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Cortical visual impairment (CVI) is a
complex and heterogeneous condition in which the eyes and optic nerves
appear healthy; yet, the patient does not have normal vision or normal
visual perception. Indeed, as the name implies, CVI is not an eye
condition but rather a brain condition. Previously, many eye doctors
referred to such patients as "cortically blind" but it is now generally
believed that many of these patients have useable, albeit abnormal,
vision.
CVI results from a number of conditions
that affect the brain and particularly the surface of the brain called
the cortex. Intracranial bleeding, head trauma, birth defects, strokes,
and seizures, among others can result in CVI. Typically diagnosed during
infancy, CVI is also associated with prematurely or more accurately
complications due to prematurely such as intracranial bleeding. Typical
visual behaviors of an infant or child with CVI include:
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Momentary fixation – the child will
look (fixate) on things only briefly, say about a second or less
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Variable vision – the child with
CVI will seem to "see" at certain times and not at other times
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Selective attention – the child may
look at some things that may be rather hard to see (e.g., small toy)
but act unaware with very salient objects (e.g., faces)
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Avoidance – Some children with CVI
will actively avoid (e.g., look away from) salient visual objects
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Prefer certain colors – Some
children with CVI will attend to colored objects (e.g., yellow) but
ignore black-white objects
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Moving objects – Some children with
CVI will track or watch an object when it is moving (e.g., a small
ball rolling across the floor) but ignore or exhibit "blind"
behavior (using hands to locate a nearby object) to the same object
when it is stationary
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Act blind but respond to objects –
Some children with CVI will act as though they’re not able to see or
identify an object but, at the same time, are able to locate and
grab or actively avoid the object.
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Hemianopsia – Some children with
CVI will be missing parts of their visual field and may prefer to
fixate on objects by looking to the left or right of the object.
It helps to understand CVI in the
context of brain centers for vision and vision information processing.
Current research suggests that there are a lot of specialized cortical
sites for vision; currently about 32 sites have been identified. Each of
these cortical sites process a certain aspect of vision; for example,
color, movement, object identification, object localization in 3D space,
categorization, etc. There are also two main visual pathways known as
the "What" and "Where" pathways in the brain. The What pathway is
important for object identification and the Where pathway is important
for object movement and localization in 3D space. As a consequence, all
children with CVI are different; the visual problems that each child has
may be dependent on the site or sites of damage.
For example, we recently saw a child
that could run after a small ball rolling along the floor. Once the ball
stopped moving, however, the child knelt-down in the general vicinity of
the ball and reached-out with his hands and started to "pat" the floor
until he located the ball. In this case the child could "see" the ball
when it was moving but could not see the ball when it was stationary.
The child’s unusual visual behavior makes sense once one thinks about
the different brain centers and pathways for vision. Apparently, the
child’s Where pathway was intact such that he could actively follow and
see the ball while it was moving, however, once the ball stopped the
child could no longer see the ball to localize it.
Because all children with CVI are
different, no single rehabilitation technique or approach will work for
all children. The most important thing is to find-out what the child can
respond to and to tailor the rehabilitation to meet the child’s needs.
Here it is very important for parents to keep a list of what the child
does and does not’t respond to. Share the list with the doctors and
rehabilitation specialists.
Children with CVI may show significant
improvement in vision with age. Other children with CVI may not be
detected until they are older and even in school. The later is
particularly evident with children with perceptual problems – they may
see 20/20 but they may not be able to use the visual information for
particular tasks like categorizing objects (e.g., animal vs object).
Also, in general, some of the best rehabilitation personnel are other
children of the same age or slightly older age. Other children can
stimulate, play with, tease and force the child with CVI to maximize
his/her residual vision. The last thing a parent should do is be
overprotective of the child – it will do more harm than good (within
reason and when considering other medical conditions). |
