Scottish Sensory Centre

Understanding Visual Fields

Presented on Friday 2 November 2007

Assessing functional vision

Dr Jennifer Skillen, Specialist Orthoptist, NHS Fife

What developmental areas can be affected by VI?

• General alertness
• Eye contact & bonding
• Communication
• Motor skills, Orientation and Balance
• Incidental learning & Integration
• Language
• Picture perception and Object recognition

How can developmental delay be avoided?

• By joint assessment
• By sharing information
• By cross-discipline communication
• By identifying best 'interventional' practice and employing it
• By the development of a multidisciplinary team

The ideal multidisciplinary team

• 1 Teacher and early interventionist
• 2 Community Paediatrician
• 3 Educational psychologist
• 4 Optometrist & Optician
• 5 Occupational therapist
• 6 Low vision counsellor
• 7 Rehabilitation officer
• 8 Mobility instructor
• 9 Ophthalmologist
• 10 Physiotherapist
• 11 Orthoptist
• 12 Secretary

Teachers wanted it

• Individualised Educational Programmes
• So as children can fulfil potential
• Enter adulthood as equal and valued members of society

Three assessmentswith different goals

• Eye department
  Diagnostic
• Community Paediatrics
  Part of developmental assessment
• Education
  Functional assessment
  Toward IEP

Common to all isvisual function assessment

Collaborative, Community-Based Assessment of The Visually Impaired Child

Potential benefits of collaboration

• Child assessed less
• Don’t get contradictory opinions
• Transfer of information
  Immediate
  Relevant
  Understandable
• Three assessors learn from each other
• Parents can ask wider range of questions
• Vision assessment done for next eye clinic

Disadvantages of Collaboration

Logistical challenge of Getting everyone together

• At same time
• In same place

Community

• Primary School VI Unit
• Special School
• Child Development Centre

Potential benefits of community

Better attendance

• Lose less school time
• Easier to access and costs less
• Child happier and more cooperative
• Easier to segment assessment

Disadvantages of Community

• Difficulty finding suitable room
• Cannot have all gadgets
• No consultant opinion

Structure of Assessment

• Get background information
• Structured functional history
• Observe behaviour
• Structured Vision Assessment
• Discuss & write report

Taking the visual history

• Try to identify main concerns with vision
• As perceived by
  Parents
  Main carers
  Teachers
  Paediatric colleagues

List of 22 questions

• Helpful structure
• Modify for your own uses
• Considers ventral and dorsal visual streams

1 Does your child recognise you before you speak?
2 Does your child recognise other family members?
3 Does your child recognise friends?
4 Does your child recognise people from photographs?
5 Can your child identify him/herself from photographs?
6 Can your child recognise shapes?
7 Can your child recognise objects?
8 Can your child name colours?
9 Can your child match colours?
10 Can your child find his/her way around the house?
11 How often does he/she ask for directions around the home?
12 Does he/she lose objects around the house?
13 Can your child find his/her way around new surroundings?
14 How often does he/she ask for directions in new surroundings?
15 Does he/she have difficulty reaching out for and grasping objects?
16 Does your child have difficulty distinguishing a line from a step?
17 Is your child able to see moving objects or are they seen only when they are stationary?
18 Does your child have difficulty seeing objects when he/she is moving quickly him/herself?
19 Can your child find objects on a patterned carpet?
20 Can your child find objects in complex pictures?
21 Does your child eat food from only one part of the plate and ignore the rest?
22 Does he/she misjudge going through doorways or along corridors?

Past Medical and Ophthalmic

• Premature
• Birth Asphyxia
• Head Injury
• Non-Accidental Injury (NAI)
• Refractive Error

When finished history

• Should have good understanding of
  Child’s main problems with vision
  Likely level of vision
  Social context
• This information helps direct the assessment

Structured Vision Assessment

• Visual acuity
• Contrast sensitivity
• Visual field
• Face recognition
• Colour vision
• Eye movements
• Accommodation
• Refraction

Visual Acuity

• Threshold for recognition of high contrast materials
• Threshold (the smallest thing)
• Recognition (not detection)
• High Contrast (blackest on whitest)

Get most important information first

• Near vision binocularly with correction
• Distance vision
• Uniocular
• Without glasses

Visual Acuity

• Allow child to use abnormal head posture
• But consider supporting child with motor impairment

Visual Acuity

• Observation
• Preferential Looking Tests
• Shape Recognition Tests

Observation

• Home
• Out and About
• School
• Hospital
• Video
• History

Preferential Looking Tests

• Teller Cards
• Keeler FCPL cards
• Lea Symbol grating paddles
• Cardiff Cards

Preferential Looking Tests

• Examiner should be 'blinded'
• Closely observe child's gaze (eye movements)
• Vertical movements maybe easier to notice because of eyelid flicker
• Beware of children with dyskinetic eye movements

Preferential Looking: Gratings

• Measured in cycles per cm (cpcm)
• Or one cycle per degree
• One cycle is a black and a white stripe
• 4 stripes per cm
• 2 cycles per cm

How many cycles?

Isoluminant

       

• Grating acuity versus Recognition acuity
• Should not equate grating cpcm acuity with Snellen notation shape recognition acuity
• Grating acuity is not a ‘recognition’ acuity, maybe just ‘detection’
  ‘Recognition’ requires higher brain functions

Cerebral Visual Impairment

• Child may have good grating acuity but
• Poor shape recognition acuity

Problems with PL tests

• Fixation
• Visual Field
• Saccades

Crowding

• Acuity maybe less with a 'linear' test than a 'single optotype' test
• This is known as 'crowding'
• Normal in younger children
• Common in children with CVI
• Educational implications

Shape recognition tests

• Kay's pictures
• Lea Symbols
• Illiterate Es
• Sheridan-Gardner
• Snellen

Kay's Picture

• Common pictures of different sizes
• Single, uncluttered
• Cultural limitations

Lea Symbols

• No cultural limitations
• Resolve into each other
• Child unaware if getting it wrong
• Flexible formats available
• Card games
• Large coloured tactile shapes

Snellen Test Type

Sheridan-Gardner

• Child shown usual Snellen chart
• Child matches letter from 'key' card
• Replaced by logMAR tests instead – more scientific measure of acuity in children

Visual Function

• Visual Acuity
• Contrast Sensitivity
• Visual Field
• Colour vision
• Eye movements
• Accommodation
• Refractive error

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

Why is it important?

• Communication, Facial expressions
• Orientation and Mobility, Kerbs
• Accessing information, Reading Text
• Activities of daily living, Eating

Conditions with loss of contrast

• Optic Atrophy
• Retinal Dystrophies
• Corneal conditions
• Cataract

There are many ways to measure Contrast Sensitivity

• Hiding Heidi
• Lea Symbols
• Pelli-Robson chart

Hiding Heidi
Preferential looking test

Lea Symbols

Visual Field

• This is the area over which a child can see when holding their eyes and head still
• Again rarely assessed in routine practice
• Important

Why is it important?

• May explain problems with mobility
• May explain abnormal head posture (AHP)
• May explain poor reading skills despite good visual acuity
• Will dictate placing in the classroom

It is difficult to assess visual fields

• Lots of practice
• Confrontation
• One examiner 'engages' child
• Other examiner slowly brings object into visual field
• Assess four quadrants

Likely patterns of field loss

• Relate to underlying pathology
• Macular dystrophy
• Retinitis pigmentosa
• Glaucoma
• Cerebral visual impairment (Brain Loss)

Brain Field Loss

• Most kind of loss if children
• Specific patterns
• When examining Think of the quadrants

Limited possibilities

• Hemianopia
  Half no vision
• Quadrantanopia
  Quarter no vision
• Right or left
• Upper and lower
• Named from child’s perspective

Impaired accommodation in a child with hemianopia

Why do you get these patterns?

One half of the visual world is seen by the temporal half of one retina and the nasal half of the other.

 

Why do you get these patterns?

• The visual information 'seen' by the nasal retina is transferred to the opposite side of the brain
• The visual information 'seen' by the temporal retina travels straight back down the same side
• As a result all the visual information from the right half of the visual world is collected by the left side of the brain
• And vice versa

Only practical to assess quadrantic field loss

• Stycar balls or diffuse light on stick
• Observer engages child's attention
• Second assessor slowly brings in target towards fixation through four quadrants
• Observe when child notices target
• Compare quadrants

Colour Vision Impairment

• X-linked Red Green colour confusion
• Cone dystrophy
• Central brain lesion, very rare

Red Green colour confusion

• Not colour blind
• X-linked
• 8% of males and 0.4% of females
• Is it a disability?
• Best screened for with Ishihara plates

Cone dystrophy

• Complete
• Partial
• Stationary
• Progressive
• Tends to affect blue/yellow end of spectrum

Why blue/yellow end?

• 95% of the cone photoreceptors are either long (red) or medium (green) wavelength responders
• Only 5% are short (blue) wavelength responders
• Therefore only need minor insult to affect blue/yellow end of perception

What is purpose of assessing colour vision

• To make clear to parents and teachers where colour confusion occurs
• Make educational recommendations as a result

Central Colour Vision Impairment

• Rare
• Temporal lobe disease
• Probably bilateral lesions for complete absence of colour vision
• Alternatively may have colour naming difficulty with matching intact

Eye movements

Two main kinds of eye movements

• Slow pursuit for following
• Fast saccadic for changing fixation

Most children with brain injury have some problem with eye movements

Assessment of slow eye movements

• Slowly move near fixation target
• Appropriate for visual acuity
• From central fixation to 'cardinal positions of gaze'

Assessment of fast eye movements

• Attempt to force fixation shifts
• May notice head turns, blinking
• Optokinetic (OKN) drum is a useful screening tool

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

Accommodation

Impaired accommodation
Common in:

• Cerebral Palsy
• Down's syndrome
• Absent
• Inadequate
• Inaccurate
• Easily fatigued

Accommodation - Down's Syndrome

Screening tool

• Dynamic retinoscopy
• Examine eye in relaxed state fixating distant object
• Compare examination when near target held close up

Rehabilitation - Reading glasses

Margaret Woodhouse, Cardiff University - Control trial on going in Down's syndrome

End of assessment

• Try to summarise for parents
• Initiates discussion
• Include in report

Write report

• Disseminate
• Transfer
• Relevant
• Understandable
• Effective
• Help child develop

Language of collaborative vision assessment report

• Accessible to whole team
• Accessible to parents
• Relevant
• Understandable

Purpose of collaborative vision assessment report

• Ensure effective sharing
• Single source
• Meets needs of whole team
• Perform their job effectively
• Promotes communication

Feedback questionnaire - parents and teachers

Parents: the report

• All parents felt it was 'useful' and three quarters (13/17) claimed it helped improve understanding
• All parents (except one) said it was the first time
• All parents considered it important that it is also given to their child’s teacher and therapists (more so than their family doctor)
• More than half (9/17) the parents felt their child was more relaxed while waiting for the assessment
  
• 11/17 parents felt their child was less stressed during the assessment

Teachers

• Almost half (14/30) the teachers had no previous written information on the visual function of the child they were trying to teach
• Almost all teachers (28/30) felt the report improved their understanding of their child’s vision with the same number stating the report helped in planning teaching strategies
• More than half the teachers (17/30) made a significant change in teaching strategies as a result of receiving the report

Take home messages

• Work as a team across disciplines
• Share information
• Skills complement each other
• Half of childhood VI is caused by the brain
• Lots of additional difficulties

Take home messages

• Seeing lots of things at once
• Attending to multiple tasks
• Making fast eye movements
• Impairment of near focussing
• Function will vary from day to day
• Simplicity
• Speed
• Varied

Take home messages

• Intimidating to assess
• Fun to work with
• Be brave
• Have no shame

Where next

• Understanding visual fields