Assessing Vision in Children with Additional Support Needs: Why and How?
Presented on Wednesday 31 October, 2012
J Margaret WoodhouseSchool of Optometry & Vision Sciences
Children with Cerebral Visual defects
WHAT kind of visual problems do children have?
Visual field defects
- May occur in cerebral palsy and other conditions associated with brain injury or maldevelopment.
- We ALL have a blind spot, of which we are NOT aware.
- A child with a visual field defect will NOT know.
- Defects affecting only the right or left field in both eyes are possible – hemianopia.
- The right visual cortex represents left visual field and vice versa.
- One study suggested 75% of children with hemiplegia had hemianopic field defects.
- The lower visual cortex represents upper visual field and vice versa.
- Defects affecting only the upper (uncommon) or lower field (more common) are possible.
HOW do professionals assess vision?
Visual field defect
- With difficulty!
- Most visual field instruments are applicable to able adults with no visual field defects.
What would make us suspect visual field defect?
- Mobility problems
- Bumping into or tripping over objects
- Failure to respond to approach from one side
- Surprise or distress if approached from one side
- Extreme difficulty on steps or stairs (lower field defect).
Understand the visual field defect
Approach the child from the seeing side BUT work with the child to ensure he/she is aware of the blind side.
Nystagmus - 15% in DS, common in CP and in other conditions
- Regular 'wobble' of the eyes.
- Associated with visual impairment, as with typical children.
- Associated with abnormal head posture (null point of nystagmus), as with typical children.
- Needs the same support in children with additional needs as in typical children.
Be aware of the extent of nystagmus when child is calm. If the movements worsen, the child is stressed or tired and needs a break.
Eye movement difficulties
- Problems in making accurate eye movements, or sustaining an eye position.
- Distinguish this from nystagmus - the two conditions are quite separate, but can occasionally occur together.
- Estimated prevalence of 25% in CP?
What are eye movements for?
To allow 'best vision' of the object of interest.
To allow localisation of objects.
To 'stabilise' the visual world.
For social interaction.
To keep both eyes aligned.
What are the consequences of being unable to make or sustain accurate eye movements?
- Difficulty in concentrating and learning?
- Poor spatial awareness?
- An unstable world?
- Limited social development?
- Double vision?
- Poor eye movementcontrol must constitute a severe visual impairment.
- Poor eye movement control complicates our assessment of a child's potential vision.
- Poor eye movement control limits a child's ability to adapt to spectacles?
- produce distortions,
- cause magnification/minification. that is, distances become difficult to judge,
- change the apparent position of objects.
Adaptation experiments (1960's)
Only subjects allowed full control of hand and body movements adapted to the spectacles.
Children with cerebral palsy may find it much more difficult to adapt to spectacle lenses if they cannot move freely.
HOW can school staff help?
- Be aware of the eye movement difficulties.
- Create a distraction free environment.
- Allow the child time to move their eyes.
Visual perceptual deficits and cerebral visual impairment (CVI)(consult Gordon Dutton or Andrew Blaikie)
- Condition in which vision is disturbed, but the eyes appear fully healthy.
- Can range from minor problems in visual interpretation to no light perception.
- Symptoms reasonably common in CP and children born prematurely.
- Symptoms also occur in DS BUT symptoms also occur in the general population – not possible at present to distinguish 'normal occurrence' from 'abnormal occurrence'.
Thanks to: all of the children who take part in our studies, and their families.