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Cortical or cerebral visual impairment in children: a brief overview.

The brain is intricate in its design and function. Neuroscientists and neuropsychologists are revamping concepts and principles that are related to brain function and vision as more information is obtained and understood. The changes that are emerging from brain research are altering our understanding of cortical or cerebral visual impairment (CVI) in children. In addition, injury to the brain can result in functional manifestations that are complex and multifaceted. These functional manifestations are related to the extent, location, and time of onset of the brain lesions, but the precise effects of these injuries cannot be readily and fully predicted in children from the brain lesions themselves. For example, we have no idea of the ways in which areas of the brain that are intact in young children who have brain damage assume the functions of damaged areas owing to the plasticity of the brain. Thus, an understanding of recovery mechanisms for CVI in children and of the effects of intervention is in its infancy. As a result, our understanding of the nature of CVI in children must be open and flexible as we incorporate and learn to apply an ever-evolving knowledge base. We must understand the issues surrounding CVI, embrace their complexity and lack of closure, and determine directions for the effective diagnosis and treatment of children with CVI from medical and educational perspectives.

WHAT IS CVI?

The story of CVI that is due to brain injury began in the late 19th century with the emergence of the concept that vision was associated with brain function, most notably with the operations of the occipital cortex. As Hoyt (2003) noted, permanent field loss came to be associated with damage to the visual cortex through work conducted by neurologist Gordon Holmes with veterans who were injured during World War I. There were puzzling discrepancies even at that time, since Gordon Riddoch, of the Royal Army Medical Corps, found that some World War I veterans with injuries to the occipital cortex could perceive motion in their "nonseeing" visual field. This ability to detect motion as well as other visual events in the nonseeing visual field has been called blindsight. Blindsight is awareness of moving targets, lights, and colors in the blind area, and this awareness can be either conscious or subconscious (called statokinetic dissociation or the Riddoch phenomenon in adults). It is difficult to determine in children because of their young age and co-occurring impairments (Boyle, Jones, Hamilton, Spowart, & Dutton, 2005).

Before the 1980s, the absence of sight that is due to bilateral damage to the occipital cortex was called cortical blindness. This term was derived from studies of adults, but was applied to children as well. Cortical blindness, however, was considered to be rare in children, according to Hoyt (2003). Many children with visual impairments that were due to brain damage recovered their visual function and were not totally blind (Hoyt, 2003; Whiting et al., 1985). In the late 1980s, the term cortical blindness gave way to the term cortical visual impairment or CVI.

At that time, the generally accepted definition of CVI was damage to the visual system between the lateral geniculate nucleus and the visual cortex. A reduction in visual acuity was the way that CVI was identified (Jan & Groenwald, 1993). Basically, the eyes appeared to be normal, yet there was diminished visual acuity because of a diagnosed brain damage. Later, it became more common in the literature to find that CVI often co-occurred with other visual conditions, as was mentioned earlier (Good, Jan, Burden, Skoczenski, & Candy, 2001).

Visual behaviors and perception related to damage to other areas in the brain were not considered "cortical," and thus children with damage outside the cortex were not included under the CVI umbrella. As researchers learned more about brain damage and visual impairment, they found that periventricular leukomalacia (PVL), damage to the white matter surrounding the ventricles in the brain, was a common cause of visual impairment in children who were born preterm (Jacobson, Lundin, Flodmark, & Ellstrom, 1998). Consequently, there was a call for the adoption of the term cerebral visual impairment, particularly in Europe. This term was proposed because damage to the brain outside the cortex could cause both visual impairment and oculomotor problems. In addition, the inclusion of the visual field, as well as visual perceptual factors, was proposed in the diagnosis of cerebral visual impairment (Jacobson, Ek, Ygge, & Marburg, 2004).

Some researchers have indicated that cognitive visual dysfunction (CVD) should be the term used for visual perceptual deficits that are related to brain damage (Good et al., 2001). There are other subtleties that may play a role in the refinement of terms related to visual impairment or visual dysfunction and brain damage. Colenbrander (2009), who has helped develop terminology related to visual impairment for the World Health Organization, attempted to tease out terminological issues pertaining to visual impairment and visual dysfunction associated with brain damage. He considered ocular visual impairment to be associated with optical and retinal problems; cerebral visual impairment to be associated with pathway problems, cortical problems, and oculomotor problems; and visual dysfunction to be associated with higher-order processing areas in the brain that serve vision for action (dorsal stream) and vision for recognition (ventral stream), as derived from the work of Dutton (2003). A visual dysfunction can co-occur with a visual impairment.

It should be obvious that terminology related to CVI has yet to be resolved, but it will be resolved over time. This point is important because definitions affect (1) the ways in which demographic data are collected for children who have this visual impairment or dysfunction that is due to brain damage, (2) the way CVI is diagnosed (if more than acuity is considered in the diagnosis, as in the traditional diagnosis for cortical visual impairment), (3) the type of personnel who will deliver intervention strategies to ameliorate its effects, and (4) the training that these interventionists receive in personnel preparation programs.

HOW DOES CVI MANIFEST IN CHILDREN?

The effects of brain damage on visual performance are much more far reaching than was initially thought (Dutton, 2003; Dutton & Jacobson, 2001; Hyvarinen, 2004; Jacobson & Dutton, 2000). CVI can have profound effects associated with severe visual impairment along with other co-occurring physical conditions. But in some cases, neurological problems may be subtle, visual acuity may not be affected, and the diagnosis of visual impairment or dysfunction that is due to brain damage may not be suspected. One group has labeled it "cryptic" or hidden CVI (Lowery, Atkinson, & Lambert, 2006).

Vision is complex and is not limited to one segment of the brain, the visual cortex. There are pathways from the visual cortex to other areas of the brain, and some pathways go to other areas of the brain before they even reach the visual cortex (Hyvarinen, 2004). Because of these intricate neural networks, if there is brain damage, there may still be vision. But the quality of that vision can be extremely varied, depending on the location, extent, and age of onset of the brain damage, as was mentioned earlier. Researchers are now identifying complex neural systems and their effects. Dutton (2009) described the effects of CVI in terms of dorsal stream (the "where" system) and ventral stream (the "what" system) functions. Dorsal stream dysfunction is thought to be more common than ventral stream dysfunction in children, and ventral stream dysfunction is usually associated with dorsal stream dysfunction. Also under examination is the impact of damage to the mirror neuron system, which has been shown to be involved in the observation and imitation of goal-directed action (Hyvarinen et al., 2010).

CVI can have a wide variety of effects, and how they manifest must be carefully evaluated. It is also critical to examine the effects of ocular visual impairment to differentiate functional issues arising from ocular visual impairment from those arising from CVI. Box 1 lists some effects of CVI described by Dutton (2003).

Data indicate that recovery for children with CVI also varies, but more research is needed. For children, recovery is equated with improvement in functioning equivalent to functional levels had there been no brain injury, taking into account developmental changes (Morris, Fletcher, & Francis, 2002). Hoyt (2003) reported that the pattern of brain damage and recovery is different for children with PVL than for those with damage to the primary striate cortex. Others have noted different patterns of recovery for children with various types of brain injury (Mercuri et al., 1997, for basal ganglion disorders; Ek, Fellenius, & Jacobson, 2003, and Jacobson & Dutton, 2000, for improved optotype acuity for PVL).
Box 1.

SOME EFFECTS OF CVI IN CHILDREN (ADAPTED FROM DUTTON, 2003)

Visual acuity

* Commonly reduced, but can be normal

Color and contrast sensitivity

* Can be normal, but both are likely reduced in most profound
injuries

Visual fields: depends on the site of damage

* Homonymous hemianopia (same side of the visual field affected for
each eye)

* Bilateral lower visual field loss commonly associated with
periventricular leukomalacia

* Impaired ability to see two targets at the same time leads to
impaired attention (this and the next item may give the impression
of a visual field restriction) * Difficulty estimating depth
(particularly moving feet through depth)

* Functional visual field may vary depending upon the amount of
visual stimuli present and the degree of attention paid to the
fixation target in "formal" field testing

Control of eye movement

* Eye motility problems

* Strabismus

* Nystagmus

* Unstable fixation

* Inaccurate fast eye movements

* Deficient following eye movements (smooth pursuit)

* Eyes intermittently deviate, usually upward (paroxysmal
deviations)

* Problems with visually guided eye movements compensated for by
using head movements

* Difficulty watching moving targets (children with CVI commonly
prefer TV shows with limited motion)

Accommodation disorders

* Incomplete accommodation to compensate for usual hyperopia
(farsightedness) found in young children so that the retinal image
is blurred

Perception of movement

* Impaired or absent perception of movement

* See only stationary objects

* See only moving objects

Visually guided movement concerns

* Difficulty moving through space

* Difficulty seeing boundaries on floors

* Difficulty negotiating curbs, stairs

* Inaccurate reach and grasp

* Motor planning

Object recognition

* Inability to recognize objects, shapes, faces, facial expressions

* Difficulty with route finding

* Difficulty with visual-memory tasks, such as copying

Visual attention and visual perception

* May have the ability to see but not use vision, especially when
tired, sick, or upset or after taking certain medications

* May not use vision to see in a particular area of vision

* May have difficulty seeing in a visually crowded environment,
either up close or at a distance

* May have difficulty separating foreground from background

Global picture versus details

* May attend to the details of an object rather than to the whole
object itself


WHO ARE THE CHILDREN WITH CVI?

Dutton (personal communication, June 10, 2008) suggested four categories of children with visual impairments that are due to brain injury. The first category includes children with cerebral blindness who have blindsight. In their retrospective analysis of 541 children aged 2 to 19 in the United Kingdom (Boyle et al., 2005), 19 of the 32 children who had no light perception or had light perception only showed a response to movement. Four of the 70 children with hemianopia had response to movement, especially noted in the peripheral field. There may be several anatomical sources for blindsight. The second category includes the population of children who have significant visual acuity or visual field impairment with no visual perceptual impairment. The third category consists of children who have significant visual acuity or visual field impairment with a visual perceptual impairment. An incomplete diagnosis for these children can affect our understanding of their functional vision, their self-understanding, and the efficacy of educational intervention approaches. The fourth category includes children who do not have the traditionally recognized hallmarks of visual impairment--reduced visual acuity or reduced visual fields--but who have a visual perceptual impairment. The primary disability of these children involves the processing of visual information. These children, according to Hoyt (2007, p. 1287), "are often misdiagnosed or even ignored because of the apparent contradictory findings of little or no visual acuity and field loss in the presence of significant and often ill-understood visual complaints." These children are the ones who fall through the cracks of the current educational-medical system.

In terms of numbers, it is safe to say that CVI is the major cause of visual impairment in children who reside in high-income countries (Gogate & Gilbert, 2007; World Health Organization, 2010). The incidence of CVI has been increasing because of improved medical care for children who were born prematurely and for children who were born with severe medical conditions (Good et al., 2001). The prevalence of children with CVI in samples of children with visual impairments has varied, and the differences may be the result of the definition of CVI; the age at which CVI is reported, since CVI may be diagnosed at a later age than other visual impairments (Hatton, Schwietz, Boyer, & Rychwalski, 2007); and differences in reporting mechanisms (Flanagan, Jackson, & Hill, 2003). In addition, most demographic data do not include children with visual processing issues who do not have visual impairments as defined by limitations in visual acuity and visual field.

WHAT ARE THE MAJOR EDUCATIONAL ISSUES RELATED TO CHILDREN WITH CVI?

Education begins with informed teaching. Teachers must understand the current literature on CVI that takes into account the various ways in which brain damage can affect vision in children. For them to do so, information about CVI must be incorporated into the curriculum of personnel preparation programs for beginning teachers and into in-service programs for veteran teachers. Teaching staff from a variety of disciplines must be exposed to information about CVI, since it can be present in children who may not fit the traditional definition of visual impairment and may be under-diagnosed in children who have multiple disabilities. Such children may be served by educational psychologists; teachers of students with visual impairments; orientation and mobility specialists; teachers who work with students who have mild to severe disabilities, including those with learning disabilities and autism spectrum disorder; and speech-language therapists, occupational therapists, and physical therapists.

Methods to identify the broad array of children with CVI must be introduced and validated. Efforts are underway to do this (see, for example, Roman-Lantzy, 2007; Dutton, 2003). In addition, children need to be identified as early as possible (Dutton & Jacobson, 2001; Good et al., 2001), with concomitant early intervention. In a survey of international groups assessing children with CVI, Lueck (2008) found that more than 400 assessment tools were used to pinpoint the visual functions and functional vision concerns of children with CVI because of the many possible effects of the condition. The tools to use and how best to implement them must be determined and disseminated to the field, along with any data that authenticate their applicability to children with CVI. In addition to the need for more valid and reliable measurement tools that are tied to the results of current research, many specialists in CVI recognize the need for the multidimensional assessment of children with CVI developed by cross-disciplinary and coordinated assessment teams owing to the complex array of effects (Jacobson & Dutton, 2000).

In addition to multidimensional assessments, there is the need for multidimensional interventions. Evidenced-based interventions for children with CVI are rare in the literature (Lueck, 2006). Interventions must go beyond the use of adaptations and sensory substitutions and include training of visual skills and behaviors and perhaps looking at methods that are used with adults (see, for example, Kingston, Katsaros, Vu, & Goodrich, 2010) and modifying these techniques for children, as well as developing specific methods for children that can lead to improved functioning when applied to tasks of daily living in the home, school, and community.

WHAT IS THE IMPACT OF CVI ON CHILDREN AND THEIR FAMILIES?

CVI is a relatively "new" phenomenon with a growing list of ramifications that are beginning to be understood. But children and families must address the behavioral consequences of CVI on a daily basis. CVI can be socially isolating for children who do not recognize faces or facial expressions. For children with visual processing disorders and near-normal acuity, it can be distressing to fall behind peers in the process of reading but to understand the content. For all children with CVI, making constant adjustments to accommodate visual needs must be both demanding and tiring. For families, it can be confusing and frustrating as they try to understand and meet the special needs of their children and plan for their children's future. Explanations of the underlying reasons for atypical behaviors can assist in the establishment of realistic expectations and goals within social contexts for education and for life planning.

WHERE DO WE GO FROM HERE.?

There are many unanswered questions about CVI in children at this time, and more research is needed related to both the medical and educational aspects of the condition. This research includes the need to (1) understand neural mechanisms that are affected when there is diffuse as opposed to localized brain damage, and the long-term consequences of each; (2) determine more specific correlations between structure and function, that is, different locations of brain insults and their functional effects; (3) identify any short-term and long-term effects of interventions on brain function and recovery; (4) pinpoint specific assessment methodologies and techniques that address the array of functional consequences of CVI for the different populations of children with brain injury; and (5) develop evidence-based interventions that include training in visual skills and behaviors, as well as adaptations and sensory substitutions that improve the quality of life of children with CVI and their families.

REFERENCES

Boyle, N. J., Jones, D. H., Hamilton, R., Spowart, K. M., & Dutton, G. N. (2005). Blindsight in children: Does it exist and can it be used to help the child? Observations on a case series. Developmental Medicine & Child Neurology, 47, 699-702.

Colenbrander, A. (2009). The functional classification of brain damage-related vision loss. Journal of Visual Impairment & Blindness, 103, 118-123.

Dutton, G. N. (2003). Cognitive vision, its disorders and differential diagnosis in adults and children: Knowing where and what things are. Eye, 17, 289-304.

Dutton, G. N. (2009). "Dorsal stream dysfunction" and "dorsal stream dysfunction plus": A potential classification for perceptual visual impairment in the context of cerebral visual impairment. Developmental Medicine & Child Neurology, 51, 170-172.

Dutton, G. N., & Jacobson, L. K. (2001). Cerebral visual impairment in children. Neonatology. 6, 477-485.

Ek, U., Fellenius, K., & Jacobson, L. (2003). Reading acquisition, cognitive and visual development, and self-esteem in four children with cerebral visual impairment. Journal of Visual Impairment & Blindness, 97, 741-754.

Flanagan, N. M., Jackson, A. J., & Hill, A. E. (2003). Visual impairment in childhood: Insights from a community-based survey. Child: Care, Health, and Development, 29, 493-499.

Gogate, P., & Gilbert, C. (2007). Blindness in children: A worldwide perspective. Community Eye Health, 20(62), 32-33.

Good, W. V., Jan, J. E., Burden, S. K., Skoczenski, A., & Candy, R. (2001). Recent advances in cortical visual impairment. Developmental Medicine & Child Neurology, 43, 56-60.

Hatton, D. D., Schwietz, E., Boyer, B., & Rychwalski, P. (2007). Babies count: The national registry for children with visual impairments, birth to 3 years. Journal of the American Association of Pediatric Ophthalmology and Strabismus, 11, 351-355.

Hoyt, C. S. (2003). Visual function in the brain-damaged child. Eye, 17, 369-384.

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Hyvarinen, L. (2004). Understanding the behaviours of children with CVI. Retrieved from http://www.aph.org/cvi/articles/hyvarinen_l.html

Hyvarinen, L., Appleby, K., Bernas-Pierce, J., Dennison, E., Jackel, B., Lueck, A. H., & Morse, M. (2010). Understanding the complexity of cerebral/cortical visual impairment. AER Report, 27(2), 26-27.

Jacobson, L. K., & Dutton, G. N. (2000). Periventricular leukomalacia: An important cause of visual and ocular motility dysfunction in children. Survey of Ophthalmology, 45(1), 1-13.

Jacobson, L., Ek, U., Ygge, J., & Marburg, M. (2004). Visual impairment in children with brain damage: Towards a diagnostic procedure? Developmental Medicine & Child Neurology, 46, 67-69.

Jacobson, L., Lundin, S., Flodmark, O., & Ellstrom, K. (1998). Periventricular leukomalacia causes visual impairment in pre-term children: A study on the aetiologies of visual impairment in a population-based group of preterm children born 1989-95 in the county of Varmland, Sweden. Acta Ophthalmologica Scandinavia, 76, 593-598.

Jan, J. E., & Groenwald, M. (1993). Visual behaviors and adaptations associated with cortical visual and ocular impairment in children. Journal of Visual Impairment & Blindness, 87, 101-105.

Kingston, J., Katsaros, J., Vu, Y., & Goodrich, G. L. (2010). Neurological vision rehabilitation: Description and case study. Journal of Visual Impairment & Blindness, 104, this issue.

Lowery, R. S., Atkinson, D., & Lambert, S. R. (2006). Cryptic cerebral visual impairment in children. British Journal of Ophthalmology, 90, 960-963.

Lueck, A. H. (2006). Issues in intervention for children with visual impairment or visual dysfunction due to brain injury. In E. Dennison & A. H. Lueck (Eds.), Proceedings of the Summit on Cerebral/Cortical Visual Impairment: Educational, Family, and Medical Perspectives, April 30, 2005 (pp. 121-130). New York: AFB Press.

Lueck, A. H. (2008). Final report for the Vice President's Assigned Time Award: Developing a comprehensive educational assessment model to evaluate the needs of children with cerebral visual impairment. Unpublished manuscript, Department of Special Education, San Francisco State University.

Mercuri, E., Atkinson, J., Braddock, O., Anker, S., Cowan, F., Rutherford, M., Pennock, J., & Dubowitz, L. (1997). Visual function in full-term infants with hyposixischaemic encephaolopatyhy. Neuropediatrics, 28, 155-161.

Morris, R. D., Fletcher, J. M., & Francis, D. J. (2002). Conceptual and psychometric issues in the neuropsycholgic assessment of children: Measurement of ability discrepancy and change. In S. Sigalowitz & I. Rapin (Eds.), Child neuropsychology, Vol. 8, Part I, of Handbook of neuropsychology (2nd ed., pp. 217-227). Amsterdam: Elsevier.

Roman-Lantzy, C. (2007). Cortical visual impairment: An approach to assessment and intervention. New York: AFB Press.

Whiting, S., Jan, J. E., Wong, P. K. H., Flodmark, O., Farrell, K., & McCormick, A. (1985). Permanent cortical visual impairment in children. Developmental Medicine & Child Neurology, 27, 730-739.

World Health Organization. (2010). Childhood blindness. Retrieved from http://www.who.int/blindness/causes/priority/en/index4.html

Amanda Hall Lueck, Ph.D., professor and coordinator, Program in Visual Impairments, Department of Special Education, San Francisco State University, 1699 Holloway Avenue, San Francisco, CA 94132; e-mail: <amandal@sfsu.edu>.
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Author:Lueck, Amanda Hall
Publication:Journal of Visual Impairment & Blindness
Article Type:Report
Date:Oct 1, 2010
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