Impairment of vision due to damage to the brain in children
Presented on Tuesday 16 December 2008
Visual limitations caused by damage to the brain in children include:
Difficulties with impaired primary processing of the image. This may affect:
- visual acuity
- contrast sensitivity
- colour vision
- visual fields
- perception of movement
Those affecting the dorsal stream, impairing
- The ability to give attention to, and thus see, the components of a crowded visual scene - and
- The use of vision to guide movement
Those affecting the ventral stream (which are less common) Involving
- recognition of what is being looked at and
- recognition for route finding
Visual limitations caused by damage to the brain in children lead to problems with:
Accessing information, whether it is
distant, such as a letter box or a tree
near, such as pictures and writing
With visual guidance of movement, whether
of the upper limbs, to reach out and pick something up
of the lower limbs, to walk freely and confidently
Social interaction. It may be difficult to:
- see someone in a group, owing to visual acuity or visual field loss, or dorsal stream problems
- recognise their face, owing to poor acuity, contrast sensitivity, or agnosia
- see the language within facial expression (for the same reasons)
- even to see a hand, for a hand shake (if it is in an absent lower visual field)
Finding out about the visual acuity, contrast sensitivity, colour vision and visual fields, is carried out by examining functional vision.
However, finding out about how visual field and dorsal stream and ventral stream visual problems interfere with vision can be done both by asking the parents and by carefully watching and interpreting the child's visual behaviour.
Bumping into door frames, and obstacles like street signs, on one side suggests that visual field impairment or inattention on that side is worth looking for.
Leaving food on one side of the plate and missing traffic from one side; missing text on one side and leaving food on the near side of the plate, all suggest such problems.
A bright marker on door frames at the child's eye level can help, for lack of attention on one side.
Early training in mobility and independence is needed for being out and about.
Rotating the plate to find the food and early training to look to the side for traffic are useful approaches.
While modifying the presentation of text on one side and moving the bowl further away, to allow the near side of the plate to be seen are further approaches to deal with such difficulties.
In the classroom hemianopia and lack of attention on one side may require:
- The teacher to be off centre to the sighted side
- Strategies to ensure that information
on the affected side is not missed, which can include:
Using tactile guides on a page
Training in scanning the information
Presenting information displaced to the sighted side
Lower visual field impairment, and impaired visual guidance of movement of the feet, cause problems with steps for which tactile guidance may be needed.
The floor needs to be kept clear of toys and low obstacles outside may cause problems.
Floor boundaries both inside and out can cause hesitation and a need to explore the boundary with the foot.
It is easier to climb up stairs than down. And a child may find it easy to run up a slope but may get stuck at the top because the lack of lower visual field means that the slope is not seen from above. The same applies to slides; when going down head first may be easier because the slide is seen that way.
Providing a tactile guide to the height of the ground ahead, whether it is a brick trolley for a younger child - or a scooter for an older child gives the child greater independence.
When walking holding hands with such a child, holding one's arm slightly backwards, like this, gives advance notice of changes in the height of the ground ahead, and keeping the arm straight like this, gives the guidance to the height itself.
We have also recently realised that lower visual field impairment leads to the child having to lift the foot up high to change shoes, this may be done lying on the back if vision, balance or leg strength are poor.
As is well recognised, a tilted work station, helps to ensure that work at the bottom of the page is not missed, as this decreases the effect of lower visual field impairment.
Dorsal stream dysfunction – questions to ask:
- Getting very close to the television
- Being unable to find a friend or relative in a group
- Having difficulty finding a toy on a patterned background
- Being unable to find an item of clothing in a pile of clothes - and having to spread out clothes to find the chosen item
- Being unable to find a toy among a pile of toys and finding it easier to find a toy against a plain background
- And it is much easier to find the sweets in the kitchen if there is no clutter!
Difficulty seeing things that move, is common amongst children who have impaired dorsal stream function, and who often prefer films in which there is limited movement.
The principles of managing dorsal stream dysfunction are:
- Storing possessions for one, not three dimensional search (one direction)
- Keeping background clutter and pattern to a minimum
- Limiting the amount to see at any one time. Children get close to the
limit the amount they are seeing at any one time.
In the classroom or home this means:
- Having good storage and putting everything away
- Minimising the amount of decoration
- Allowing the child to get close to the front
- Ensuring that there is not too much on the page and that the separation of words and numbers is sufficient
- (Consider san serif text like this)
Additional strategies include:
- Limiting all forms of distraction for the child
- Using a 'quiet table'
- Choosing the 'neighbours' to be the most calm in the class
- Using large well spaced material for group presentation
- Matching the speed of presentation to the speed of processing
Visual function that is variable
Do you lose things when you're tired? So do affected children, only more so! Many people with cognitive and perceptual visual problems find this.
Dorsal stream functions like visual search and visual guidance of movement
often seem to be affected by tiredness.
This may explain why parents see the typical visual problems often than at school, because when the child gets home after school, he or she is tired.
Variability of visual function is typical in children with cerebral visual impairment but is difficult to test for.
Occurs following prolonged visual processing
Inattentive periods due to tiredness and reduced 'functional reserve' can be helped by:
- Minimising clutter
- Keeping distraction to a minimum
- Reducing detail and complexity
- Giving well earned breaks, ideally in a calm undecorated, and non-crowded environment
Dorsal stream dysfunction affects attention
It can be difficult to engage, to maintain and to break visual attention.
Shared attention during listening and talking can be very difficult to keep going. It is difficult to watch a face and listen to what is being said, so the child may look away. To say "Look at me when I'm talking to you", can make the problem worse!
The child may lose visual attention when things are moving at the side, and find it difficult to return to the work in hand.
Rooms with a lot of pattern and clutter, and being in crowds and supermarkets are associated with difficult behaviour or distress. (Do you find the background under these words annoying?)
Angry reactions can take place when other restless children cause distraction,
particularly when a child is concentrating.
But plain undecorated places and quiet open countryside are associated with better behaviour (Isn't this lower text more relaxing to read?)
Ventral stream dysfunction - results in impaired recognition
In the context of adequate visual acuities
Impaired recognition of faces may come to light, when a window prevents the use of sound or smell as alternative cues for recognition.
If a child has only partial difficulty with recognising people, he or she may find it easier if the other person faces square on. Side views may be much more of a problem.
The act of not recognising someone who is not known is a complex 'computing' task, and children with impaired recognition commonly approach strangers thinking that they know them.
Remembering the colour of clothing and the shape of identifiers such as earrings, and voice recognition are all strategies to circumvent the problem.
Many children who cannot recognise faces are unable to see the language of facial expression. As are children with poor visual acuities.
Clearly communicating feelings and emotions is essential for these children, working on training about the meaning of the expressions.>
We have found that some affected children are unable to tell one animal from another, visually but can do so by touching models.>
Object recognition may need to be enhanced by touch. And the family car may only be recognised by colour.>
The ventral stream is also required for orientation. Orientation at home in the garden and at school may be very difficult, and more profoundly disturbed than the orientation problems due to dorsal stream dysfunction, (where overload of the visual system probably causes the problem).>
Some families have found that colour coding doors and routes can help considerably.>
The social problems due to CVI
- Labelled as having 'behavioural problem'
- Feelings of isolation
- School support
- Identify problems and solutions
- Encourage child to overcome them
- Well known peer group
- Buddy system
- Find activities child enjoys and can excel in
The 'Tree' of Visual Perception and Cognition
Disabilities due to CVI can beobscure, and are often missed. Yet the resultant problems may be disabling. Recognition and habilitation for this common disorder are essential, to prevent long term educational and social disadvantage of affected children
Our current team comprises:
Dr Kathy Spowart - paediatrician
Gillian McDaid - Occupational therapist
Debbie Cockburn - Occupational therapist
Ruth Hamilton - Physicist
Roisin Mackie - Optometrist
Claire Leslie - Secretarial services
Catriona Macintyre-Beon, David Bennett,
Beth McDonald, Hussein Ibrahim, Julie Calvert