at the time spectacles were prescribed. These effects can be
readily viewed in a graph of the model (fig 3). The graph of the model shows that the mean SE
refractive error versus time after spectacles were prescribed
according to the age when spectacles were prescribed. The graph
illustrates that the SE refractive error did not peak for
several years after spectacles were prescribed for the youngest
patients, whereas for children who were prescribed spectacles
at an older age there was almost an immediate decline in their
SE refractive error.
Accurately assessing the refractive errors of young children is challenging owing to their inability to give subjective responses and the difficulty of having children maintain fixation on a distant target. While retinoscopy with either hand held lenses or a phoropter has traditionally been used to determine the refractive errors of young children, autoretraction is gradually supplanting retinoscopy as a result of its greater accuracy.7,8 Unfortunately, it is quite difficult to autorefract most children 2 years of age or younger using the Nidek ARK-700A autorefractor. This shortcoming limited the autorefraction data available for the youngest age group. We found that the SE refractive error peaked 3 years after
spectacles were prescribed and gradually decreased thereafter.
Repka and colleagues9
and Raab2,10
have reported that the SE refractive error increases in
children with accommodative esotropia until they are 7 years of
age and then decreases thereafter. However, we found that the
longitudinal change in the SE refractive error varied as a
function of the age of the child when spectacles were
prescribed. For children who were less than 2 years of age when
spectacles were prescribed, the SE refractive error peaked 6
years after they were prescribed spectacles. In contrast,
hyperopia peaked more quickly for children who were prescribed
glasses at a later age. Children in the oldest age group also
experienced a greater myopic shift over time. The effect of
age on the change in SE refractive error versus time is shown
in figure 3 While wearing plus lenses has been shown to consistently interfere
with emmetropisation using various animal models, the effect
of wearing plus lenses on the emmetropisation of children is
less certain. Ingram11
randomised a group of infants with 4D or more of hyperopia to
no treatment or to a partial correction with spectacles. After
a 3 year follow up, more of the children randomised to
spectacle wear who consistently wore their spectacles retained
3.5D or more of hyperopia. Richardson (Richardson S, AAPOS
Meeting, 2004, Abstract) randomised a group of children with
anisometropic amblyopia to spectacle correction or no treatment
for 1 year. Spectacle correction impeded emmetropisation in
the normally sighted eyes, but not in the amblyopic eyes. The
most pronounced effect occurred in children with 3D or more
of baseline hyperopia. These results would suggest that
amblyopic eyes may be less sensitive to the effects of
spectacle wear on emmetropisation than normally sighted eyes.
We had only a small number of amblyopic eyes in our study, but
we did not find a qualitative difference in the longitudinal
changes in the SE refractive errors of the amblyopic eyes. In a
small prospective study of children with high hyperopia and a
family history of strabismus, Aurell and Norsell12
reported that the children who developed accommodative
esotropia and were treated with spectacles maintained or
increased their hyperopia, whereas the children who did not
develop accommodative esotropia and who were not treated with
spectacles lost most of their hyperopia by the time they were 4
years of age. In contrast, Atkinson and colleagues13
reported that spectacle wear had only a small, transient effect
on emmetropisation for infants with at least one meridian of
hyperopia This study has a number of limitations. Firstly, the study was retrospective, resulting in incomplete data for some patients. Secondly, retinoscopic refractions and autorefractions were combined for some of the data analyses. It would have been preferable if autorefraction data alone could have been used; however, this requirement would have significantly reduced both the sample size and the length of follow up. Thirdly, it would have been instructive to have studied a control group of age matched children who were not treated with spectacles. The most appropriate control group would be age matched children with accommodative esotropia who were not treated with spectacles; however, it would be unethical to withhold spectacle treatment from these children. Alternatively, age matched children without accommodative esotropia, but who had similar refractive errors could serve as a control group. However, it would be difficult to identify a large sample size of patients with these characteristics and their refractive development may differ from children with accommodative esotropia independent of spectacle wear. Finally, a longer follow up interval would have been preferable. The effects we noted may have been more or less pronounced had the follow up been longer. While spectacle wear has been proved to be an effective means of restoring ocular alignment, averting amblyopia, and maintaining stereopsis for many children with accommodative esotropia,14,15 it may also interfer with emmetropisation. Further studies will hopefully elucidate the optimal means to optically correct children with accommodative esotropia to minimise the effect of spectacle wear on emmetropisation.16,17
Supported in part by National Institutes of Health, Departmental Core Grant EY 06360 and Research to Prevent Blindness, Inc.
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ABSTRACT
METHODS
1.5
D.
