Ocular disorders: pathology of the eye(s)
Neurological visual disorders: disturbed or reduced vision due to various brain abnormalities.
The two types of visual disorders (ocular & neurological) can coexist.
Cortical visual impairment (CVI) is a neurological visual disorder. It is the fastest growing visual impairment diagnosis today.
Definition for Medical Purposes:
Cortical visual impairment (CVI) may be defined as bilaterally diminished visual acuity caused by damage to the occipital lobes and or to the geniculostriate visual pathway. CVI is almost invariably associated with an inefficient, disturbed visual sense because of the widespread brain disturbance. See brain diagrams.
Definition for Educational Purposes:
Cortical visual impairment (CVI) is a neurological disorder, which results in unique visual responses to people, educational materials, and to the environment. When students with these visual/behavioral characteristics are shown to have loss of acuity or judged by their performance to be visually impaired, they are considered to have CVI.
Note: A student whose visual functioning is reduced by a brain injury or dysfunction may be considered blind for educational purposes if visual function is equal to or less than the legal definition of ocular blindness. See Federal Quota.
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.
Both of these terms are often used to describe CVI. Blindness to most people means total absence of vision, and individuals with CVI are rarely, if ever, totally blind, the word "blindness" tends to be replaced with "visual impairment." People living in the United States, Canada, Mexico, and many other countries prefer to use "cortical" visual impairment for CVI, while some European countries refer to it as "cerebral" visual impairment. OCCIPITAL BLINDNESS should not be used to describe CVI. The term suggests that the occipital lobes are the brain centers for vision but it is the entire brain which "sees." The understanding of CVI is still evolving, which is one of the reasons for some of the inappropriate terms used today. (One of the aims of this project is to eliminate inappropriate terms.)
This term is often used to indicate that the visual disorder(s) is(are) caused by brain rather than eye abnormalities. CVI is one of the neurological visual conditions because it is caused by brain abnormalities. There are many different neurological visual disorders in addition to CVI such as visual agnosia, visual neglect, lack of face recognition, homonymous hemianopia, poor depth perception, various visual perceptual disorders, among others.
These are medical terms which imply that a visual field defect (blind area) affects the same half of each eye, either on the right or left side. These blind areas are caused by brain lesions which are on the opposite side from the visual field defect. Double, homonymous hemianopia would imply that the visual field defects involve both halves of each eye. Individuals with CVI very frequently have visual field loss, but in addition, their remaining visual sense is severely disturbed. Therefore homonymous hemianopia is not the same as CVI.
This term implies that there is a non-seeing, blind area within the visual field which may occur due to damage of the visual pathways, or to the retina. Scotomas can be large or small. Individuals who only have scotomas should have no difficulties interpreting visual messages outside the visual field loss, therefore this term should not be confused with CVI.
Children are not born with a fully developed visual sense but acquire their visual skills gradually. Delayed visual maturation is diagnosed when young infants exhibit markedly delayed visual function, due to various causes. Delayed visual development is a more appropriate term because while the delayed visual function in most instances improves, with appropriate management and with time; it only rarely becomes entirely normal.
Occasionally individuals claim to have disturbed, decreased, or even absent vision without corroborating evidence of abnormality found on examination and detailed visual testing. These complaints need to be taken seriously because they may be due to underlying psychological problems which require treatment. Functional visual disorders can have many different causes and some individuals may even fake their disturbed vision for various reasons. Functional blindness should not be confused with CVI because it is an entirely different visual condition.
This term is used to identify the inability to recognize common objects because of specific brain problems, regardless of visual acuity.
This is characterized by the inability or impaired perception of visual information, usually on one side of the body, due to disturbances with attention mechanisms in the presence of normal acuity.