Author: Jan, James E
Date published: February 1, 2011
Cortical Visual Impairment Is Not the Same as Cerebral Visual Impairment
James E. Jan
The entire October 2010 issue of the Journal of Visual Impairment & Blindness (JVIB) was devoted to children and adults with visual disorders caused by brain abnormalities. JVIB and all the authors should be congratulated for their contributions. It was a pleasure for me to note the increasing interest and the progress made in this neurological condition since the early 1980s, when individuals like myself tried to convince professionals to pay attention to children who had various visual problems due to brain damage. However, I do have some concerns about a few misunderstandings that have surfaced in this issue.
It should be pointed out that the term cerebral visual impairment, which was introduced by a group of European ophthalmologists, was born out of a major neurophysiological misconception. This group felt that cerebral visual impairment was a more appropriate term than cortical visual impairment (both terms were abbreviated as CVI). The reasons for this were stated in the October issue of JVIB: "Since the optic radiations are not part of the cortex, and since periventricular leucomalacia (injury to white matter of the brain-tissue containing nerve fibers) is a frequent finding in children with CVI, the anatomical designation of cerebral is a more inclusive designation" (Colenbrander, 2010, p. 583). This statement is highly problematic from the neurophysiological point of view.
Major progress has been made during the last 20 years in understanding human cognition. In general terms, environmental and perceptual information is transduced and encoded into electrical synaptic activity. In this process, groups of neurons communicate with a vast number of other neuronal assemblies, including the thalamus, by high frequency electrical oscillations. Cognition requires this type of coordinated communication and "connectivity" between myriads of neuronal assemblies and the thalamus, through which various regions of the brain are connected to each other (Ribary, 2005). The nerve fibers in the white matter conduct these oscillatory signals and when they are interrupted by injury, cortical dysfunction and neuronal death may occur. Even the alpha rhythms seen in waking electroencephalograms are the result of oscillations mainly between occipital neurons and the thalamus. These rhythms are the electrical signatures of vision, including visual acuity (Cantero et al., 2009), and when such communication is abolished by brain damage, acuity and fields are adversely affected. It can no longer be postulated that specific centers in the brain are entirely responsible for complex physiological mechanisms. It needs to be strongly emphasized, therefore, that visual functions including acuity are cortical in nature, that is, they originate from the cortex. The cortex (gray matter) is a folded sheet of neuronal tissue covering the cerebrum. It consists of layers of unmyelinated neurons that play a key role in language, memory, and vision - including acuity, attention, executive brain functions, and consciousness - and its destruction results in a vegetative state. Our neurological predecessors were indeed correct when they considered visual loss or impairment due to brain damage to be neuronal and cortical.
Proponents of the term cerebral visual impairment made another major mistake by restricting visual function and visual disorders to the cerebrum. The term cerebral excludes numerous areas of the brain that are anatomically outside the cerebrum but still very much involved in vision. Examples of these are the cerebellum, the limbic system, the brain stem, and even the autonomic nervous system. For instance, there are important visual pathways from the eyes to the hypothalamus that modulate circadian rhythmicity. The amygdala of the limbic structures, which closely participates in the formation of emotions, is also involved in visual cognition and visual memory. These structures are outside the cerebrum anatomically but not functionally. Vision is a highly complex cortical function that is influenced by circadian rhythms, environmental factors, sleep loss, emotions, illness, medications, neurotransmitters, neuromodulators, a very large number of genes, and numerous other factors. Thus, it is highly incorrect to restrict vision and its disorders to the cerebrum because literally the entire brain is involved in this process.
A useful term requires a clear definition. Cerebral visual impairment, however, cannot be accurately defined because it is an umbrella term. It includes a huge variety of vastěy different visual disorders that not only present clinically in different ways but require vastly different management techniques. Lumping together different visual disorders under one diagnostic label does not help a patient obtain more appropriate services. Amanda Hall Lueck and Gregory L. Goodrich in their Guest Editorial of that issue of JVIB (p. 579) said it so clearly: "Terminology is also a significant issue that must be considered by me medical, réhabilitation, and special education communities. Terminology affects the ways in which education and rehabilitation treatment and programs are developed. . . ." Do neurologists lump together the diagnosis of epilepsy, headaches, and strokes; do ophthalmologists lump together glaucoma, ocular malignancies, or cataracts? No! So why should professionals in vision services lump together vastly different conditions? It would make much more sense to carefully describe individual conditions, characterize them, apply an appropriate definition, and design optimal management techniques.
Furthermore, it was most disturbing mat cerebral and cortical visual impairments were equated with each other by some contributors to the October issue of JVlB. During the last 30 years, the definition of cortical visual impairment has always included the phrase bilateral loss or impairment of visual acuity or fields even though it was almost always associated with numerous other visual and nonvisual problems. The definition of cortical visual impairment was further explained in a statement in this journal, which defined it as "impaired vision that is due to bilateral dysfunction of the optic radiations or visual cortex or both" (Roman et al., 2010, p. 69). The purpose of this definition was to categorize a group of individuals who had a specific visual disorder and required special medical and educational management. It is imperative that the medical, rehabilitation, and special education communities separate individuals with cortical visual impairment from those who have typical visual acuity or fields but have other visual disorders, because the management of such cases require vastly different services. This is where the term cortical visual impairment is so useful! The proper management of individuals with a loss (inefficient) or impairment in their visual acuity or fields requires a great deal of training, understanding what vision is, experience, and a special set of skills. These management techniques are less beneficial to disabled "sighted" children who have global intellectual deficits, various neurodevelopmental syndromes and autism, or visuomotor difficulties. We know that these conditions are associated with impaired visual components and according to the vague umbrella term of cerebral visual impairment they belong under this category. Are the proponents of the term cerebral visual impairment suggesting that special education teachers with the same training should treat all varieties of vastly different neurological visual conditions? If they are, it is a totally unrealistic concept.
The introduction of the inappropriate term, cerebral visual impairment, has already created much confusion and unfortunately will continue to create confusion until it dies a natural death. I would like to suggest that JVIB, by publishing some neurophysiological and so-called connectivity studies on visual functions, should promote better understanding of disturbed vision due to brain damage. This would lead to improved diagnostic terminology, more accurate diagnosis of many neurological visual disorders, and better management.
Cantero, J. L., Atienza, M., Gomez-Herrero, G., Cruz-Vadell, A., Gil-Neciga, E., Rodriguez-Romero, R., et al. (2009). Functional integrity of thalamocortical circuits differentiates normal aging from mild cognitive impairment. Human Brain Mapping, 30, 3944-3957.
Colenbrander, A. (2010). What's in a name? Appropriate terminology for CVI. Journal of Visual Impairment & Blindness, 104, 583-585.
Hall Lueck, A., & Goodrich, G. L. (2010). Guest editors' page. Journal of Visual Impairment & Blindness, 104, 579-582.
Ribary, U. (2005). Dynamics of thalamocortical network oscillations and human perception. Progress in Brain Research, 150, 127-142.
Roman, C, Baker-Nobles, L., Dutton, G. N., Luiselli, T. E., Flener, B. S., Jan, J. E., et al. (2010). Comment: Statement on cortical visual impairment. Journal of Visual Impairment & Blindness, 104, 69-72.
James E. Jan, M.D., FRCP(C), senior research scientist emeritus, Diagnostic Neurophysiology, BC Children's Hospital, 4480 Oak Street, Vancouver, BC, V6H 3Nl, Canada; e-mail: <firstname.lastname@example.org>.
Response to the Letter to the Editor from James E. Jan
Amanda Hall Lueck and Gregory L. Goodrich
As mentioned in our comments as guest editors of the JVIB Special Issue on Vision and the Brain, terminology is a changing and unresolved issue associated with visual disorders due to brain anomalies. To date, terminology has not yet been definitively established by the entire international medical community. Since there are differences in medical opinion on appropriate terminology, we presented an overview of current terms for readers of the journal. Rather than confuse the readers of JVIB, our intent was to inform them so that readers could be made aware that such terminology is under scrutiny and under debate. Our intent was to present the full range of issues associated with vision and the brain despite the lack of clear-cut terminology at this time.
We welcome the thoughtful letter from James Jan, who pioneered work with children with cortical visual impairment (CVI) and whom we admire and respect greatly. His letter offers additional insight into the ever-evolving issue of terminology. We anticipate that future issues of JVIB will contain comments from other medical professionals surrounding these issues and urge readers to continue following these important discussions.
What we believe is most critical for educators and rehabilitation personnel to understand at this juncture is that there is a full spectrum of issues that can arise for children and adults who have vision problems due to brain injury. Visual sequelae to brain damage have been documented to include more than visual acuity and visual field limitations. Children and adults with vision disorders due to brain injury can have varied visual issues associated with visual functions, visual-cognitive limitations, and visualmotor consequences. These consequences may also have psychological ramifications that affect the child or adult and their families. As a result, their cases cannot and should not be solely addressed by teachers of students who are visually impaired, vision rehabilitation therapists, low vision therapists, or orientation and mobility specialists. Each individual case is unique and may also require input from occupational therapists, physical therapists, speech-language pathologists, recreation therapists, general education teachers, various special education teachers, psychologists, neurologists, ophthalmologists, optometrists, and others. We emphasized in our commentary in the special issue that the populations under discussion require comprehensive assessments from all specialists whose necessary expertise may be to provide the multidimensional interventions required by each individual.
William Good (2009) a noted pediatric ophthalmologist has stated: "Whether neurologic vision loss is termed 'cortical visual impairment', 'cerebral visual impairment', or 'retrogeniculate visual impairment' matters less than understanding its pathogenesis and many manifestations" (p. 663). Terminology, from the perspectives of our education and rehabilitation experiences, is of course important. We look forward to the eventual closure of the discussion on terminology by the medical community when the most appropriate term or terms are selected for neurologic vision loss.
However the terminology debate is resolved, our belief is that it is secondary to the fact that children and adults with vision disorders due to brain injuries are increasing in number. These individuals must be identified so they may receive comprehensive and appropriate assessments and services. These services should include their family and other supporting individuals. Unless we take into account the full gamut of possible effects of damage to the visual and associated areas of the brain, the provision of a full range of services will not happen.
Good, W. V. (2009). Cortical visual impairment: New directions. Optometry & Visual Science, 86(6), 663-665.
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: <email@example.com>. Gregory L· Goodrich, Ph.D., supervisory research psychologist and coordinator, Optometrie Clinical Research Program, Psychology Service and Western Blind Rehabilitation Center, VA Palo Alto Health Care System, 3801 Miranda Avenue, Palo Alto, CA 94304; e-mail: <gregory. firstname.lastname@example.org>.
Further Response to the Letter to the Editor from James E. Jan
Dr. Jan's Letter to the Editor has prompted me to respond from the point of view of terminology. Dr. Jan's opinions deserve attention, since the fact that the field of cerebral vision disorders is presently well recognized and that brain injury-related vision loss was considered worthy of a special issue of this journal is due in no small part to his efforts.
One of Dr. Jan's objections to the term cerebral visual impairment is that it is an "umbrella term." This is true, as it is true for its counterpart: ocular visual impairment. I have never heard the argument that the umbrella term ocular visual impairment is unfortunate, since it would detract from a more detailed diagnosis. The umbrella term cerebral visual impairment is not a definitive diagnosis either, but requires a closer examination of its causes, symptoms, and rehabilitation.
Neuroscientists know that some brain structures that play a role in vision are not strictly part of the cerebrum. For an umbrella term, I am satisfied with the general dictionary definition of cerebral, which describes it as pertaining to the brain without dealing with the finer distinctions between the prosencephalon, mesencephalon, and thencephalon. Similarly, when using the umbrella term ocular visual impairment, there is no need to differentiate between the neurodermal, mesodermal, and ectodermal parts of the eye.
How should cerebral visual impairment be subdivided? For disorders of the eye, an anatomical subdivision is natural, since ophthalmologists can directly observe most parts of the eye. For disorders of the brain, a detailed anatomical subdivision is less practical, since the brain anatomy is more difficult to observe than the anatomy of the eye, and since we know that most functions involve a wide array of interspersed brain areas. As information from the eyes enters the brain, it still carries the imprint of the retinal organization (that is, retinotopic organization). As the information progresses to perception and cognition and to visually guided behavior, the retinotopic organization gives way to an organization around concepts and perceptions. These involve not only a larger spatial range (visual acuity defines only the resolution at the point of fixation), but also a larger range in time. Recognition requires prior cognition and memory. Comparing current information to stored information is one of the essential parts of perception.
This aspect of perception is why I advocate for function-based terminology, using the term visual impairment to indicate changes in basic visual parameters, such as visual acuity and visual field, while using the term visual dysfunction for deficiencies in functional vision due to the inappropriate processing of visual information.
Visual impairment and visual dysfunction may very well coexist. On the web site dedicated to CVI of the American Printing House for the Blind, Dr. Jan is quoted as saying,
The vast majority [of children with brain damage] have tended to have severe multiple disabilities, including a variety of learning difficulties. . . . Traditionally, educators for the visually impaired assisted only those whose eye conditions were associated with visual loss (reduced acuity). Now it has become necessary to offer services for those whose visual loss is due to brain damage. (Jan, 2004)
This quote makes it clear that there is no sharp dividing line between impairment and dysfunction, as there is no sharp dividing line between lesions involving white matter and lesions involving gray matter. Dr. Jan acknowledges this in a Comment, of which he was a contributing author, that was published in JVlB in February 2010 that defined CVI as "impaired vision that is due to bilateral dysfunction of the optic radiations [white matter] or visual cortex [gray matter] or both" (Roman et al., 2010, p. 69).
When using the anatomically restrictive term cortical visual impairment, Dr. Jan suggests a footnote stating that it may include subcortical damage and that it excludes cortical damage to higher centers that do not affect visual acuity. Dr. Jan does not offer a term to capture these other conditions. I prefer to use the umbrella term cerebral visual impairment and to differentiate the functional consequences with the terms visual impairment and visual dysfunction. Within each of these subcategories we should then strive for better delineations of specific symptoms and problems. As these are developed, the use of broad umbrella categories, such as ocular versus cerebral visual impairment, may be less necessary.
My main concern is that if use of the acronym CVI is limited, as Dr. Jan suggests, then the other aspects of cerebral visual impairment may not get the attention they deserve. As a consequence, those unfortunate enough to suffer from CVI in its broader sense may not be recognized and treated adequately and may be denied appropriate rehabilitative services because they do not meet visual acuity requirements that date back to the days when only ocular visual impairment was recognized.
Jan, J. E. (2004). Welcome to the APH CVI website. [Online.] Retrieved from http:// www.aph.org/cvi/index.html
Roman, C, Baker-Nobles, L., Dutton, G. N., Luiselli, T. E., Flener, B. S., Jan, J. E., et al. (2010). Comment: Statement on cortical visual impairment. Journal of Visual Impairment & Blindness, 104(2), 69-72.
August Colenbrander, M.D., affiliate senior scientist, Smith-Kettlewell Eye Research Institute, San Francisco, CA 94115; mailing address: 664 Atherton Avenue, Novato, CA 94945; e-mail: <email@example.com>.