Refractive errors and visual anomalies in Down syndrome
Joav Merrick and Kenneth Koslowe
A comparatively high incidence of ocular and orbital abnormalities has been reported in persons with Down syndrome. Eighty six children (50% male, 50% female) with Down syndrome in several institutions for individuals with learning difficulties (age range 5-18 years, mean 12.5) were examined for visual impairment in order to relate the ocular impairment to the level of learning difficulty. 6% had mild, 7% moderate, 45% severe and 42% profound learning difficulty. 9% of the children had no refractive errors. A significant (P<0.01) positive correlation was found between progressive amounts of strabismus and ocular pathology with increasing amount of learning difficulty. On the other hand no correlation was found between refractive errors and the level of learning difficulty. Due to the significant number of ocular disorders found it is recommended that all children with Down syndrome should have an eye examination during the first six months of life and annually thereafter.
Merrick J, Koslowe K. Refractive errors and visual anomalies in Down syndrome. Down Syndrome Research and Practice. 2001;6(3);131-133.
doi:10.3104/reports.105
Introduction
Ocular and orbital abnormalities are common features in persons with Down syndrome
and several researchers have reported their findings. Wong and Ho (1997)
evaluated 140 Chinese children in Hong Kong with detailed opthalmologic examination,
da Cunha and Moreira (1996)
examined 152 children in Brazil, Berk et al. (1996)
examined 55 patients in Turkey, Castane et al. (1995)
saw 25 patients in Spain, Roizen et al. (1994)
evaluated 77 children in Chicago, Courage et al. (1994)
tested 51 children in Canada, Hestnes et al. (1991)
saw 30 patients in an institution for individuals with learning difficulties in
Norway and Caputo et al. (1989)
evaluated 187 medical records in New Jersey.
In the present study we would like to present ocular findings in a group of children
with Down syndrome and relate the ocular defects to the level of learning difficulty.
Methods
Children with Down syndrome in several institutions for individuals with learning
difficulties were examined for visual impairment by one of the authors (KK). The
children had mild, moderate, severe and profound learning difficulties.
Distance refractive status was determined by cycloplegic examination or by using
assistants to maximize fixation on a distant target, when consent for the use of
cycloplegia could not be obtained. Opthalmoscopy was also performed.
The refraction results were divided into low myopia/hyperopia (less than or equal
to 2.00 diopters), moderate (2.25-6.00) and (>6.00) high myopia. In cases of
astigmatism the spherical equivalent was used and in cases of anisometropia the
result was expressed on the basis of the better of the two eyes.
The Chi-squared test and Pearson correlation coefficient were used in the statistical
analysis of the data.
Results
A total of 86 children (aged 5-18 years with a mean age of 12.5 years) were examined
in the institutions. Sex distribution was 50% male and 50% female. Mild learning
difficulty was found in 6% of the children, 7% had moderate, 45% severe and 42%
profound learning difficulty. 9% of the children did not have any refractive errors.
The group with low or no refractive errors included all of the children with mild
learning difficulty, 50% of those with moderate learning difficulties, 34% of those
with severe learning difficulties and 50% of those with profound learning difficulties.
None of the children with mild learning difficulties had moderate refractive errors,
but 50% of the subjects with moderate learning difficulties had moderate refractive
errors as did 38% of the children with severe learning difficulties and 42% of the
children with profound learning difficulties. Twenty eight percent of those with
severe learning difficulties and 8% of those with profound learning difficulties
had high refractive errors while none of the children with mild or moderate learning
difficulties had this degree of refractive error.
No strabismus was found in the children with mild learning difficulties, but strabismus
was found in 25% of those with moderate learning difficulty, 41% of those with severe
learning difficulties and 50% of the children with profound learning difficulty.
No other types of ocular pathology was found in the group of children with mild
learning difficulty, but 25% with moderate learning difficulties, 34% with severe
learning difficulties and 50% of the children with profound learning difficulties
had other types of disorder. The following conditions were found: cataract (in 37%),
corneal anomalies (in 6%), retinal anomalies (in 9%), blepharitis (in 9%), keratoconus
(in 13%) and nystagmus (in 9%).
The relationship between ocular disorder and the level of learning difficulty is
shown in Table 1. A significant correlation was found between
greater levels of cognitive impairment and increasing amounts of strabismus and
additional ocular pathology. On the other hand no correlation was found between
refractive errors and the level of learning difficulty.
Table 1. The relationship between refractive errors and
visual anomalies to the level of learning difficulty in persons with Down syndrome.
|
Group
|
Correlation coefficient
|
Significance
|
|
Strabismus versus learning disability
|
0.988
|
P < 0.01
|
|
Low refractive error versus learning disability
|
0.818
|
Not significant
|
|
Moderate refractive error versus learning disability
|
0.448
|
Not significant
|
|
High refractive error versus learning disability
|
0.789
|
Not significant
|
Discussion
The faces of persons with Down syndrome display narrow interpupillary distance,
upward and outward slanting palpebral fissures and epicanthus. These clinical features
were of diagnostic importance before it became possible to base the diagnosis of
Down syndrome on chromosomal analysis.
Ocular and orbital abnormalities in persons with Down syndrome are common and have
been reported with varying frequency in different surveys (Catalano,
1992): blepharitis (2-47%), keratoconus (5-8 %), glaucoma (less than 1%),
iris anomalies (38-90%), cataract (25-85%), retinal anomalies (0-38%), optic nerve
anomalies (very few cases), strabismus (23-44%), amblyopia (10-26%), nystagmus (5-30%)
and refractive errors (18-58%). The earlier mentioned researchers and clinical centres
for persons with Down syndrome reported on the overall occurrence of ocular problems,
but we have not been able to find reports relating the ocular findings with cognitive
level.
In our study we found a significant correlation between increased ocular pathology
and strabismus with an increased level of learning difficulty. The results for refractive
disorders did not follow such a pattern. While low refractive errors were present
in the entire group of persons with mild learning difficulties they were present
to the same extent in persons with moderate and profound learning difficulties.
While moderate refractive errors were absent in the group with mild learning difficulties,
they were fairly evenly distributed in the other groups. The one factor that seemed
to emerge was the relatively high prevalence of high refractive errors in the children
with severe learning difficulties.
Conclusion
A very significant number of persons with Down syndrome have undiagnosed or underdiagnosed
ocular problems that can affect their quality of life if uncorrected. It is therefore
recommended that all children with Down syndrome should have an eye examination
during the first six months of life and annually thereafter.
Acknowledgements
We would like to thank all the personnel in the institutions for their cooperation.
Correspondence
Joav Merrick, MD, DMSc, Medical Director, Division for the Mentally Retarded, Box
1260, IL-91012 Jerusalem, Israel, • Email jmerrick@aquanet.co.il
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