Blindness

What is 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 and define blindness. Total blindness is the complete lack of form and visual light perception and is clinically recorded as "NLP", an abbreviation for "no light perception". Blindness is frequently used to describe severe visual impairment with residual vision.

In order to determine which people may need special assistance because of their visual disabilities, various governmental jurisdictions have formulated more complex definitions referred to as legal blindness. In North America and most of Europe, legal blindness is defined as visual acuity (vision) of 20/200 or less in the better eye with best correction possible. This means that a legally blind individual would have to stand 20 feet from an object to see it—with vision correction—with the same degree of clarity as a normally sighted person could from 200 feet.

In 1987, it was estimated that 598,000 people in the United States met the legal definition of blindness. Of this number, 58% were over the age of 65. In 1994-1995, 1.3 million Americans reported legal blindness.

In November 2004 article Magnitude and causes of visual impairment, the WHO estimated that in 2002 there were 161 million (about 2.6% of the world population) visually impaired people in the world, of whom 124 million (about 2%) had low vision and 37 million were blind.

Blindness
The long white cane is the international symbol of blindness

Causes of blindness

Serious visual impairment has a variety of causes:

Diseases

Most visual impairment is caused by disease and malnutrition. According to WHO estimates in 2002, the most common causes of blindness around the world are:

• cataracts (47.8%),
• glaucomauveitis (10.2%),
• age-related macular degeneration (AMD) (8.7%),
• trachoma (3.6%),corneal opacity (5.1%),
• anddiabetic retinopathy (4.8%), among other causes.

Vision impairment is most common in people over age 60 across all regions, children in poorer communities are more likely to be affected by blinding diseases.In developed countries where parasitic diseases are less common and cataract surgery is more available, age-related macular degeneration, glaucoma, and diabetic retinopathy are usually the leading causes of blindness.

Abnormalities and injuries

Eye injuries, most often occurring in people under 30, are the leading cause of monocular blindness (vision loss in one eye). Injuries and cataracts affect the eye itself, while abnormalities such as optic nerve hypoplasia affect the nerve bundle that sends signals from the eye to the back of the brain, which can lead to decreased visual acuity.

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

Genetic defects

People with albinism often suffer from visual impairment to the extent that many are legally blind, though few of them actually cannot see. Leber's congenital amaurosis can cause total blindness or severe sight loss from birth or early childhood.

Recent advances in mapping of the human genome have identified other genetic causes of low vision or blindness. One such example is Bardet-Biedl syndrome.

Poisoning

Rarely, blindness is caused by the intake of certain chemicals. A well-known example is methanol, which ironically is only mildly toxic and minimally intoxicating, but when not competing with ethanol for metabolism, methanol breaks down into the substances formaldehyde and formic acid which in turn can cause blindness, an array of other health complications, and death. Methanol is commonly found in methylated spirits and denatured ethyl alcohol. Methylated spirits are sometimes used by alcoholics as a desperate and cheap substitute for regular ethanol alcoholic beverages.

Treatment

A 2008 study published in the New England Journal of Medicine tested the effect of using gene therapy to help restore the sight of patients with a rare form of inherited blindness, known as Leber Congenital Amaurosis or LCA. Leber Congenital Amaurosis damages the light receptors in the retina and usually begins affecting sight in early childhood, with worsening vision until complete blindness around the age of 30.

The study used a common cold virus to deliver a normal version of the gene called RPE65 directly into the eyes of affected patients. Remarkably all 3 patients aged 19, 26 and 26 responded well to the treatment and reported improved vision following the procedure.It is more applicable to younger patients who have experienced a limited loss of vision.

Adaptive techniques

(A tactile feature on a Canadian banknote)

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:

• Adaptive computer and mobile phone software that allows people with visual impairments to interact with their computers and/or phones via screen readers or screen magnifiers.
• Adaptations of banknotes so that the value can be determined by touch. For example:
  • In some currencies, such as the euro, the pound sterling and the Norwegian krone, the size of a note increases with its value.
  • Some currencies' banknotes have a tactile feature to indicate denomination. For example, the tactile feature is a system of raised dots in one corner, based on Braille cells but not standard Braille.
  • It is also possible to fold notes in different ways to assist recognition.
• Labeling and tagging clothing and other personal items
• Placing different types of food at different positions on a dinner plate
• Marking controls of household appliances

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

Tools

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

Mobility

(Folded long cane)

Many people with serious visual impairments can travel independently, using a wide range of tools and techniques. Orientation and mobility specialists are professionals who are specifically trained to teach people with visual impairments how to travel safely, confidently, and independently in the home and the community. These professionals can also help blind people to practice travelling on specific routes which they may use often, such as the route from one's house to a convenience store. Becoming familiar with an environment or route can make it much easier for a blind person to navigate successfully.

Tools such as the white cane with a red tip - the international symbol of blindness may also be used to improve mobility. A long cane is used to extend the user's range of touch sensation. It is usually swung in a low sweeping motion, across the intended path of travel, to detect obstacles. However, techniques for cane travel can vary depending on the user and/or the situation. Some visually impaired persons do not carry these kinds of canes, opting instead for the shorter, lighter identification (ID) cane. Still others require a support cane. The choice depends on the individual's vision, motivation, and other factors.

A small number of people employ guide dogs to assist in mobility. These dogs are trained to navigate around various obstacles, and to indicate when it becomes necessary to go up or down a step. However, the helpfullness of guide dogs is limited by the inability of dogs to understand complex directions.

Reading and magnification

(Watch for the blind)

Most visually impaired people who are not totally blind read print, either of a regular size or enlarged by magnification devices. Many also read large-print, which is easier for them to read without such devices. A variety of magnifying glasses, some handheld, and some on desktops, can make reading easier for them.

Other aids

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

Blindness in animals

Statements that certain species of mammals are "born blind" refers to them being born with their eyes closed and their eyelids fused together; the eyes open later. One example is the rabbit. In humans the eyelids are fused for a while before birth, but open again before the normal birth time, but very premature babies are sometimes born with their eyes fused shut, and opening later. Other animals such as the blind mole rat are truly blind and rely on other senses.