CORTICAL VISUAL IMPAIRMENT (CVI)
"Due to improved medical care, children with severe brain insults have increasingly begun to survive over the last 30 years. The vast majority have tended to have severe multiple disabilities, including a variety of learning difficulties. A minority of them also has permanent visual loss, but normal or minimally abnormal eye examinations.
Traditionally, educators for the visually impaired assisted only those whose eye conditions were associated with visual loss (reduced acuity). Now it has become necessary to offer services for those whose visual loss is due to brain damage. Thus, the definition of CVI was born."
Dr. James E. Jan
Visual impairment was defined in the past by loss of acuity (how far we see) and also by the severity of visual field loss (blind area). This definition was originally designed for characterizing visually impaired adults who required social assistance and not for children with visual impairment caused by various eye conditions. Even though it did not accurately represent visual abilities, the definition was widely accepted, but it adversely influenced our thinking about visual impairment. Services were developed worldwide for only those people with visual problems fitting this definition while others with obvious visual difficulties who required intervention were excluded.
During the last several decades, our understanding of vision has markedly improved. It is now realized that vision is not a single sense but a combination of complex senses which have evolved over millions of years. Almost the entire brain is involved in the process of seeing. In different locations there are specialized areas for distance vision, recognition of faces, objects, colors, contrast, and movement. There are also areas of the brain that coordinate visually-directed movements, and process visual information to achieve perceptions of directionality and depth. CVI is caused by widespread damage to the brain, which affects most of the specialized visual centers, resulting in a damaged, inefficient visual sense. When only a small visual area is affected, it can result in a specific visual disorder, but not in CVI.
Because in the past everyone who was considered to be visually impaired had to have reduced or absent visual acuity, the medical definition of CVI also emphasized loss of ability to see in the distance (reduced acuity). It was hoped that once the correct diagnosis was made, children with CVI would be appropriately managed by a variety of professionals, including educators.
The medical definition of CVI is not well understood by non-medical professionals. While acuity testing is difficult in the young and disabled for physicians, it is even more difficult for teachers. Also, there are many children with visual problems similar to CVI, except they have normal acuity. This visual condition is called "cortical visual dysfunction" (CVD). The educational management of children with CVI and CVD is similar. It is now known that with time the visual acuity of children with CVI tends to improve. Therefore the diagnosis of CVI could change to CVD over time. Both groups require remedial education, which necessitates an increased number of specialized teachers. Based on the above discussion, it is clear that there is a need for an educational definition of CVI and CVD, which addresses the needs of these children.