Fact Sheet by Keri Burton for SPE 516
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Condition:
Cortical Visual Impairment
Basic Description:
Cortical visual impairment (CVI) is a form of visual impairment that is caused
by a brain problem rather than an eye problem (the latter is sometimes termed
"ocular visual impairment" when discussed in contrast to cortical visual
impairment). Some people have both CVI and a form of ocular visual impairment
as well.
CVI is sometimes known as Delayed Visual Maturation because the person's
vision can sometimes seem (to an outside observer) to be improving over time.
This can be due to the person's learning how to make better use of the unusual
types of information that their malfunctioning visual system presents to them, and
to take into account the context and other clues in a piece of continuous
detective work. CVI is also sometimes known as Cortical Blindness, although
most people with CVI are not totally blind.
The parts of the visual system affected:
The retina and the brain
Effects on the visual system:
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Vision appears to be variable: sometimes on, sometimes off; changing
minute by minute, day by day.
Many children with CVI may be able to use their peripheral vision more
effectively than their central vision.
One third of children with CVI are photophobic, others are compulsive light
gazers.
Color vision is generally preserved in children with CVI (color perception is
represented bilaterally in the brain, and is less susceptible to complete
elimination).
The vision of children with CVI has been described much like looking
through a piece of Swiss cheese.
Children may exhibit poor depth perception, influencing their ability to
reach for a target.
Vision may be better when either the visual target or the child is moving.
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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.
Common treatments, including medications:
Developing a proper diagnosis is the key to treating CVI. There are now
testing techniques that do not depend on the patient's words and actions, such
as FMRI scanning, or the use of electrodes to detect responses to stimuli in both
the retina and the brain. These can be used to verify that the problem is indeed
due to a visual cortex malfunction.
Younger patients, who have not reached developmental maturity will
require special learning environments that promote maximum stimulation of
residual vision. Such environmental stimulation may help to prevent
developmental delays. Research indicates that developmental milestones that
normally require vision ('reaching' and 'walking')are often delayed in children with
visual impairment, even in the absence of other disabilities.
Treatments that incorporate neural based stimulation methods and natural
developmental sequences are preferable such as: using movement, using high
contrast such as black on white or yellow pictures on a black background, use
boundaries to help eyes know where to focus, use stimulus of touch and vision
together, use selective colors (children usually have preferences), ensure proper
lighting and seating, simplify visual environment (students must know where to
focus), use stimulus materials that are common and used frequently, allow extra
time for processing, and use technology to enlarge and help students to focus.
Whether the condition is congenital, adventitious, progressive, or stable:
The disease is congenital or developed in an adult by a trauma or disease. As
children develop, their vision may improve.
Anticipated functional implications of the condition:
The degree of vision impairment can range from severe visual impairment
to total blindness. The degree of neurological damage and visual impairment
depends upon the time of onset, as well as the location and intensity of the insult.
It is a condition that indicates that the visual systems of the brain do not
consistently understand or interpret what the eyes see.
If CVI is from birth, many neural based stimulation methods and
developmental growth can cause the child to see and adapt better as time and
development continue to mature.
References:
http://www.blindbabies.org/factsheet_cvi.htm
http://www.aph.org/cvi/define.html
http://www.childrenshospital.org/az/Site2100/mainpageS2100P0.html
http://en.wikipedia.org/wiki/Cortical_visual_impairment
http://www.aph.org/cvi/articles/good_1.html
http://escholarship.bc.edu/cgi/viewcontent.cgi?article=1176&context=education/tecplus
http://aapnews.aappublications.org/cgi/content/citation/30/5/17
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.
Diagnosing CVI is difficult. A diagnosis is usually made when visual performance is
poor but it is not possible to explain this from an eye examination. Before CVI was
widely known among professionals, some would conclude that the patient is faking their
problems or has for some reason engaged in self-deception. However, there are now
testing techniques that do not depend on the patient's words and actions, such as FMRI
scanning, or the use of electrodes to detect responses to stimuli in both the retina and the
brain. These can be used to verify that the problem is indeed due to a visual cortex
malfunction
Symptoms of CVI usually include several (but not necessarily all) of the following:
Variable vision. Visual ability can change from one day to the next but it can also
fluctuate from minute to minute, especially when the person is tired. When undertaking
critical activities, people with CVI should be prepared for their vision to fluctuate, by
taking precautions such as always carrying a white cane even if they don't always use it
to the full, or always having giant print available even if they don't always need it (for
example, consider the consequences of losing vision while giving a public speech).
Managing fatigue can reduce fluctuations but does not eliminate them.
One eye may perform significantly worse than the other, and depth perception can be
very limited (although not necessarily zero).
The field of view may be severely limited. The best vision might be in the centre (like
tunnel vision) but more often it is at some other point and it is difficult to tell what the
person is really looking at. Note that if the person also has a common ocular visual
impairment such as nystagmus then this can also affect which part(s) of the visual field
are best (sometimes there exists a certain gaze direction which minimises the nystagmus,
called a "null point") and both conditions come into play when restricting the field of
view.
Even though the field of view may be very narrow indeed, it is often possible for the
person to detect and track movement outside this area. (Movement is handled by the 'V5'
part of the visual cortex, which may have escaped the damage.) Sometimes a moving
object can be seen better than a stationary one; at other times the person can sense
movement but cannot identify what is moving (this can be annoying if the movement is
prolonged, and to escape the annoyance the person may have to either gaze right at the
movement or else obscure it). Sometimes it is possible for a person with CVI to see
things while moving their gaze around that they didn't detect when stationary. However,
movement that is too fast can be hard to track; some people find that fast-moving objects
"disappear".
Some objects may be easier to see than others. For example, the person may have
difficulty recognising faces or facial expressions but have fewer problems with written
materials. This is presumably due to the different way that the brain processes different
things.
Importance of colour and contrast. The brain's colour processing is distributed in such a
way that it is more difficult to damage, so people with CVI usually retain full perception
of colour. This can be used to advantage by colour-coding objects that might be hard to
identify otherwise. Sometimes yellow and red is easier to see, as long as this does not
give poor contrast between the object and the background.
Strong preference for a simplified view. When dealing with text, the person might prefer
to see only a small amount of it at once. This allows for more magnification, which may
be needed due to ocular visual impairments or in order to ensure that important things
such as letters are not completely hidden behind scotomas (small defects in parts of the
functioning visual field), but more importantly it simplifies the view and reduces the
chances of getting lost in it. However, the simplification of the view should not be done
in such a way that it requires too rapid a movement to navigate around a larger view,
since too much motion can cause problems (see above) although some is acceptable.
For the same reason (simplified view), the person may also dislike crowded rooms and
other situations where their functioning is dependent on making sense of a lot of visual
stimuli.