by Maggie Woodhouse: The Down’s Syndrome Vision Research Unit, School of Optometry & Vision Sciences, Cardiff University
One of our most important findings is that vision is poorer in children with Down’s syndrome than in typical children of the same age, and remains poorer even when the children have glasses for any long or short sight.
Our research team has been studying visual development in children with Down’s syndrome for over 20 years. We have a study group of more than 250 children and young people (some in their twenties who have been with us since the beginning). When we have needed to compare our results with typical children, brothers and sisters have joined in too.
How can we measure vision in children?
When you go along for an eye test, we ask you to read a letter chart. We score your visual acuity, or detail vision, as the smallest line of letters that you can read correctly. Older children with Down’s syndrome may also use a letter chart. Non-readers and younger children can match letters, or identify pictures, by naming, matching or signing. For toddlers, we can use a type of test called ‘preferential looking’ (PL). For tiny babies (weeks or months of age), we use a similar test that has black/white stripes rather than a picture. Stripes happen to be very attention-grabbing for a baby, but the testing principle is the same, we simply hold up the card and watch where the child looks.
Another aspect of a child’s vision that we measure is contrast sensitivity. This is the ability to see faint (rather than fine) objects. If we use a letter chart for this, the letters fade down the chart rather than get smaller. We have preferential looking versions of contrast sensitivity tests too.
Whichever aspect of vision we are measuring, and whatever type of test we use, we find that children with Down’s syndrome don’t score as well as typical children.
Why don’t children with Down’s syndrome see as well as other children?
One obvious explanation of the low scores (and, I suspect, the reason eye clinics don’t point it out to parents) is that the children have a learning disability and they don’t always try hard when tests get difficult. To test this theory we also measured vision in children in a way that didn’t require the children to try at all using Visual Evoked Potentials (VEPs). These are the brain signals that arise when a subject looks at a target. We can detect these tiny signals by placing sensors on the scalp, and recording the electrical activity. In our study all the child had to do was watch a TV screen for 10 seconds. During those 10 seconds the stripes on the screen got finer or fainter and we knew when they disappeared to the child, because the brain signals disappeared too.
The tests we have carried out show that children with Down’s syndrome have poorer scores even when we removed the need to concentrate or try. It is not lack of motivation or attention that gives the children with Down’s syndrome poorer scores – they really are trying when they do the tests, but they have a genuine visual deficit that mean they do not see as well as other children.
What does this mean for the way children with Down’s syndrome see the world?
The difference in vision has huge implications for the classroom where the children’s sight is pushed to the limit. Children with Down’s syndrome have to work considerably harder than other children to read or to do any school tasks, because they are not seeing their work as easily. As children’s reading skills progress, the print gets smaller. There may come a time when a child with Down’s syndrome can’t make the next step in the reading scheme, not because he or she can’t manage the cognitive step to more complex text, but because he or she simply can’t see the smaller text.
Encourage children from a young age to write in pen rather than with a faint pencil which a child with Down’s syndrome would find very hard see. If a child needs to write letters on a line, make the line bold so the child can see it.
What causes this poor vision?
Kathryn Saunders and Julie-Anne Little, from the University of Ulster in Northern Ireland carried out a study to determine what might be causing the problem. This study showed the biggest factor in poor vision is the optical quality of the children’s eyes. Imagine the difference between a magnifier that comes out of a Christmas cracker and one bought from a craft shop. The image seen through the cracker magnifier is not clear, compared to the expensive magnifier.
What can we do about this poor vision?
It is sometimes difficult for teachers to appreciate that a child with Down’s syndrome in their classroom sees the world differently to the other children. Their world lacks fine detail and sharp contrast.
It is essential that all teaching staff, at every level of education, are aware that every child with Down’s syndrome has a genuine visual problem. This is the case even if the child doesn’t need glasses or is wearing the correct glasses.
If a child struggles with a task don’t assume it is because they have a learning disability; it may be that the child can’t see the task.
Make all classroom materials BIG and BOLD – doing so can mean the difference between success and failure and everything that this implies for the child’s learning.
Furthermore, the visual deficit MUST be recorded in the Statement of Special Educational Need or EHCP and, ideally, every child with Down’s syndrome should be supported by the Visual Impairment Service. A Qualified Teacher of the Visually Impaired can check out the visibility of the materials in the classroom and advise on any modifications that might help
Finally, I believe there is always a bright side and in this case, it’s this: the easiest way to envisage how the world looks to a child with Down’s syndrome is to picture it in soft focus. There are no sharp edges in your child’s world and that’s quite a romantic idea isn’t it?
This blog is adapted from an article that appeared in DSA Journal 127 Spring/Summer 2013. The article can be downloaded here