Cortical Visual Impairment
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.
History
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.
CVI
is suspected by:
Four
major causes of CVI:
Unique
visual/behavioral characteristics of CVI:
Other
Neurological Vision Disorders:
Cortical And Cerebral Blindness
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.
Resource
http://www.aph.org/cvi/define.html
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.
History
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.
CVI
is suspected by:
- a
normal or close to normal eye examination; - a
medical history which includes neurological problems;
and - the
presence of unique visual/behavioral characteristics.
Four
major causes of CVI:
- Asphyxia
- Brain
maldevelopment - Head
injury - Infection
Unique
visual/behavioral characteristics of CVI:
- Normal
or minimally abnormal eye exam (CVI may co-exist with optic nerve atrophy,
hypoplasia or dysplasia and ROP.) - Difficulty
with visual novelty (The individual prefers to look at old objects, not new,
and lacks visual curiosity.) - Visually
attends in near space only - Difficulties
with visual complexity/crowding (Individual performs best when one sensory
input is presented at a time, when the surrounding environment lacks
clutter, and the object being presented is simple.) - Non-purposeful
gaze/light gazing behaviors - Distinct
color preference (Preferences are predominantly red and yellow, but could be any color.) - Visual
field deficits (It is not so much the severity of the field loss, but where the field loss is located.) - Visual
latency (The individual's visual responses are slow, often delayed.) - Attraction
to movement, especially rapid movements. - Absent
or atypical visual reflexive responses (The individual fails to blink at
threatening motions.) - Atypical
visual motor behaviors (Look and touch occur as separate functions, e.g.,
child looks, turns head away from item, then reaches for it.) - Inefficient,
highly variable visual sense
Other
Neurological Vision Disorders:
Cortical And Cerebral Blindness
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.
Resource
http://www.aph.org/cvi/define.html