WHAT IS CORTICAL VISUAL IMPAIRMENT?
Cortical Visual Impairment (CVI) is a temporary or permanent visual impairment caused by the disturbance of the posterior visual pathways and/or the occipital lobes of the brain. The degree of vision impairment can range from severe visual impairment to total blindness. The degree of neurological damage and visual impairment depends upon the time of onset, as well as the location and intensity of the insult. Children born with impaired sight do not know how they are supposed to see the world. Those who develop vision problems as young children may not have the language to communicate information that could help detect these problems. It is a condition that indicates that the visual systems of the brain do not consistently understand or interpret what the eyes see. The presence of CVI is not an indicator of the child's cognitive ability. Early professional intervention can make a major difference in your child’s development.
Camille’s recent improvement in seizure control has improved her vision dramatically. At one time, she was nearly functionally blind – only able to see bright lights. That evolved into partial vision and now we believe she can see most objects, including faces. For those with CVI, visual functioning can fluctuate based on the neurological state, as in Camille’s case. And with children with Infantile Spasms, the neurological state can fluctuate based on seizure control. To better understand “partial vision”, please visit the Foundation for the Junior Blind web site. Click on the link to “partial vision” to “see through their eyes”.
VISION IS MORE THAN 20/20 EYE SIGHT
Having 20/20 eye sight is not necessarily perfect vision. The standard eye chart used in the offices of doctors and school nurses measures how well a child can recognize a black letter from a distance of twenty feet with one eye. But this test detects less than 20% of children’s vision problems. It does not evaluate how well a child performs on reading distance, eye-hand coordination, tracking skills (following movement), eye teaming skills (how well both eyes work together), and visual processing skills. Vision is the ability to take in, process and understand visual information. It includes eye sight, eye movement skills, eye teaming, focusing, depth perception, color vision, peripheral vision, visual perception and processing, and the ability to integrate all of this information with our other senses.
CAUSE
The major causes of CVI are asphyxia, perinatal hypoxia ischemia ("hypoxia": a lack of sufficient oxygen in the body cells of blood; "ischemia": not enough blood supply to the brain), developmental brain defects, head injury, hydrocephalus, and infections of the central nervous system, such as meningitis and encephalitis.
CHARACTERISTICS
Initially, children with CVI appear blind. However, vision tends to improve. Therefore, Cortical Visual Impairment is a more appropriate term than Cortical Blindness. A great number of neurological disorders can cause CVI, and CVI often coexists with ocular visual loss so the child should be seen by both a pediatric neurologist and a pediatric ophthalmologist. The diagnosis of Cortical Visual Impairment is a difficult diagnosis to make. It is diagnosed when a child has poor or no visual response and yet has normal pupillary reactions and a normal eye examination. The child's eye movements are most often normal. The visual functioning will be variable. The result of an MRI (Magnetic Resonance Imaging) in combination with an evaluation of how the child is functioning visually provide the basis for diagnosis.
BEHAVIORAL/VISUAL CHARACTERISTICS
Children with CVI have different abilities and needs. The presence of and type of additional handicaps vary. Some children have good language skills and others do not. Spatial confusion is common in children with CVI because of the closeness of the occipital and pariental lobes of the brain. Habilitation should be carefully planned. A full evaluation by a number of professionals is essential. The evaluation team could include: teachers (of the visually impaired or severely handicapped), Physical Therapists (PT's), Occupational Therapists (OT's), Speech Therapists, and Orientation and Mobility Specialists.
Common characteristics of visual function demonstrated by children with CVI
1. Vision appears to be variable: sometimes on, sometimes off; changing minute by minute, day by day.
2. Many children with CVI may be able to use their peripheral vision more effectively than their central vision.
3. One third of children with CVI are photophobic, others are compulsive light gazers.
4. Color vision is generally preserved in children with CVI (color perception is represented bilaterally in the brain, and is less susceptible to complete elimination).
5. The vision of children with CVI has been described much like looking through a piece of Swiss cheese.
6. Children may exhibit poor depth perception, influencing their ability to reach for a target.
7. Vision may be better when either the visual target or the child is moving.
The behaviors of children with CVI reflect their adaptive response to the characteristics of their condition
8. Children with CVI may experience a "crowding phenomenon" when looking at a picture: difficulty differentiating between background and foreground visual information.
9. Close viewing is common, to magnify the object or to reduce crowding.
10. Rapid horizontal head shaking or eye pressing is not common among children with CVI.
11. Overstimulation can result in fading behavior by the child, or in short visual attention span.
12. The ability of children with CVI to navigate through cluttered environments without bumping into anything could be attributed to "blindsight", a brain stem visual system.
13. Children are often able to see better when told what to look for ahead of time.
Children with CVI may use their peripheral vision when presented with a visual stimulus, appearing as if they are looking away from the target. Some children look at an object momentarily and turn away as they reach for it.
MODIFICATION OF THE CLASSROOM FOR THE CHILD WITH VISION PROBLEMS
Position the child optimally in classroom. To reduce glare, for example, have the child’s back towards the window.
Provide adequate lighting, preferably full spectrum, fluorescent or incandescent lighting.
Use a slant desk to provide easier head and eye posture. Monitor the posture of the child who is writing.
Use bold line paper and felt tip and #1 pencil for writing.
Bold chalk on a blackboard is easier to see than a dry erase marker on a white board.
Perform most reading and writing activities during the morning.
Allow the child to do near work for fifteen minute intervals, taking breaks between.
Be sure the child is wearing glasses when recommended.
Reduce the amount of visual distraction in the room. Try not to overdecorate the chalkboard.
Double spaced sentences are easier to read. Try to be consistent with the type or font style used.
Encourage visual thinking.