A Review of the Literature to Inform the Development of a Practice Framework for Supporting Children with Cerebral Visual Impairment (CVI)

Cerebral visual impairment (CVI) is now the most common cause of visual impairment affecting children in the developed world. Due to the increased survival rates of preterm infants and other early insult brain conditions, such as cerebral palsy, hydrocephalus and periventricular white matter injury, the numbers of children with CVI will also continue to rise. As such, focus needs to turn to developing effective approaches for supporting the growing number of children with this condition. Currently, many children with CVI are being supported using approaches and strategies that have been developed for children with ocular visual impairments (OVI). This is despite current evidence suggesting that many of these strategies may not be effective for children with CVI and in fact, in some situations, may actually be detrimental for them. This detailed review of relevant medical/scientific, educational and rehabilitation literature outlines a potential practical framework that could be implemented to help support each individual child with CVI. The proposed CVI practice framework has three main components, including: individual CVI profiles that detail the child's visual, emotional and behavioural needs; individualised habilitation/rehabilitation programmes based on the child's individual CVI profile; and empowerment of the child with CVI and their family.

Keywords: Cerebral visual impairment; practice framework; empowerment

Although effective education and habilitation/rehabilitation practices for children who are blind or have low vision are well established internationally, the majority of these practices have been informed by research focused on those with ocular impairments (OVI) (Gorrie et al. [35]). However, given that cerebral visual impairment (CVI) has now overtaken ocular pathologies to become the most common form of visual impairment affecting children in the developed world (Fazzi et al. [29]; Macintyre-Beon et al. [50]), the focus needs to expand to ensuring the diverse needs of children with CVI are being met. Although there is a current international research focus on understanding and supporting children with CVI more effectively, many children with CVI are still being supported with strategies that have been designed for individuals with OVI (Martin et al. [52]). This is despite current evidence that many of these approaches are not effective in the case of CVI and in some instances, could actually be detrimental (Martin et al. [52]). This highlights the pressing need in the field, for a practice framework focused on supporting the specific visual, emotional and behavioural needs of children with CVI and their families. This literature review therefore, begins by considering the complex nature of this condition in order to better understand the main requirements of such a framework. The review also explores the main components that would be necessary to make such a framework effective for all children with CVI.[1]

It is well documented that visual impairment has a considerable impact on the lives of not only the affected individuals, but also on their families (Atowa, Hansraj, and Wajuihian [2]; Ravenscroft et al. [66]; Kong et al. [44]). For children that are either born with a visual impairment or develop it shortly after birth, the impact can be even more significant. As early visual experiences help to build the infrastructure for later learning, the role visual function plays in the early years in terms of development is crucial (Ortibus, De Cock, and Lagae [59]; Fazzi et al. [28]). When a child's early experiences are limited by reduced visual functioning, this can cause substantial constraints on later development in areas such as integration of input from other senses, motor competence, language and cognitive concepts (Sonksen and Dale [70]). Long term, this can have a negative impact on a child's academic outcomes, future career choices, social interactions and development of a fulfilling social life (Atowa, Hansraj, and Wajuihian [2]; Ravenscroft et al. [66]). To help reduce these negative impacts, early diagnosis, intervention and habilitation/rehabilitation for any visual difficulty is vital.

Although it is difficult to calculate the prevalence of childhood vision impairment and blindness worldwide, the World Health Organisation (WHO) estimates the rates of blindness to range from 1.2 per 1,000 children in low-income countries, through to 0.2 per 1,000 in high income regions (Keeffe [43]). For the numbers of children with low vision, the WHO estimates the prevalence is three times the rate of blindness (Keeffe [43]), although the incidence and cause of childhood vision impairment and blindness differ considerably between developed and developing countries. Overall, there has been a significant shift in the main causes of these impairments in the last forty years.

Previously, the main cause of visual impairment for children was ocular pathologies, such as congenital cataracts and retinopathy of prematurity (Fazzi et al. [29]). In more recent times, these ocular conditions are detected early and treated effectively, due to improvements in postnatal healthcare, especially in developed countries (Gorrie et al. [35]). However, this improvement of postnatal healthcare has also seen the emergence of a significant visual condition known as cerebral visual impairment (CVI) (Chong and Dai [12]). CVI is caused by damage to some parts of the visual brain (the totality of brain elements that serve or support vision) (Dutton [17]) and can be defined as 'a verifiable visual dysfunction which cannot be attributed to disorders of the anterior visual pathways or any potentially co-occurring ocular impairment' (Sakki et al. [67]). CVI can occur at any time from pre-birth through to adulthood, however, one of the main causes of CVI is prematurity (Jacobson, Flodmark, and Martin [42]). Other common causes include; lack of oxygen and low blood sugar at birth, closed head injury, damage to specific brain locations, epilepsy, metabolic disorders and infections of the central nervous system (Macintyre-Beon et al. [50]; Dutton [18], [19]; Soul and Matsuba [71]). The resulting change in the panorama of childhood visual impairment has meant that CVI has become the most common cause of visual impairment affecting children in the developed world (Fazzi et al. [29]; Macintyre-Beon et al. [50]).

It is predicted that the incidence of CVI will continue to increase due to the advancement in medical care for many of the conditions that are associated with CVI (Good et al. [32]). Recent figures indicate that around 15 million babies annually are born premature worldwide, with children born extremely premature (between 26 and 32 weeks) having a high risk of experiencing neurological damage (Kooiker et al. [45]). Researchers estimate that as many as 86% of infants born before 32 weeks will be affected by cerebral visual dysfunctions (Jacobson, Flodmark, and Martin [42]). Given that there has been an increase in survival rates of infants born before 26 weeks in the last forty years, going from 25% to 73%, potentially there could continue to be a significant rise in the number of children presenting with CVI related visual difficulties (Ortibus, De Cock, and Lagae [59]). The incidence of CVI in other early insult brain conditions, such as cerebral palsy, hydrocephalus and periventricular white matter injury (PVL) is approximately 33% to 58% (Fazzi et al. [29]; Houliston et al. [36]; Ego et al. [25]; Andersson et al. [1]; Stiers et al. [73]). Despite this awareness of the prevalence of CVI in certain conditions, it is currently very difficult to get exact figures for the numbers of children with CVI worldwide.

Although many countries are attempting to get a clearer picture of the incidence of this condition, many of these studies are limited by the criteria used to define CVI or the population on which the study was conducted (Chong and Dai [12]; Kong et al. [44]). For instance, Chong and Dai ([12]) state that CVI is responsible for approximately 30% of documented childhood visual impairment in New Zealand. However, they also quantify this by recognising that due to the strict acuity criteria used for diagnosing CVI in their study, the true prevalence of CVI in New Zealand may actually be much higher than suggested in their findings. The incidence of CVI in the United Kingdom has been reported to be much higher, partially due to less restrictive acuity criteria, with 48% of childhood visual impairment being caused by CVI in 2007 (Rahi [65]). However, this number could have increased further, with recent figures of 57% of childhood visual impairment in Scotland being brain related (J. Ravenscroft, personal communication, August 13, 2019). The figure provided for the prevalence of CVI in the United States was much lower, at only 18%. However, this percentage was taken from a study that focused on schools for the blind and did not allow for the fact that many children with CVI do not attend these schools, especially those with CVI and multiple disabilities (Kong et al. [44]).

The figures on the prevalence of CVI stated above may also be inaccurate due to the current definitions of vision impairment and blindness. The latest International Classification of Diseases (ICD-11), classifies mild vision impairment as having an acuity of between 6/12 and 6/18 and severe low vision being worse than 6/60 and equal to or better than 3/60 (as shown in Table 1) (World Health Organisation [79]). However, these definitions are potentially failing to recognise the full range of visual difficulties associated with CVI and forcing the diagnosis of vision impairment to be based on the singular criterion of visual acuity, which does not characterise the true overall functioning of the child (Martin et al. [52]). CVI can result in an extensive range of impairments, including: decreased visual acuity (ranging from no impairment to profound blindness), reduced contrast sensitivity, visual field deficits, eye movement disorders and difficulties in image processing or interpretation (visual perceptual difficulties) (Williams et al. [77]; Ortibus, De Cock, and Lagae [59]). As such, CVI is a descriptor for a wide spectrum of visual disorders, with those severely affected appearing functionally blind with limited useable vision. Whereas, at the other end of the spectrum, individuals can have near-normal or normal visual acuity, but be greatly affected by higher functioning visual difficulties (often referred to as visual perceptual difficulties) (Fazzi et al. [27]). When children with visual perceptual difficulties are included in the prevalence statistics, the prevalence is significantly higher than previous studies have indicated. The most recent research from the UK looking at the prevalence of unrecognised CVI in children in mainstream schools, estimates the proportion to be as high as 3.8% of the population (Williams et al. [78]). Further analysis of the data from this study has also shown that 1 in 7 children identified as having educational learning needs, has CVI. With figures out of New Zealand of 1 in 5 school-aged children needing extra support for their learning (Ministry of Education [57]), and a likelihood of 1 in 7 of them having CVI (Williams et al. [78]), it is possible to surmise that the proportion of children with CVI in developed countries is significantly higher than that currently being recognised.

Table 1. ICD-11 Definitions of vision impairment and blindness (World Health Organisation [79]).

Historically, children with brain related visual difficulties have received a general diagnosis of CVI. However, as the term CVI is used to describe a myriad of different visual impairments, it is being recognised more and more that CVI should be referred to as an umbrella term (Martin et al. [52]; Ortibus, De Cock, and Lagae [59]; Goodale [33]). With over 40% of the brain being involved in processing and supporting vision, damage or injury to the brain can impair vision in a variety of ways (Lueck and Dutton [49]). When identifying what specific visual difficulties a child has, it is important to understand the two main areas of visual functioning that need to be assessed; the basic visual functions and the higher, or perceptual visual functions. The basic visual functions include visual acuity, contrast sensitivity and oculomotor control. Difficulties in these areas could be either a result of changes in the anterior parts of the visual pathways, which often masks brain damage-related vision impairment, or a result of injury in some part of the primary visual cortex (Hyvärinen et al. [39]) or middle temporal lobes responsible for detecting and quantifying movement (Dutton [18]). Disorders of refraction and impaired focusing (accommodation), which affect the ability to see near information clearly, are also common in children with CVI and need to be diagnosed and managed appropriately (Philip and Dutton [64]). This includes establishing whether the wearing of spectacles will aid their overall visual functioning (Hyvärinen [37]).

The ability to see a wide area or field of vision is another basic visual function, which is often impaired in children with CVI. A visual field deficit occurs when there is damage to some parts of the pathway from the eyes to the occipital lobes at the back of the head, in what is known as the primary visual cortex (Dutton [17]). The area of visual field deficit experienced depends on the parts of the pathway that are damaged or dysfunctional. However, the most common form of visual field deficit for children with CVI, especially children who have been born prematurely, is a lower visual field deficit, which is commonly caused by periventricular white matter injury such as that due to periventricularleukomalacia (PVL) (Jacobson and Dutton [41]; Jacobson, Flodmark, and Martin [42]), hydrocephalus or stroke (Dutton et al. [24]). Other forms of visual field deficit are shown in Figure 1. Issues with the basic visual functions are easily detected within a clinical setting and are, therefore, part of any routine ophthalmic assessment (van Genderen et al. [75]).

PHOTO (COLOR): Figure 1. Visual field deficits due to damage to the brain. From Lueck and Dutton ([49]). Vision and the Brain: Understanding cerebral visual impairment in children. Copyright: 2019 by Gordon Dutton. Note: Published with permission from Gordon Dutton.

The second area of visual functioning associated with CVI comprises the higher visual processes associated with the visual pathways mediated by the dorsal and ventral streams of visual processing (shown in Figure 2). The dorsal stream runs from the occipital lobe to the posterior parietal cortex at the top of the cerebral hemispheres and is often referred to as the 'vision for action' or the 'where' pathway (Goodale and Milner [34]; Dutton [17]). When there is bilateral injury to the posterior parietal lobes, it causes dorsal stream dysfunction. Common visual difficulties associated with this dysfunction include; simultanagnosia (an inability to see more than a few objects at a time), optic ataxia (impaired visual guidance of movement), and apraxia of gaze (the inability or difficulty with moving the eyes from one visual target to another) (Goodale [33]; Pawletko, Chokron, and Dutton [61]; Dutton [19]). The ventral stream of visual processing, runs from the occipital lobe to the bottom and sides of the cerebral hemispheres in the inferior temporal region and is often referred to as 'vision for perception' or the 'what' pathway (Goodale and Milner [34]; Dutton [17]). When there is a bilateral injury in this area, the associated visual issues include; an inability to recognise text, objects and familiar people, difficulty with negotiating complex environments and difficulty with recognising faces and reading facial expressions (Pawletko, Chokron, and Dutton [61]; Philip and Dutton [64]; Hyvärinen et al. [39]). Currently, many of the visual difficulties associated with either a dorsal or ventral stream dysfunction are not routinely assessed in most paediatric eye clinics, resulting in many children going undiagnosed and experiencing significant challenges in their daily activities (Williams et al. [77]).

PHOTO (COLOR): Figure 2. Dorsal and ventral visual pathways. From Lueck and Dutton ([49]). Vision and the Brain: Understanding cerebral visual impairment in children. Copyright: 2019 by Gordon Dutton. Note: Published with permission from Gordon Dutton.

In general, the behavioural responses associated with the difficulties of the basic visual functions are often clearly visible and well understood in terms of habilitation/rehabilitation requirements. For instance; prescribing appropriate spectacles to cater for both refractive errors and lack of accommodation, providing good clear outlines and increasing font size on teaching material, establishing optimal luminance level and introducing magnification devices (Buultjens et al. [10]). For this reason, the impact of their visual difficulties can be greatly reduced, as long as a child has an effective support team around them. However, the visual difficulties associated with a dorsal or ventral stream dysfunction can be more problematic, especially when they have not been correctly diagnosed. A dorsal stream dysfunction impacts on three main areas: a child's ability to access information, their mobility and navigation in familiar and unfamiliar environments, and their social interactions (Hyvärinen et al. [39]). However, what makes a dorsal stream dysfunction more complicated, is that it affects unconscious visual functions, which means that the affected child and those around them, do not understand that the difficulties they are experiencing are actually related to their vision (Dutton [17]; Goodale and Milner [34]). For this reason, a dorsal stream dysfunction and the visual difficulties associated with it, can lead to the adoption of specific behaviours, including:

• Avoidance of crowded and cluttered environments, or the increase of negative behaviour when in these environments, such as tantrums and crying (Lam, Lovett, and Dutton [47]).
• Social withdrawals due to difficulties in finding their friends when they are in a group of people (Philip and Dutton [64]).
• Avoidance of schoolwork as a result of issues with copying information from the board, difficulty processing the visual and auditory information that is occurring at the same time, impaired ability to find numbers on the printed page and problems locating items in their work station and within the wider classroom environment (Philip and Dutton [64]; Hyvärinen et al. [39]).
• Reluctance to move around both familiar and unfamiliar environments due to past embarrassing experiences of walking into objects and people and appearing clumsy (Hyvärinen et al. [39]; Lam, Lovett, and Dutton [47]; Dutton et al. [22]).
• Unwillingness to participate in sporting activities due to issues with depth perception and eye-hand coordination (Hyvärinen et al. [39]).
• Memory difficulties, as visual information cannot be encoded in a robust and clear way (Fazzi et al. [27]).

The overall effect of living with these behaviours is that a child is often in a highly anxious state (Philip and Dutton [64]).

Visual difficulties associated with a ventral stream dysfunction may also lead to the adoption of specific behaviours, including: avoidance of travelling independently in a familiar or unfamiliar environment due to the fear of getting lost, avoidance of social situations because of the inability to recognise people and follow facial expressions, and a reluctance to participate in specific classroom activities because of the inability to recognise objects (i.e. shapes) (Philip and Dutton [64]). Added to this, there is often a frustration from parents and teachers due to the inconsistencies with the child's visual behaviour, which leads to incorrect assumptions that the child is not trying hard enough or associating labels to a child, such as 'noncompliant' or 'irritable' (Pawletko, Chokron, and Dutton [61]).

There are several known impacts of constantly dealing with a combination of issues relating to the basic visual functions and either a dorsal or ventral stream dysfunction, including avoidable mental health problems like anxiety, stress and low self-esteem (University of Bristol Research [74]; McDowell [54]). These issues can also lead to the child being affected by visual fatigue, which results in children performing less well in vision related tasks in some situations, as compared with others. This disparity in relation to a child's overall visual functioning often leads to parents and teachers incorrectly concluding that the child is choosing not to perform in different situations, or that they are just being lazy (Erasmus [26]). Added to this, often the behaviours of children with CVI are put down to other causes, or in some cases even diagnosed as other conditions, such as learning difficulties or psychological disorders (Dutton et al. [22]; Martin et al. [52]). When the cause of the behaviour is unknown and the child is incorrectly diagnosed with another condition, it can impact on their levels of academic attainment (Williams et al. [77]). Constant criticism from adults around them, can also lead to children with CVI starting to develop negative feelings of self-worth, which ultimately leads to low self-esteem.

Added to this, there are also a number of little-known emotional impacts of living with CVI that have recently been described by people with lived experience of this condition. These emotional impacts can have a considerable effect on an individual's overall mental wellbeing (McDowell [54]). An example of this is the description of a CVI meltdown. A CVI meltdown is defined as an incapacitating behavioural reaction to an overload of visual, auditory and other sensory information, which leaves the affected person completely unable to cope and is mentally incapacitated for a period of time (CVI Scotland [15]; McDowell [54]). As with other CVI related behaviours in a child that has not been correctly identified as having CVI, a CVI meltdown may be misinterpreted as a child misbehaving or simply having a tantrum. As such, any habilitation/rehabilitation plan developed to support a child affected by CVI, will also need to include strategies specifically focused on supporting their mental and emotional wellbeing.

Given the continued rise in the prevalence of CVI, especially in developed countries, many in the field are starting to recognise that this condition needs to be acknowledged as a pressing public health issue (Gorrie et al. [35]; Martin et al. [52]). As such, the focus needs to turn to how children with CVI related visual issues are being identified to ensure that the needs of all children with this condition are being met. Currently, in most countries around the world, CVI is seen as a medical problem requiring an official diagnosis by an ophthalmologist. However, as a number of recent studies have outlined, due to a common lack of awareness of the condition amongst healthcare providers and with few ophthalmologists being confident in the clinical markers of CVI, many children with CVI are not being identified (Gorrie et al. [35]; Maitreya, Rawat, and Pandey [51]; Martin et al. [52]). There are also many children who are not even recognised as having visual difficulties, as they have normal or near normal visual acuities despite having visual perceptual difficulties (Fazzi et al. [27]). Since these children are not recognised as having a visual impairment and they do not have additional ocular pathologies they do not get referred to an ophthalmologist (van Genderen et al. [75]; Gorrie et al. [35]). The impact of not detecting visual perceptual difficulties in children can have a significant impact on their learning, development and independence (Martin et al. [52]). Children with these sorts of issues can develop certain behaviours to help cope with their visual difficulties that can be misinterpreted as developmental disorders such as: attention deficit hyperactive disorder (ADHD), autism spectrum disorder (ASD), dyslexia and dyspraxia (Pawletko, Chokron, and Dutton [61]), and auditory processing difficulties (Dutton [18]).

An alternative approach to identifying children with CVI through population screening of at risk children has, therefore, been suggested (Gorrie et al. [35]). Such an approach would greatly reduce the number of children who are currently being misdiagnosed with behavioural or developmental disorders, as well as the number of children who undergo costly expert testing, by ensuring that only the children who warrant clinical assessments are actually assessed. Two parent-related screening questionnaires developed for this purpose; the CVI Questionnaire (Ortibus, Laenen et al. [60]) and the Five Questions (Dutton et al. [21]) have been shown to have good construct validity and, therefore, could potentially be used for screening purposes (Gorrie et al. [35]). Once the possibility of CVI has been established through the use of a screening approach, further assessment of the child's visual functioning would need to be carried out in order to understand the overall picture of the child's visual abilities.

However, given that injury can occur and affect any part of the overall visual system in any combination and degree, giving rise to a wide range of patterns of visual dysfunction, it needs to be recognised that CVI is heterogeneous in its expression (McKillop and Dutton [56]; Hyvärinen [38]). Additionally, as the way an individual sees the world is also shaped by their own individual experiences and preferences, no two people will ever experience CVI in the same way, even if they present with the same visual difficulties (Dutton and Bauer [20]). This highlights the need for an individual CVI profile for each child, which outlines the specific nature of their individual visual issues. This is the first main component of a CVI practice framework.

Historically, CVI has been investigated as a medical problem and although clinical investigation still has its place in detecting certain visual issues, such as reduced visual acuity, visual field deficits, or impaired contrast sensitivity and stereopsis (related to associated squint/strabismus), other issues are going undetected (Hyvärinen [37]). However, in order to develop an overall picture of a child's visual functioning, all areas must be assessed, highlighting that different approaches for assessing a child's vision need to be used. In particular, a child's visual perceptual abilities, which can appear differently in the real world as compared with experimental tasks in clinical settings, need to be assessed within everyday situations (Williams et al. [77]; Hyvärinen et al. [39]). A transdisciplinary assessment approach that is based on observations and testing by teachers, parents, caregivers and therapists, in addition to the clinical assessments by medical specialists (Hyvärinen [38]) is required.

Dutton et al. ([21]) emphasise the important role parents can play in a transdisciplinary assessment approach in terms of profiling a child and have developed a structured history-taking inventory for parents. The aim of the inventory is to elicit vital information about a child's visual behaviours and their overall functioning in different environments based on parents' observations. The inventory runs through a number of specific areas related to visual dysfunctions and allows the interviewer to establish what areas are more problematic for a child and where the assessment of vision and functional vision needs to focus (Dutton [16]; McCulloch et al. [53]). An approach such as this, could be used as the first step in developing an effective CVI profile for each individual child. This view is also supported by Hyvärinen et al. ([39]) who state that the perceptions of the parents and those teaching or caring for the child could be better utilised, as they observe these children completing day to day activities that cannot be observed in clinical situations. Currently, teachers of students with visual impairments (QTVIs/TVIs) conduct functional vision assessments (FVAs), which focus on real-life evaluations of visual functions, with both eyes open, within the performance of activities, and often involves qualitative judgments of how vision is used and the limits it imposes on daily living (Kran and Mayer [46]). Within these assessments, common areas of focus are: visual acuity, visual field, contrast sensitivity, colour vision, light sensitivity, what modifications or changes to the environment are needed and adaptations or tools needed to access information (Kran and Mayer [46]). However, assessing visual perceptual difficulties in FVAs can be more challenging than for other aspects of vision, as there are a number of specific areas that need focusing on. These include: visual attention (the ability to highlight specific features or places within the visual field); visual search or apraxia of gaze (the ability to move the eyes within a scene to detect relevant targets); perceptual grouping or simultanagnostic visual dysfunction (the ability to combine components of a scene into a meaningful whole); unconscious use of visuospatial information to programme movements that interact with objects in 3-dimensional space; route finding and recognition of objects and people or optic ataxia (Williams et al. [77]; Goodale [33]; Goodale and Milner [34]). At present however, the recommendations for assessing these issues are complicated, time consuming and difficult for vision educators to implement unless they have a comprehensive understanding of how visual perceptual difficulties impact on a child's day to day functioning.

Indicators of visual perceptual difficulties. To support vision educators to conduct simple assessments to detect visual perceptual difficulties as part of their FVAs, it is, therefore, vital that more is understood about the manifestations of these difficulties. Research is beginning to explore this area, with work by Josef Zihl, outlined in Zihl and Dutton ([80]), looking at the differences in how long it took children with and without a dorsal stream dysfunction (a combination of the visual perceptual difficulties of simultanagnostic visual dysfunction, optic ataxia and apraxia of gaze) to find a diamond in a diagram that was surrounded by an increasing number of dots. This research showed that children without visual perceptual difficulties, found the diamond at around the same time even when the number of dots increased. Whereas, the children with visual perceptual difficulties took longer as the dots increased.

What was also evident in this test, was that the children with visual perceptual difficulties used a more random search pattern to find the diamond than the children without difficulties. This often resulted in an increased number of darting eye movements compared with the children without difficulties and when the children with difficulties did find the diamond, it was possibly down to chance (Zihl and Dutton [80]). This work is supported by recent research conducted by Bennett et al. ([6]) who used a virtual reality (VR) toy box test to assess the visual search patterns and spatial processing strategies used by children with CVI. The test was based on the awareness that children with visual perceptual difficulties often have difficulty recognising familiar objects while viewing complex visual scenes and allowed for the tracking of eye and hand movements as the children completed the test (Bennett et al. [6]). Results from the toy box test showed that children with CVI had longer search patterns and reduced focus on the target compared to the control children, which was evident by an increased number of darting eye movements. However, a result that is more revealing for children with CVI, is that as the number of distractions (unique distractor toys, a colour/theme matched toy, background clutter), were increased within the VR toy box, their speed and quality of performance decreased rapidly (Bennett et al. [6]).

In regards to hand tracking, the VR toy box test showed that the children with CVI were slower at reaching and virtually touching the toy than the control children and their reaction times continued to decrease as the number of distractors increased (Bennett et al. [6]). Another common observation related to hand movement in people affected by a common visual difficulty; optic ataxia, or impaired visual guidance of movement, is the adaptive hand position when reaching out to grasp an object (Goodale and Milner [34]). Often, the finger and thumb are opened wider inflight than the object being grasped, indicating that the person is unable to accurately identify the size of the object and is overcompensating to ensure that they are able to grasp the object once it is reached (Goodale and Milner [34]).

From the research outlined above, it can be ascertained that key indicators of visual perceptual difficulties include: darting eye movements, random search patterns, increased time to find objects as the complexity of the scene increases, and adaptive hand positions when reaching and grasping for objects (Bennett et al. [6]; Goodale and Milner [34]; Zihl and Dutton [80]). With these indicators in mind, it is now theoretically possible to develop a simple and effective assessment tool that could be used to help detect more of the growing number of children affected by CVI within functional vision assessments. This could also meet the need outlined by Bennett et al. ([6]), to develop novel methods to better characterise visual perceptual deficits beyond what can be achieved within standard clinical testing. Once a thorough FVA and any other assessment of a child using their vision in everyday activities has been conducted, the information can be collated and analysed to determine the most appropriate education strategies that need to be implemented to ensure the child can access, understand and learn the relevant curricula material. As such, the overall picture of a child's visual difficulties and resulting needs, is not based on a clinical assessment only, but rather on their functional needs.

Understanding the whole child. Once a child's visual difficulties have been identified and understood, it is also important to recognise that the impact on the child will depend on the severity of the visual issues, the child's abilities, temperament, strengths and weaknesses and the extent to which their difficulties hinder their daily lives, and also, whether there are any additional disabilities (University of Bristol Research [74]). In addition, a child's surroundings and family dynamics, and whether allowance is made for their impairment and/or strategies to help have been implemented, will also impact on a child's overall functioning and emotional well-being (University of Bristol Research [74]). As such, a social-ecological framework needs to be considered when developing an individual profile for a child with CVI, as it will help to better understand the interaction of the many different areas relating to a child's life and develop an overall picture of the child within their own environment. One framework that has been suggested for this purpose, is the International Classification of Functioning, Disability and Health (ICF) (Hyvärinen et al. [39]; Ortibus, De Cock, and Lagae [59]). This framework considers the interaction between a person's disability and their functioning of an activity and participation level, taking into account environmental factors, as well as internal factors relating specifically to the individual (as shown in figure 3) (World Health Organisation [79]).

Graph: Figure 3. International classification of functioning, health and disability (World Health Organisation [79]).

By using a framework such as the ICF, it would also be possible to ascertain the behaviours that a child has developed as a result of their visual difficulties, and the impacts the combination of the visual difficulties and associated behaviours is having on their overall mental and emotional well-being. This is an important component of understanding and supporting a child with CVI, as it has been reported that children with these kinds of visual difficulties have an increased risk of mental health problems such as anxiety and depression and are less likely to have positive self-esteem (University of Bristol Research [74]). Again, those closest to the child are in the best position to be able to provide relevant and useful information around a child's behaviours and emotional well-being. By following a similar format to that of the history-taking inventory (Dutton [16]), parents, teachers and other support people could be questioned about how they feel the child's visual difficulties impact on a child's behaviour and emotional well-being.

The second component of a CVI practice framework is the development of an individual programme based on the needs established from the individual CVI profile. This is an important element of the framework, as it ensures that the specific needs of the child can be met. As outlined by Dutton and Bauer ([20]), the main aim for all children with CVI should be to give them full access to all information and skills they need to learn and to live in a visual world. However, as CVI has many possible variables, every affected child has their own unique pattern of visual experience, limitations and resulting behaviours, that needs a holistic approach to develop an effective habilitation/rehabilitation plan (Dutton and Bauer [20]). As such, this plan will need to be based on areas related to the child's visual difficulties, address any adaptive behaviours that have developed, as well as introducing strategies to support their emotional well-being. Another important aspect of a habilitation/rehabilitation plan, is that any strategies suggested will need to be able to be implemented in all aspects of a child's life, as CVI can influence any aspect of daily living (Dutton and Bauer [20]).

Developing effective strategies in relation to specific areas of difficulty may depend on the child's overall level of visual functioning, whether or not there are additional disabilities and their cognitive abilities. For this reason, Dutton and Lueck ([23]) have identified that from a practical perspective in terms of working with children who have CVI, there are three main categories that children can be separated into. These include;

• Children with profound visual impairment due to CVI, many of whom also have additional disabilities.
• Children with CVI who have functionally useful vision and cognitive challenges.
• Children with CVI who have functionally useful vision and who are able to work in or near the expected academic level for their age group.

In terms of specific strategies, these need to be based on what is known to be effective for children with CVI, as strategies based on the needs of typical children, or children with ocular visual impairments (OVI) may not be effective (Dutton and Bauer [20]; Martin et al. [52]). For helping to alleviate the impact of the visual difficulties, strategies may include:

- De-cluttering the environments the child spends time in (i.e. their bedroom at home, other rooms in the house, their classroom) in order to decrease the amount of visual information they need to process at any one time (McDowell and Budd [55]; Little and Dutton [48]).

- Implementing 'safe places' at home and school, by creating a place which is clutter free that the child can go to for a break when they are feeling overwhelmed (CVI Scotland [14]; Little and Dutton [48]).

- Using tents in a classroom environment to block out all visual information to allow the child to have use of their intact visual functions (Little and Dutton [48]).

- Creating an area of blank wall space for the child to face into when they are required to do concentrated focused work at school (McDowell and Budd [55]).

Although the overarching principles in relation to the visual difficulties will be the same for each category, the strategies used within a child's individual habilitation/rehabilitation plan may have to be adapted slightly, depending on what category the child is in.

For any approaches to be effective, however, a child must also be encouraged to develop strategies to deal with the behavioural and emotional reactions they have as a result of dealing with CVI. As outlined by Goleman ([31]), when an individual feels anxious or panicked, their sympathetic nervous system causes a fight or flight response in their primitive brain and when someone is experiencing the fight or flight sensation, their ability to think logically and coherently is diminished or absent. Relating this back to a child with CVI, if the environment or activity is overwhelming and making them feel highly stressed and anxious, they may not be in a position to implement any strategies that have been suggested. The constant drain of being on high alert and the resulting high levels of visual fatigue, may also cause an overall fatigue that again, makes it difficult to implement specific strategies. To help reduce this, the child also needs to be introduced to techniques that help calm them down and lessen fatigue levels.

One suggestion for this, is to introduce the child to regular mindfulness practices in a format that suits their abilities and functioning (i.e. through a child friendly mindfulness app or internet-based mindfulness programme). Mindfulness has been shown to be effective in treating a variety of mental health conditions in adults and children, including anxiety and stress (Bohlmeijer et al. [8]; Chiesa and Serretti [11]; Bailey et al. [4]; Spijkerman, Pots, and Bohlmeijer [72]; Bauer et al. [5]). Although there is currently no literature around supporting children with CVI using such strategies, there is evidence of the effectiveness of these cognitive-based strategies in children with other developmental disorders, such as ASD and anxiety disorders (Conaughton, Donovan, and March [13]; Perry-Parrish et al. [62]; Vigerland et al. [76]). Mindfulness interventions are also known to target regulation of emotions and coping processes associated with stress (Perry-Parrish and Sibinga [63]), which suggests this could be an effective strategy for children with CVI, given that they are constantly under high levels of stress. A sample programme of mindfulness-based visualisation was recently trialled at the Royal Blind School in Edinburgh. Although not all the students involved in the programme had CVI, the students all had multiple disabilities, including visual impairments (Godek [30]). After using the programme for three school terms, staff involved in the programme reported a reduction in students agitation and anxiety both at home and at school, especially when doing specific activities that used to cause high anxiety (Godek [30]).

The third component of the proposed CVI practical framework encompasses an important element needed to ensure the success of any intervention recommended for a child with CVI; the empowerment of the child, their family, and their education and therapy teams. Empowerment can be described as a process of gaining personal power and control (Mulligan et al. [58]), with parental empowerment occurring as a result of parents utilizing knowledge, skills and resources to gain a sense of control and improve their families' quality of life (Singh et al. [69]). Crucial to empowering those supporting a child with CVI, is the attainment of CVI specific knowledge in a language framework matched to their ability to understand and learn this new information. This is vital, because in order to best support a child with CVI, a well-informed, loving, positive and supported model of care needs to be implemented (Dutton and Bauer [20]).

When the team supporting a child with CVI is well-informed and understands intuitively the impact of the child's visual difficulties; the strategies and support will become logical and intrinsic (Dutton and Bauer [20]). This process is often helped when the parents are recognised and respected by medical and education practitioners as 'experts in their own right' (Avdi, Griffin, and Brough [3]), as they are the ones closest to the child and have seen the impact of their visual difficulties on their functioning and emotional well-being in many different contexts. When parents are respected, they may feel more confident to actively participate in the services their child receives, be more aware of their choices in relation to their child, and be more involved in decision making (Shulman [68]). The benefits of parents actively engaging in their child's habilitation/rehabilitation plan is significant, as they are able to serve multiple roles in supporting their child's quality of life, including being advocates, consumers, and implementers of strategies aimed at enhancing their children's well-being (Bode et al. [7]).

One simple way of ensuring parental empowerment, is through medical practitioners providing relevant information about the child's visual difficulties. This can occur when they are first identified and CVI is suspected, when a CVI diagnosis is confirmed, or as soon as possible following this. This would be in line with the process that is used when diagnosing other conditions such as ASD (Mulligan et al. [58]). This should include information about CVI in general, information on the specific visual difficulties their child has, how these difficulties will impact upon them on a daily basis, and how to best circumvent limitations to access to knowledge, social interaction and mobility (Dutton and Bauer [20]; Jackel, Wilson, and Hartmann [40]). In terms of how this information is shared, Mulligan et al. ([58]) highlight that information about a condition that a child has been suspected of having or has been diagnosed as having, should be provided verbally by the diagnosing professional, with follow up information being provided in the form of printed material. Given the age of technology and an abundance of information on many different platforms, websites and support organisations that are scientifically accurate, research and evidence based and peer reviewed could also be utilised by parents. As outlined by Boshoff et al. ([9]), an empowered parent, who has been provided with relevant information about their child's disability, may feel more in control and more confident in their ability to support their child. This feeling of empowerment can also have a positive impact on the parents' quality of life and, therefore, their child's quality of life (Dutton and Bauer [20]).

This literature review has explored in detail the complex, yet common condition of CVI as it relates to children. This has included the causes and prevalence of CVI within the developed world, the visual difficulties associated with CVI and their impact on a child's visual and overall functioning, and also, the difficulty with identifying children with CVI. This detailed analysis of CVI identified three critical components for a practice framework to support children with CVI to be effective. The three components are:

• Individual CVI profiles that include information on a child's visual, emotional and behavioural responses related to CVI.
• Individualised habilitation/rehabilitation plans that are based on the child's unique CVI profile.
• Empowerment of the child and their family through education about CVI, to enable them to take a central role in their habilitation/rehabilitation plans.

When these three elements are executed efficiently and cohesively by everyone involved in supporting a child with CVI, the child's overall quality of life could be greatly improved. As such, these critical components are the foundations for a practice framework for supporting children with CVI.

No potential conflict of interest was reported by the author(s).