Cortical Visual Impairment (CVI) is a temporary or permanent visual impairment caused by the disturbance of the posterior visual pathways and/pr the occipital lobes of the brain. The degree of vision impairment can range from mild to severe visual impairment. 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.
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, development and degree of neurological damage. 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 papillary reactions and a normal eye examination. The child’s eye movements are usually normal; however nystagmus can be present in some children. The visual functioning will be variable.
CVI accounts for the majority of cases of legal blindness due to neurological vision impairment among children. These children have vision but their vision does not improve to normal. Their visual acuity may range from the ability to perceive light to 20/100. They frequently have fluctuating vision where their vision may be different at various times of the day. Their central vision may have spotted blind spots and their vision may be analogous to looking through Swiss cheese. Consequently, they often do not make eye contact and their eye hand coordination may be poor. Children with CVI often have many interesting behaviors. Aside from not making eye contact, they are highly stimulated by high contrast, rotating, and moving objects. They frequently look at ceiling fans, the scrolling credits on videos, and some stare at blinking and flashing lights. A small percentage are extremely sensitive to glare and bright light and will keep their eyes closed or turn away and stare into a corner of the room. Children with CVI frequently have very sensitive peripheral vision and they can become overwhelmed when they are in crowded places that have a lot of visual noise. Department stores, amusement parks, and confined quarters can be very stressful for these children. Their visual attention fluctuates tremendously and they may demonstrate short periods where they use their central vision to focus and identify objects but their attention quickly weakens and they then glance at objects with their peripheral vision. During these times, they appear totally blind and use their hands to interact with their environment rather than using their vision to guide their hands.
Children with CVI often have many other problems that interfere with their general development. Because the entire brain is often involved, they frequently have motor, language, feeding, and cognitive problems. These neurological problems often present a major challenge to parents, teachers, and therapists. The neurological and cognitive problems of children with CVI are usually the greater limiting obstacle that interferes with their development as compared to the vision impairment. The cognitive deficits create unique difficulties in attempting to teach children how to use non-visual clues for learning.