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Vision in children with Down's syndrome
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Vision in children with Down's syndrome
School of Optometry &
Vision Sciences, Cardiff University, Cardiff CF10 3NB
Vision in children with Down's
syndrome
Because children with Down's syndrome
often have particular difficulties with language, educationalists describe
the children as 'visual learners' and recommend the use of visual
aids in the classroom. It is therefore especially important that
the children's vision is as good as it possibly can be and that the
children are given every opportunity to access visual stimuli. Unfortunately,
children with Down's syndrome are at much greater risk of eye and vision
disorders than are typically developing children. They therefore need
regular eye examinations, are more likely to need glasses than typical
children, and may need compensation in the classroom / learning environment
for visual deficits. Classroom and advisory teachers as well as parents
need to be aware of the visual difficulties that the children may experience.
At the Down's Syndrome Vision Research
Unit, we have been studying visual development in children with Down's
syndrome since 1992. We have a large group of enthusiastic and highly
committed families taking part in our studies, many of whom have been
with us since the beginning, and we see over 100 children regularly.
Our most significant findings are described below.
Refractive Errors
Long-sight, short-sight and astigmatism
are much more common in children with Down's syndrome than in typical
children, and many more will need to wear glasses. Ordinary children
are often long or short-sighted in early infancy, but grow out of these
errors over the first few years of life. Children with Down's syndrome
start out with a similar range of errors as do ordinary children, but
are much less likely to outgrow the errors and much more likely to become
more long or short-sighted.
Figure 1. Long and short sight amongst 6 year olds
It is important (as for any child in
the classroom) that the teacher understands when a child will need his/her
glasses, and what level of vision he/she will have both with and without
glasses. Long-sight of low to moderate degree can be overcome in typical
children by accommodation (active focusing) and not all children who
are long-sighted need glasses. However, children with Down's syndrome,
because they have difficulty in focusing (see later), will be much more
dependent on their glasses for clear comfortable vision than will typical
children. Children who are short-sighted, on the other hand, may be
better off without glasses for close work.
Squint
Children with Down's syndrome are at
much greater risk of developing a squint (eye-turn) than are typical
children. A child with a squint is likely to have a poorer level of
binocular vision especially depth perception. Tasks requiring fine depth
discrimination, such as threading beads, will be more difficult.
Accommodation (focusing at near)
Children's interests are mostly close
at hand, and most of children's learning takes place at near. And
it is at near that we find the greatest differences between vision in
children with Down's syndrome and typical children.
Usually, children focus very easily and
very accurately on near targets and it is only as we approach middle
age that we expect to experience difficulty in focusing at near. We
find, however, that most (over 70%) children with Down's syndrome focus
very poorly at near - they tend to under-accommodate by quite a large
amount. This is consistent for any individual child, and persists even
when the children wear their glasses to correct long sight. This means
that near work, especially in school, must be more difficult for the
children because it is out of focus.
Figure 2. Near focusing in children
We don't yet know the reason for the
poor focusing and we have studies underway to examine various possibilities.
However, we do now know that the children's focusing improves dramatically
with bifocal spectacles. In a controlled trial, we supplied bifocals
to a group of 17 primary school children with Down's syndrome, and conventional
spectacles to a second group (the control group). The two groups were
matched for all of the factors that might influence spectacle use or
near work, such as age, cognitive ability, school placement etc. Over
a 20-week trial, the children in the bifocal group consistently focused
more accurately on near work than did the children in the control group.
Figure 3
Bifocal lenses
Conventional (single vision) lenses
Figure 4. Measures
of accommodation (near focusing) in children with Down's syndrome wearing
bifocals and children wearing conventional spectacles (control)
In the trial, and now that we prescribe
bifocals clinically, we find that children with Down's syndrome wear
bifocals very successfully. None, so far, have encountered any problems,
and several of the children prefer to wear their bifocals all of the
time rather than keep them for school use. Two children were very reluctant
to wear glasses when they had conventional ones, but now wear bifocals
very happily. In some cases teachers and classroom assistants have reported
improvement in concentration and quality of work when the children wear
bifocals. We are now, therefore, recommending that all children with
Down's syndrome who show poor focusing are prescribed bifocals.
The positioning of the bifocal is
very important. The top of the bifocal should lie across the child's
pupil (this is a much higher position than usual for bifocals) so that
the child can look down through the bifocal without effort. We provide
an information leaflet that parents may take along to their child's
eye examination; this specifies the correct position for the bifocal.
Visual Acuity (detail vision)
Detail vision is usually measured in
adults with the familiar letter chart. For children (and people of any
age with learning disabilities) there are lots of alternatives that
don't need reading skills. These include picture naming, matching
or signing and the preferential looking tests that only require the
child to look towards a picture or target. It is, therefore, possible
to measure how well someone can see whatever the age and ability.
At birth, detail vision is quite poor
for all children, and rapidly develops over the first two to three years.
Acuity in children with Down's syndrome also improves in childhood,
but it lags behind typical visual development at all but the youngest
ages. The difference is the equivalent of perhaps two or three lines
on a conventional letter chart at both distance and near, and is there
even when children are wearing glasses that correct any long or short
sight.
The clinical ways of measuring acuity
such as described above, using letters or pictures, are known as 'behavioural'
tests because they measure aspects of a child's behaviour or performance
as well as vision. One reason why we record a poorer visual acuity for
children with Down's syndrome is that the children might under-perform
on the test, not trying as hard when a test becomes difficult. In one
of our latest studies we have measured acuity objectively using EEG
techniques to record the brain's responses to visual targets (EEG's
measured this way are known as visual evoked potentials or VEP's).
Our data show that even with this technique, visual acuity is poorer
in all children with Down's syndrome than it is in typical children.
Figure 5.
A Behavioural tests
B VEP acuity
Children with Down's
syndrome, filled markers; control children, open markers
Our results show that acuity deficits
are genuine and represent a (mild) visual impairment. It is important
that teachers acknowledge that, even if children wear bifocals successfully,
or if they focus accurately without spectacles, their visual acuity
will still be below normal. Thus reading materials, for example, do
NOT look the same to a child with Down's syndrome as they do to his/her
classroom peers. The material does not appear to have the same level
of detail. Enlarging the print may help the child to access print more
easily, but does NOT restore a 'normal' appearance to the material.
In similar studies, we have also shown
that children with Down's syndrome are poorer at discriminating low
contrasts and at detecting when a scene is out of focus. All of this
may indicate that the children have a poorer ability in all visual discriminations
than typical children. Visual tasks are
therefore more difficult for children with Down's syndrome for reasons
over and above any learning disability that they have.
For this reason, we recommend that children
with Down's syndrome are registered with their local education authority's
visual impairment support service. A support teacher can advise the
classroom teacher on whether materials are adequate.
Additional problems
Blepharitis is an inflammation of the
eye lash follicles that causes debris to collect along the margins of
the eyelids and can cause irritation of the eyes. Children with Down's
syndrome are particularly prone to this condition, which although not
usually sight threatening, can be a source of discomfort and itching,
and can result in scarring of the follicles and in-growing eyelashes.
Blepharitis responds very well to simple treatment and parents should
be encouraged to take their child to a local optometrist for advice.
Children with Down's syndrome sometimes
have problems finding glasses that fit well. In general, the children
have smaller noses and a shorter distance from ears to face than typical
children, and so glasses have a tendency to slip down. This is not only
irritating for the child, but means that he or she isn't looking through
the correct part of the lens. It is almost always possible (although
time-consuming) for an optometrist/optician to adjust a frame, replace
pads, shorten sides etc so that glasses fit properly. Children with
Down's syndrome have as much right as other children to expect glasses
that fit properly and comfortably without slipping.
J. Margaret Woodhouse
Tel: 029 2087 6163
Email: <a href=mailto:woodhouse@cf.ac.ukwoodhouse@cf.ac.uk
<a href=http://www.cardiff.ac.uk/optom/DownsSyndromeGroup/Home.htmlhttp://www.cardiff.ac.uk/optom/DownsSyndromeGroup/Home.html
The work of the Down's Syndrome Vision
Research Unit has been funded over the years by:
The Down's Syndrome Association
Mencap with the Community Fund
Mencap City Foundation
PPP Foundation
National Eye Research Centre
Vision in children with Down's syndrome
School of Optometry &
Vision Sciences, Cardiff University, Cardiff CF10 3NB
Vision in children with Down's
syndrome
Because children with Down's syndrome
often have particular difficulties with language, educationalists describe
the children as 'visual learners' and recommend the use of visual
aids in the classroom. It is therefore especially important that
the children's vision is as good as it possibly can be and that the
children are given every opportunity to access visual stimuli. Unfortunately,
children with Down's syndrome are at much greater risk of eye and vision
disorders than are typically developing children. They therefore need
regular eye examinations, are more likely to need glasses than typical
children, and may need compensation in the classroom / learning environment
for visual deficits. Classroom and advisory teachers as well as parents
need to be aware of the visual difficulties that the children may experience.
At the Down's Syndrome Vision Research
Unit, we have been studying visual development in children with Down's
syndrome since 1992. We have a large group of enthusiastic and highly
committed families taking part in our studies, many of whom have been
with us since the beginning, and we see over 100 children regularly.
Our most significant findings are described below.
Refractive Errors
Long-sight, short-sight and astigmatism
are much more common in children with Down's syndrome than in typical
children, and many more will need to wear glasses. Ordinary children
are often long or short-sighted in early infancy, but grow out of these
errors over the first few years of life. Children with Down's syndrome
start out with a similar range of errors as do ordinary children, but
are much less likely to outgrow the errors and much more likely to become
more long or short-sighted.
Figure 1. Long and short sight amongst 6 year olds
It is important (as for any child in
the classroom) that the teacher understands when a child will need his/her
glasses, and what level of vision he/she will have both with and without
glasses. Long-sight of low to moderate degree can be overcome in typical
children by accommodation (active focusing) and not all children who
are long-sighted need glasses. However, children with Down's syndrome,
because they have difficulty in focusing (see later), will be much more
dependent on their glasses for clear comfortable vision than will typical
children. Children who are short-sighted, on the other hand, may be
better off without glasses for close work.
Squint
Children with Down's syndrome are at
much greater risk of developing a squint (eye-turn) than are typical
children. A child with a squint is likely to have a poorer level of
binocular vision especially depth perception. Tasks requiring fine depth
discrimination, such as threading beads, will be more difficult.
Accommodation (focusing at near)
Children's interests are mostly close
at hand, and most of children's learning takes place at near. And
it is at near that we find the greatest differences between vision in
children with Down's syndrome and typical children.
Usually, children focus very easily and
very accurately on near targets and it is only as we approach middle
age that we expect to experience difficulty in focusing at near. We
find, however, that most (over 70%) children with Down's syndrome focus
very poorly at near - they tend to under-accommodate by quite a large
amount. This is consistent for any individual child, and persists even
when the children wear their glasses to correct long sight. This means
that near work, especially in school, must be more difficult for the
children because it is out of focus.
Figure 2. Near focusing in children
We don't yet know the reason for the
poor focusing and we have studies underway to examine various possibilities.
However, we do now know that the children's focusing improves dramatically
with bifocal spectacles. In a controlled trial, we supplied bifocals
to a group of 17 primary school children with Down's syndrome, and conventional
spectacles to a second group (the control group). The two groups were
matched for all of the factors that might influence spectacle use or
near work, such as age, cognitive ability, school placement etc. Over
a 20-week trial, the children in the bifocal group consistently focused
more accurately on near work than did the children in the control group.
Figure 3
Bifocal lenses
Conventional (single vision) lenses
Figure 4. Measures
of accommodation (near focusing) in children with Down's syndrome wearing
bifocals and children wearing conventional spectacles (control)
In the trial, and now that we prescribe
bifocals clinically, we find that children with Down's syndrome wear
bifocals very successfully. None, so far, have encountered any problems,
and several of the children prefer to wear their bifocals all of the
time rather than keep them for school use. Two children were very reluctant
to wear glasses when they had conventional ones, but now wear bifocals
very happily. In some cases teachers and classroom assistants have reported
improvement in concentration and quality of work when the children wear
bifocals. We are now, therefore, recommending that all children with
Down's syndrome who show poor focusing are prescribed bifocals.
The positioning of the bifocal is
very important. The top of the bifocal should lie across the child's
pupil (this is a much higher position than usual for bifocals) so that
the child can look down through the bifocal without effort. We provide
an information leaflet that parents may take along to their child's
eye examination; this specifies the correct position for the bifocal.
Visual Acuity (detail vision)
Detail vision is usually measured in
adults with the familiar letter chart. For children (and people of any
age with learning disabilities) there are lots of alternatives that
don't need reading skills. These include picture naming, matching
or signing and the preferential looking tests that only require the
child to look towards a picture or target. It is, therefore, possible
to measure how well someone can see whatever the age and ability.
At birth, detail vision is quite poor
for all children, and rapidly develops over the first two to three years.
Acuity in children with Down's syndrome also improves in childhood,
but it lags behind typical visual development at all but the youngest
ages. The difference is the equivalent of perhaps two or three lines
on a conventional letter chart at both distance and near, and is there
even when children are wearing glasses that correct any long or short
sight.
The clinical ways of measuring acuity
such as described above, using letters or pictures, are known as 'behavioural'
tests because they measure aspects of a child's behaviour or performance
as well as vision. One reason why we record a poorer visual acuity for
children with Down's syndrome is that the children might under-perform
on the test, not trying as hard when a test becomes difficult. In one
of our latest studies we have measured acuity objectively using EEG
techniques to record the brain's responses to visual targets (EEG's
measured this way are known as visual evoked potentials or VEP's).
Our data show that even with this technique, visual acuity is poorer
in all children with Down's syndrome than it is in typical children.
Figure 5.
A Behavioural tests
B VEP acuity
Children with Down's
syndrome, filled markers; control children, open markers
Our results show that acuity deficits
are genuine and represent a (mild) visual impairment. It is important
that teachers acknowledge that, even if children wear bifocals successfully,
or if they focus accurately without spectacles, their visual acuity
will still be below normal. Thus reading materials, for example, do
NOT look the same to a child with Down's syndrome as they do to his/her
classroom peers. The material does not appear to have the same level
of detail. Enlarging the print may help the child to access print more
easily, but does NOT restore a 'normal' appearance to the material.
In similar studies, we have also shown
that children with Down's syndrome are poorer at discriminating low
contrasts and at detecting when a scene is out of focus. All of this
may indicate that the children have a poorer ability in all visual discriminations
than typical children. Visual tasks are
therefore more difficult for children with Down's syndrome for reasons
over and above any learning disability that they have.
For this reason, we recommend that children
with Down's syndrome are registered with their local education authority's
visual impairment support service. A support teacher can advise the
classroom teacher on whether materials are adequate.
Additional problems
Blepharitis is an inflammation of the
eye lash follicles that causes debris to collect along the margins of
the eyelids and can cause irritation of the eyes. Children with Down's
syndrome are particularly prone to this condition, which although not
usually sight threatening, can be a source of discomfort and itching,
and can result in scarring of the follicles and in-growing eyelashes.
Blepharitis responds very well to simple treatment and parents should
be encouraged to take their child to a local optometrist for advice.
Children with Down's syndrome sometimes
have problems finding glasses that fit well. In general, the children
have smaller noses and a shorter distance from ears to face than typical
children, and so glasses have a tendency to slip down. This is not only
irritating for the child, but means that he or she isn't looking through
the correct part of the lens. It is almost always possible (although
time-consuming) for an optometrist/optician to adjust a frame, replace
pads, shorten sides etc so that glasses fit properly. Children with
Down's syndrome have as much right as other children to expect glasses
that fit properly and comfortably without slipping.
J. Margaret Woodhouse
Tel: 029 2087 6163
Email: <a href=mailto:woodhouse@cf.ac.ukwoodhouse@cf.ac.uk
<a href=http://www.cardiff.ac.uk/optom/DownsSyndromeGroup/Home.htmlhttp://www.cardiff.ac.uk/optom/DownsSyndromeGroup/Home.html
The work of the Down's Syndrome Vision
Research Unit has been funded over the years by:
The Down's Syndrome Association
Mencap with the Community Fund
Mencap City Foundation
PPP Foundation
National Eye Research Centre