Vision Impairment
Vision impairment means that a person's eyesight cannot
be corrected to a "normal" level. It is a loss of vision that makes
it hard or impossible to do daily tasks without specialized
adaptations. Vision impairment may be caused by a loss of visual
acuity, where the eye does not see objects as clearly as usual. It
may also be caused by a loss of visual field, where the eye cannot see as
wide an area as usual without moving the eyes or turning the head.
There are different ways of describing how severe a
person's vision loss is. The World Health Organization defines "low
vision" as visual acuity between 20/70 and 20/400, with the best possible
correction, or a visual field of 20 degrees or less. "Blindness" is
defined as a visual acuity worse than 20/400, with the best possible
correction, or a visual field of 10 degrees or less. Someone with a
visual acuity of 20/70 can see at 20 feet what someone with normal sight
can see at 70 feet. Someone with a visual acuity of 20/400 can see
at 20 feet what someone with normal sight can see at 400 feet. A
normal visual field is about 160-170 degrees horizontally.
Vision impairment severity may be categorized
differently for certain purposes. In the United States, for example,
we use the term "legal blindness" to indicate that a person is eligible
for certain education or federal programs. Legal blindness is
defined as a visual acuity of 20/200 or worse, with the best possible
correction, or a visual field of 20 degrees or less.
Visual acuity alone cannot tell you how much a person's
life will be affected by their vision loss. It is important to also assess
how well a person uses the vision they have. Two people may have the
same visual acuity, but one may be able to use his or her vision better to
do everyday tasks. Most people who are "blind" have at least some
usable vision that can help them move around in their environment and do
things in their daily lives. A person's functional vision can be
evaluated by observing them in different settings to see how they use
their vision. A functional vision evaluation can answer questions
such as these:
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Can the person scan a room to find someone or
something?
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What lighting is best for the person to do different
tasks?
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How does the person use his or her vision to move
around in a room or outside?
Vision impairment changes how a child understands and
functions in the world. Impaired vision can affect a child’s cognitive,
emotional, neurological, and physical development by possibly limiting the
range of experiences and the kinds of information a child is exposed
to.
Nearly two-thirds of children with vision impairment also
have one or more other developmental disabilities, such as mental retardation,
cerebral palsy, hearing loss, or epilepsy. Children with more severe vision
impairment are more likely to have additional disabilities than are children
with milder vision impairment.
You can learn more about vision impairment
below, including answers to the following questions:·
Vision impairment is not very common among children. To learn just
how common it is, CDC is tracking the number of children with vision impairment
in a five-county area in metropolitan Atlanta, Georgia. This activity is part
of the Metropolitan Atlanta Developmental Disabilities Surveillance Program
(MADDSP). For 1991-1994, we found that, on average, about nine in every 10,000
children ages 3 to 10 years had low vision or blindness. We also found that
vision impairment was more common in older children (ages 6 to 10 years) than
in younger children (ages 3 to 5 years). Two-thirds of the children
had one or more other disabilities in addition to their vision impairment.
CDC also studied how many children in metropolitan
Atlanta were legally blind in the mid-1980s. This project was done as part
of the Metropolitan Atlanta Developmental Disabilities Study (MADDS), which
studied how common certain disabilities were in 10-year-old children.
We found that nearly 7 of every 10,000 children 10 years of age had legal
blindness. Two-thirds of the children also had another disability, such as
mental retardation, cerebral palsy, or epilepsy.
Vision impairment is more common in older people
than in children.. A 2002 report by the National Eye Institute and Prevent
Blindness America estimates that more than 1 million people ages 40 years
or older in the United States are blind (best corrected visual acuity of 20/200
or worse or a visual field of less than 20 degrees). Another 2.4 million
are visually impaired (best corrected visual acuity of 20/40 or worse).
The report states that the number of adults with vision impairment likely
will double over the next 30 years.
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Vision impairment can be caused by damage to
the eye itself that affects its ability to receive or process visual
information. Impairment can also be due to the eye being shaped
incorrectly, which can make it harder to focus on things. Vision
impairment can also occur if the brain does not process visual information
correctly. Vision impairment can occur anytime during a person's
life, even before birth.
CDC studied the causes of low vision and blindness
in 3- to 10-year old children in metropolitan Atlanta, Georgia. We found
that most of the causes happened before the child was born or before they
were 1 month old. The most common cause was retinopathy of prematurity
(ROP), which refers to abnormal blood vessel growth or scarring of the retina
of the eye. Children who are born very early or who have very low birth
weight are most at risk of having this condition. ROP usually gets better
on its own before severe damage can occur, and if not, it can often be treated.
However, a small percentage of children with ROP have a severe form and will
have low vision or blindness. Other common causes of vision impairment
found in the CDC study were albinism (a genetic condition that results in
decreased skin pigmentation and affects parts of the eye), hydrocephalus (a
condition in which there is too much fluid in the brain), congenital cytomegalovirus
(a viral infection that occurs before a baby is born), and birth asphyxia
(where a baby does not get enough oxygen before or during birth).
The most common causes of vision impairment among
adults in the United States are diabetic retinopathy, age-related macular
degeneration, cataracts, and glaucoma. Diabetic retinopathy is a common
complication of diabetes in which the blood vessels in the retina break down,
leak, or become blocked, leading to vision impairment. Age-related macular
degeneration affects the part of the retina that is responsible for sharp
central vision. Cataracts are a clouding of the eye's lens, which is
normally clear. Glaucoma is increased fluid and pressure within the
eye that leads to enlargement of the eyeball. The risk of vision loss
from many of these conditions can often be reduced if the condition is found
early and treated.
If you would like to learn more about a specific
genetic condition that you think could cause vision impairment, you can go
to the National Library of Medicine's Genetics Home Reference Web site. Information
on each genetic condition includes symptoms, how common it is, related genes,
treatments, and links to resources where you can learn more about the condition.
The Genetics Home Reference also can help you learn more about genetics, including
genetic testing, genetic counseling, and gene therapy.
You can search for CDC guidelines on preventing
vision impairment by visiting the "CDC Recommends: The Prevention Guidelines
System" Web site. The guidelines include information about vision problems
caused by diabetes, infections, eye injuries caused by fireworks, and other
topics. Enter "blindness" or "low vision" in the Search For box, then click
the "Search" button.]
Healthy People 2010 is a national effort to promote
health and prevent disease. It includes goals related to vision impairment,
such as preventing eye injuries, increasing the number of people who have
their eyes examined, decreasing the number of children under 17 years old
who are blind or visually impaired, decreasing the number of people who lose
their vision due to diabetes, and others. The National Eye Institute
(NEI) has created a Web site named "Healthy Vision 2010" that provides more
information about the vision-related goals in Healthy People 2010.
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Many people with vision impairment need
long-term services. The average lifetime cost for one person with vision
impairment is estimated to be $566,000 (in 2003 dollars). This represents
costs over and above those experienced by a person who does not have a
disability.
It is estimated that the lifetime costs for
all people with vision impairment who were born in 2000 will total $2.5
billion (in 2003 dollars). These costs include both direct and indirect
costs. Direct medical costs, such as doctor visits, prescription drugs,
and inpatient hospital stays, make up 6% of these costs. Direct nonmedical
expenses, such as home modifications and special education, make up 16% of
the costs. Indirect costs, which include the value of lost wages when a
person dies early, cannot work, or is limited in the amount or type of
work he or she can do, make up 77% of the costs.
These estimates do not include other expenses,
such as hospital outpatient visits, emergency department visits, and family
out-of-pocket expenses. The actual economic costs of vision impairment are,
therefore, even higher than what is reported here.
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National
Information Center on Children and Youth with Disabilities (NICHCY)
MEDLINEplus:
Eyes and Vision; Vision Disorders and Blindness
National
Eye Institute (NEI)
NCBDDD
(NCBDDD) Publications
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