Blindness Causes Of Blindness Diseases Abnormalities And

The term "blindness" also applies to partial visual impairment: 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. This means that an legally blind individual would have to stand 20 feet from an object to see it with the same degree of clarity as a normally sighted person could from 200 feet.

People with average 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 (WHO) defines legal blindness as vision of 20/400 (3/60) or less in the better eye with correction, or a visual field of less than 10 degrees.

Approximately ten percent of those deemed being legally blind, by any measure, are actually sightless. The rest have some vision, from light perception alone to relatively good acuity. Those who are not legally blind, but nonetheless have serious visual impairments, possess Low vision.

1 Causes of blindness

Serious visual impairment has a variety of causes, almost all of which can be traced back to damage in some part of the visual system.

1.1 Diseases

Most visual impairment is caused by disease and malnutrition: The most common causes of blindness around the world 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. 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 diseases than are their more affluent peers.

The link between poverty and treatable visual impairment is most obvious when conducting regional comparisons of cause. Most adult visual impairment in North America and Western Europe is related to age-related Macular degeneration and Diabetic retinopathy. While both of these conditions are subject to treatment, neither can be cured.

In developing countries, wherein people have shorter life expectancies, cataracts and water-borne parasites - both of which can be treated effectively - are most often the culprits. Of the estimated 40 million blind people located around the world, 70-80% can have some or all of their sight restored through treatment.

1.2 Abnormalities and injuries

Eye injuries, most often occurring in people under 30, are the leading cause of monocular blindness - vision loss in one eye - throughout the United States. Both of these conditions - injuries and cataracts - affect the eye itself. Abnormalities such as Optic nerve hypoplasia affect the nerve bundle that sends signals from the eye to the back of the brain, and can lead to decreased visual acuity.

People with injuries to the occipital lobe of the brain can, despite having perfectly normal eyes and optic nerves, still be legally or totally blind.

2 Alternative techniques

Visually impaired and blind people have devised a number of techniques that allow them to complete daily activities using their remaining senses. These might include the following:

Most people, once they have been visually impaired for long enough, devise their own adaptive strategies in all areas of personal and professional management.

3 Tools

Designers, both visually impaired and sighted, have developed a number of tools for use by blind people.

3.1 Mobility

People with serious visual impairments can travel independently using a white caneMany people who are blind or visually impaired use the white cane both as a mobility tool, and as a courtesy to others. Not all modern white canes are designed to fulfill the same primary function, however: There are at least four different varieties of t, the interntational symbol of blindness.

A long cane is used to extend the user's range of touch sensation, being 'swept' back and forth across the intended path of travel to detect obstacles. Some visually impaired people do not carry these kinds of canes, however; opting instead for the shorter, lighter identification (ID) cane. Still others require a support cane.

Each of these is painted white for maximum visibility, and to denote visual impairment on the part of the user. In addition to making rules about who can and cannot use a cane, some governments mandate the right-of-wayRight-of-way is a legal term which may have any of several meanings: priority at a crossing, or in traffic. The one vehicle must yield either to pedestrians or to other vehicles that have priority. It is not an absolute right as it must be exercised in a be given to users of white canes or guide dogs.

A small number of people - about one percent - employ guide dogLabrador Retriever guide dogs resting. Guide dogs are assistance dogs especially trained to lead blind or visually impaired people around obstacles. These dogs spend their early lives in foster homes where they are socialized through exposure to loving ats. These companions are trained to lead blind individuals around obstacles on the ground and overhead. Though highly intelligent, guide dogs neither interpret street signs nor determine when the team ought to cross a street. Visually impaired people who employ these animals must already be competent travelers.

3.2 Reading and magnification

Most blind and visually impaired people read print, either of a regular size or enlarged either on the paper itself or through the use of magnification devices. The rest either read BrailleThere is also an asteroid 9969 Braille Braille is a tactile writing system used by blind people. It was invented by Louis Braille of France who was blinded in a childhood accident. At the age of 15 he modified a military system for reading orders at night and Moon typeMoon type (or Moon code is a system of writing for the blind, using embossed symbols mostly derived from the Roman alphabet (but simplified). It is claimed by its supporters to be easier to understand than Braille though it is mainly used by people who ha, or rely upon talking books and readers.

A variety of magnifying glassA magnifying glass is a single convex lens which is used to produce a magnified image of an object. The lens is usually mounted in a frame with a handle. The magnifying glass is the simplest form of optical microscope. A magnifying glass works by creatinges, some of which are hand-held while others rest on desktops, can make reading easier for those with decreased visual acuity.

Closed-Circuit Televisions - pieces of equipment that enlarge and contrast textual items - are a more high-tech alternative to traditional magnification devices. So too are modern web browsers, which can increase the size of text on some web pages through browser controls or through user-controlled style sheet s.

3.3 Computers

Contrary to widely held belief, most legally blind people - 70% of them, across all ages, according to the Lighthouse for the Blind - do not use computers. Only a small fraction of them, when compared to the sighted community, have internet access.

A movement towards greater web accessibility is changing through, by opening a far wider number of websites to adaptive technology such as text-to-speech software.

3.4 Other aids

People may use Talking Thermometer s, enlarged or marked oven dials, talking watches, talking clocks, talking scales, talking calculators, talking compasses and other talking equipment.

4 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.

5 See also:

disability Ophthalmology

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