Understanding the Complexity of Cerebral/Cortical Visual Impairment (C/CVI)
Lea Hyvarinen, MD, PhD, FAAP Technical University of Dortmund University of HelsinkiMembers 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 wemay 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 oftenin 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 understandthe 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 usualplaces 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 awareof 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 objectstops 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, vision-hand coordination or visionfoot 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 ofanother 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 havea 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 visualrecognition 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 orimpossible to perceive. This is often called a problem in figure-ground 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 sensoryproblems. 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 needto have large texts.
Recent findings, in the function of the early processing in V1-V2, show that there might be a connection withshort-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 oroccupational 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