Assessing Vision in Children with Additional Support Needs: Why and How?
Presented on Wednesday 31 October, 2012
J Margaret Woodhouse School of Optometry & Vision Sciences
Focusing on near tasks
Children learn at near
How do professionals assess vision?
Typical pre-school children focus accurately. Typical older adults struggle to focus.
Children with visual impairment replotted from Leat and Mohr, IOVS, 2007.
Children with additional needs
- Are likely to have difficulties with focusing on near tasks
- Among children with DS, 76% have poor focusing for near targets
- Among children with CP, 58% have poor focusing for near targets (JF McClelland, J Parkes , N Hill, AJ Jackson, KJ Saunders IOVS, 2006: 47; 1824-1830)
- Children have a focusing error EVEN WHEN THEY WEAR GLASSES FOR LONG- OR SHORT-SIGHT
HOW can school staff assess vision?
What would make us suspect poor accommodation?
- Bringing near tasks very close.
- Lack of interest in near tasks, compared to distance.
- Bringing head back if objects get too close .
Usually, it is NOT possible to spot poor accommodation in a child - all children should have an examination.
What would make us suspect poor accommodation?
In CP, using patches for dribbling.
- The patches contain hyoscine, which is a cycloplegic, a similar substance to that used to paralyse accommodation during eye tests.
- Paediatricians may not know that hyoscine is a cycloplegic.
- Any child using patches should have an eye exam.
If accommodation is poor we can correct the problem
- With bifocals
- With miltifocals
- With glasses just for near work
- With two pairs, for distance and near
Two groups (17 pairs of children; all of whom under-accommodate) matched for:
- age
- cognitive ability
- type of school
- members of the cohort/new recruits
- type of refractive error
- current use of spectacles
Bifocal group - given specs with a +2.50D add (for use in school only) and had single vision specs for home.
Control group - had new 'single vision' specs for school use and kept their current specs at home.
Results
- Excellent co-operation from all schools, teachers and classroom aides
- Positive response from children in both groups to new glasses, and compliance good
FOUR children wore their bifocals at home as well as at school in 3 cases parents requested this in 1 case the child refused to remove the bifocals at the end of the school day!
Accommodation
At the outset there was no difference in the accommodation between the two groups (p=0.851)
- control group: mean accommodative deficit = 3.37D ± 1.31
- bifocal group: mean accommodative deficit = 3.44D ± 1.07
Outcomes of trial
- Children in the bifocal group accommodated more accurately.
(Stewart, Woodhouse, Trojanowska, (2005) Ophthalmic and Physiological Optics 2005: 25; 514-522) - Teachers reported better concentration and writing skills in the children wearing bifocals.
- Recent study from Waterloo, Canada shows significant improvement in literacy and visual perceptual skills with bifocals.
(Nandakumar, Leat, Acta Ophthalmologica, 2010: 88; 196-204)
Bifocal wear
- The children use their bifocals very successfully.
- We begin with bifocals for school use only, but most children choose to wear their bifocals full-time.
- Even (the few) children who are reluctant to wear ordinary specs will wear bifocals happily.
Ethan - went into bifocals aged 3 yrs 9 months: email from Mum
Just thought I'd let you know that he took to the bifocals straight away and hasn't put his old glasses back on since wearing them.
Just this morning his key worker at pre school asked me if I'd noticed a difference in Ethan since he's been wearing his bifocals - steadier on his feet, better communication and attention when looking at flash cards and so on. It's nice that someone else has noticed too.
Also, I know I mentioned to you that I was worried about his peripheral vision when we visited because he only seemed to look at 1 out of 4 words on a matching board when we were practising reading. I think it's because he had to try so hard to focus that he could only look at 1 at a time. Now he looks at the whole board and understands better what I'm asking him to do!
Prescribing guidelines
Bifocals may be temporary – ONE THIRD of children begin to accommodate accurately through the distance part of the lens and can return to single vision lenses.
- The Coleraine study showed that children benefit from near corrections.
- Report from Glasgow Caledonian demonstrates the successful use of varifocals. (Ross, Heron, Mackie, McWilliam, Dutton (2000) Developmental Medicine & Child Neurology 2000: 42; 701-3)
- Poor head and eye movement control MUST be taken into account when considering near corrections
WHAT kind of visual problems do children have?
- Below-normal acuity (detail vision)
- Special school studies showed 12-15% were visually impaired.
- Published papers show that 23% of children with cerebral palsy and 30% children with autism have below-normal acuity.
- Our work shows that 100% children with Down's syndrome have below-normal acuity.
Behavioural acuity
VEP acuity
- Children with Down's syndrome have poorer vision than their peers
- This applies to children with no other eye defects, and to children wearing their glasses
- The difference is 1-3 lines on a letter chart
- Children with Down's syndrome MAY have additional eye problems such as nystagmus, which will reduce vision further
Children with cerebral palsy
- May have poor vision associated with CVI
- Vision can range from normal to no light perception.