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Cortical Visual Impairment (CVI) is often referred to as cerebral visual impairment in Europe, although it is known as cortical visual impairment in the U.S. and Canada.
At times, it is referred to as cortical or cerebral blindness, but that is considered an incorrect reference as CVI typically does not involve blindness. It is both an ocular, and a neurological visual disorder. An ocular disorder is a disorder, or irregular condition, of the eye. A neurological visual disorder is a type of visual disorder that is caused by abnormalities in the brain.
The definition of a CVI can be interpreted two ways, for medical and for educational purposes. The educational definition of a CVI is that it is a neurological disorder that causes a student to respond to their environment, people and educational materials in a way that leads to the determination that he or she is impaired visually or has a loss of visual acuity. It should be further noted that when a student's reduced visual ability is the result of an injury to the brain and is the equivalent to what is deemed the legal definition of ocular blindness, he or she may be deemed blind for the purpose of education. For medical purposes, CVI is defined as visual impairment that is the result of brain damage, such as occipital lobe damage and widespread disturbances to the brain's visual centers.
In the past, there was a very narrow definition of what visual impairment meant. This definition was not designed for children with certain eye or brain conditions, or even adults who did not fall within the strict guidelines of the definition. The definition only involved reduced visual acuity and the area, or field of vision, affected by this loss. As a result, only those who met this definition were eligible for social assistance while others were not. As the understanding of vision and visual impairment grew, so did the realization that the various aspects of seeing, such as viewing colors, movement, recognition and even the processing of information, involved the use of a person's entire brain. This realization broadened the definition and helped them to understand how damage to large areas of the brain, and it's specialized visual centers, causes CVI.
Testing the vision of children with CVI is often difficult for educators. Some may confuse it with a condition called Cortical Visual Dysfunction (CVD). This is similar to CVI with the exception that the affected children have normal visual acuity. They are managed in a similar fashion, and in some cases, children diagnosed with CVI may note an improvement in vision. If this happens, the diagnosis may change to CVD.
There are four primary causes of CVI in children. Each of these causes results in widespread injury to the brain and damage to the brain's visual centers. If a child asphyxiates, or cannot breathe, he or she is unable to get adequate oxygen to the brain and can suffer from brain damage. Asphyxiation can occur as a result of choking while eating, or even as a result of asthma. Brain and central nervous system infections may also cause damage, as will head trauma from an accident or physical abuse. CVI may also occur if the brain fails to develop normally.
A child with CVI may display certain characteristics and symptoms. These often seem unusual; however, they should not be ignored. The child may have a preference for a specific color, such as a vivid yellow or red. Although those are the most common color preferences, other children might prefer other bright colors, such as green. A child with CVI may intently gaze at lights or at far off objects, or may favor looking at objects from a specific direction or angle. When a child has CVI, a parent or teacher may note that the child will turn his or her head to the side or at an odd angle to see. Other signs include failing to blink when objects come close to the eyes, a lack of visual curiosity in terms of new objects, and difficulty looking at objects when reaching for them. The child may express difficulty viewing cluttered images or environments; however they may see best if an object is in motion.
CVI is not the only type of neurological visual disorder. Other types of neurological visual disorders may be referred to as neurological visual impairments, which are also caused by damage to the brain. These disorders include, but are not limited to, homonymous hemianopia, absolute scotomas, visual neglect, visual agnosia, delayed visual maturation and functional blindness.
Homonymous hemianopia differs from CVI in that it involves a loss of one's field of vision. With CVI however, there is often no loss of one's visual field, although their vision is often disturbed or has some form of dysfunction. With homonymous hemianopia, there is a blind area, or defect that appears on the same half of each eye. For example, if the right half of a person's vision has a blind area in the right eye, the left eye will also have a blind area in the right half of the vision in that eye. A scotoma is a blind area in a person's field of vision that is completely devoid of light. The person with a scotoma can see around it, as the rest of his or her vision will be unaffected by the area of loss.
Another neurological visual disorder is called visual neglect. This is the result of a brain abnormality that might have been caused by an injury or a stroke. When a person displays visual neglect, he or she is able to see an entire object clearly, but will tend to ignore one side of it. Visual agnosia, on the other hand, is a condition in which a person is unable to recognize objects. This occurs even though the person is able to see the object. When there is no evidence upon examination that a person is unable to see, however, he or she claims that they are unable to, it is called functional blindness. These claims are often not taken seriously, but they may indicate a serious underlying problem that should be treated.
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