Visual impairment is vision loss

Vision loss

Vision loss or visual loss is the absence of vision where it existed before, which can happen either acutely or chronically .-Ranges of vision loss:...

 (of a person) to such a degree as to qualify as an additional support need through a significant limitation of visual

Visual perception

Visual perception is the ability to interpret information and surroundings from the effects of visible light reaching the eye. The resulting perception is also known as eyesight, sight, or vision...

 capability resulting from either disease

Disease

A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...

, trauma

Physical trauma

Trauma refers to "a body wound or shock produced by sudden physical injury, as from violence or accident." It can also be described as "a physical wound or injury, such as a fracture or blow." Major trauma can result in secondary complications such as circulatory shock, respiratory failure and death...

, or congenital or degenerative conditions that cannot be corrected by conventional means, such as refractive correction, medication, or surgery. This functional loss of vision is typically defined to manifest with

1. best corrected visual acuity
   Visual acuity
   Visual acuity is acuteness or clearness of vision, which is dependent on the sharpness of the retinal focus within the eye and the sensitivity of the interpretative faculty of the brain....
   
    of less than 20/60, or significant central field defect,
2. significant peripheral field defect including homonymous or heteronymous bilateral visual, field defect or generalized contraction or constriction of field, or
3. reduced peak contrast sensitivity with either of the above conditions.

In the United States, the terms "partially sighted", "low vision

Low vision

Low vision is a subspecialty within the professions of optometry and ophthalmology dealing with individuals who have reduced vision even when using the best possible spectacle or contact lens correction available. It can be a result of either congenital disease Low vision is a subspecialty within...

", "legally blind" and "totally blind

Blindness

Blindness is the condition of lacking visual perception due to physiological or neurological factors.Various scales have been developed to describe the extent of vision loss and define blindness...

" are used by schools, colleges, and other educational institutions to describe students with visual impairments. They are defined as follows:

1. Partially sighted indicates some type of visual problem, with a need of person to receive special education in some cases;
2. Low vision generally refers to a severe visual impairment, not necessarily limited to distance vision. Low vision applies to all individuals with sight who are unable to read the newspaper at a normal viewing distance, even with the aid of eyeglasses or contact lenses. They use a combination of vision and other senses to learn, although they may require adaptations in lighting or the size of print, and, sometimes, Braille
   Braille
   The Braille system is a method that is widely used by blind people to read and write, and was the first digital form of writing.Braille was devised in 1825 by Louis Braille, a blind Frenchman. Each Braille character, or cell, is made up of six dot positions, arranged in a rectangle containing two...
   
   ;
   1. Myopic
      Myopia
      Myopia , "shortsightedness" ) is a refractive defect of the eye in which collimated light produces image focus in front of the retina under conditions of accommodation. In simpler terms, myopia is a condition of the eye where the light that comes in does not directly focus on the retina but in...
      
      - unable to see distant objects clearly, commonly called near-sighted or short-sighted
   2. Hyperopic
      Hyperopia
      Hyperopia, also known as farsightedness, longsightedness or hypermetropia, is a defect of vision caused by an imperfection in the eye , causing difficulty focusing on near objects, and in extreme cases causing a sufferer to be unable to focus on objects at any distance...
      
      - unable to see close objects clearly, commonly called far-sighted or long-sighted
3. Legally blind indicates that a person has less than 20/200 vision in the better eye after best correction (contact lenses or glasses), or a field of vision of less than 20 degrees in the better eye; and
4. Totally blind students learn via Braille or other non-visual media.

Visual impairment is the consequence of a functional loss of vision, rather than the eye disorder itself. Eye disorders which can lead to visual impairments can include retina

Retina

The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...

l degeneration, albinism

Albinism

Albinism is a congenital disorder characterized by the complete or partial absence of pigment in the skin, hair and eyes due to absence or defect of an enzyme involved in the production of melanin...

, cataracts, glaucoma

Glaucoma

Glaucoma is an eye disorder in which the optic nerve suffers damage, permanently damaging vision in the affected eye and progressing to complete blindness if untreated. It is often, but not always, associated with increased pressure of the fluid in the eye...

, muscular problems that result in visual disturbances, cornea

Cornea

The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is...

l disorders, diabetic retinopathy

Diabetic retinopathy

Diabetic retinopathy is retinopathy caused by complications of diabetes mellitus, which can eventually lead to blindness....

, congenital disorder

Congenital disorder

A congenital disorder, or congenital disease, is a condition existing at birth and often before birth, or that develops during the first month of life , regardless of causation...

s, and infection

Infection

An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...

." Visual impairment can also be caused by brain and nerve disorders, in which case it is usually termed cortical visual impairment

Cortical visual impairment

Cortical visual impairment is a form of visual impairment that is caused by a brain problem rather than an eye problem. Some people have both CVI and a form of ocular visual impairment.CVI is also sometimes known as cortical blindness, although most people with CVI...

 (CVI).

The American Medical Association

American Medical Association

The American Medical Association , founded in 1847 and incorporated in 1897, is the largest association of medical doctors and medical students in the United States.-Scope and operations:...

's Guides to the Evaluation of Permanent Impairment attempts to provide "a standardized, objective approach to evaluating medical impairments." The Visual System chapter "provides criteria for evaluating permanent impairment of the visual system as it affects an individual's ability to perform activities of daily living." The Guide has estimated that the loss of one eye equals 25% impairment of the visual system and 24% impairment of the whole person; total loss of vision in both eyes is considered to be 100% visual impairment and 85% impairment of the whole person.

Visual impairments have considerable economic impact on even developed countries. 'A major proportion of global visual impairment is preventable'.

See also

• Accessible image
  Accessible image
  An accessible image is an image that is made accessible to the visually impaired through touch, sight,smell and sound.-External links:*****...
  
  
• Maguire v SOCOG 2000
  Maguire v SOCOG 2000
  Maguire v SOCOG 2000 was a legal case in Australia about making a website accessible to a visually impaired person.-Complaint:On 7 June 1999, Maguire made a complaint to the human rights and equal opportunity commission , alleging that SOCOG had discriminated against him on the grounds of...
  
   (Australia
  Australia
  Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
  
  n legal case about making a website accessible to a visually impaired person)
• GPS for the visually impaired
  GPS for the visually impaired
  There have been many attempts to integrate Global Positioning System into a navigation-assistance system for the blind. GPS was introduced in the late 1980s and since then there have been several research projects to increase it's usefulness for the visually impaired.Satellite navigation...
  
  
• Touch user interface
  Touch user interface
  A touch user interface is a computer-pointing technology based upon the sense of touch . Whereas a graphical user interface relies upon the sense of sight, the TUI enables not only the sense of touch to innervate and activate computer-based functions, it also allows the user, particularly those...
  
  
• Center for the Partially Sighted
  Center for the Partially Sighted
  The Center for the Partially Sighted is an American non-profit organization with the goal of promoting independent living for people with visual impairments...
  
  

External links

• http://www.direct.gov.uk/disability Directgov disabled people - UK govt information
• CDC’s National Center on Birth Defects and Developmental Disabilities
• World Health Organization site on blindness and visual impairment
• Eye Conditions (RNIB)
• Center for the Partially Sighted Low Vision Information and Resources