Cortical Visual Impairment
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 moderate 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. The terms Cortical Visual Impairment, Neurological Visual Impairment, and Cerebral Visual Impairment, are sometimes used interchangeably; however they may refer to different conditions.
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.
Initially, children with CVI appear blind. However, vision tends to improve. Therefore, Cortical Visual Impairment is a more appropriate term than Cortical Blindness. Most children show some recovery after being diagnosed with CVI but very few recover completely. Usually the most dramatic improvement happens in the first two years after the diagnosis. Improvement is related to children’s brain plasticity and development. 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 usually 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.
Children with CVI have different abilities and needs. The presence of and type of additional disabilities vary. Some children have good language skills and others do not. Sometimes selected neurological problems occur, such as spatial confusion or difficulty recognizing faces. 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 disabled), 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.
- Some children with CVI are light sensitive; however others are attracted to light and can have difficulty switching their gaze to other visual targets, particularly right after the onset of CVI.
- Color vision is generally preserved in children with CVI (color perception is represented bilaterally in the brain, and is less susceptible to complete elimination).
- Frequently children with CVI can see color better than black and white. Some children with CVI show preference for specific colors while others show no such preference.
- 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.
- A common characteristic of children with CVI is difficulty looking at faces for any length of time (lack of facial regard).
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.