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Blindness
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Blindness

Blindness can be defined physiologically as the condition of lacking sight. The definition as it applies to people thus legally classified is, however, more complex.

In North America and most of Europe, legal blindness is defined as vision of 20/200 (6/60) or less in the better eye with correction. People with normal acuity who nonetheless have a visual field of less than 20 degrees - the norm being 180 degrees - are also classified as being legally blind.

The World Health Organization defines legal blindness as vision of 20/400 (3/60) or less in the better eye with correction. They also accept people with a visual field of less than 10 degrees under that heading.

Approximately ten percent of those classified as being legally blind are actually sightless. The rest have some vision, from light perception alone to relatively good acuity.

Table of contents
1 Low vision
2 Causes of blindness
3 Alternative techniques and tools
4 A word on guide dogs
5 Social attitudes towards blindness
6 See also
7 External links

Low vision

Many countries also have a legal provision for people who, though not legally blind, have vision poor enough to affect their performance of daily tasks using traditional methods.

Causes of blindness

Diseases of the eye

The most common causes of blindness in the world today are cataracts (43% in 1997, according to WHO), Glaucoma (15%), Trachoma (11%), and Vitamin A deficiency found in children under 5 (6%).

People in developing countries are significantly more likely to experience visual impairment as a consequence of treatable or preventable conditions, than are their counterparts in the developed world. Moreover, while vision impairment is most common in people over age 60 across all regions, children in poorer communities are more likely to be affected by a blinding condition than are their more affluent peers.

The most common causes of adult visual impairment in North America and Western Europe include age-related Macular Degeneration and Diabetic Retinopathy.

Conditions and disorders

Another kind of visual impairment, cortical blindness, is the result of brain injury affecting a vital area of the visual system called the occipital lobe. People with cortical blindness can, despite having perfectly normal eyes and optic nerves, still be legally or totally blind.

Other conditions, such as Optic Nerve Hypoplasia and Optic Nerve Atrophy, cause visual impairment by affecting those nerve bundles that send visual signals from the eyes to the brain for interpretation.

Alternative techniques and tools

Many blind and visually impaired people use a wide range of alternative techniques and specialized tools to accomplish tasks traditionally done using sight. Techniques can include, but are no limited to, the following:

Tools can include, but are not limited to, the following:

A word on guide dogs

A very small number of visually impaired people employ the services of guide dogs. These companions are especially trained to lead blind individuals around obstacles on the ground and overhead. Though highly intelligent, guide dogs neither interpret streets signs nor determine when the team ought to cross a street. Visually impaired people who employ these animals must, then, already be competent travelers.

Social attitudes towards blindness

Historically, blind and visually impaired people have either been treated as if their lack of sight were an outward manifestation of some internal lack of reason, or as if they possessed extra-sensory abilities. Stories such as The Cricket on the Hearth (Dickens) provided yet another view of blindness, wherein those affected by it were ignorant of their surroundings and easily deceived.

The authors of modern educational materials (see: blindness and education for further reading on that subject), as well as those treating blindness in literature, have worked to paint a truer picture of blind people as three-dimensional individuals with a range of abilities, talents, and even character flaws. Certain individuals are gifted, and others licentious, but nothing definitive can be said of the blind as a class but that they cannot see well.

See also

External links