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REFRACTIVE DEVELOPMENT IN CHILDREN WITH DOWN SYNDROME: A POPULATION-BASED, LONGITUDINAL STUDY

Carr, Joanne K. OD, MPH

Clinical Studies
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Haugen OH, Hovding G, Lundström I. Refractive development in children with Down's syndrome: a population based, longitudinal study. Br J Ophthalmol 2001;85:714–719.

Original study reprint requests: Olav H. Haugen, Department of Ophthalmology, Haukeland University Hospital, N-5021 Bergen, Norway.

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Research Objective

To elucidate new aspects of the increased frequency of refractive error in children with Down syndrome (DS).

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Study Design

Prospective case studies series.

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Location

Hordaland County, Bergen, Norway.

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Funding Sources

None listed.

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Relevant Methodology

An unselected population of 60 children with Down syndrome was followed with repeated cycloplegic retinoscopies for 2 years or more (mean follow-up time 55 [SD 23] months). In the last 2–3 years of the study, each examination included dynamic retinoscopy. Normal accommodation was defined as a distinct shift from “with” to “against” motion. Children were categorized as having an accommodative weakness when no shift in the retinoscopy reflex occurred.

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Outcome Measures

Refractive error findings in 40 infants during the first year of life (mean age, 7.1 [SD 3.0] months.) Refractive error findings in 60 children with DS.

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Results

From longitudinal spherical equivalent values of the right eye, three main categories of refraction were defined: stable hypermetropia (<1.5 D difference between the first and last visit) (n = 34), increasing hypermetropia (“hypermetropic shift,” >1.5 D difference) (n = 11), and decreasing hypermetropia/development of myopia (“myopic shift”, >1.5 D difference) (n = 9). Patients with anisometropia (n = 6) were evaluated separately. In the stable hypermetropia group, three sublevels were chosen: low (<+2.0 D at the last visit), moderate (+2.25 to +4.0 D), and high (<+4.0 D). An accommodation weakness was found in 55% of the children. Accommodation weakness was significantly less frequent in the stable, low-grade hypermetropia group (22%) than in all the other groups (p = 0.008). The frequency of astigmatism >1.0 D at the last visit was 57%, the direction of axis being predominantly “with the rule.” All 12 eyes with oblique astigmatism had a side-specific direction of axis; the right eyes belonging to the 135° axis group and the left eyes to the 45° axis group.

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Conclusions

Stable, low-grade hypermetropia was significantly correlated with normal accommodation. Accommodation weakness appears to be associated with the high frequency of the refractive errors encountered in patients with Down syndrome. Additionally, as the authors state, “A striking right-left specificity in the oblique astigmatic eyes suggests that mechanical factors on the cornea from the upward slanting palpebral fissures may be a major aetiological factor in the astigmatism.”

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Comment

Refractive errors have been reported to be higher in individuals with Down syndrome. 1 In the present investigation, cytogenetic records in Hordaland county, Norway were used to identify all children with Down syndrome born between 1988 and 1999 to conduct a prospective study of refractive error development in an unselected Down syndrome childhood population. The Hordaland study met its objective of elucidating new aspects of the greater frequency of refractive error in DES children. The published article gives a poor account of this investigation.

Among numerous ambiguous points are the lack of data relating age to accommodative weakness. It is also not clear whether a lack of the “breakdown” in dynamic retinoscopy reflex is a reliable criterion for accommodative weakness in children with Down syndrome. The main analyses use subgroups based on the last examination findings. The advantage of a prospective study design is that rates of refractive error change during the study period can be determined from the first examination. Apparently, this was not done in the study.

The concluding sentence of the article's abstract suggests that the mechanics of the slanting palpebral fissure in Down syndrome could account for the observed development of oblique astigmatism. This poorly substantiated sentence could mislead readers who scan just the abstract. The predominant with-the-rule astigmatism (minus cylinder) finding, also noted in other studies, 2 does not support this hypothesis. Moreover, only five children (8.3%) demonstrated a shift to oblique astigmatism and three other children who lost their initial oblique astigmatism are not accounted for.

The Hordaland study shows that 53% of the infants evaluated were emmetropic or low hyperopes (<2.0 D). The longitudinal study showed little change in astigmatism between the first and last examinations and some support for accommodative weakness and lack of emmetropization in children with Down syndrome. One could conclude that children with Down syndrome might be consistently defocused at near, particularly when there is moderate hyperopia or a change in refraction. If the findings of the Hordaland study are confirmed in further studies, it would be wise to schedule routine refractions for children with Down syndrome who have hyperopia >2 D or who have a change in hyperopia or a decrease in myopia greater than or equal to 1.5 D. However, given the ambiguities in the report of this study, practitioners should await better evidence.

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References

1. Woodhouse JM, Pakeman VII, Cregg M, et al. Refractive errors in young children with Down syndrome. Optom Vis Sci 1997; 74:844–851.
2. Cregg M, Woodhouse JM, Pakeman VII, et al. Accommodation and refractive error in children with Down syndrome: cross-sectional and longitudinal studies. Invest Ophthalmol Vis Sci 2001; 42:55–63.
© 2002 Lippincott Williams & Wilkins, Inc.