Maryke Groenveld, Ph.D. R.Psych.
This article was used by the author as a handout at her workshops between 1994 and 1997.
Cortical visual impairment (CVI) refers to visual impairment due to damage to the visual cortex, the posterior visual pathways or both.
Early neurologists saw vision as a process by which an image of the real world around us was impressed on the retina and there coded. These codes were then transmitted via the optic tract to the visual cortex where it was decoded. The received impressions were then associated with previous experiences, which was felt to lead to understanding of the decoded image. However, with more advanced techniques of measuring brain activity during exposure to visual stimuli, there was more support for the theory that incoming visual information is analyzed separately in a number of different areas in the brain (Zeki, 1992, Crick, 1994). Zeki and other, independent researchers have identified a number of different areas in the occipital cortex which respond to distinct attributes of visual information. It has been demonstrated that the retina is directly linked with the primary visual cortex through the lateral geniculate nucleus. In the lateral geniculate nucleus there are a number of distinct cell layers. These layers respond to different aspects of the visual image and excite corresponding cell groups in the primary visual cortex. This information is then communicated with areas of the visual cortex which are further specialized. Some deal with color, some with motion, others with shape or a combination of shape and motion. Information is exchanged between these areas as well as the primary visual cortex. Damage to any of these areas can lead to what we call cortical visual impairment, although the resulting behaviors may be quite different.
When the entire primary visual cortex is destroyed, one would expect total blindness; however, there is evidence that some of the signals are routed directly to the specialized area, bypassing the lateral geniculate body. This is what is referred to as "blind sight" in some of the literature. Some people with this condition are able to discriminate between motion in different directions or between different wavelengths of light. However, they do not appear to be consciously aware of this ability.
There are several ways to detect CVI. A Visual Evoked Potential Map (VEP Map) is a form of computerized Electro Encephalogram (EEG) and can detect the electrical activity, or lack thereof, in the visual cortex when the person is exposed to visual stimuli. Several types of imaging techniques, such as Ultrasonography, Computerized Tomography (CT Scan), or Magnetic Resonance Imaging (MRI) can indicate areas of affected brain tissue. Positron Emission Tomography (Pet scan) can measure localized differences in blood flow in the brain when people perform specific tasks. PET is rarely used with newborns and children with CVI because it is generally not readily available and requires long examination times (Good et al., 1994). An EEG measures the electrical activity in the brain and can also provide information regarding the functioning of the occipital cortex: with permanent CVI or total blindness there is no alpha rhythm over the visual cortex.
Ever since we started keeping records of CVI at British Columbia's Children's Hospital (BCCH), the population of children with CVI has been steadily increasing. In a study done at BCCH in the late eighties of 123 children with CVI, it was felt that it was about 10% of legally blind children. Now this percentage is much higher (Groenveld, Jan, and Leader, 1990). This is in part due to a better understanding of how the brain functions and better detection methods, but also because of medical advances. Children who are severely compromised at birth or critically ill children who previously would have died, now can survive, but often with severe brain damage which may also involve their occipital cortex.
Generally more boys than girls appear to have CVI. In our population the ration is about 2:1, while for most forms of ocular impairment the incidence is about the same for boys and girls.
One of the major causes of CVI in our study was asphyxia, which means that the oxygen supply to the brain or parts of it, is interrupted. Since the visual cortex is the furthest away from the main blood supply, the oxygen is carried by the blood, the visual cortex is most vulnerable in case of interruption of blood supply. Of course, when this happens the visual cortex is not the only area affected, which is one of the reasons why CVI rarely occurs by itself.
The great majority of children with CVI have additional handicaps, with varying degrees of severity, which of course all interact with each other.
Other causes of CVI are developmental brain defects, head injuries, and infections of the central nervous system such as encephalitis or meningitis. Among the head injuries about half of the cases were due to battery or shaking of infants.
The onset in the vast majority of cases (about 80% in our 1990 study) is at or before birth and therefore affects an immature brain and visual system. Thus the information from studies with animals, mature stroke victims or the shot wound studies from the first world war, do not always apply to the functioning of children with CVI, since it deals with the destruction of part of the visual system after it was already fully developed. It does not take into account the much greater plasticity of a still developing brain, nor does it allow for the effect of preexisting, sight based, understanding of the world.
The eye examination in more than half of the children in our study was normal, however, conditions such as optic nerve atrophy, optic nerve hypoplasia, retinal abnormalities and other ocular problems may coexist. Therefore, a child with CVI may have nystagmus associated with the additional ocular problem; however, a child with "pure" CVI will not exhibit nystagmus (Whiting et al., 1985, Jan and Groenveld, 1993), although unusual, roving eye movements may be present.
Visual acuity testing in most children with CVI is difficult to do with standard optotype material, because many are either too young or too low functioning and therefore not capable of the verbal and/or motor responses these tasks require. However, it can be done with Forced-choice Preferential Looking charts (FPL), provided the child is capable of the eye movements required to indicate a preference. These test do not measure exactly the same function as optotype material, since they do not involve shape recognition or matching, and therefore from the FPL results optotype acuity of the same value cannot be assumed.
Most children with CVI show some degree of improvement in their visual function. Children with acquired CVI due to a hypoxic insult generally tend to have a good recovery rate (60-70%) (Good et al., 1994). With congenital CVI the prognosis is generally not that good. When an MRI scan shows extensive periventricular leukomalacia (damage to the white matter surrounding the ventricles, including the optic radiations), the prognosis generally is poor as well (Lambert, Hoyt, Jan, Barkovich, and Flodmark, 1987). When preserved alpha rhythm in the occipital region can be demonstrated on an EEG, the chances of recovery are usually better (Jan and Wong, 1988). Improvement in the use of vision will also occur through general maturation of the brain, experience through the other senses, and intervention. Sometimes improvement can be noticed over a period of several years.
As stated earlier, children with CVI rarely are free of additional handicaps. We found a large percentage with cerebral palsy (about 80%), epilepsy (about 60%), hydrocephalus (about 20%) and deafness (about 10%). Many children had more than one disability. About 80% of the children could be classified as cognitively deficient. This should not be regarded as a separate disability, but rather as the result of a combination of disabilities, which compromises the accessibility of information, as well as the ability to integrate information the way unaffected people do.
The complexity of the problems of children with CVI poses great difficulty for remediation. It makes it impossible to provide strategies which will work for all children with CVI, nor is it possible to find an unaffected channel to work through. Therefore the planning for children with CVI will have to be done on an individual basis and requires a thorough multidisciplinary assessment.
Children with CVI differ significantly from children with an ocular impairment and therefore require different intervention strategies. With an ocular visual loss the visual signal may be incomplete or diminished, but the processing mechanism is the same as that of normally sighted children. Therefore, visual enrichment, teaching of scanning techniques with complex visual material, etc., are likely to be effective. With the child with CVI these methods tend to be less successful. Children with CVI appear to have a disturbance of the interpretation mechanism, while the signal itself may be complete initially (Cannao, Moretti, and Ricci, 1986).
When we see behavior which would seem to be much more visually impaired than one would expect on the basis of an eye report, chances are high that we are dealing with a CVI, although some other conditions, such as delayed visual maturation or ocular motor apraxia can at first encounter also appear as CVI. Also, when the visual functioning appears to be highly variable for no apparent reason, there may be cause to suspect a CVI.
The visual behavior of children with CVI tends to differ in a number of other ways from children with an ocular disorder. The eyes seem normal, although the children do not seem to focus properly. 40% of the children diagnosed with CVI at BCCH showed intent light gazing while virtually no light gazing was found among children with an ocular disorder (Jan, Groenveld, and Sykanda, 1987). 30% of the children with CVI were light sensitive, but this did not necessarily exclude light gazing behavior (Jan, Groenveld, and Anderson, 1993). Eye pressing, which is commonly seen in children with retinal disorders was never seen in our group of children with CVI, although some forms of eye poking have been observed.
Children with CVI often show a characteristic head turn when they look at or reach for an object in which they are interested. They seem to focus on the object very fleetingly and then turn their head to the side as they reach. They seem to use a combination of central and peripheral vision. They also are frequently seen to reach or point just beside an object and then slide their hand or finger to the target.
Color perception is frequently preserved in children with CVI. This is felt to be due to the fact that the area in the visual cortex that are concerned with color have unusually high concentrations of blood vessels nourishing them, which protects them to a greater degree from the effects of oxygen deprivation. Many children seem to perceive yellow or red more easily. The perception of color is not necessarily associated with the perception of an object. We have seen children, who, when they have to place colored pegs in a board, go through the entire process using touch only, but when they are asked to pick our a peg of a particular color, do so entirely on sight and without hesitation.
Many children with CVI appear to have difficulty with depth perception, although there does not appear to be an ocular reason. They also do appear to have a lot of difficulty with foreground/background perception when they look at objects against a patterned background. It is felt that children with CVI may have a lot of difficulty with suppressing unnecessary information (Rizzo and Hurtig, 1987). Background information may therefore interfere with the perceptual organization of the object at which they are trying to look. The shape of the object, when seen in isolation, may also not be properly processed.
Verbal or tactile cueing may help to achieve the proper visual organization to perceive the object properly. The behavior of the children with CVI sometimes seems to resemble the experience one has when looking at an incomplete picture: at first the lines make no sense, but as soon as we are told what the drawing represents, we can integrate the information into a meaningful whole and "see" it.
Many of the children with CVI have been observed to bring objects very close to their eyes, although they have no known acuity problems. This dose not only provide them with magnification and therefore more information, but it may also be related to difficulty with suppressing background information. If the object is close to the eyes, it fills almost the entire visual field and background information no longer interferes as much. Some mothers have reported that their infants were more responsive to them when they were lying on their back rather than sitting up. Possibly this is because the mother's face is backed by a blank ceiling and therefore more easily identified as a whole.
The inability to perceive objects spaced closely together is referred to as the crowding effect. It seems very difficult for children with a CVI to perceive closely grouped objects and it may be helpful to teach them to search for the individual objects tactually and then space them at a distance from each other, which may make visual perception possible for them.
With higher functioning children, who are beginning to count, the crowding phenomenon should not be confused with lack of one to one correspondence.
All children with CVI who have a lesion in the primary visual cortex, have field defects corresponding to the affected area in the visual cortex. When objects are in the area of the field defect, the child will not be able to see them, but will be unaware that they cannot see. They most likely will not see an area that is blurry or unclear, but the brain will fill in the missing information based on what is present in the healthy areas of the visual field. When an object is presented it may be better to do so from the side of the intact visual field to prevent objects from coming out of a vacuum. Some children appear to have very patchy visual fields which are sometimes compared to "Swiss cheese." They will have spots throughout their visual field in which they will not be able to see.
Most children with CVI have additional neurological problems which can make an assessment of their functioning levels very complex. It is therefore wise to evaluate them both for diagnosis and therapy with a multidisciplinary team.
The assessment team at the Visually Impaired Program in British Columbia is comprised of a number of professionals, including a: pediatric neurologist, pediatric ophthalmologist, psychologist, physiotherapist, audiologist, speech and language pathologist, nurse clinician, vision consultant, and other professionals involved in the daily care of the children, such as the parents, educators, child care workers, social workers or other relevant people in the community. A report of each individual assessment is sent to all those immediately concerned with the care and education of the child, provided the parents have signed a consent form. Suggestions for remedial intervention are made through the itinerant teacher for the visually impaired, the vision consultant, or the nurse clinician. Recall is arranged at critical periods in the child's life, such as school entry, or as the need arises.
Children with CVI are likely to process incoming information quite differently from normally sighted children, especially when there are a number of additional neurological problems. Since the access to information varies so much from child to child, it will be very difficult to assess them with standardized tests (Groenveld 1990).
Test materials and situations frequently have to be tailor made so that the children will have the opportunity to show what they can and cannot see or do.
It will be important to try and find out if the concepts that are being taught or have been acquired are functional in the sense that the children are able to use them in a meaningful way in their daily living activities. The acquired information also should be relevant to the child and not be entirely isolated from other activities or experiences.
The reasoning ability of the child should be investigated to see if it is developing to its highest potential. In order to be able to have realistic expectations of the child, one has to evaluate how the child compares to the group he/she is expected to function in.
When assessing children with CVI it is usually advisable to avoid direct light sources to prevent unnecessary distractions. Diffuse lighting usually works best and if natural light is used it may be better to have the child's back to the window.
Visual clutter should be avoided on the work surface and in the background. The level of contrast between the test material and the background should be optimal. If possible, brightly colored material without unnecessary embellishment should be used. The examiner's clothing can also be a factor and is best kept simple and of a single color. The test material should be used where feasible. Field restrictions should be taken into account, and the material should be presented from the side of the better field.
Children with CVI frequently have a much lower information processing speed than typical children. It is often helpful to slow down the presentation speed as well as the rate of speech production in the examiner. This is often difficult to do since the speed at which we speak or move is part of our temperament and, therefore, difficult to control. Sometimes it is helpful to lower one's voice. This slows down the presentation rate automatically, and usually the child moves a little closer to hear better. In this way the child takes the initiative in determining the body space, which may be more comfortable than when a strange adult does it. It also tends to eliminate some of the background information and thus create a clearer visual unit.
The child may need more time to explore test material than a child who is able to perceive information at a glance. The time needed for the child to generate a response often is longer as well, and sufficient time should be allotted before a stimulus is modified or removed. Warm up examples through demonstration are often needed with the higher functioning children to communicate the intent of a task.
In children with severe multiple impairment it will be important to assess the difference in functioning level between typical, everyday conditions and optimal conditions since from that difference a lot of information can be gathered about the direction modification or intervention strategies should take. This will provide information about the conditions which will facilitate learning.
Careful observation of the child's play and exploration style may give indication for the type of activities which will facilitate learning. If it is possible to tap into an existing skill or interest, the rate of learning will be much higher than with an imposed activity.
Before any intervention decisions are made, a lot of time needs to be spent in observation.
Children with CVI usually do not take well to an evaluation in an unfamiliar office setting. Although these setting may be perfectly suitable to interview the parents, it often does not provide enough opportunity for the direct observation of the coping strategies of especially the younger, multiply impaired child.
Checklists, completed by the parents as well as the teachers, can be helpful to determine a global functioning level.
Home and school visits can provide an opportunity for direct observation in a natural setting.
Video tapes can be very helpful. Care should be taken that the child is taped when doing well as well as when having difficulty, since the information is quite often in the difference between the circumstances.
Diaries and communication books, which travel with the child from the home to the school and vice versa also can provide useful information.
Observing differences in coping strategies between familiar and less familiar activities can give further indication about intervention strategies that are likely to be successful.
Whatever the source of the information, there are a number of important indicators to attend to when one wants to plan an intervention strategy.
One is the level of sustained attention the child is capable of. This should be evaluated for visual, auditory, as well as tactile activities.
The presence of object permanence is also important in knowing to which degree a child is able to maintain independent involvement with a task. A child who realizes that an object still must be there, although he can no longer see it, may engage in searching behavior and maintain attention longer than a child who loses interest as soon as the object is no longer obviously there.
If the ability to imitate is present, it will have a considerable effect on learning new skills. An extension of this skill is the ability to match, which will eventually lead to an ability to categorize and generalize.
The understanding of cause and effect is another significant factor in learning. This understanding can initially be seen in anticipatory behavior. Without demanding a specific response, one may observe a child become still, move, or laugh when a reaction to a certain action is expected.
The ability to indicate a choice is important in learning to communicate with others. Careful attention needs to be paid to the consistency of the choice. Many people are convinced that a child is capable of indicating a preference because, when asked, the child always points. However, often the child has learned that pointing is the required behavior rather than choosing.
Problems with spatial orientation can often be observed by watching the child move through a familiar environment versus an unfamiliar one. Watching what the child does when unexpected obstacles or empty spaces are encountered can give a lot of information about exploration techniques. Another skill to look for is the ability to locate people or objects in space. Some children seem to do much better when they or the object they are looking for are in motion, for others it appears to be the other way around, depending on the site of their lesion.
Investigating their ability to suppress unnecessary visual, but also auditory, information will help in determining how material is going to be presented and to which degree the child can be expected to adapt to an integrated learning setting.
A measure of how much exploration a child does in a given time unit, with and without direct intervention, may provide an estimate of the rate of learning a child is capable of and what the amount of one to one intervention should be.
One of the most important considerations with intervention strategies for children with CVI is not to intervene too quickly or too much. What we see is not so much what is there, but more the result of complex interactions of nerve cells. If groups of these cells are somehow damaged or altered, our perception and understanding of the world around us will change profoundly. Because we perceive reality differently from children with CVI it is very difficult to understand how they see and we cannot expect them to be "brought around to seeing things our way" by applying cookbook strategies, if at all.
A lot of time will have to be spent in observation and more passive forms of communication to be able to enter in some of their modes of perception. It is very easy to jump to conclusions too quickly and thus to miss certain behavioral expressions because they do not fit with what we know or how we see things. Trying to find explanations or even words for what we see too quickly could be risky because words flash freeze parts of observations and make it difficult to combine them with other observations. This may interfere with discovering something new. Words make us categorize our observations, and to do this we have to shave off the edges to make them fit into the category. If we start categorizing too quickly we do not know if what we discard is not what we need. Words also encourage us to ignore perceptions that cannot easily be put into language. However, this does not mean that we cannot or should not intervene at all.
Some of the suggestions for intervention will be more passive and deal more with improving the access to information, others will be more directed to the information itself. The list is by no means exhaustive or useful for every child with CVI. To be of any practical use, they will have to be adapted to the needs of the individual child.
In play the use of common objects may provide a greater amount of information than most commonly available toys. A large number of preschool toys are based on a visual similarity with common objects, which may be difficult to appreciate for a child with CVI.
Many toys are made of the same kind of plastic and differ little from each other in taste, smell, or tactile quality. Using, for instance, and orange instead of a plastic ball to encourage the child to roll an object back and forth, or using a metal pot and a wooden spoon rather than a plastic drum may encourage the children to stay longer with the objects because there is more to explore while they are exposed to the same abstract concepts, such as shape, size, cause and effect, etc.
Since most children with CVI have additional problems, they are usually exposed to a number of exercise programs, which may originate from different sources. It is important that these are not all carried out at the same time. A child who has to practice head or trunk control while having to concentrate at the same time on a visual task, may have little energy left to invest in vision. In addition, with poor head control the visual field will shift a great deal involuntarily. We found improvement in the visual attentiveness of children with poor head and trunk control with good trunk support and the use of a neck collar which holds the head upright, but still permits lateral movement.
Children with CVI do not seem to experience as much incidental visual learning as normally sighted children do, and therefore they have to maintain a much higher level of concentration to perceive. This requires a consistently high level of energy. Children with CVI therefore seem to tire much more quickly and may need more frequent rest breaks.
Many of them also show a tendency to "fade." Their ability to process any information seems to stop momentarily. This is sometimes mistaken for a seizure, but is not. Care should be taken that instruction is stopped during this moment and continued from the point just before where the child faded out, once the information processing continues, otherwise there will be a gap in the information which will complicate the learning process even further.
Some of these children may respond to stimulant medication, especially if part of the problem is related to a very low information processing speed. This will need to be addressed for each child individually with their pediatrician (Copeland and Copps, 1995).
The eye not only serves vision, but also plays a major part in establishing biological rhythms, by transmitting light through a visual subsystem. Sleep-wake rhythm disorders are therefore relatively common in the visually impaired, depending on the degree of visual loss (Sasaki et al., 1992).
The light-dark cycle is felt to be the strongest factor in the production of melatonin, a hormone secreted by the pineal gland. However, other factors, such as behavioral, social, nutritional, and environmental cues also play a role. Melatonin is secreted most actively at night and is suppressed by light in the morning.
A study done by Espezel, Jan, O'Donnell, and Milner (1996) showed that in their sample sleep disorders in children with CVI were much more frequent than in children with ocular disorders. Administration of synthetic melatonin proved successful in many of the children and the energy levels improved in them as well as their families. In several cases, if the melatonin was paired with well-structured sleep habits, the melatonin could be withdrawn, with maintenance of the sleep-wake rhythm.
Because of the complexity of their problems, children with CVI habitually are confronted with a large number of people who work with them. Since it is difficult for them to adapt to change because of their multiple perceptual difficulties, they may perceive similar tasks as quite different and learn them side by side with little transfer. (It is not uncommon to find a multiply handicapped child with CVI who is toilet trained in one setting, but not in another.) Extensive interaction between people involved in the education planning, including the parents, is therefore important to ensure continuity of the learning process. To reduce the number of people actively involved with the child, it may be helpful to combine training or exercise plans with some of the professionals functioning as consultants.
Introducing tasks or objects in a multisensory fashion, in a meaningful, natural sequence, will enhance the chances of recognition of a particular task in slightly different circumstances.
Clearly marking the beginning and the end of a task may make the transition from one activity to another easier.
The expectation a person has about what he is about to see in a given situation may to some degree affect the perceptual organization of what he is looking at, especially if that information is ambiguous. Children with CVI are therefore likely to be able to use their residual vision more effectively if the object they are expected to see belongs in the setting in which it is presented. The likelihood of visual recognition of a spoon or a plate during dinnertime is much higher than when it is pulled out of the bag of the vision teacher during visual stimulation time. Creating natural settings for the visual recognition can be a powerful aid in stimulating the use of vision.
There is some experimental evidence that combining color and shape may facilitate the perception of shape (Merril and Kewman, 1986). This could be used in teaching children to recognize objects by keeping the color and shape of the object constant until the object is recognized visually. Then it can be expanded to different colors or different forms of the same object.
For higher functioning children who do respond to some degree to pictures, simple shapes and only one picture to a page could be used. Unnecessary embellishment, which usually delights the normally sighted child, can confuse a child with CVI and could be painted out by recoloring the picture in bright colors.
Color coding with lines or dots could help children with mild CVI with finding their place in reading or seatwork assignments.
Beginning counters are likely to do better with well-spaced objects of a single color per object. However, with children who have a "Swiss cheese" visual field, one has to be careful that the objects are not partially or wholly in the blind spots. With them it may be easier to work entirely within their preserved islands of vision. They may need to group the material themselves after having it handed to them. Once they have placed it, continual visual access should not be assumed, since movement of the head is likely to change the field.
For higher functioning children, who are able to read, the use of masks to block off the line above as well as below may help in avoiding perceptual confusion. Increasing the spaces between lines and words may have a similar effect.
Some children may be quite high functioning, but do not have sufficient shape recognition ability to make reading a feasible option. For them reading braille may be a better alternative.
In drawing, tracing the outlines of the figures first and verbalizing the changes of direction may assist the children with the perceptual processing.
Some children with CVI seem to be able to perceive moving objects better than stationary ones, while for others it is the other way around, depending on which area of the visual cortex is affected. These children may be able to navigate around objects without ever bumping into them, but they may have great difficulty with perceiving shapes. In our clinic we have a boy who is able to ride a bicycle in traffic, but he cannot discriminate between pictures or shapes or place pegs in a pegboard without using touch. He is aware of objects and seems to know what they are if he is in motion or if they are. However, he has not been able to learn to read print, and he is currently a braille reader.
A regular classroom setting with all of its richness in auditory and visual stimulation may be too complex for consistent learning for children with CVI. Reduction of auditory and visual stimulation will enable the child to focus better on the required task and will save energy.
Many children with CVI are mistakenly labeled as having an attention deficit disorder. When their visual environment is too complex, it is not accessible to them, and they quickly lose interest. This is not the same as a child who is unable to maintain attention under normal access conditions.
Some children may start to display self stimulating behavior when they are under stimulated because there is nothing in their present environment that is accessible to them. Others may show self stimulating behavior because they are overloaded by the level of stimulation. In either case these children will need direct intervention to be able to continue to process what is going on around them.
Partial or reverse integration may offer more opportunity for social, emotional, and cognitive development than full integration. Of course these decisions have to be made for each child individually and the overall functioning level as well as available alternatives need to be taken into account.
Many children with CVI, because of the complexity of their disabilities, will not be able to live independently. However, those children all will become employers of caregivers and, within this function, have an effect on the job satisfaction of those looking after them. Social interactive skills therefore should have great emphasis when planning a curriculum. People who are able to acknowledge another person, at however a simple level, tend to receive more compassionate care than those who don't. The frequency of interaction and with that, stimulation, is likely to increase when a person is able to show pleasure because of someone's presence or at having a need met. With greater job satisfaction on behalf of the employee, turn-over is likely to be lower, and with that, the continuity of care, more consistent. As educators it is our duty to make these children into the best employers of caregivers they can be. Care should be taken that the individual education plans for them are not driven by curriculum demands of typical children and that they acquire skills which will be functional in their everyday life at a later date.
Children with CVI differ a great deal from each other, because of variation in the site of the lesion and the complex interaction of CVI with additional disabilities. Due to the nature of the original brain insult, many children will have more than one specialized subsystem of the visual cortex affected to varying degrees, which makes generalizations with regards to potential visual function even more difficult. Careful observation in a multitude of settings, in addition to more standardized assessment procedures, is therefore very important in the planning for an individual child. This paper has attempted to describe some of the features children with CVI may share, but it is by no means exhaustive, nor may an individual child display all features. Continued study and exchange of experiences is essential for understanding this group of children better.
Cannao, M., Morretti, G., & Ricci, A. (1986). Complex visual problems in childhood. Neuro-ophthalmology, 6, 321-327.
Copeland, E. D., & Copps, S. C. (1995). Medications for attention disorders (ADHD/ADD) and related medical problems. Plantation Florida: Specialty Press Inc.
Crick, F. (1994). The astonishing hypothesis. New York: Simon and Schuster.
Espezel, H., Jan, J. E., O'Donnell, M. E., & Milner, R. (1996). The use of melatonin to treat sleep-wake-rhythm disorder in children who are visually impaired. Journal of Visual Impairment and Blindness. 90(1), 43-50.
Good, W.V., Jan, J. E., DeSa, L., Barkovich, A.J., Groenveld, M., & Hoyt, C. S. (1994). Cortical visual impairment in children. Survey of Ophthalmology. 38, 351-364.
Groenveld, M., Jan, J. E., & Leader, P. (1990). Observations on the habilitation of children with cortical visual impairment. Journal of Visual Impairment and Blindness. 84, 11-15.
Groenveld, M. (1990). The dilemma of assessing the visually impaired child. Developmental Medicine and Child Neurology. 32, 1105-1113.
Jan, J. E., & Wong, P. K. (1994). Behavior of the alpha rhythm in electoencephalograms of visually handicapped children. Developmental Medicine and Child Neurology. 30, 444-450.
Jan, J. E., Groenveld, M., & Sykanda, A. M. (1990). Lightgazing by visually impaired children. Developmental Medicine and Child Neurology. 32, 755-759.
Jan, J. E., & Groenveld, M. (1990). Visual behaviors and adaptations associated with cortical and ocular impairment in children. Journal of Visual Impairment and Blindness. 87, 101-105.
Jan, J. E., Groenveld, M., & Anderson, D. P. (1993). Photophobia and cortical visual impairment. Developmental Medicine and Child Neurology. 35, 473-477.
Lambert, S. R., Hoyt, C. S., Jan, J.E., Barkovich, J., Flodmark, O., (1987). Visual recovery from hypoxic cortical blindness during childhood. Archives of Ophthalmology. 105, 1371-1377.
Merrill, M. K., & Kewman, D. G. (1986). Training of color and form identification in cortical blindness: A case study. Archives of Physical Medicine and Rehabilitation. 67, 479-483.
Rizzo, M., & Hurtig. (1987). Looking but not seeing: Attention, perception and eye movements in simultanagnosia. Neurology. 37. 1642-1648.
Sasaki, H., Nakata, H., Murakami, S., Uesegi, R., Harada, S., & Teranishi, M. (1992). Cicadian sleep-waking rhythm disturance in blind adolescents. Japanese Journal of Psychiatry and Neurology. 27, 730-739.
Whiting, S., Jan., J. E., Wong, P.K.H., Flodmark, O., Farrell, K., & McCormick, A. Q., (1985). Permanent cortical visual impairment in children. Developmental Medicine and Child Neurology. 27, 730-739.
Zeki, S. (1992). The visual image in mind and brain. Scientific American. 257, 69-76.