Children with Vision Impairment: Assessment, Development, and Management: 1st Edition

Vision impairment is a long-term condition caused by disorders of the eye, optic nerve, and brain. Using evidence-based knowledge, theory, and research, this book provides practical guidance for practitioners who are involved in the care and management of children with long-term vision impairment and disability. The book is divided into four sections following the ICF-CY model: (1) eye disorders, vision and brain, (2) child development and learning from birth to older childhood, (3) habilitation, orientation, reading and assistive technologies and (4) social relationships and participation in everyday contexts.

International team of experts present up to date vision and neuroscience research and assessment and management approaches.

Multidisciplinary approaches for improving function, learning and activity in children with vision impairment.

New approach to childhood vision impairment with a focus on assessment, function and participation.

Covering all vision disorders and levels of vision impairment, including eye disorders, cerebral vision impairment and complex disability.

• Language: English
• Publisher: Mac Keith Press
• Release date: Dec 17, 2021
• ISBN: 9781911612353

Book preview

CHAPTER 1

Introduction

Naomi Dale, Alison Salt, Jenefer Sargent, and Rebecca Greenaway

Vision impairment is a long-term condition, arising from multiple disorders of the eye, optic nerve, and brain. The child’s vision may range from no functional vision (profound vision impairment) to severe, moderate, or mild levels of impairment. It is estimated that in 2015 there were 1.14 million children worldwide with profound visual impairment and blindness, though causes and prevalence vary between countries with avoidable causes being higher in those with lower incomes (Gilbert et al. 2017; see further Chapter 2). Although these children may face many potential barriers and limitations, with the support of parents, friends, and professionals, many of these children are able to fully participate in their society and achieve their aspirations.

There are many challenges for the child’s learning and activity due to the significant impact of vision reduction on development and learning. Genetic and other biological factors may influence the child’s eyes and brain, development, and learning. This very diverse population of children has varying intellectual abilities and may have co-occurring conditions including cerebral palsy, autism spectrum disorder, attention-deficit/hyperactivity disorder, epilepsy, and hearing impairment. They may have neuropsychiatric and behavioural disorders, as well as mental health issues. Some rare eye disorders are associated with neurometabolic and neurodegenerative conditions. Cerebral visual impairment may lead to disorders in basic and higher vision processing including visual perceptual problems.

The functional needs and habilitation of children with vision impairment are the main emphasis of this book. The focus is primarily on those with very early causation and onset of vision impairment as the majority of childhood vision impairment is congenital (Teoh et al. 2021). However, the needs of children with progressive vision impairment of later onset and children with acquired vision impairment are also considered in the relevant chapters.

GUIDING PRACTICE

This book is designed as a Practical Guide to support practitioners in their management of care of children who have long-term vision impairment and disability. Its main themes are assessment of the child, the child’s function and activity, and habilitation or remedial intervention.

Assessment is key to understanding the child’s current vision and developmental needs and establishing any co-occurring issues, such as intellectual or motor disability or autism spectrum disorder, and for guiding habilitation and intervention. A focus on the child’s function and activity guides what needs to be assessed and possibly targeted for support, such as vision, motor function, cognition, language and social functions, and mental health. Habilitation covers the range of interventions and supports for everyday living and learning, from early years’ intervention to mobility and navigation, everyday living skills, social relationships and participation, and augmentative and assistive technological supports. To cover the breadth of topics of relevance, we bring together an international group of leading multidisciplinary experts from health, education, habilitation, and social care.

A number of conceptual models are adopted to shape the content and consideration of the issues covered:

• First, the World Health Organization International Classification of Functioning, Disability and Health: Children and Youth Version (ICF-CY) informs practice and the short- and long-term goals for the child and their family. In contrast to a disability focus that is primarily biomedical, this model takes us to a bio-functional-social (or biopsychosocial) perspective that aims to enhance the child’s and their family’s function and participation in everyday life and society (see Fig. 1.1).

• Second, a multi-factorial model of risk and protective factors (Pennington 2006) considers multiple and interacting factors of risk and protection for the child and how they may influence the child’s developmental progress and resilience. This model supports a holistic multidisciplinary approach and can inform timely preventative and interventionist strategies to meet the child’s needs and to minimise longer-term risks and improve outcomes.

• Third, a family capacity-building model (Dunst et al. 2014) includes family-centred partnerships between children/young users, parents and practitioners and advocates for listening to the voices of the child or young person and parents. All practice is more effective if it is well communicated to the parents and child/young person, their viewpoint is heeded and a negotiation approach is undertaken to bring the perspectives of the parent and child/user when appropriate and professional together, and differences are resolved constructively (Dale 1996). This approach aims to empower the child or young person and their family and inclusion and participation in society. Chapters from a young person and from parents provide this important perspective.

• Fourth, a habilitation model focussing on the child’s developmental growth and optimising the child’s strengths and outlook. This approach includes preventative and interventionist strategies to support the child thriving and learning, and overcoming challenges arising from the vision disability. Rehabilitation is also relevant to those children when vision has become impaired at a later age through late onset or acquired disorders and compensatory strategies are required.

• Finally, the book is evidence-based in that it draws on recent and contemporary scientific research to support practice and each chapter covers the relevant research available to support developments in practice. Areas that would be useful for future research are also highlighted, reflecting that practice methods are changing, dynamic, and ongoing.

Figure 1.1 ICF-CY model for health or disability (World Health Organization 2007)

SERVICE DELIVERY AND CONTEXT

Each country has different models of service delivery and degrees of resources, but all children with vision impairment are likely to need inputs from a range of health, education, and social care practitioners at primary, secondary, and tertiary levels to comprehensively meet their changing needs. This book endeavours to be of international relevance and has authors from different countries.

Whether in higher or low-moderate income countries, the most appropriate model of delivery is the World Health Organization pyramid of service delivery, which has been developed in the NHS tiered health care system (United Kingdom). Figure 1.2 highlights the delivery needed at each tier. Tiers 2 and 3 will need practitioners who have more training and experience and expertise in childhood vision impairment. Screening for vision and developmental disability is often likely to start in neonatal and maternity centres/hospital and in the community in Tier 1. Multidisciplinary specialist and diagnostic services at Tier 3 and targeted interventions from Tier 2 support the inclusion and participation of the child and family in universal services at Tier 1. Tier 3 will include specialist paediatric and ophthalmological services for diagnostic and highly specialist care and management of the eye and vision disorder. Tier 2 ideally provides specialist community out-reach services such as specialist early intervention, habilitation, and education for children with vision impairment to support the child developing and learning and supporting the family in their daily lives. As countries further build their services in this field they can increase the expertise and specialisation of professionals in Tiers 2 and 3, along the lines of suggestions in this book.

Figure 1.2 Tiered model of child care services for children with visual impairment

In a lower-resourced country, a vision service to support children and families through the lifespan may be set up. This could run in conjunction with a specialist ophthalmology and paediatric service, with community outreach workers. Some key areas that may be relevant to start with are early intervention (Chapter 8), habilitation (Chapter 14), psychological wellbeing and mental health (Chapter 18), and adolescence and transition (Chapter 20). These chapters provide accessible practice tips and guidance that may be useful for the more generalist community or outreach practitioner from health or education who is starting off in the field.

ORGANISATION OF BOOK

The book is divided into four parts following the ICF-CY model (see Fig. 1.1): Part 1 Eye Disorders, Vision, and Brain focussing on body functions and structure; Part 2 Child Development and Learning From Birth to Older Childhood focussing on child function and development and learning across childhood; Part 3 Further Approaches to Habilitation focussing on functional activity and leisure and participatory activities; and Part 4 Social Relationships and Participation focussing on social relating and participation in everyday contexts.

Part 1 Eye Disorders, Vision, and Brain has chapters on causes, vision functions, and classification of childhood vision impairment; genetics and phenotype presentations of congenital eye disorders; cerebral visual impairment: identification, assessment, and management; brain plasticity and vision impairment; vision assessment of children with complex disorders; and assessment and habilitation of vision in infants and young children.

Part 2 Child Development and Learning From Birth to Older Development has chapters on early years, early intervention, and family support; motor development and hand skills; language and communication development; social communication and autism spectrum disorder; cognition; and the parental perspective.

Part 3 Further Approaches to Habilitation has chapters on orientation, mobility, and adaptive behaviour; low vision aids and assistive technologies; reading approaches for braille users and technological aids for spatial perception and mobility.

Part 4 Social Relationships and Participation has chapters on behaviour, psychological wellbeing, and mental health; quality of life, self-concept, and social relationships; towards autonomy and independence in adolescence; and the young person’s experience and perspective.

Each chapter, after an introduction, is divided into four areas. The first sections cover relevant theory, contemporary research evidence, and practice insights. Scientific research provides the systematic evidence to inform, validate, and guide evidence-based practice that is effective. We have focussed on research published since 2000 but this does not deny the importance of earlier research and insights that these studies build on. Some earlier seminal studies are included where appropriate. The next sections provide practical guidance and strategies for assessment and management including for multidisciplinary management of care. As this is a continually changing field, each chapter concludes with signposts for ways forward for future research and practice. A reference list of the research cited and for further reading is available at the end of each chapter.

LANGUAGE USE AND DEFINITIONS

To clarify the language terms used in the book, the term parent refers to the mother, father, and/or significant caregiver as an inclusive term for all adults who regularly look after the child in the home environment. Where research has been carried out with the mother or father specifically, this is denoted. The term child refers to children of all ages up to late adolescence unless a particular age range is specified. Throughout this book, we refer to habilitation, a process aimed at helping people with a disability attain, consolidate, or improve skills and functioning for daily living, and which is particularly applicable to those children with very early onset of vision impairment. Rehabilitation may be considered more appropriate for those children who lose vision later in childhood and may be referred to specifically in some chapters. In this scenario, rehabilitation refers to regaining skills, abilities, or knowledge, and learning compensatory strategies for those that may have been lost or compromised.

Although there are different references and traditions in the field in relation to terminology regarding vision disability, we have chosen to mainly use the term vision impairment. A vision impairment is any visual condition that impacts on an individual’s ability to successfully complete the activities of everyday life. At different points in the book, the term ‘vision impairment’ may be replaced by related terms such as ‘blindness’, ‘vision disability’, and ‘severely visually impaired’ or ‘severe/profound visual impairment’, according to terms used in a research study or the author’s preference.

SUMMARY

This Practical Guide aims to support and equip practitioners to provide quality interventions and practice to achieve the most reliable assessments, effective interventions, and successful outcomes in life opportunities and quality of life for children with vision impairment and their families, in partnership with the child/young person and family. We and all the authors hope that this Practical Guide will be helpful in this endeavour.

REFERENCES

Dale N (1996) Working with Families of Children with Special Needs: Partnership and Practice. London: Routledge.

Dunst CJ, Bruder MB, Espe-Sherwindt M (2014) Family capacity-building in early childhood intervention: do context and setting matter? School Community Journal 24(1): 37–148.

Gilbert C, Bowman R, Malik ANJ (2017) The epidemiology of blindness in children: changing priorities. Community Eye Health 30(100): 74–77.

Pennington BF (2006) From single to multiple deficit models of developmental disorders. Cognition 101: 385–413. doi: 10.1016/j.cognition.2006.04.008.

Teoh LJ, Solebo AL, Rahi JS et al. (2021) Visual impairment, severe visual impairment, and blindness in children in Britain (BCVIS2): a national observational study. The Lancet 5(3): 190–200.

World Health Organization (2007) ICY-CY: International Classification of Functioning, Disability and Health: Children and Youth Version. Switzerland: World Health Organization Publications.

PART 1

Eye Disorders, Vision, and Brain

CHAPTER 2

Vision Functions, Classification, and Causes of Childhood Vision Impairment

Ameenat Lola Solebo and Jugnoo Sangeeta Rahi

INTRODUCTION

Vision comprises several different integrated vision functions (Braddick and Atkinson 2011), which together contribute to a child’s health, developmental and social experiences, and learning (Rahi et al. 2009).

Visual acuity (the resolution of detail) is the primary function, with several important secondary functions including depth perception, visual field, and colour and contrast sensitivity. These permit higher-order visual processes, such as perception of faces, motion, or environment mapping. Abnormalities of visual function can range in type and severity, affecting one or both eyes, and can be due to eye or brain and visual pathway disease.

Severe bilateral impairment of acuity potentially confers significant everyday living demands or ‘burden’ for the child, family, and society (Rahi et al. 2003). Across the world the pattern of causes for vision impairment and blindness vary, reflecting the regional balance of the determinants of diseases and resources. The most significant global causes of severe vision impairment are retinal disorders, corneal scarring, congenital ocular structural anomalies, cataract, and brain disorders (Solebo et al. 2017). This chapter explores the different vision functions, the anatomy of the eye, causes of vision impairment, and the identification of vision disorders.

VISION AND VISION IMPAIRMENT

The eyes process light, turning it into neural signals that are transmitted to the brain via the visual pathways. The brain translates these signals into meaningful perceptions of the physical or social world, such as mapping one’s environment and picking out objects within a crowded scene or interpreting the facial expressions of another person. Very poor vision is caused by impaired functioning of the eyes or by damage to the visual pathways of the brain (see Chapter 5).

Vision Functions

Acuity is the ability of the functioning visual system to ‘resolve’ edges in space, which is essential for analysis of detail. It is measured in terms of the degree of separation (or resolution) of the component parts of the images needed for them to be seen distinctly and separately. Secondary visual functions are largely dependent on acuity, with significantly impaired visual acuity leading to deficits of all other visual functions (Braddick and Atkinson 2011).

3D vision or depth is perceived using discrepancies between images generated by information from each of the eyes. It is also possible to detect depth with vision in only one eye, using cues such as shade and perspective (Harris and Wilcox 2009). Depth perception (stereopsis) also relies on higher-order processing of spatial information (see Chapter 5). Other visual functions such as perception of movement, visual guidance of movement, visual search, visual attention, and visual recognition, also require higher visual processing in vision association areas in the brain and are addressed in this chapter (see Chapter 5).

Eye movements enable tracking of moving objects and relocation of gaze (smooth pursuit and saccades respectively). There are six cardinal eye movements, in both directions horizontally (left and right) and vertically (up and down), and two additional rotatory movements (incyclotorsion and excyclotorsion), which stabilise an individual’s eyes during head tilting. These movements are enacted by six muscles attached to each eye and choreographed by the central nervous system.

The visual field is the total area of space perceived when the eyes and head are still and typically extends furthest temporally (to the sides). The quality of acuity is distributed unequally with the central field being the most sensitive area (Patel et al. 2015). The peripheral visual field is also of importance as this is needed to perceive moving targets, and to guide and facilitate movement through 3D visual space.

Colour vision and contrast sensitivity are the ability to discriminate between different hues and areas of different luminance respectively. Perception of large differences in luminance, such as a black font on a white background, require less contrast sensitivity than perception of grey images on lighter grey background. Poor environmental lighting has significant negative impact on contrast sensitivity (Braddick and Atkinson 2011). The retina can also automatically adjust to accommodate to light intensity, known as light and dark adaptation.

Figure 2.1 Refractive errors and emmetropia

In order to perceive clarity of ‘form’, the curved surfaces on and within the eyeball bend (refract) light as it enters the eye so that a focussed image is formed upon the retina (Fig. 2.1). Refraction can also be an active process, called accommodation, when a person changes their focus from a more distant to a nearer object. The optical or refractive power of the eye alters with lens shape, while the eyes converge, and this dual process of accommodation and convergence ensures that the image remains in focus and singular irrespective of its distance from the eyes.

The common refractive errors (Fig. 2.1) are:

• Hypermetropia. Due to the higher curvature and shorter length of a smaller child’s eye, a degree of hypermetropia is the natural state in many children until age 4 or 5 years of age.

• Myopia occurs when the eyeball is too long or when the cornea is less curved and may be associated with a family history of myopia (being ‘short-sighted’).

• Astigmatism, in which there are different degrees of refraction within an individual eye as measured at separate axes.

Amblyopia

In typically developing children, visual functions, particularly acuity, rapidly improve during the first years of life as a result of the maturation of ocular anatomy and neural pathway circuitry (Lewis and Maurer 2005). Sensory and motor functions have a sensitive window, which is a finite early developmental period during which high quality stimuli must be experienced in order for the function to fully develop. Consequently, any disorder that impedes the presentation of a clear focussed image to the brain in early childhood can lead to delayed or abnormal development of the visual system (see Box 2.1). This abnormal development (amblyopia) can be reversed in children with sufficient vision potential and the developmental trajectory reset if treatment is undertaken during the sensitive window (Holmes and Clark 2006). Prevention of permanent amblyopia where feasible lies at the heart of the management of childhood eye and vision disease and disorder (see Chapter 4).

Measuring Vision in Childhood

Visual acuity is recorded numerically using fractions (e.g. 20/20 or 6/6 vision) or decimal scores, or is estimated in gross terms (e.g. able to fix gaze on external stimuli or able to perceive light). The preferred scale for quantifying visual acuity is the logarithm of the Minimum Angle of Resolution or logMAR because of its standardised charts and its linear arithmetic progression, which enables robust quantification of acuity (vs the historical Snellen geometric scale and non-standardised charts) (Rosser et al. 2001). Vision of 0.0 logMAR is the normal adult level, with vision of 1.0 logMAR (a logarithm unit of change) being 10 times worse.

A full-term infant will be able to perceive and show attention preference for human facial features and high contrast (black on white) patterns within a few hours of birth. However, neonates typically have an acuity of only 1.5 logMAR. This rapidly improves to 1.0 logMAR at 1 month of age and 0.5 logMAR by 12 months of age. ‘Adult’ levels of acuity (0.0–0.1 logMAR) are reached by 5 to 6 years of age (Sonksen et al. 2008). Accompanying this rapid improvement in acuity are developing cognitive and motor skills and therefore choice of the appropriate tests to assess a child’s vision requires understanding of their current developmental status (Chapter 4).

In infants and pre-verbal children, it is not possible to measure recognition acuity using optotypes (letters, shapes, or pictures). Resolution acuity can be measured through observation of preferential looking responses to boards with high contrast gratings on one half and grey background on the other (Teller et al. 1986). A recent innovation reports on the presentation of stimuli on a touchscreen device (Livingstone et al. 2018). Once children can match or name optotypes, recognition acuity can be measured using standardised charts. Systematic assessment of detection vision is useful when acuity is below the range of resolution or recognition testing materials (Sonksen and Dale 2002; see Chapter 4).

Other visual functions can be assessed using validated tools such as formal perimetry (to map the visual field) or Ishihara plates (colour vision) or stereoscopic testing plates.

Definition and Classification of Childhood Vision Impairment

Acuity is the primary visual parameter used in formal national and international definitions of visual impairment (Table 2.1). It is difficult to apply these taxonomies to children when recognition acuity at distance cannot be measured (see Chapter 4).

Practical methods of quantifying detection vision such as the Near Detection Scale (Sonksen and Dale 2002) have been developed for clinical and research purposes with infants and children with no or very low levels of vision (Sonksen and Dale 2002). This includes measurement and categorisation of profound vision impairment (no vision or light perception at best) and severe vision impairment (basic non-light reflecting ‘form’ vision; see Chapter 4).

New empirically driven methods of classification of cerebral vision impairment that do not rely on acuity alone are now also being developed (Sakki et al. 2021; see Chapter 5).

Prevalence and Incidence of Childhood Vision Impairment

In the UK, as in other high-income countries, childhood vision impairment is uncommon. The annual incidence of childhood vision impairment, severe visual impairment, or blindness (VI/SVI/BL, using ICD-10 definitions) is estimated at 5 to 6 per 10 000 in the first year of life, with a cumulative incidence of 10 per 10 000 by the child’s 16th birthday (Rahi et al. 2003; Teoh et al. 2021). Half of these children will have severe visual disability (SVI/BL). The majority of the children with SVI/BL have additional non-ophthalmic disorders or impairments and/or present before their first birthday, and almost 10% of those with SVI/BL will die in the first year following diagnosis. In the UK, certain ethnic minority groups, or lower socioeconomic strata, are over-represented amongst children with SVI/BL (Rahi et al. 2003; Teoh et al. 2021).

Table 2.1 Classification of vision impairment (World Health Organization 2006)

Childhood blindness is more common in lower and middle-income countries due to dietary and infection-related disorders but with universal prevention programmes the rates of preventable disorders are reducing. The prevalence of global childhood blindness is between 0.3 and 1.2 per 1000 individuals aged 0 to 16 years, with an estimated 1.4 million children who are blind and 14 million children with vision impairment (Solebo et al. 2017).

Causes of Childhood Vision Impairment

Vision impairment is classified according to the anatomical site of the impaired eye or visual system, recognising that most children have more than one site affected (Rahi et al. 2003). The eye is divided into three coats (see Fig. 2.2):

1. The external coat, comprising the transparent cornea anteriorly and the thick white outer supportive layer of the sclera.

2. The middle coat, comprising the uvea, which holds much of the blood supply in the eye and which is visible anteriorly as the pigmented iris.

3. The inner coat, the retina, which holds the neurosensory cells which detect light. The centre of the retina is called the macula, which contains the highest concentration of cone cells and therefore provides fine visual discrimination. Temporal (towards the temples, away from the nose) to this is the opening in the coats through which passes the ganglion fibres from cells in the retina that make up the optic nerve.

Figure 2.2 The anatomy of the eye, with indicative pie chart showing relative contribution of each site to childhood severe visual impairment or blindness (Rahi et al. 2003)

The conjunctiva is a thin fibrovascular sheet coating the inside of the eyelids and the front surface of the sclera. The eye has anterior and posterior segments divided by the natural intraocular crystalline lens. Understanding the anatomy of the eyes and optic nerves enables the understanding of the impact of congenital and early ocular disease (or congenital disorders of the peripheral visual system) on childhood visual functions (see Fig. 2.2).

This chapter highlights the most impactful disorders at population level, but is not intended to be a comprehensive list of all visually disabling conditions of childhood, nor intended to describe the treatment or management of individual disorders.

Refractive Error

Globally, refractive error is one of the most important preventable and readily treatable causes of mild and moderate childhood visual impairment (Malik et al. 2018). Sensory stimulus plays a potentially important role in the growth of the eye but the mechanism is not yet understood (Mutti et al. 2009). All children with eye or vision disorders are at greater risk of refractive errors, which can, if not corrected with glasses or contact lenses, be an additional avoidable cause of permanent reduced vision due to refractive amblyopia. However, for some of these children vision can be so poor that correction of refractive error does not result in benefit.

Corneal Disorders

In high-income countries such as the UK, corneal diseases accounts for 2% of childhood ‘blindness’ (WHO definition), and can be congenital, such as the anterior segment dysgenesis anomalies, secondary to trauma, a sequelae of inflammatory disorders such as atopic conjunctivitis, or due to idiopathic progressive disorders such as keratoconus. Congenital and acquired infections, and nutritional and genetic disease can also lead to corneal scarring. Once present, the scarring is permanent. Corneal disorders are an important contributor to childhood blindness in low-income countries (Foster et al. 2008), with vitamin A deficiency being a key factor in the development of xerophthalmia (severely dry eye) and resultant corneal scarring (Solebo et al. 2017).

Globe Anomaly

Congenital anomalies of globe development, which occur in almost 10% of children with severe-profound vision impairment (Rahi et al. 2003) include poor overall formation of the eye (microphthalmia or anophthalmia) or poor