An introduction to paediatric cerebral visual impairment: This article outlines the characteristics and clinical investigation of children presenting with cerebral visual impairment and considers strategies to support these patients.
Cerebral visual impairment (CVI), which may also be referred to as brain-based visual impairment (BBVI) or perceptual visual impairment (PVI) is one of the major causes of low vision in the developed world and the most common cause of visual impairment registration in children, accounting for 21-31% of all cases. (1) It is acknowledged that CVI may not always be identified, especially for children with complex needs, (2,3) so these figures are likely to underestimate its true incidence.
CVI can be defined as visual dysfunction caused by damage to, or malfunctioning of, the retrochiasmal visual pathways in the absence of damage to the anterior visual pathways or any major ocular disease. (4) Ocular examination is often umremarkable, in some cases with normal visual acuities. Despite its prevalence, CVI is not routinely tested for in primary optometric practice or in most paediatric eye clinics. (2,3)
Historically, CVI has also been termed cortical visual impairment but, as the visual problems it describes may originate in an area of the brain other than the visual cortex, this terminology is now usually avoided.
Visual perceptual problems are commonly associated with many conditions and risk factors as outlined in Tables 1 and 2, respectively. CVI may result from brain damage or brain development disorders with their onset in the pre-, peri--or postnatal period. Seizures, traumatic or infective head injury in later childhood may also result in these visual dysfunctions. CVI covers a wide spectrum of visual impairments from mild to profound. Acquired brain injury in adulthood may produce visual symptoms similar to those seen in children with CVI; however, this article will focus on CVI presenting in childhood.
It is notable that the annual incidence of new paediatric sight impairment registration has doubled since the 1980s; (5) this may well be attributed to improved survival rates in very premature infants (born at 22-26 weeks gestation), (6) with these children having a very high risk of neurological and developmental anomalies. (7)
Frequent causative factors for CVI are hypoxicischaemic encephalopathy (HIE) and periventricular leukomalacia (PVL). (8) Both HIE and PVL are brain injuries caused by deprivation of blood and oxygen during birth. PVL is most commonly seen in pre-term babies. In PVL, the white matter surrounding the ventricles of the brain is softened due to deprivation of blood and oxygen. HIE usually involves damage to the basal ganglia, cerebral cortex and watershed regions of the brain. The damage from HIE and PVL may lead to cerebral palsy, epilepsy, developmental delay, learning disabilities, motor disorder, hydrocephalus and speech disorders. Therefore, CVI is frequently comorbid in these conditions. Over 30% of children born before 34 weeks gestation are affected by CVI. (8)
The complexities of normal visual processing
Useful vision is of course much more complicated than optical image resolution. Successful visual processing involves many complex neural pathways beyond the elements we routinely assess clinically, that is to say, visual acuity, contrast sensitivity, colour vision, visual field, stereopsis, and ocular movements. For example, consider the neural processes involved in the act of taking a drink from a cup. You see the detail of the object (using visual acuity, contract sensitivity), move your eyes to fixate on it (using the oculomotor system). You then recognise it as a cup and distinguish it from its background surroundings (object recognition), you decide to pick it up, work out how far away it is from you (stereopsis), reach out with your hand (visually guided reach) observing its advance towards you before picking it up (movement detection) and then manipulate your hand into a shape to hold it and move it up to your lips (fine motor skills).
The initial decision to take a drink was made in the frontal lobes. (9) The analysis of the detail we quantify as visual acuity and contrast sensitivity takes place in the occipital lobes. (9) Visual recognition takes place in the temporal lobes. (9) The cup's position in space is mapped in the parietal lobes and interpreted by combined activity in the middle temporal and posterior parietal lobes. (10) The task is performed effortlessly and quickly due to previous learning, including oculomotor, motor, perceptual and spatial experience, mostly in the frontal and parietal lobes. (10) A transient sub-conscious 'mental map' of the position of the cup as it moves through space is created by the occipital and posterior parietal lobes. (11) The changing spatial coordinates of the shape and location of the cup as it moves towards the mouth reach the motor cortex which, supported by the timing system in the cerebellum, the overall balance system, and the reflex motor support systems in the brain stem and thalamus, brings about the necessary finely tuned act of putting it to the lips and drinking it.
Dorsal and ventral stream visual processing
The principal cognitive visual pathways have been described as the dorsal and the ventral streams. (12,13) The dorsal stream is responsible for localising visual images and the ventral stream for identifying them; in other words, the dorsal stream is the 'where' pathway and the ventral stream is the 'what' pathway. The dorsal stream runs between the occipital lobes (which process incoming visual data), the posterior parietal lobes (which process the whole visual scene and give attention to component parts), the motor cortex (which makes it possible to move using vision as a guide) and the frontal cortex (which directs attention to chosen parts of the visual scene). The dorsal stream is automatic, immediate, unconscious and not memory based. The ventral stream runs between the occipital lobes and the temporal lobes and processes recognition of people and objects, facilitates route finding and is a store of 'visual memory.'
Problems with visual processing
If we consider all of the different processes and neural pathways used to 'make sense' of the visual input from the eyes, we can immediately understand that damage to different elements of the pathway can manifest in many ways, making CVI an umbrella term for numerous visual impairments.
Children with CVI may present with normal to severely reduced visual acuity and contrast sensitivity, and with normal or poorly controlled smooth and saccadic eye movements. There are often no ocular abnormalities, although optic nerve anomalies and refractive error are more common than in the general childhood population. (14) Optic nerve anomalies and refractive error are also associated more frequently with learning disability, prematurity and other neurological disorders and so may not be a causative link.
CVI may cause problems to varying degrees with object recognition, face recognition, visual memory, orientation, visual spatial perception, motion perception and simultaneous perception. Signs and symptoms may be inconsistent and/or transitory.
Vision is fundamental to all elements of a child's development and so difficulties with visual processing will impact on personality, ability to acquire knowledge and skills as well as understanding of the world and of other people. Children with CVI who have no other obvious neurodevelopmental problems can present with difficulties at school, behavioural problems and sometimes even a misdiagnosis with attention deficit disorder or autism. (15)
Investigation and signs of CVI
Enquiring about birth history is important for all children. Where children have a history of prematurity or a traumatic birth, careful questioning regarding functional vision along with observation of functional vision is recommended. This is also the case for children with a diagnosis of cerebral palsy or other brain injury or infection.
Each child affected by CVI has its own unique clinical picture, which needs to be identified, and individually profiled. (16) In-depth history taking allowing a parent to describe their child's visual behaviours, should identify processing problems, even where visual acuities and other ocular clinical signs are normal. Parents are the experts in their own child, therefore, reports and observations of abnormal visual behaviour, in the absence of ocular abnormalities, may indicate CVI.
Children with autism may also have visual processing problems and it has been suggested that some of the difficulties with social interactions and recognising visual cues to emotion from facial expressions experienced by autistic children may result from problems with face processing. (17)
Visual field abnormalities are common in children with CVI and it is recommended that gross visual fields are assessed by confrontation in all children with neurodevelopmental disorders. Inferior field defects, often dense and complete, are frequently seen in patients whose CVI is attributable to HIE or PVL. Children with cerebral palsy may often present with a hemianopia, which may or may not be associated with a hemiplegia.
There is currently insufficient research to allow the nature of a child's likely CVI to be accurately predicted from the aetiology or location of brain injury. (4) Hence, functional visual processing ability is currently the recommended means of identifying and classifying CVI. However, neuroimaging techniques, such as MRI, functional MRI, diffusion tensor imaging and /or electrophysiological testing, such as sweep visual evoked potentials can be useful in correlating structural defects and deficits in function (see Figure 1). Neuroplasticity means a child's clinical presentation may not be easily predicted from neuroimaging.
Dorsal stream dysfunction
Dorsal stream dysfunction results from posterior parietal damage and is often associated with cerebral palsy, birth trauma, premature birth, hydrocephalus and Williams syndrome. Similar visual difficulties are becoming apparent in children with autistic spectrum disorder. (17) Signs of dorsal stream dysfunction may include varying degrees of:
* Difficulty with maintaining and holding concentration
* Crowding, impaired ability to recognise objects in clutter (especially if peripheral distractions are moving)
* Difficulty 'finding' and fixing on a target, particularly a moving target
* Inconsistent responses to a visual stimulus--sometimes a child may react to the same object or toy on one occasion but appear unable to see it on another. This may be due to crowding or tiredness or 'sensory overload.' If a child is engaged in auditory, tactile or gustatory processing they may be unable or less able to process visual stimuli. For example, a child may be visually unresponsive if they are listening, feeling a toy, or chewing food
* Inability to perceive an object as a component of a set of details or objects in a context (literal inability to see the forest for the trees); this is termed simultanagnosia
* Looking away from or beyond a target while reaching for it
* Inability to use visuospatial information to guide arm movements--known as optic apraxia (poor or absent 'visually guided reach')
* Problems with movement detection/inability to determine if targets are in motion or stationary.
Ventral stream dysfunction
This is seen less frequently in children and usually accompanies dorsal stream dysfunction. It is not uncommon in children with hydrocephalus. It manifests as impaired visual recognition. If our ventral stream is intact we can recognise an object from many different viewpoints, even though the ocular images of that object may be very different from one another. For example, we can identify a chair from a photograph or a drawing of a chair from many different angles. We can still usually recognise a chair even from a picture of only part of a chair, as well as being able to identify many different objects as different types of chair.
Signs of ventral stream dysfunction may include varying degrees of:
* Difficulty with recognising objects
* Difficulty with recognising people/faces
* Getting lost in familiar place. Vision for navigation may be much worse than indicated by visual acuities and/or visual fields.
Strategies for support
If you encounter a child with suspected or previously diagnosed CVI in primary optometric practice, never assume they are getting the support they need. Children with learning disabilities and/or complex needs are at particular risk of undiagnosed CVI, despite being a high-risk population. They may not be known to the eye clinic even though they may be experiencing significant vision problems. (3,18) When managing these patients, it is important to:
* Give any necessary refractive correction and encourage adaption strategies for spectacles if they are not well tolerated--for example, making positive associations, recommending initial use during tasks where it is believed a visual benefit is most likely to be perceived by the child. A recent review of effective intervention in cases of CVI indicates that support of the use of a spectacle correction is recommended to encourage processing ability by giving a clear retinal image to process (19)
* Check dynamic retinoscopy to explore if a near prescription is indicated as reduced accommodation is common in cerebral palsy (20) and other neurodevelopmental disorders. If so, prescribe as appropriate
* Provide as much information as you can for family and teachers to enable them to understand the child's visual needs, limitations and abilities. Confusion can arise from parents being told that their child's eyes are healthy in the presence of CVI. The CVI Society is an excellent source of information and advice (21)
* Consider referral to an ophthalmologist to confirm diagnosis and/or for certification of visual impairment, highlighting your suspicions of CVI.
Structured inventories with questions relating to visual function have been developed to allow profiling of a child's visual difficulties and strategies to support them (habilitation strategies). (16) These may be used by habilitation specialists and teachers for the visually impaired. You can signpost directly to support strategies developed by Debbie Cockburn and Professor Gordon Dutton, experts in CVI, which are accessible on the Ulster University website. (22,23)
If the child is not getting support from local authority habilitation specialists or a qualified teacher for the visually impaired practitioners can arrange these referrals, either directly or alternatively by referring to a local eye clinic liaison officer (ECLO) for signposting. It isn't necessary to wait for the child to be seen by an ophthalmologist first so it is better for the practitioner to action these interventions. Provide as much information as possible on the child's ocular and functional visual status to the habilitation specialist/ teacher for the visually impaired to assist them in their support of the child.
Habilitation, teaching or occupational therapy professionals to promote improved function may implement training/practice programmes, and environmental modifications may facilitate engagement of children with their surroundings. An example is the use of 'sensory tents' to gradually introduce individual visual stimuli to children with profound CVI. (24)
These tents work by providing minimal background stimulation/clutter in a simple one-coloured environment and then using individual single stimuli to attempt to elicit a sensory response.
Table 3 outlines some suggested strategies for some common processing difficulties.
Practitioners need to be aware of the characteristics of CVI in children in order to ensure the appropriate management of these patients.
Alfie Fox, a young man with CVI has made a brilliant video: How I See: Alfie Fox, which describes the visual challenges he experiences and is highly recommended. It can be found here: https://www.youtube.com/watch?v=NoPMX51qT6 A.
Under the enhanced CET rules of the GOC, MCQs for this exam appear online at www.optometry.co.uk. Please complete online by midnight on 26 July 2019. You will be unable to submit exams after this date. Please note that when taking an exam, the MCQs may require practitioners to apply additional knowledge that has not been covered in the related CET article.
CET points will be uploaded to the GOC within 10 working days. You will then need to log into your CET portfolio by clicking on 'MyGOC' on the GOC website (www.optical.org) to confirm your points.
Visit www.optometry.co.uk, and click on the 'Related CET article' title to view the article and accompanying 'references' in full.
Course code: C-70969 Deadline: 26 July 2019
* Be able to communicate effectively with children presenting with CVI (Group 1.2.2)
* Be able to assess the visual function of patients presenting with CVI (Group 7.1.6)
* Be able to communicate effectively with children presenting with CVI (Group 1.2.2)
* Be able to understand the methods used to assess visual function in patients presenting with CVI (Group 7.1.4)
Lisa Donaldson MCOptom
* Lisa Donaldson is an optometrist and head of eye health at SeeAbility--a charity that supports people with sight loss and learning disabilities. Lisa is clinical lead of SeeAbility's Children in Focus special school eye care service which has provided over 2S00 sight tests and over 1000 pairs of glasses to children in their special school. She has many years' experience in hospital and community practice as well as teaching paediatrics and clinical skills at City, the University of London. Lisa has a research interest in ophthalmic public health for people with learning disabilities and for children.
Caption: Figure 1 Electrodiagnostic testing may not accurately predict symptoms of CVI (4)
Table 1 Causes of CVI Hypoxic ischaemic encephalopathy (due to birth trauma) Periventricular leukomalacia (often due to prematurity) Traumatic brain injury Congenital anomalies, for example, occipital encephalocele, corpus callosum defects Other neurodevelopmental anomalies, for example, Williams syndrome Idiopathic--cause never identified Meningitis, encephalitis Head injury Shunted hydrocephalus Table 2 Risk factors for CVI Low blood sugar after birth (Neonatal hypoglycaemia) Premature birth Traumatic birth Cerebral palsy Learning disability Epilepsy Developmental delay Motor disorder Speech disorders Table 3 Suggested strategies for some of the more commonly re sorted and observed signs of CVI Dorsal stream dysfunction Difficulty with maintaining and Keep visual tasks simple/short holding concentration Crowding, impaired ability to Use plain carpets, bedspreads and recognise objects in clutter decoration. Minimise 'clutter.' (especially if peripheral Visit shops when they are quiet distractions are moving) Determine whether masking surrounding text improves reading ability Difficulty 'finding' and fixing Wait for eight'-give the child on a target, particularly a time to find the target with their moving target eyes, or when this is not possible place it directly in their line of sight. Where possible keep targets static (however, note that some children find it easier to locate a moving target) Inability to perceive an object Reduce visual 'clutter'--present as a component of a set of individual visual targets details or objects in a context (literal inability to see the forest for the trees)--this is termed simultanagnosia Responding to a visual stimulus Encourage visual tasks silently, inconsistently--sometimes a in the absence of other sensory child may react to the same stimuli object or toy on one occasion but Don't ask the child to 'look at me appear unable to see it on while I'm speaking to you' another. This may be due to Avoid 'walking and talking' to crowding or tiredness, or assist in vision for mobility sensory overload.' If a child is engaged in auditory, tactile or gustatory processing they may be unable or less able to process visual stimuli. For example, a child may be visually unresponsive if they are listening, feeling a toy, or chewing food Looking away from or beyond a Be aware this may be a necessary target while reaching for it adaption to aid sensory processing and do not discourage Inability to use visuospatial Occupational therapy training information to guide movements-- Lower limbs: feeling with the foot may mean unable to detect steps/ for the height of the ground ahead mobility issues at floor boundaries Provision of tactile guides to the height of the ground ahead. For example, pushing a toy pram or holding on to the belt pocket or elbow of an accompanying person Problems with movement detection/ Present stationary visual stimuli inability to determine if targets where possible. Significant are in motion or stationary support with mobility training may be needed that may not necessarily be expected from visual acuity/ visual fields Ventral stream dysfunction Use tactile training to identify Difficulty with recognising objects objects Difficulty with recognising Family and friends introduce people/faces themselves and wear consistent identifiers Training to identify and recognise identifiers Getting lost in familiar place. Training to seek and identify Vision for navigation may be much landmarks worse than indicated by visual acuities and/or visual fields
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|Title Annotation:||Visual impairment|
|Date:||Jun 1, 2019|
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