School of Special Education and Disability Studies
Children who are deafblind present a unique challenge to professionals. They are learners who receive and interpret auditory information in a different way (Kelley, 1998). Children who are deaf blind may be blind and "hard of hearing", deaf and vision impaired. They may have additional physical disabilities, severe developmental delays, or medical problems (Chen and Haney, 1995). The causes of visual disabilities are numerous and varied. They may be the result of syndromes, inherited eye conditions, pre-natal or post natal factors.
Vision impairment has traditionally been associated with a problem with the eyes. There are a number of students with disabilities, however, who have vision loss as a result of disturbance to the posterior visual pathways and/or the visual cortex which deal with the processing and integration of visual information (Hughes, 1995). This is known as cortical vision impairment. These childrenís eyes may appear normal. There is normal pupillary response and no nystagmus yet the child appears to be blind. Vision may appear intermittent. The children are usually attracted to bright shiny moving objects. They will frequently use one sense at a time eg they may look at an object but when they touch it they look away and move around the environment with out bumping into anything. Cortical vision impairment can be described as a condition in which the vision is more severely reduced than ophthalmological findings indicate.
Students who are deafblind may have vision loss due to cortical vision impairment. This paper will focus on students with cortical vision impairment. It will define the condition, discuss identification, causes and characteristics, outline behaviours associated with cortical vision impairment, and provide an overview of educational intervention and important pedagogical considerations.
Cortical vision impairment is a complex phenomenon and possibly more common than one would expect. Children with cortical vision impairment are a diverse group whose vision impairment spans a continuum from those who appear to have no vision to those who present with minimal visual perceptual difficulties which are only obvious when they attempt certain tasks (Hughes, 1995).
Cortical vision impairment is not a structural problem of the ocular system, but a disruption in the function of the brain. It is a condition that presents with contradictions. The eyes of children with cortical vision impairment may appear normal. They usually present with normal pupillary response and no nystagmus. Some appear to be blind yet they are able to move around the environment without bumping into anything. Others, appear to have vision which is intermittent. These children are usually attracted to bright shiny moving objects. However while they will reach for an object one moment they may ignore one that is equally as bright the next. They will frequently use one sense at a time, eg they may look at an object but when they touch it they look away.
Groenveld (1997) claims that a multidisciplinary approach is essential in order to obtain a correct diagnosis of CVI and to devise appropriate approaches to learning and management. She recommends intervention by a small group of professionals with a high level of cooperation to ensure continuity.
This paper will focus on students with cortical vision impairment. It will define the condition, discuss identification, causes and characteristics, outline behaviours associated with cortical vision impairment, and provide an overview of educational intervention and important pedagogical considerations.
What is Cortical Vision Impairment?
Cortical Vision Impairment is not the result of damage to the eye itself or the optic nerve (it can co-exist) but to the visual systems in the brain which deal with the processing and integration of visual information (Hughes, 1995). It is caused by disturbance of the posterior visual pathways and/or occipital lobes. Jan and Groenveld (1993) emphasise that although changes to visual behaviours and perception can be caused by damage to almost any part of the brain, ìonly damage to the posterior visual pathways, including the visual cortex, can cause cortical visual lossî (p.101).
The clinical definition of cortical vision impairment is a bilateral loss of vision with normal pupillary response and an eye examination that shows no other abnormalities (Good, Jan, DeSA, Barkovich, Groenveld and Hoyt, 1994; Moore 1995). In other words, it is a condition in which the vision is more severely reduced than can be explained by the ophthalmological findings (Steendam, 1989). It may result in a temporary or permanent visual loss (Hein 1995).
The Brain and Vision
Vision has been described Groenveld (1997) as a process. She claims that incoming information is analysed in various areas of the brain. She discusses the findings of Zeki, (1992) and other independent researchers who have identified a number of different areas on the occipital cortex ìwhich respond to distinct attributes of visual informationî (p. 1). She notes that these researchers have demonstrated that the retina is directly linked with the primary visual cortex through the ìlateral geniculate nucleusî (p. 1). The distinct cell layers of the ìlateral geniculate nucleusî respond to different aspects of the visual image, according to Groenveld, and ìexcite corresponding cell groups in the primary visual cortexî (p. 1). Specialisation occurs when information is communicated with the areas of the visual cortex, some of which deal with colour, some with motion and others with shape or a combination of all three. She suggests that information is exchanged between these areas and also the primary visual cortex and that damage to any of them can result in cortical vision impairment. In addition she explains it could be expected that when the entire primary visual cortex is destroyed, total blindness could realistically be expected. This is not the case, however. Groenveld claims that there is evidence that some signals are ìrouted directly to the specialized areas, bypassing the lateral geniculate bodyî (p, 2). When this occurs, people have, what is referred to as ìblind sightî, and are able to discriminate between motion in different directions or between different wavelengths of light. She adds that these individuals appear to be unconscious of this ability.
The eye is often compared to a camera and the brain to a computer. When light is focused on the retina, it is transformed by photochemical process into electrical messages that are transmitted to the occipital lobes (visual cortex) where they are decoded. Damage to the occipital lobes means that information is only partially analysed, or at times not analysed at all. Jan and Groenveld (1993) explain that the eyes of most children with ocular disorders look abnormal and visual behaviour is usually consistent. They claim the children with CVI, on the other hand, do not appear blind, they have a short visual attention span, see little, and their visual skills vary from minute to minute. Their visual perception according to Jan and Groenveld (1993) can be ìdramaticallyî impeded by fatigue, ìminor illness, an unfamiliar environment, suboptimal lighting, poor contrast, medications, limited and varying energy levels and innate processing factorsî (P.101). The following table taken from Jan and Groenveld (1993, p.101) compares some characteristic differences between cortical vision impairment and ocular disorders.
Table 3.1: Characteristic differences between ocular vision impairment and cortical vision impairment
Characteristics Ocular disorder Cortical disorder
Eye examination Usually abnormal Normal
Visual function Consistent Highly variable
Visual attention span Usually normal Markedly short
NystagmusPresent when congenital and early onset Not present
Poor coordination of eye movements Present when congenital and early onset Usually normal
Light sensitivity Dependent on the eye disorder In a third of the cases
Eye pressingEspecially in congenital retinal disorders Never
Close viewing Common, used for magnification Common, used for magnification, a reduction in crowding or both
Colour perception Dependent on the eye disorder Preserved
Appearance Appears to be vision impaired Usually normal
Peripheral field loss Occasionally Nearly always
Presence of additional neurological handicapsFairly common Nearly always
Cortical vision impairment frequently exists with ocular vision loss. It is complex and diagnosis is difficult to determine. It requires thorough medical investigation and careful assessment of functional vision. According to Moore (1995) most children with CVI have some residual vision. He also asserts that the majority of children in developed countries who have cortical visual impairment (10% of CVI cases in the world) have additional neurological deficits, eg, intellectual disability, cerebral palsy, epilepsy, or various spinal and cranial defects (Moore, 1995). This increases the challenge for educators who may find inherent difficulty in differentiating between a visual acuity problem, a perceptual problem, or a delay in vision maturation.
The role of vision in learning
Vision leads to the development of integrative functions such as:
eye-hand coordination - all visual-motor activities are delayed in infants with CVI, or who are blind
visual-object recognition and learning
visual-spatial recognition and learning. In children with CVI, both visual-object and visual spatial recognition and learning, including the concept of object-constancy are severely impaired
visual-motor learning and coordination
Vision is the vital trigger that stimulates head raising. Children with CVI show a developmental delay in head raising functions. Rolling over, raising up on upper limbs, pushing back or forwards and eventually sitting, crawling, creeping, cruising and walking are all believed to be driven initially by visual stimulation triggered by something in the environment, coupled with the drive to obtain objects, explore and manipulate them and thus learn about them. Hence almost all behaviour is visually driven throughout life including all movements, reading, writing, maths, inventing, discovering and creating (Moore, 1995).
Causes of CVI
In the past students with vision impairment have been supported on the basis of ocular conditions alone. With the increase in survival rate of infants and children with damage to the central nervous system and an increase of interest, research and knowledge about cortical vision impairment, this area is now being addressed. One of the major causes of cortical vision impairment that emerged from a study by Groenveld (1997) was asphyxia. This is often referred to in the literature as cerebral hypoxic-ischemia (reduced flow of oxygen and blood to the brain which causes extensive brain damage). Groenveld explains that the visual cortex is most vulnerable when the blood supply is interrupted because it is the furthest from the main blood supply, and oxygen is carried by the blood. When this happens, other areas are also affected and, according to Groenveld, this is one of the reasons why CVI rarely occurs in isolation.
Other causes of CVI include head injuries (Kelley, 1998; Groenfeld, 1997; Hughes, 1995), shunt failure in children with hydrocephalus (Kelley, 1998; Connolly, Jan, & Cochrane, 1991), developmental brain defects (Hein, 1995; Groenfeld, 1997), infections of the central nervous system such as encephalitis and meningitis (Kelley, 1998; Groenfeld, 1997) and infantile spasms (Kelley, 1998). Groenveld (1997) claims that about half the cases of head injury found in the infant participants in a study carried out with Jan and Leader in 1990 were due to battery or shaking.
Hughes (1995) describes CVI as being ìpermanent to some degree, or transientî (p. 4). She explains that this is dependent on a number of factors such as time of onset of the trauma, the location and the degree of damage to the visual system. Hughes sums up the causes of CVI in the following way:
Table 3.1 Causes of CVI
brain damage as a result of lack of oxygen to the brain. This results in changes to the grey matter of the brain which then ceases to function appropriately
Uraemia is a toxic condition that is caused by retention of waste substances in the blood. These waste substances are normally excreted in the urine. The characteristics of uraemia are fatigue, nausea, malaise, anorexia and neurological problems. The symptoms may include lethargy, loss of appetite, vomiting, anaemia, blood clotting disorders, an abnormal mental state, pericarditis, and colitis.
A high proportion of children with cortical vision impairment also have additional disabilities with varying degrees of severity which, of course, all interact with each other (Sacks, 1998; Groenveld, 1997). The following conditions are frequently associated with cortical vision impairment:
1. Cerebral Palsy
2. Intellectual disability
4. Microcephaly (Hughes 1995).
Characteristics of children with CVI
The characteristics of students with cortical vision impairment vary considerably. Hughes (1997) comments that few children will present the same characteristics all of the time and this makes the assessment of their visual function and the development of appropriate programs extremely difficult. An examination of the literature indicates that the following characteristics may be seen in some learners some of the time:
eyes appear to be normal (the results of the eye examinations of half of the children who participated in Groenveldís 1990 study were normal: reported in Groenveld, 1997). The other students presented with eye conditions such as optic nerve atrophy, optic nerve hypoplasia, retinal abnormalities and other ocular problems. Groenveld points out that ocular problems may coexist with CVI and this makes diagnosis difficult).
fluctuating visual abilities/variable visual performance, inconsistent or lack of visual motivation or attention
stereotypic head positions, tilts or turns. Peripheral vision may be used when looking or reaching for an object, or the child may turn their head away.
eye closure - the child may blink or quickly close their eyes when visually moving from one target to another, or close one eye in order to see better.
appears to respond to selective stimuli, eg certain colours, patterns, movement. Some children are attracted by bright lights, or coloured objects. They may ignore black and white objects. Stereotypical searching and staring at brightly coloured objects can be diagnostic for CVI
navigating vision. Children with CVI who are diagnosed as blind can move about in an unfamiliar environment without bumping into objects.
photophobia, (abnormal sensitivity to light). I/3 of children diagnosed with CVI may demonstrate photophobia as opposed to attraction to light and colour
saccadic movement is abnormal. Children with CVI may have difficult in following objects with smooth visual pursuit. In addition they may be unable to comprehend what is seen, whether it moves or where the object is located in space.
frequent use is made of touch
will listen rather than look. Hughes (1997) comments that students may avoid looking. She suggests that they sometimes turn away from visual stimuli, opt out, close their eyes, cover their eyes or go to sleep.
some children have pockets of vision scattered throughout their visual fields. Moore describes this as a ìSwiss cheese effectî (Moore, 1995, p. 117- 119).
uses vision as a secondary confirming sense (Hughes, 1995)
looks away when reaching. The child will locate an object visually, but turn away when touching (Hughes, 1997)
no nystagmus (unless ocular problems also exist). Groenveld claims that ìa child with pure CVIî will not exhibit nystagmus, although unusual, roving eye movements may be presentî (Groenveld, 1997, p.4).
May appear to ëseeí without looking (Hughes, 1995, p.5).
It is necessary to assess the level of development of the childís visual skills before commencing an intervention program. This is to ensure that prerequisite skills have been mastered and the childís program is pitched at an appropriate level. It is also important to verify the existence of, and qualify the nature of the vision impairment.
Most children with CVI have physical and or intellectual disabilities, but this does not mean that all children with additional disabilities have CVI. However, all children with CVI have a visual perceptual problem (Hein, 1995).
A number of clinical tests can be used to determine CVI. These are shown in the table below which has been compiled from information from Kelley (1998) and Good et al. (1994).
Table 3.2: clinical tests that can be used to determine CVI
Functional vision assessments of the child interacting within their environment are often more relevant. Methods of assessment can include
collection of anecdotal records
interviews with parents and significant others
formalised and structured observations
informal screening using standardised vision screening materials
A functional vision assessment should be conducted by the vision specialist. Langley and Dubose (1989) recommend that the following skills should be evaluated (see table 3.3 below).
Table 3.3: Table showing skills to be evaluated in a functional assessment test
pupillary response blink reflex muscle imbalance visual field preference visual behaviours tracking reaching towards objects that are visually perceived reaching towards sound scanning skills
Adapted from Langley and Dubose (1989) in Kelley, Davidson and Sanspree (1993, p. 397).
Table 3.4: Table showing skills to be evaluated in a functional assessment test Hughes (1995)
Hughes, 1995 recommends testing for: awareness of light location of light relocating light fixing on a light shifting gaze following a light awareness of any stimuli locating, fixing and following any stimuli
The assessment should be conducted in the environments in which the child functions (Morse, 1991). The vision consultant can then make suggestions for managing the environment, targeting visual behaviours for intervention, and developing teaching techniques for improving visual behaviours (Downing & Bailey, 1990; and Hall & Bailey, 1989, cited in Kelley, Davidson & Sanspree, 1993, p. 397).
Refractive errors, lighting and field losses
Refractive errors need to be checked and glasses prescribed if necessary. Appropriate lighting is very important. According to Groenveld Jan and Leader (1990) some children require bright light while others are sensitive to it. Field losses should be taken into account when materials are presented to children. Groenveld Jan and Leader (1990, p. 14) point out that the side of the field loss does not necessarily correspond to the better hand function.
During assessment it is necessary to eliminate other sensory cues as much as possible. This is to ensure that responses are a result of visual stimuli alone (Hughes 1995). In conducting vision assessments Hughes (1995) suggests that vision specialists need to be aware that:
Children need time to respond. There may be a response delay which could be longer if the child has cerebral palsy.
Visual response to stimuli may not occur immediately. Teachers need to look for other signs. These may be changes in breathing, ceasing to cry or vocalise, shutting eyes, turning the head away, putting hands over ears/eyes, or blinking Hughes (1995).
The child may give a visual response, but it may be difficult to interpret, as the child may use peripheral vision or use only one eye while the other wanders. Hughes suggests getting the child to indicate their response in some way, for example, by reaching for the stimulus.
Avoidance can be another problem. Some children will avoid looking and shut their eyes. With these children it is necessary to persevere.
The emphasis on the collaboration of the various professionals and caregivers to:
interpret data on the student
use the most accurate information to plan an integrated program to increase visual functions
are the key components of comprehensive assessments and the development of basic individual programs (Kelley, Davidson and Sanspree, 1993, p. 397).
The colour perception of children with cortical vision impairment is usually intact, even when they have minimal residual vision. Groenveld Jan and Leader (1990) claim that findings from experimental data suggest that the use of colour as a stimulus with forms facilitates the perception of forms by individuals with CVI. They suggest that when teachers introduce simple shapes and letters, it may be helpful to outline them with colour, making sure, of course, that the contrast between the shapes/letters and the background is high. They indicate that yellow and sometimes red are thought to be more easily perceived and recommend that in the initial stages, the identification of objects can be assisted by keeping the colour of the objects constant until the concept has been established. Some children have enough functional vision to deal with picture books and stories. Groenveld Jan and Leader (1990) suggest that for these students it is important to ensure that there is no crowding of material and stress that stories with a single simple picture on a page will be more useful than cluttered pictures and text.
“Variable visual performance is characteristic of CVI infants/childrenî (Moore, 1995, p.114). Since children with CVI often present with fluctuating visual abilities they are frequently described as lazy or malingering. They do in fact function well at times and yet exhibit severe vision defects and operate poorly at others as mentioned previously. Their visual behaviour can be influenced by fatigue, lighting conditions, contrast, context and the environment. It can also be related to medication, and the type and severity of the CVI.
Sensory bombardment is considered detrimental to students with cortical vision impairment
Sensory bombardment is now considered to be detrimental to students with cortical vision impairment (Hein, 1995). Research has proven that busy, stimulating environments may in fact inhibit learning. This is because these students are unable to filter salient information from the mass of sensory information to which they are exposed. Students with CVI may use vision as a secondary or confirming sense.
locate objects using tactile cues
close their eyes when they reach for objects
behave in ways that suggest that the attempt to process several stimuli is confusing.
Students with CVI exhibit changes in vision
These students may demonstrate differences in vision on an hour-by-hour basis. The frustrating thing for teachers and caregivers is the difficulty in determining whether these changes relate to motivation and attention or to true neurological variations. In addition, according to Groenveld et al (1990), many children tend to improve over time. There are wide variations in educational services, approaches to teaching and treatments applied to these children, and this makes it difficult to draw conclusions about the approaches that influence change.
Students with CVI respond selectively to visual stimuli
Children with cortical vision impairment often respond selectively to visual stimuli.
colour appears to make objects discernible for many children
lighting or movement are key characteristics which make certain features of the environment significant for others.
previous experience with an object or form is a critical characteristic.
Although this varies greatly from child to child, the preference for, and attentiveness to, certain classes of visual stimuli is more notable among children with CVI than among children with other vision problems.
Important pedagogical considerations
It is important when students are working on visual perceptual tasks that other handicaps are accommodated as much as possible so that all available energy may be concentrated on the task itself. For example Children with cortical vision impairment may also have epilepsy. Reasonable seizure control needs to be achieved before remediation for cortical vision impairment occurs. Children with multiple disabilities need far more energy to maintain a perceptual continuum than their non disabled peers (Groenveld, Jan & Leader, 1990, p. 14). This is because they need to analyse visual information in much smaller units and with much greater intensity to interpret its meaning (Groenveld, Jan & Leader, 1990, p. 14). It is like learning a foreign language. Students find it :
tiring to keep up with the flow of conversation and overload occurs easily.
a large amount of energy goes into posture, rather than into maintaining visual perception when they have poor balance
visual targets are lost involuntarily by students with poor head control if their heads are not supported properly.
Tasks should be repetitive. They should have a clear beginning and end: this helps to conserve energy. When childrenís energy levels are low, they fade in and out of tasks. Their eyes cease to focus for brief periods. Facial expressions should be watched for attending behaviour (Groenveld, Jan & Leader, 1990, p. 14).
Groenveld, Jan and Leader, (1990) suggest that a multidisciplinary approach is necessary to obtain a correct diagnosis and to devise appropriate management strategies. They argue that:
a small number of people should be involved in the intervention
cooperation between team members should be high
the amount of visual stimulation and nonessential information should be reduced to enhance visual efficiency
visual efficiency may be improved using additional cuing through language, touch, and colour coding
the accommodation of additional handicaps can assist in maximising available energy for perceptual tasks
because of the visual complexity of regular classroom settings, full inclusion is not advisable as it may reduce the opportunity for meaningful visual perception. Partial inclusion, however, is important for the social and emotional development of the student.
The contribution of the vision specialists should expand beyond basic programming to improve visual functioning. Their role as a member of the transdisciplinary team should include sharing information on:
the impact of cortical vision impairment on learning
other specific areas of functioning
-skills of every day living
-orientation and mobility
ways to increase opportunities to use vision and other sensory information
ways to use special materials and adaptive techniques
ways to teach specific skills for protection, safety, and ease of movement.
These are all essential components of any program for a child with a vision impairment and should be equally available to a child with additional impairments (Kelley, Davidson & Sanspree, 1993, p.397).
Teachers of students with cortical vision impairment may need to consider:
using tactual, gustatory, or olfactory replacements for the use of vision.
Students gain more independence through the use of outline movement, verbal prompting, and cuing. Orientation and mobility instructors are needed to train teachers and caregivers in techniques for the individual child. The emphasis should be on guiding not helping.
Visual and Multisensory Programs
To reduce the specific problems the children have, programs should be designed with the following guidelines in mind:
consistency across all learning environments in materials, methods and language
short frequent periods of work
much repetition of familiar activities to maintain skills
learning in a visually uncluttered environment. This will assist in:
1. limiting the childís spatial and figure ground problems
2. minimising distractions
3. encouraging a focus on the work in hand
ensuring the material to be viewed is well lit from behind the child. Some writers suggest spot-lighting materials in a dim room
ensuring there is a strong contrast between the material to be viewed and the background
providing material that is visually motivating and attractive: use shiny, florescent, luminous, coloured, black and white or other starkly contrasting patterns
presenting material close to the child, level with their eyes and in a position where you expect optimal response. It is very important to be consistent
reinforcing improved visual performance
planning a program using a multisensory approach when a child begins to show awareness to visual cues alone
using other senses to confirm visual input and aid memory recall. Always presenting the visual information first, then adding the other sensory input otherwise the child may not bother to look
using every day materials
trying to involve children as much as possible to decrease passivity
communicating what is happening to students and showing them the materials you are using Let them feel the objects against their skin, smell and hear them and encourage reaching.
allowing plenty of time for response
re-assessing and re-evaluating the program regularly.
The participation of teachers trained in the education of students with vision impairment (vision consultants) and orientation and mobility instructors is vital to enhance the studentís access to, and participation in the education process. There needs to be an emphasis on collaboration between various professionals and caregivers. Participation in the transdisciplinary team allows the vision consultant to influence the students complete program and ensure that it is time effective. A collaborative effort allows the vision consultant to educate others about the unique needs of the child resulting from the vision impairment (Kelley, Davidson & Sanspree, 1993, p.397).
It is well documented, according to Moore (1995), that infants and children with CVI are delayed to a greater or lesser degree in reaching developmental milestones and in all sensori-motor activities and social development. Direct intervention and stimulation at an early age and support for caregivers is essential particularly in the early years. Moore (1995) reports that 70% of children who have CVI or who are blind have some degree of intellectual disability and/or other disabilities.
In conclusion the problems of children with CVI are usually complex. A multidisciplinary or a transdisciplinary approach is necessary to obtain a proper diagnosis and to devise appropriate management strategies. The number of people involved in the program should be limited, with a high level of cooperation between them. Visual efficiency can be increased by reducing the amount of visual stimulation and eliminating non-essential information. Additional cuing through language, touch and colour coding may improve visual efficiency also. The level of available energy for visual perceptual tasks should be maximised by accommodating additional disabilities.
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