Neurological Visual Impairment:
Also Known as: Cortical Visual Impairment,
Delayed Visual Maturation, Cortical Blindness
Neurological Visual Impairment (NVI) is now the preferred name for a type
of vision impairment that has been and is still referred to as Cortical
Visual Impairment or Cortical Blindness. NVI is now divided into three categories:
Cortical Visual Impairment, Delayed Visual Maturation, and Cortical Blindness.
These divisions are made according to what area of the brain has been effected.
A variety of studies indicate that the percentage of children with vision
impairments who have NVI is between 3.6 and 21%, making it the major cause
of vision impairment in children who are deaf-blind. NVI occurs when the
part of the brain that is responsible for seeing is damaged. In other words,
the eye itself is normal but the brain does not process the information
properly. NVI has a variety of causes, including, but not limited to, lack
of oxygen before, during, and after birth, viral or bacterial illness such
as meningitis and cytomegalovirus, or traumatic brain injury. These children
can, but do not always, have additional disabilities. Other types of vision
impairments such as optic atrophy (defect of the optic nerve resulting in
the inability of the nerve to conduct images to the brain) and optic nerve
hypoplasia (a vision impairment caused by a congenital defect of the optic
disk) are more common in children with NVI.
NVI effects vision in a variety of ways and causes vision loss that can
be from mild to severe, temporary or permanent. There is no way to predict
what a young child's vision will be like as they mature but many children
with NVI experience improvement in their vision. Fluctuating vision is common.
This is most pronounced in children with seizure disorders or in those on
certain medications such as Dilantin, Tegretol, or Phenobarbital. A child
may be able to see an object one day and be unable to the next. These children
may also have better peripheral than central vision and thus look at objects
out of the side of their eye. They may have visual field losses that are
not symmetrical (one eye may be worse than the other). This uneven loss
does not necessarily correspond to hand function. If the left eye is better
than the right, the left hand is not necessarily stronger than the right.
Children with NVI experience problems with specific types of visual tasks.
They have difficulty with figure-ground (seeing an object instead of the
background), and with complex visual displays such as cluttered pictures
(a picture of five different animals instead of two). Spatial confusion
is common; for example being unable to locate their chair even though they
can see it. They may also be visually inattentive, not wanting to look at
objects, and may prefer their sense of touch. It is common to see a child
turn his/her head away as they explore an object with their hands. Seeing
with NVI can be compared with trying to listen to one voice in a noisy room
or to speaking a foreign language.
Vision stimulation is proven to help most children with vision impairments
improve the way they use their vision; this is especially true of children
with NVI. For vision stimulation to be effective it needs to happen in everyday
real life situations, not only in therapy sessions. Identifying colors in
an activity, visually tracking their classmate as they move across the room,
and identifying the shape of every day objects are examples.
Suggested Instructional Strategies for Children with NVI:
1. Materials, such as pictures, should be simple in form, high contrast (the colors of a picture or object should
be different such as a yellow toy against a black background instead of
an orange one), and presented one at a time.
2. Bright lighting can help a child see and attend to visual materials more
consistently. Adjust the light both natural and artificial to determine
what is best. Controlled incandescent lighting may be better than fluorescent
lighting.
3. Give the child time to respond to the materials that are being presented.
4. Color vision is usually intact, and color can be used effectively. Yellow
and red are possibly easier to see and can be used to outline numbers, letters,
or pictures, to color code, or to attract attention to something you want
the child to look at.
5. It is also important to keep the color of materials constant to avoid
confusion. This also applies to visual cues in general which should also
be consistent over time and location. If the child uses a red bowl at home,
and this is how he knows it is time to eat, then the same should be done
at school. Watch to see if the child has a preference for size or color.
6. Use a multisensory approach such as pairing an
object that you want them to see with a sound.
7. Touch should be considered as a major sense
for learning. Children with NVI appear to learn effectively through this
sense.
8. Repetition and routines can help the child understand
their visual environment. If changes are needed, make them slowly to allow
time to adjust.
9. Fluctuations in visual performance can be limited
by reducing fatigue. Try working in short spurts, or divide a long task
into shorter periods.
10. Reduce outside noise and other environmental
stimulation that may distract the child.
11. Objects can be more easily seen when they are
moving. This is especially true when they are in the peripheral fields.
12. Positioning is also important. The more energy
being expended on holding yourself up the less can be used for seeing.
13. Language helps a child to understand a visual
situation by adding meaning to it. Be consistent in the language you use.
References:
Groenveld, M, Jan, J.E, & Leader, P. (1990).
Observations on the Habilitation of Children with Cortical Visual Impairment.
Journal of Visual Impairment and Blindness, 84, 11-15.
Levack, N. (1991).
Low Vision: A Resource Guide with Adaptations for Students with Visual Impairments.
Austin: Texas School for the Blind.
Morse, M.T. (1990).
Cortical Visual Impairment in Young Children with Multiple Disabilities.
Journal of Visual Impairment and Blindness, 84, 200-203.
Takeshita, B. (1996, March).
Neurological Visual Impairment.
Paper presented at the Annual Conference of the California Transcribers and Educators of
the Visually Handicapped.
Fact sheets from California Deaf-Blind Services are
to be used by both families and professionals serving individuals with dual
sensory impairments. The information applies to students 0-22 years of age.
The purpose of the fact sheet is to give general information on a specific
topic. More specific information for an individual student can be provided
through individualized technical assistance available from CDBS. The fact
sheet is a starting point for further information.
Order Number 022.