Common Causes of Visual Loss in Children
Presented on Friday 15 May 2009
Visual Challenges and Strategies to help
Dr J Skillen
Hints and tips for all involved in children with visual impairments
Features of VI
- Refractive Error (O)
- Glare (O)
- Reduced Vision (B or O)
- Poor contrast sensitivity (mostly O)
- Absent colour vision (mostly O)
- Poor accommodation (Mostly O)
- Eye movement disorders (B or O)
- Field Loss (B or O)
- Simultagnosia (B)
- Prosopagnosia (B)
- Other Visual Processing Difficulties (B)
Refractive error
- Assess whether child might benefit from glasses
- Tolerance of wearing glasses related to developmental age
- Related less to visual benefit for child
- Fitting of glasses critical
Glare (ocular)
- Different eye conditions often give rise to ocular glare.
- In classroom – good
positioning in relation to source of natural light
- watch whiteboards
- use matt laminated surfaces for reading material - Different eye conditions often give rise to ocular glare.
- RP - Adequate diffuse light levels
- Cone dystrophies excessive lights causes discomfort
- Optic Nerve - good background lighting required
- Macular disorders - bright focal light behind and close to target
- Cataract, Corneal Opacities, Aniridia - Avoid focal light in front of child
Reduced Vision
- Vision score - Snellen or Logmar at distance
near acuity scores - Stretegies
enlarged print|
Low Visual Aids - high tech and low tech - Any null point - in case of nystagmus - often will adopt head posture
Enlarged Print
- Assess reading print size that child is able to comfortably read
(differs from medical threshold) - Lighting levels and reading comfort must be considered.
- Repeated assessments during different times in the day often useful to coincide with range of tiredness levels.
Low tech magnifiers
- Work well with angle poised book holders or tilted working areas can help
- Shorter working distances increased field of view
- Higher magnification – reduced field of view
- New magnifiers just produced specifically for children's market
- Don't forget importance of distance LVA's
High Tech LVA's
- Greater range of magnification
- Adjust brightness and contrast
- Easier to read when using tracking devices
- Child has more control over focusing and zooming
Distribution of LVA use across age groups in Scotland
Contrast Sensitivity
- This is a measure of how well a child can see shades of grey against white
- Rarely performed in routine clinical practice
- Relatively easy to perform
- Important
Conditions with loss of contrast
- Optic Atrophy
- Retinal Dystrophies
- Corneal conditions
- Cataract
Communication, Facial expressions Orientation and Mobility, Kerbs Accessing information, Reading Text Activities of daily living, Eating
Increase Contrast Wherever Possible
- Communication and facial expressions - lipstick? Maybe not for the men
- Orientation and Mobility - Kerbs
in an environment that you have control over - mark steps and door frames in contrasting colour - Accessing information/ Reading Text - using white on black or vv, or yellow on black
- Eating - contrast between food and plate, plate and table
Colour Issues
- Most likely to have true colour vision issue if retinal aetiology affecting the cones
- Although poor recognition of colour can be secondary to reduced vision in general – or due to difficulties with colour naming (if brain aetiology)
- Colour matching is a good way to try and distinguish root difficulty
- Colour confusion can result from reduced vision and/or poor contrast sensitivity
- Colour code pictures and shapes for extra clues
- Use their favourite colours and work from there
- Outline object with colour - more success with vibrant rather than pastels
- Link objects with colours - yellow lemon, yellow sun Blue sky, blue ball, etc
Impaired accommodation common in:
- Cerebral Palsy
- Down's syndrome (60% require glasses)
- Absent
- Slow
- Inaccurate
- Easily fatigued
- Unstable
Strategy
Add a reading lens
- + lens
- Presbyopic – what people tend to require when >40 years old
- Interesting findings
- With time reading aid can be withdrawn
May 1st 2008 – Science Daily
- Maggie Woodhouse – Cardiff School of Optometry and Vision Sciences Down's Syndrome Research Unit
- 1/3 of children with Down's who have been prescribed bifocal prescription can get out of glasses after a period of two years.
- Wearing a bifocal teaches the visual system the benefit of clear vision (it's not that they can't focus but they don't focus)
Control of eye movements
Squint
- Nystagmus
- Dysmetric saccades
- Deficient smooth pursuit
- Compensate by head movements
- Adopting a head position
- Closing one eye
Assessment of fast eye movements
- Attempt to force fixation shifts
- May notice head turns, blinking
- Optokinetic (OKN) drum is a useful screening tool
Visual Fields
- Common behaviours observed in children with field defects
- Tilting and turning head
- Bumping into objects
- Losing items frequently
- Clumsy
- Hesitates when using stairs and tips head down
- Difficulty locating food on a plate - Central or peripheral loss
- Different strategies to overcome - maximise use of residual field
Testing in Children under 10
- Quick
- Ensure good fixation
- More interactive
- Need good technician
- Better for peripheral defects
Example of a normal Peripheral field in 10 year-old
- Central field – central 30 deg
- Filled in circles – show blind spot
- Test carried out using two separate visual stimuli for each eye which differ in brightness
Field Loss
- Prompting and consistent vocabulary
- Scanning techniques to improve mobility
- Use eccentric viewing
- Use raised work surface in cases of lower field defects (underdiagnosed in MDVI?)
- Allow compensatory head postures
Simultagnosia (B)
Unable to single out information when in crowded and busy environments
-
difficulty hunting for a toy in a tightly packed box of toys
-
Difficulty finding Mum in a crowd of Mums
-
Overloaded with information when trying to read.
Behavioural changes in busy crowded surroundings
Strategies Keep things simple
- Uncluttered environments reduce stress
- Keep areas tidy and minimalism style - esp peg areas in school
- Keep walls simple displays
- One thing at a time
- Using a typescope for reading material
- Often hold things close to reduce field of view and reduce clutter
How to make things easier at home
- Try to make environments visually quiet
- Go shopping at quieter less busy times
- Play with only one or two toys on a plain background
- A plain bedcover can help children find clothes more easily
- Open spaces
- One to one communication in a quiet place
Other Signs of Dorsal 'WHERE' Pathway deficits
- Difficulties reaching and grasping
- Uniting frontal cortex for visually directed movement and attention selection.
- Control of eye movements - gaze shifts in response to attention
- Clumsy child syndrome tripping up and difficulty with stairs
Notes: By understanding where in the brain different types of visual information are processed we can then begin to understand the difficulties that may arise when things go wrong. Problems with the 'what' and 'where' pathway gives rise to specific types of visual difficulties which can be tricky to recognise during normal eye tests. In fact the ability to read letters on a chart can be completely normal and yet a person may be profoundly affected by dorsal or ventral based visual difficulties.
Prosopagnosia
- Unable to recognise familiar people
- Unable to recognise people out of context
- Associated consistent cues may help non-audio recognition
- feet are always bigger than Mum's he has flat shoes she wears heels
Other Signs of Temporal Lobe/ Ventral 'What' Pathway deficits
- In addition to difficulty recognising faces 'Prosopagnosia'
- Difficulty understanding language conveyed by facial expression
- Route finding and Visual memory/Visual Library Damage leads to problems finding way around even familiar places or difficulty finding clothes, toys
Remembering what is seen and visual imagination
- Copying something requires a visual memory
- Visual memory dependent on interaction between hippocampi and temporal and frontal lobes
- Interference with these structures can lead to difficulty copying - do better without having to change viewing distances to copy
Facial expression Six basic emotions
- Happiness
- Sadness
- Anger
- Fear
- Disgust
- Surprise
The facial expression recognition distance
- Useful in any child with VI (even if only suspected)
- Try smiles and frowns at different distances
- Avoid giving clues with voice
- May explain impassive nature of children with poor vision
- Unable to emulate facial expression that they can't see or recognise (ventral deficit)
The BIG Picture
Royal College of Ophthalmologists Guidelines