Chapter 1 - Vision
Theory
Development of vision
• Vision is the sense of processing visual information from the environment
and interpreting it as conscious visual stimuli.
• The visual pathways are divided into subcortical networks (from the eye to
the posterior of the brain) and the cortical networks (linking different regions
within the brain).
• The ocular system includes the iris, which regulates light intensity, and an
adjustable system of lens for focusing light into an image.
• When visual information leaves the retina, it travels via the optic nerve,
which becomes the optic tract, to a nucleus of the thalamus called the lateral geniculate nucleus (LGN).
● This main subcortical pathway progresses along a tract called the optic radiation. The axons of the optic radiation curve
around the wall of the lateral ventricle in each cerebral hemisphere to reach the visual striate cortex (V1) in the
occipital lobe.
• The magnocellular pathway is specialised to detect movement (e.g. location, speed, and direction), whilst the parvocellular
pathway is important for spatial resolution (e.g. shape, colour, and size of object).
• The areas around the visual cortex (known as the visual association areas or extra-striate cortex) are involved in complex
visual processing.
● Information from the visual cortex travels to the posterior parietal lobe and this
‘dorsal stream’ (also known as the ‘where’ pathway) is believed to be involved
in perception of motion and spatial relationships in the visual world.
● Information travelling to the inferior temporal lobe from the visual cortex is
known as the ‘ventral stream’ (or ‘what’ pathway) and believed to carry
information involved with object form and recognition.
Development of the visual system
• The visual system develops rapidly in the first year of life and continues to develop during the early years of childhood. There
appears to be ‘sensitive periods’ of neuroplasticity of the visual system.
● E.g. if one eye is deprived of a normal visual input in early life that eye may never develop normal vision.
• A basic measure of vision is called ‘visual acuity’, that is, the level at which fine detail can be resolved.
● At birth, visual acuity is very poor. It improves rapidly over the first year of life, and then slowly improves up to adult
levels by around 7 years of age.
Childhood vision impairment
• The majority of childhood vision impairments are congenital, though some occur later in childhood through late-onset
genetic disorders, infection, brain injury, or tumor.
● In congenital cerebral visual impairment, visual dysfunction occurs due to damage to areas of the brain involved in
processing visual stimuli.
• Severe vision impairment is acuity of 1.0 logMAR (6/60 meaning seeing at 6m what a typically sighted person can see at 60m)
or worse.
● Children at this level of vision will need additional low vision aids to help enlarge print or bring distant images to close
vision.
Early development
• In the months following birth, early learning with limited vision creates a major developmental challenge.
● The greatest delays are apparent in young children with profound vision impairment who have light perception at best
and these children are particularly vulnerable.
,Intellectual and learning profiles
• Children with vision impairment are at high risk of intellectual disability, as there is a high co-occurrence of vision and
neurological differences. Nevertheless, across the full spectrum of vision impairment there are children who excel intellectually
and progress to higher education and successful employment.
● For those without additional needs, early delays in cognition may be overcome in the school years, as they compensate
by using auditory and haptic modalities as well as the considerable benefit derived from their developing language
skills.
○ These children, however, remain vulnerable in the classroom.
Attention, executive functions, and memory
• Children with profound vision impairment are found to be weaker in their response to adults’ attempts to establish and
maintain their attention and also in flexibly shifting attention from one object to another.
• Parent responses on questionnaires assessing everyday executive function indicated more difficulties for children with vision
impairment, particularly those with more severe profound vision impairment.
● It’s suggested that lack of environmental visual feedback during everyday executive function tasks may increase the
cognitive load and disrupt dynamic executive performance.
• Of the limited studies in children, there is evidence that episodic verbal memory is either similar or superior to typically
sighted comparison groups.
Language and social communication
• Of the limited research in this area, there is some evidence for relative weakness in pragmatic compared to structural
language, which for some may be related to social communication weaknesses.
● The rate of ASD is estimated to be 31 times that of peers who are typically sighted.
● Social communication may be more vulnerable because of the role of vision in the precursors of social communication
development including gaze following, joint attention, and the difficulties for parent and young child in achieving joint
referencing using coordinated vision and gesture.
Adaptive behaviour
• Results from recent studies indicated that there is a cluster of visuocognitive deficits in visual attention, visuomotor skills,
motion sensitivity, and spatial cognition that are common across many disorders, including children with vision impairment.
This has been called ‘dorsal stream vulnerability’ as these deficits relate largely to development of different neural networks
within the dorsal stream.
Assessment and formulation
Preparation of the assessment
• Given the paucity of measures for assessing individuals with vision impairment, taking a careful history interview is very
important. The history should include:
● Developmental questions adapted to consider the child’s vision,
● Observation and information from the child, parent, and other relevant professionals working with the child
● The degree of vision impairment →children with moderate vision impairment may be able to access some pictorial and
visual materials, whilst those with severe or profound vision impairment should not be administered assessments
involving visual stimuli.
● It’s important to know the child’s usual way of working in school and whether they are using braille, enlarged print,
and/or low vision aids and to find out about other visual deficits that may affect the assessment, including adaptability
to light, eye movement disorders, and visual field loss.
Behaviour, social relating, and adaptive skills
• There are challenges in assessing children with vision impairment as many of the items rely on vision.
,Issues of cognitive and attainment testing
• For a comprehensive assessment of intellectual abilities, both verbal and nonverbal domains should be assessed using
normative standardised assessment tools. Where standardised haptic non-verbal assessment is not possible, the
neuropsychologist needs to restrict their assessment to the verbal domains and be aware of the limitations of this.
• Allowances need to be made for the preschool child underperforming on a normative developmental test. By the time the
child is at school they are beginning to learn at a roughly similar rate to the peers with typical sight if they do not have
additional learning needs.
● Nevertheless, the possibility of general intellectual and specific learning disabilities should be given consideration if a
child is having sustained and significant difficulties with learning in the classroom environment and they continue to
score significantly below normative expectations.
• Further considerations are required for attainment testing:
● For children who access enlarged print, it may be possible to adapt attainment assessments to the child’s mode of
access (e.g. enlarged print or use of a magnifier for reading, using the child’s usual writing equipment for spelling).
● Braille reading skills can be assessed via the braille version. Braille isn’t directly comparable with print; it’s typically
slower to learn and associated with slower reading speed.
○ Specific learning disorders in reading are recognised in a proportion of braille readers and higher processing
demands have been linked to the strictly sequential nature of braille, which place high demands on
phonological skills.
Assessment measures
• The majority of subtests used in any standard neuropsychological battery involve visual presentation. Alternative tests have
therefore been developed for children with vision impairment, though these are rarely fully standardised or widely available.
● The standardisation of vision impairment-specific measures or norms is hampered by the rare heterogeneous and
complex nature of vision disorders. Factors leading to heterogeneity include variation in vision level, intellectual and
other comorbidities, aetiology (such as congenital or acquired through head injury or tumor), and age or onset.
● Where standardisation is achieved, these challenges mean that norms are rarely updated and are at risk of becoming
obsolete and need interpreting with caution (e.g. the Flynn effect, which describes the tendency for increased scores
at population level over time).
• Given the limited availability of vision impairment-specific tests or norms, traditional neuropsychological measures involving
verbal/auditory presentation normed on sighted populations can be cautiously used in individuals with vision impairment as
they do not involve much adaptation for this population.
● It’s argued that cognitive assessments normed on typically sighted children should not be used to assess children with
vision impairment. However, in the absence of widely available vision impairment-specific standardized assessments or
norms, it’s our stance that when interpreted cautiously and with expertise this can be beneficial for the child in order
to highlight strengths and needs, to ensure the child is meeting their potential and inform support needs and
intervention.
Intervention and management
• Given the impact of severe vision impairment on early development and the importance of parental guidance and support,
there has been a growing focus on home-based, parent-mediated early intervention.
● A recent study has shown that home-based early intervention using the Developmental Journal for babies and young
children with vision impairment (DJVI) led to clinically relevant advances in cognition and language, reduction in
behaviour difficulties, and enhanced support for parents (including reduced parenting stress) compared to
home-based ‘other support’.
• Bardin and Lewis highlighted the importance of creating multiple opportunities to increase active participation and
engagement in learning. Creating alternative opportunities for accessible multisensory learning for children with vision
impairment include tactile graphics, hands-on-learning, and audio support. A commonly used classroom strategy for managing
attention difficulties is to reduce auditory distractors. As information received by the non-visual senses may be more salient for
children with vision impairment, understanding the nature and impact of stimuli that are distracting for the individual is
important when making recommendations regarding environmental modifications.
, • Executive function development is hardly understood in children with vision impairment, in part due to the visual nature of
most executive function standardised measures. Verbal mediation strategies, which draw on strengths in verbal and sequential
processing, may be particularly beneficial in promoting self-regulation via language and developing metacognitive strategies.
• Self-determination has been reported to be weaker among children and adolescents with vision impairment, whilst higher
self-determination is associated with better employment outcomes. Researchers suggest providing the young person with
opportunities for decision-making and active participation in education planning and vocational choices to promote
self-determination.
Theory
Development of vision
• Vision is the sense of processing visual information from the environment
and interpreting it as conscious visual stimuli.
• The visual pathways are divided into subcortical networks (from the eye to
the posterior of the brain) and the cortical networks (linking different regions
within the brain).
• The ocular system includes the iris, which regulates light intensity, and an
adjustable system of lens for focusing light into an image.
• When visual information leaves the retina, it travels via the optic nerve,
which becomes the optic tract, to a nucleus of the thalamus called the lateral geniculate nucleus (LGN).
● This main subcortical pathway progresses along a tract called the optic radiation. The axons of the optic radiation curve
around the wall of the lateral ventricle in each cerebral hemisphere to reach the visual striate cortex (V1) in the
occipital lobe.
• The magnocellular pathway is specialised to detect movement (e.g. location, speed, and direction), whilst the parvocellular
pathway is important for spatial resolution (e.g. shape, colour, and size of object).
• The areas around the visual cortex (known as the visual association areas or extra-striate cortex) are involved in complex
visual processing.
● Information from the visual cortex travels to the posterior parietal lobe and this
‘dorsal stream’ (also known as the ‘where’ pathway) is believed to be involved
in perception of motion and spatial relationships in the visual world.
● Information travelling to the inferior temporal lobe from the visual cortex is
known as the ‘ventral stream’ (or ‘what’ pathway) and believed to carry
information involved with object form and recognition.
Development of the visual system
• The visual system develops rapidly in the first year of life and continues to develop during the early years of childhood. There
appears to be ‘sensitive periods’ of neuroplasticity of the visual system.
● E.g. if one eye is deprived of a normal visual input in early life that eye may never develop normal vision.
• A basic measure of vision is called ‘visual acuity’, that is, the level at which fine detail can be resolved.
● At birth, visual acuity is very poor. It improves rapidly over the first year of life, and then slowly improves up to adult
levels by around 7 years of age.
Childhood vision impairment
• The majority of childhood vision impairments are congenital, though some occur later in childhood through late-onset
genetic disorders, infection, brain injury, or tumor.
● In congenital cerebral visual impairment, visual dysfunction occurs due to damage to areas of the brain involved in
processing visual stimuli.
• Severe vision impairment is acuity of 1.0 logMAR (6/60 meaning seeing at 6m what a typically sighted person can see at 60m)
or worse.
● Children at this level of vision will need additional low vision aids to help enlarge print or bring distant images to close
vision.
Early development
• In the months following birth, early learning with limited vision creates a major developmental challenge.
● The greatest delays are apparent in young children with profound vision impairment who have light perception at best
and these children are particularly vulnerable.
,Intellectual and learning profiles
• Children with vision impairment are at high risk of intellectual disability, as there is a high co-occurrence of vision and
neurological differences. Nevertheless, across the full spectrum of vision impairment there are children who excel intellectually
and progress to higher education and successful employment.
● For those without additional needs, early delays in cognition may be overcome in the school years, as they compensate
by using auditory and haptic modalities as well as the considerable benefit derived from their developing language
skills.
○ These children, however, remain vulnerable in the classroom.
Attention, executive functions, and memory
• Children with profound vision impairment are found to be weaker in their response to adults’ attempts to establish and
maintain their attention and also in flexibly shifting attention from one object to another.
• Parent responses on questionnaires assessing everyday executive function indicated more difficulties for children with vision
impairment, particularly those with more severe profound vision impairment.
● It’s suggested that lack of environmental visual feedback during everyday executive function tasks may increase the
cognitive load and disrupt dynamic executive performance.
• Of the limited studies in children, there is evidence that episodic verbal memory is either similar or superior to typically
sighted comparison groups.
Language and social communication
• Of the limited research in this area, there is some evidence for relative weakness in pragmatic compared to structural
language, which for some may be related to social communication weaknesses.
● The rate of ASD is estimated to be 31 times that of peers who are typically sighted.
● Social communication may be more vulnerable because of the role of vision in the precursors of social communication
development including gaze following, joint attention, and the difficulties for parent and young child in achieving joint
referencing using coordinated vision and gesture.
Adaptive behaviour
• Results from recent studies indicated that there is a cluster of visuocognitive deficits in visual attention, visuomotor skills,
motion sensitivity, and spatial cognition that are common across many disorders, including children with vision impairment.
This has been called ‘dorsal stream vulnerability’ as these deficits relate largely to development of different neural networks
within the dorsal stream.
Assessment and formulation
Preparation of the assessment
• Given the paucity of measures for assessing individuals with vision impairment, taking a careful history interview is very
important. The history should include:
● Developmental questions adapted to consider the child’s vision,
● Observation and information from the child, parent, and other relevant professionals working with the child
● The degree of vision impairment →children with moderate vision impairment may be able to access some pictorial and
visual materials, whilst those with severe or profound vision impairment should not be administered assessments
involving visual stimuli.
● It’s important to know the child’s usual way of working in school and whether they are using braille, enlarged print,
and/or low vision aids and to find out about other visual deficits that may affect the assessment, including adaptability
to light, eye movement disorders, and visual field loss.
Behaviour, social relating, and adaptive skills
• There are challenges in assessing children with vision impairment as many of the items rely on vision.
,Issues of cognitive and attainment testing
• For a comprehensive assessment of intellectual abilities, both verbal and nonverbal domains should be assessed using
normative standardised assessment tools. Where standardised haptic non-verbal assessment is not possible, the
neuropsychologist needs to restrict their assessment to the verbal domains and be aware of the limitations of this.
• Allowances need to be made for the preschool child underperforming on a normative developmental test. By the time the
child is at school they are beginning to learn at a roughly similar rate to the peers with typical sight if they do not have
additional learning needs.
● Nevertheless, the possibility of general intellectual and specific learning disabilities should be given consideration if a
child is having sustained and significant difficulties with learning in the classroom environment and they continue to
score significantly below normative expectations.
• Further considerations are required for attainment testing:
● For children who access enlarged print, it may be possible to adapt attainment assessments to the child’s mode of
access (e.g. enlarged print or use of a magnifier for reading, using the child’s usual writing equipment for spelling).
● Braille reading skills can be assessed via the braille version. Braille isn’t directly comparable with print; it’s typically
slower to learn and associated with slower reading speed.
○ Specific learning disorders in reading are recognised in a proportion of braille readers and higher processing
demands have been linked to the strictly sequential nature of braille, which place high demands on
phonological skills.
Assessment measures
• The majority of subtests used in any standard neuropsychological battery involve visual presentation. Alternative tests have
therefore been developed for children with vision impairment, though these are rarely fully standardised or widely available.
● The standardisation of vision impairment-specific measures or norms is hampered by the rare heterogeneous and
complex nature of vision disorders. Factors leading to heterogeneity include variation in vision level, intellectual and
other comorbidities, aetiology (such as congenital or acquired through head injury or tumor), and age or onset.
● Where standardisation is achieved, these challenges mean that norms are rarely updated and are at risk of becoming
obsolete and need interpreting with caution (e.g. the Flynn effect, which describes the tendency for increased scores
at population level over time).
• Given the limited availability of vision impairment-specific tests or norms, traditional neuropsychological measures involving
verbal/auditory presentation normed on sighted populations can be cautiously used in individuals with vision impairment as
they do not involve much adaptation for this population.
● It’s argued that cognitive assessments normed on typically sighted children should not be used to assess children with
vision impairment. However, in the absence of widely available vision impairment-specific standardized assessments or
norms, it’s our stance that when interpreted cautiously and with expertise this can be beneficial for the child in order
to highlight strengths and needs, to ensure the child is meeting their potential and inform support needs and
intervention.
Intervention and management
• Given the impact of severe vision impairment on early development and the importance of parental guidance and support,
there has been a growing focus on home-based, parent-mediated early intervention.
● A recent study has shown that home-based early intervention using the Developmental Journal for babies and young
children with vision impairment (DJVI) led to clinically relevant advances in cognition and language, reduction in
behaviour difficulties, and enhanced support for parents (including reduced parenting stress) compared to
home-based ‘other support’.
• Bardin and Lewis highlighted the importance of creating multiple opportunities to increase active participation and
engagement in learning. Creating alternative opportunities for accessible multisensory learning for children with vision
impairment include tactile graphics, hands-on-learning, and audio support. A commonly used classroom strategy for managing
attention difficulties is to reduce auditory distractors. As information received by the non-visual senses may be more salient for
children with vision impairment, understanding the nature and impact of stimuli that are distracting for the individual is
important when making recommendations regarding environmental modifications.
, • Executive function development is hardly understood in children with vision impairment, in part due to the visual nature of
most executive function standardised measures. Verbal mediation strategies, which draw on strengths in verbal and sequential
processing, may be particularly beneficial in promoting self-regulation via language and developing metacognitive strategies.
• Self-determination has been reported to be weaker among children and adolescents with vision impairment, whilst higher
self-determination is associated with better employment outcomes. Researchers suggest providing the young person with
opportunities for decision-making and active participation in education planning and vocational choices to promote
self-determination.
