Understanding the Complexity of Cerebral/Cortical Visual
Impairment (C/CVI)
Lea Hyvarinen, MD, PhD, FAAP Technical University of Dortmund
University of Helsinki Members of FOVI, Focus on Vision
Impairments:
Kathleen Appleby, M.A., Educational Vision Consultant, TVI, Vision
Associates
Julie Bernas-Pierce, M.A., Executive Director, Blind Babies
Foundation
Elizabeth Dennison, M.S., Co-Director of SKI-HI Institute, Utah State
University, Vision Consultant
Bernadette Jackel, Parent of son with CVI
Amanda Hall Lueck, Ph.D, Professor, Department of Special
Education, San Francisco State University
Mary Morse, Ph.D, Special Education Consultant and Teacher of the
Visually Impaired (TVI)
Michelle Wilson, Ph.D, Parent of daughter with CVI
Cortical/Cerebral Vision Impairment (C/CVI) is a prenatal or postnatal insult
to the brain that causes damage to one or more defined areas or results in
widespread brain damage. The most common cause of C/CVI is lack of
oxygen in the brain tissue, called hypoxia or asphyxia, due to insufficient
blood flow, otherwise known as ischemia. Other common causes are
accidental and non-accidental head injury, developmental brain defects, and
infections during pregnancy or after birth.
Teachers, therapists, and parents are often challenged and sometimes
confused by the reaction of children with C/CVI to everyday activities, but it
is a very complex visual condition. Most people think they see with their
eyes. In part, this is true. If our eyes do not work properly, we are not able
to see well. However, what we experience as vision occurs not in the eyes
but in the brain.
Think of our eyes as a digital camera and our brain as a computer. When
our camera takes a picture, the picture needs to be downloaded to the
computer to be used for various purposes. If the computer does not have
the proper hardware or software, images will not download successfully so
we may not be able to use image processing programs to edit the pictures.
Similarly, some specific areas in the brain can be poorly functioning and
thus some components of our vision can be lost.
Traditionally, the term "cortical visual impairment" has been used in the
United States to describe brain-damage-based vision loss. The damage can
be outside the cortex, quite often in the pathways; therefore, in other
countries this condition has several names:"cerebral visual
impairment,""cognitive visual impairment,""visual processing disability," and
others in attempts to more clearly define the origin and nature of the
disability.
The three networks
In order to understand the complexity of C/CVI, one needs to understand
the three visual systems: the dorsal visual stream, the ventral visual
stream, and the mirror neuron system. Our knowledge of these structures in
the brain and their functions is based on investigations of monkey brains
and clinical findings after damage to previously normal brains. In children,
brain damage is most often congenital. Therefore, the development of the
brain has been different from normal development and some functions may
not be in their usual places or processed in a typical manner. Even a part of
the main streams may not function, as happens in total damage of the optic
radiation and occipital cortex, which leads to hemianopia, loss of half of the
visual field.
Before the information flows into the dorsal and ventral stream it is coded in
the primary visual cortex. Irregularities and defects in coding lead to
defective structure of the information. This is often seen in the perception of
gratings (black and white lines) which are not seen as straight lines at
higher frequencies but as an irregular mesh.
Dorsal stream
The dorsal stream is the large network between the primary visual cortex
and posterior parietal lobe. It uses visual information in two main functional
areas. In the upper part are cell groups that we use in on-line control of
movements. In the lower part (inferior parietal lobule, IPL) are structures
that we use to develop our actions toward objects, how we reach and grasp.
Their function lays the foundation for us to be aware of space around us,
directions and distances, both in the near space within reach and further
away. There are also important networks in this area that allow us to
observe other persons' actions and immediately understand the intention of
that action.
During actions we use visual information moving at different speeds. If
movement vision, or motion perception are not normal it disturbs on-line
control. Typically, children with this issue look at an object, turn their head
away, and then reach and grasp the object. Some children have lost parts of
motion perception; they do not see fast moving objects like balls in games.
Some other children see objects as long they move but when the object
stops moving or the child stops moving, the objects disappear. In
communication, part of the face may seem blurred, and may look so
unpleasant that the child turns his or her head away. This is often
misunderstood as a sign of autistic behavior.
Awareness of space, directions, and distances is essential for orientation in
space and safe moving. When we move, we perceive the relative locations of
objects based on the relative speed with which they seem to move in our
visual field (called parallax). Thus, gaining visual information regarding a
person's motion perception is very important. Unfortunately, this is not
measured in typical clinical eye examinations.
Some children with C/CVI have difficulties when functioning within certain
spaces and environments. This can affect their orientation in space, visionhand coordination or vision-foot coordination. It also can affect their
understanding of the abstract space of mathematics, visual imagining, and
interpreting other persons' actions.
Mirror neurons
The neuron groups that respond to motor actions, and also observation of
another person performing the same action, are in several parts of the
brain. They were first found in the pre-motor cortex; cells that were active
during a goal-directed action in monkeys were also active when the monkey
saw the experimenter perform the same action (Pellegrino 1992). For
example, when the monkey grasped a piece of food, certain neurons were
active in the F5 area in the pre-motor cortex. The same neurons showed
similar activity when the monkey observed the experimenter grasping a
piece of food. But, if the experimenter mimicked grasping a piece of food,
the neurons remained inactive. This has been interpreted as the monkey
perceiving/understanding that the motor activity did not have a goal. The
cells respond to intention to perform a goal-directed action.
Mirror neurons in the pre-motor cortex receive visual information from
several areas in the lower part of the parietal lobe where the structure and
content of the vision for action is processed. Some neuron groups in
monkeys are active during actions related to eating, other groups during
visual communication using mouth region or gestures. These active observations of goal-directed functions are also seen in infants. They make it
possible for young infants to understand and anticipate actions long before
they can move their own limbs sufficiently well. It is also the foundation for
imitation of expressions already at birth in healthy well awake infants, which
is important for the development of emotional bonding.
The mirror neuron system has been given an important role in early
interaction and in the development of understanding of adult persons'
intentions. In infants who have reduced vision, such that they cannot see
facial expressions, visually activated minor neurons remain quiet. However,
activation by tactile and auditory information exists and can be effectively
used in early intervention.
Ventral stream
Ventral stream functions are located in the lower temporal or inferotemporal
cortex and are responsible for purely visual recognition functions.
Recognition requires that we have seen the object or person earlier, have
been able to store the image in our visual memory, find the old image,
compare the new with the old image and if they are sufficiently alike, we
recognize them to represent the same object or person.
Different types of recognition functions are located in specific networks,
which are closer to or farther apart from each other. For example, children
who do not recognize familiar faces often have problems in the recognition
of landmarks. Some children have no other recognition problems except that
they do not perceive body language, which is a big problem in interactions
with others, be they with teachers, parents, peers.
Picture perception problems are common. The child may not be able to
detach the parts of a complex picture and see them as individual objects but
sees a blob of colors without recognizable form. Texts on pictures may be
difficult or impossible to perceive. This is often called a problem in figureground perception. Recognition difficulty may be very specific. Some
children cannot recognize letters or numbers. Some other children cannot
recognize concrete objects and their pictures but use tactile information or
kinesthetic information to recognize the forms. Geometric forms are a
specific area of recognition difficulties, which should be compensated by
using teaching strategies of blind children.
Other complicating problems
Children with cortical/cerebral visual problems may have pure sensory
problems. However, many children also have ocular motor problems,
problems in hand functions, head and body control and locomotion.
Reading uses both sensory and motor functions. It requires stable fixations,
accurate and fast eye movements (saccades) focusing to reading distances,
and convergence of the eyes if used binocularly. At the same time, the child
has to control head and body stability and hand movements. There are
numerous reading strategies so weak functions are compensated or avoided
during reading. A pointer or an arrow on a magnifier helps when a child has
fixation problems. Increased crowding requires wider spacing of letters and
lines to find the optimal text size and spacing. Even children with normal
clinical findings may need to have large texts.
Recent findings, in the function of the early processing in V1-V2, show that
there might be a connection with short-term memory and image analysis
already at this early level of processing. In addition, these children often
have insufficient accommodation as a sign of problems in their motor
functions. If a child with "normal" findings prefers 40-point font for learning
to read, he or she is highly likely to have some problems that we cannot
diagnose in the very early years.
When we assess eye-hand coordination it is important to have an
experienced pediatric physiotherapist or occupational therapist assessing the
motor functions. After that it is easier to observe whether the visual and
motor functions are synchronous or out-of-synch. For example, children who
learn to move very late may be unable to use vision and moving
simultaneously. They look — walk —stop — look — walk.
There are so many different visual functions that a thorough visual
assessment requires a skilled multidisciplinary team, and should be based
on:
(a) clinical findings that assess a wide array of visual functions, skills
and behaviors;
(b) observations and functional evaluations, especially in reading and
mathematics by special teachers trained to assess children with
varying types of brain damage.
The authors submit this overview as a contribution to the broadening of your
understanding of the child with C/ CVI and other areas of vision
assessments.
AER Report Summer 2010, Volume 27, No. 2