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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:

  • Can the person scan a room to find someone or something?

  • What lighting is best for the person to do different tasks?

  • 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:

How common is vision impairment?

Photo of child with vision impairment drawing on an easelVision 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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What causes vision impairment?  Can it be prevented?

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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What is the cost or economic impact associated with vision impairment?

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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Where can I go to learn more about vision impairment?

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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Vision Impairment