When a child with CVI needs to control his head, use his vision, and perform fine motor tasks, the effort can be compared to a neurologically intact adult learning to knit while walking a tightrope.

DEFINITION

Cortical Visual Impairment (CVI) is a 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. 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.

OTHER NAMES FOR CVI

CVI is sometimes called Cortical Visual Impairment, Cerebral Visual Impairment, Neurological Visual Impairment, Cortical Blindness, Cerebral Blindness, Neurological Blindness.  Some fo these names are missleading. The most accurate name for this type or visual impairment is Cortical Visual Impairment.

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

Vision appears to be variable: sometimes on, sometimes off; changing minute by minute, day by day.

Many children with CVI may be able to use their peripheral vision more effectively than their central vision.

One third of children with CVI are photophobic, others are compulsive light gazers.

Color vision is generally preserved in children with CVI (color perception is represented bilaterally in the brain, and is less susceptible to complete elimination).

The vision of children with CVI has been described much like looking through a piece of Swiss cheese.

Children may exhibit poor depth perception, influencing their ability to reach for a target.

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

Children with CVI may experience a "crowding phenomenon" when looking at a picture: difficulty differentiating between background and foreground visual information.

Close viewing is common, to magnify the object or to reduce crowding.

Rapid horizontal head shaking or eye pressing is not common among children with CVI.

Overstimulation can result in fading behavior by the child, or in short visual attention span.

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.

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.

 TEACHING STRATEGY

A great deal of energy is needed to process information visually. The child might tire easily when called upon to use his visual sense. Allow for intermittent "break" times.

Positioning is important. Keep the child comfortable when vision use is the goal in order that "seeing" is the only task.

Head support should be provided during play or work sessions, to avoid involuntary shifting of the visual field.

Try many different positions to find the one in which the child feels most secure. Infants and toddlers will demonstrate when and where they see best by their adaptive behaviors.

If the child needs to use a lot of energy for fine motor tasks, work on fine motor and vision separately, until integration of the modalities is possible.

The simpler, more constant and more predictable the visual information, the better the child with CVI is likely to deal with it. Keep toys and environment simple and uncluttered. Use books with one clear picture on a contrasting simple background.

Use familiar/real objects (bottle, bowl, plate, bath toy, diaper, cup, spoon, favorite toy) one at a time. Familiarity and simplicity are very important.

Since the color system is often intact, use bright fluorescent colors like red, yellow, pink, and orange. Colored mylar tissue seems to evoke visual responses.

Repetition is very helpful: use the same objects and same process each time to provide familiarity and security for the child. Familiarity breeds response.

Look for toys and activities that motivate the child.

Vision is often best stimulated when paired with another sensory system. For example, auditory cues from the handling of mylar may help attract the child's attention.

Introduce new and old objects via touch and verbal description.

Try different lighting situations to assess optimal conditions for viewing. Try locating a light source behind, and/or to the side of the child.

Try moving the target that you want the child to see. Try different visual fields.

Allow lots of time for the child to see and to respond to what is being seen.

Learn to interpret each child's subtle response cues: such as changes in breathing patterns, shifts of gaze or body position, etc.