VISUAL IMPAIRMENT, also known as VISION IMPAIRMENT or VISION LOSS, is
a decreased ability to see to a degree that causes problems not
fixable by usual means, such as glasses . Some also include those
who have a decreased ability to see because they do not have access to
glasses or contact lenses .
The most common causes of visual impairment globally are uncorrected
refractive errors (43%), cataracts (33%), and glaucoma (2%).
World Health Organization
As of 2015 there were 940 million people with some degree of vision loss. 246 million had low vision and 39 million were blind. The majority of people with poor vision are in the developing world and are over the age of 50 years. Rates of visual impairment have decreased since the 1990s. Visual impairments have considerable economic costs both directly due to the cost of treatment and indirectly due to decreased ability to work.
* 1 Classification
* 1.1 United Kingdom
* 2 Health effects
* 2.1 Associated problems
* 3 Cause
* 4 Diagnosis * 5 Prevention
* 6 Treatment
* 6.1 Mobility * 6.2 Reading and magnification * 6.3 Computers * 6.4 Other aids and techniques
* 6.5 Communication
* 6.5.1 Adjusting attitude
* 6.5.2 Surroundings
* 220.127.116.11 Sound * 18.104.22.168 Touch * 22.214.171.124 Smell
* 6.5.3 Communication development
* 126.96.36.199 Social development * 188.8.131.52 Language development
* 6.6 Healthcare access
* 7 Epidemiology
* 8 Society and culture
* 8.1 Legal definition
* 8.2 Literature and art
* 8.2.1 Antiquity * 8.2.2 Modern times
* 8.3 Sports * 8.4 Metaphorical uses
* 9 Research * 10 Other animals * 11 See also * 12 References * 13 External links
The definition of visual impairment is reduced vision not corrected
by glasses or contact lenses . The
World Health Organization
* 20/30 to 20/60 : is considered mild vision loss, or near-normal vision * 20/70 to 20/160 : is considered moderate visual impairment, or moderate low vision * 20/200 to 20/400 : is considered severe visual impairment, or severe low vision * 20/500 to 20/1,000 : is considered profound visual impairment, or profound low vision * More than 20/1,000 : is considered near-total visual impairment, or near total blindness * No light perception : is considered total visual impairment, or total blindness
Severely sight impaired
* Defined as having central visual acuity of less than 3/60 with normal fields of vision, or gross visual field restriction. * Unable to see at 3 metres what the normally sighted person sees at 60 m.
* Able to see at 3 m, but not at 6 m, what the normally sighted person sees at 60 m * Less severe visual impairment is not captured by registration data, and its prevalence is difficult to quantify
* A visual acuity of less than 6/18 but greater than 3/60. * Not eligible to drive and may have difficulty recognising faces across a street, watching television, or choosing clean, unstained, co-ordinated clothing.
In the UK , the Certificate of Vision Impairment (CVI) is used to certify patients as severely sight impaired or sight impaired. The accompanying guidance for clinical staff states: "The National Assistance Act 1948 states that a person can be certified as severely sight impaired if they are "so blind as to be unable to perform any work for which eye sight is essential". The test is whether a person cannot do any work for which eyesight is essential, not just his or her normal job or one particular job."
In practice, the definition depends on individuals' visual acuity and the extent to which their field of vision is restricted. The Department of Health identifies three groups of people who may be classified as severely visually impaired.
* Those below 3/60 (equivalent to 20/400 in US notation) Snellen (most people below 3/60 are severely sight impaired). * Those better than 3/60 but below 6/60 Snellen (people who have a very contracted field of vision only). * Those 6/60 Snellen or above (people in this group who have a contracted field of vision especially if the contraction is in the lower part of the field).
The Department of Health also state that a person is more likely to be classified as severely visually impaired if their eyesight has failed recently or if they are an older individual, both groups being perceived as less able to adapt to their vision loss.
In the United States, any person with vision that cannot be corrected to better than 20/200 in the best eye, or who has 20 degrees (diameter) or less of visual field remaining, is considered legally blind or eligible for disability classification and possible inclusion in certain government sponsored programs.
In the United States, the terms partially sighted, low vision, legally blind and totally blind are used by schools, colleges, and other educational institutions to describe students with visual impairments. They are defined as follows:
* Partially sighted indicates some type of visual problem, with a need of person to receive special education in some cases.
* Myopic – unable to see distant objects clearly, commonly called near-sighted or short-sighted. * Hyperopic – unable to see close objects clearly, commonly called far-sighted or long-sighted.
In 1934, the
American Medical Association
Central visual acuity of 20/200 or less in the better eye with corrective glasses or central visual acuity of more than 20/200 if there is a visual field defect in which the peripheral field is contracted to such an extent that the widest diameter of the visual field subtends an angular distance no greater than 20 degrees in the better eye.
United States Congress
An individual shall be considered to be blind for purposes of this title if he has central visual acuity of 20/200 or less in the better eye with the use of a correcting lens. An eye which is accompanied by a limitation in the fields of vision such that the widest diameter of the visual field subtends an angle no greater than 20 degrees shall be considered for purposes of the first sentence of this subsection as having a central visual acuity of 20/200 or less. An individual shall also be considered to be blind for purposes of this title if he is blind as defined under a State plan approved under title X or XVI as in effect for October 1972 and received aid under such plan (on the basis of blindness) for December 1973, so long as he is continuously blind as so defined.
Visual impairments may take many forms and be of varying degrees.
American Medical Association
Some people who fall into this category can use their considerable residual vision – their remaining sight – to complete daily tasks without relying on alternative methods. The role of a low vision specialist (optometrist or ophthalmologist) is to maximize the functional level of a patient's vision by optical or non-optical means. Primarily, this is by use of magnification in the form of telescopic systems for distance vision and optical or electronic magnification for near tasks.
People with significantly reduced acuity may benefit from training
conducted by individuals trained in the provision of technical aids.
The subjects making the most use of rehabilitation instruments, who lived alone, and preserved their own mobility and occupation were the least depressed, with the lowest risk of suicide and the highest level of social integration.
Those with worsening sight and the prognosis of eventual blindness are at comparatively high risk of suicide and thus may be in need of supportive services. These observations advocate the establishment and extension of therapeutic and preventative programs to include patients with impending and current severe visual impairment who do not qualify for services for the blind. Ophthalmologists should be made aware of these potential consequences and incorporate a place for mental health professionals in their treatment of these types of patients, with a view to preventing the onset of depressive symptomatology, avoiding self-destructive behavior, and improving the quality of life of these patients. Such intervention should occur in the early stages of diagnosis, particularly as many studies have demonstrated how rapid acceptance of the serious visual handicap has led to a better, more productive compliance with rehabilitation programs. Moreover, psychological distress has been reported (and is exemplified by our psychological autopsy study) to be at its highest when sight loss is not complete, but the prognosis is unfavorable.10 Therefore, early intervention is imperative for enabling successful psychological adjustment.
It has been estimated that over half of completely blind people have non-24-hour sleep–wake disorder , a condition in which a person's circadian rhythm , normally slightly longer than 24 hours, is not entrained (synchronized) to the light/dark cycle.
The most common causes of visual impairment globally in 2010 were:
* Refractive error (42%) * cataract (33%) * glaucoma (2%) * age related macular degeneration (1%) * corneal opacification (1%) * diabetic retinopathy (1%) * childhood blindness * trachoma (1%) * undetermined (18%)
The most common causes of blindness in 2010 were:
* cataracts (51%) * glaucoma (8%) * age related macular degeneration (5%) * corneal opacification (4%) * childhood blindness (4%) * refractive errors (3%) * trachoma (3%) * diabetic retinopathy (1%) * undetermined (21%)
About 90% of people who are visually impaired live in the developing world . Age-related macular degeneration, glaucoma, and diabetic retinopathy are the leading causes of blindness in the developed world.
Among working age adults who are newly blind in England and Wales the most common causes in 2010 were:
* Hereditary retinal disorders (20.2%)
Of these, cataract is responsible for >65%, or more than 22 million cases of blindness, and glaucoma is responsible for 6 million cases.
The burden of onchocerciasis : children leading blind adults in Africa
Childhood blindness can be caused by conditions related to pregnancy, such as congenital rubella syndrome and retinopathy of prematurity . Leprosy and onchocerciasis each blind approximately 1 million individuals in the developing world.
The number of individuals blind from trachoma has decreased in the past 10 years from 6 million to 1.3 million, putting it in seventh place on the list of causes of blindness worldwide.
Central corneal ulceration is also a significant cause of monocular blindness worldwide, accounting for an estimated 850,000 cases of corneal blindness every year in the Indian subcontinent alone. As a result, corneal scarring from all causes is now the fourth greatest cause of global blindness.
Re-educating wounded. Blind French soldiers learning to make baskets, World War I.
Eye injuries, most often occurring in people under 30, are the
leading cause of monocular blindness (vision loss in one eye)
Cortical blindness results from injuries to the occipital lobe of the brain that prevent the brain from correctly receiving or interpreting signals from the optic nerve . Symptoms of cortical blindness vary greatly across individuals and may be more severe in periods of exhaustion or stress. It is common for people with cortical blindness to have poorer vision later in the day.
Blinding has been used as an act of vengeance and torture in some
instances, to deprive a person of a major sense by which they can
navigate or interact within the world, act fully independently, and be
aware of events surrounding them. An example from the classical realm
People with albinism often have vision loss 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 .
Rarely, blindness is caused by the intake of certain chemicals. A
well-known example is methanol , which is only mildly toxic and
minimally intoxicating, and breaks down into the substances
formaldehyde and formic acid which in turn can cause blindness, an
array of other health complications, and death. When competing with
ethanol for metabolism, ethanol is metabolized first, and the onset of
toxicity is delayed.
Play media Scientists track eye movements in glaucoma patients to check vision impairment while driving
It is important that people be examined by someone specializing in
low vision care prior to other rehabilitation training to rule out
potential medical or surgical correction for the problem and to
establish a careful baseline refraction and prescription of both
normal and low vision glasses and optical aids. Only a doctor is
qualified to evaluate visual functioning of a compromised visual
system effectively. The
American Medical Association
Screening adults who have no symptoms is of uncertain benefit.
World Health Organization
Tommy Edison, a blind film critic, demonstrates for his viewers how a blind person can cook alone.
Aside from medical help, various sources provide information, rehabilitation, education, and work and social integration.
Folded long cane A blind man is assisted by a guide dog in Brasília, Brazil Blind girl feels shape of vehicle near Mana village, Uttarakhand Visually impaired girl negotiating a rock while rock climbing
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 helpfulness of guide dogs is limited by the inability of dogs to understand complex directions. The human half of the guide dog team does the directing, based upon skills acquired through previous mobility training. In this sense, the handler might be likened to an aircraft's navigator, who must know how to get from one place to another, and the dog to the pilot, who gets them there safely.
GPS devices can also be used as a mobility aid. Such software can assist blind people with orientation and navigation, but it is not a replacement for traditional mobility tools such as white canes and guide dogs.
Some blind people are skilled at echolocating silent objects simply by producing mouth clicks and listening to the returning echoes. It has been shown that blind echolocation experts use what is normally the "visual" part of their brain to process the echoes.
Government actions are sometimes taken to make public places more accessible to blind people. Public transportation is freely available to the blind in many cities. Tactile paving and audible traffic signals can make it easier and safer for visually impaired pedestrians to cross streets. In addition to making rules about who can and cannot use a cane, some governments mandate the right-of-way be given to users of white canes or guide dogs.
READING AND MAGNIFICATION
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.
Some people access these materials through agencies for the blind, such as the National Library Service for the Blind and Physically Handicapped in the United States, the National Library for the Blind or the RNIB in the United Kingdom.
Closed-circuit televisions , equipment that enlarges and contrasts textual items, are a more high-tech alternative to traditional magnification devices.
There are also over 100 radio reading services throughout the world that provide people with vision impairments with readings from periodicals over the radio. The International Association of Audio Information Services provides links to all of these organizations.
Access technology such as screen readers , screen magnifiers and
Blind people may use talking equipment such as thermometers , watches, clocks, scales , calculators , and compasses . They may also enlarge or mark dials on devices such as ovens and thermostats to make them usable. Other techniques used by blind people to assist them in daily activities include:
* Adaptations of coins and banknotes so that the value can be determined by touch. For example:
* In some currencies, such as the euro , the pound sterling and the
* 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.
For the blind, there are books in braille, audio-books, and text-to-speech computer programs, machines and e-book readers . Low vision people can make use of these tools as well as large-print reading materials and e-book readers that provide large font sizes.
Computers are important tools of integration for the visually
impaired person. They allow, using standard or specific programs,
screen magnification and conversion of text into sound or touch
In adults with low vision there is no conclusive evidence supporting one form of reading aid over another. In several studies stand-based closed-circuit television and hand-held closed-circuit television allowed faster reading than optical aids. While electronic aids may allow faster reading for individuals with low vision, portability, ease of use, and affordability must be considered for people.
Children with low vision sometimes have reading delays, but do benefit from phonics-based beginning reading instruction methods. Engaging phonics instruction is multisensory, highly motivating, and hands-on. Typically students are first taught the most frequent sounds of the alphabet letters, especially the so-called short vowel sounds, then taught to blend sounds together with three-letter consonant-vowel-consonant words such as cat, red, sit, hot, sun. Hands-on (or kinesthetically appealing) VERY enlarged print materials such as those found in "The Big Collection of Phonics Flipbooks" by Lynn Gordon (Scholastic, 2010) are helpful for teaching word families and blending skills to beginning readers with low vision. Beginning reading instructional materials should focus primarily on the lower-case letters, not the capital letters (even though they are larger) because reading text requires familiarity (mostly) with lower-case letters. Phonics-based beginning reading should also be supplemented with phonemic awareness lessons, writing opportunities, and lots of read-alouds (literature read to children daily) to stimulate motivation, vocabulary development, concept development, and comprehension skill development. Many children with low vision can be successfully included in regular education environments. Parents may need to be vigilant to ensure that the school provides the teacher and students with appropriate low vision resources, for example technology in the classroom, classroom aide time, modified educational materials, and consultation assistance with low vision experts.
Communication with the visually impaired can be more difficult than communicating with someone who doesn't have vision loss. However, many people are uncomfortable with communicating with the blind, and this can cause communication barriers. One of the biggest obstacles in communicating with visually impaired individuals comes from face-to-face interactions. There are many factors that can cause the sighted to become uncomfortable while communicating face to face. There are many non-verbal factors that hinder communication between the visually impaired and the sighted, more often than verbal factors do. These factors, which Rivka Bialistock mentions in her article, include:
* Lack of facial expressions, mimics, or body gestures/responses * Non-verbal gestures that could imply the visually impaired individual not appearing interested * Speaking when not anticipated or not speaking when anticipated * Fear of offending the visually impaired * Standing too close and invading the personal comfort level * Having to exercise or ignore feelings of pity * Being uncomfortable with touching objects or people * A look of detachment or disengagement * Dependency * Being reminded of the fear of becoming blind
The blind person sends these signals or types of non-verbal communication without being aware that they are doing so. These factors can all affect the way an individual would feel about communicating with the visually impaired. This leaves the visually impaired feeling rejected and lonely.
In the article Towards better communication, from the interest point of view. Or—skills of sight-glish for the blind and visually impaired, the author, Rivka Bialistock comes up with a method to reduce individuals being uncomfortable with communicating with the visually impaired. This method is called blind-glish or sight-glish, which is a language for the blind, similar to English. For example, babies, who are not born and able to talk right away, communicate through sight-glish, simply seeing everything and communicating non-verbally. This comes naturally to sighted babies, and by teaching this same method to babies with a visual impairment can improve their ability to communicate better, from the very beginning.
To avoid the rejected feeling of the visually impaired, people need to treat the blind the same way they would treat anyone else, rather than treating them like they have a disability, and need special attention. People may feel that it is improper to, for example, tell their blind child to look at them when they are speaking. However, this contributes to the sight-glish method. It is important to disregard any mental fears or uncomfortable feelings people have while communicating (verbally and non-verbally) face-to-face.
Individuals with a visual disability not only have to find ways to communicate effectively with the people around them, but their environment as well. The blind or visually impaired rely largely on their other senses such as hearing, touch, and smell in order to understand their surroundings.
Sound is one of the most important senses that the blind or visually impaired use in order to locate objects in their surroundings. A form of echolocation is used, similarly to that of a bat. Echolocation from a person's perspective is when the person uses sound waves generated from speech or other forms of noise such as cane tapping, which reflect off of objects and bounce back at the person giving them a rough idea of where the object is. This does not mean they can depict details based on sound but rather where objects are in order to interact, or avoid them. Increases in atmospheric pressure and humidity increase a person's ability to use sound to their advantage as wind or any form of background noise impairs it.
Touch is also an important aspect of how blind or visually impaired people perceive the world. Touch gives immense amount of information in the person's immediate surrounding. Feeling anything with detail gives off information on shape, size, texture, temperature, and many other qualities. Touch also helps with communication; braille is a form of communication in which people use their fingers to feel elevated bumps on a surface and can understand what is meant to be interpreted. There are some issues and limitations with touch as not all objects are accessible to feel, which makes it difficult to perceive the actual object. Another limiting factor is that the learning process of identifying objects with touch is much slower than identifying objects with sight. This is due to the fact the object needs to be approached and carefully felt until a rough idea can be constructed in the brain.
Certain smells can be associated with specific areas and help a person with vision problems to remember a familiar area. This way there is a better chance of recognizing an areas layout in order to navigate themselves through. The same can be said for people as well. Some people have their own special odor that a person with a more trained sense of smell can pick up. A person with an impairment of their vision can use this to recognize people within their vicinity without them saying a word.
Social development includes interactions with the people surrounding the infant in the beginning of its life. To a child with vision, a smile from a parent is the first symbol of recognition and communication, and is almost an instant factor of communication. For a visually impaired infant, recognition of a parent's voice will be noticed at approximately two months old, but a smile will only be evoked through touch between parent and baby. This primary form of communication is greatly delayed for the child and will prevent other forms of communication from developing. Social interactions are more complicated because subtle visual cues are missing and facial expressions from others are lost.
Due to delays in a child's communication development, they may appear to be disinterested in social activity with peers, non-communicative and un-education on how to communicate with other people. This may cause the child to be avoided by peers and consequently over protected by family members.
With sight, much of what is learned by a child is learned through imitation of others, where as a visually impaired child needs very planned instruction directed at the development of postponed imitation. A visually impaired infant may jabber and imitate words sooner than a sighted child, but may show delay when combining words to say themselves, the child may tend to initiate few questions and their use of adjectives is infrequent. Normally the child's sensory experiences are not readily coded into language and this may cause them to store phrases and sentences in their memory and repeat them out of context. The language of the blind child does not seem to mirror their developing knowledge of the world, but rather their knowledge of the language of others.
A visually impaired child may also be hesitant to explore the world around them due to fear of the unknown and also may be discouraged from exploration by overprotective family members. Without concrete experiences, the child is not able to develop meaningful concepts or the language to describe or think about them.
* A prerequisite of effective health care could very well be having staff that are aware that people may have problems with vision. * Communication and different ways of being able to communicate with visually impaired clients must be tailored to individual needs and available at all times.
The WHO estimates that in 2012 there were 285 million visually impaired people in the world, of which 246 million had low vision and 39 million were blind.
Of those who are blind 90% live in the developing world. Worldwide for each blind person, an average of 3.4 people have low vision, with country and regional variation ranging from 2.4 to 5.5.
BY GENDER: Available studies consistently indicate that in every region of the world, and at all ages, females have a significantly higher risk of being visually impaired than males.
Since the estimates of the 1990s, new data based on the 2002 global population show a reduction in the number of people who are blind or visually impaired, and those who are blind from the effects of infectious diseases, but an increase in the number of people who are blind from conditions related to longer life spans.
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.
SOCIETY AND CULTURE
To determine which people qualify for special assistance because of
their visual disabilities, various governments have specific
definitions for legal blindness. In
LITERATURE AND ART
See also: Blindness in literature
The Moche people of ancient
In Greek myth,
The parable of the blind men and an elephant has crossed between many
religious traditions and is part of Jain ,
Three Blind Mice
The Dutch painter and engraver
H. G. Wells
Contemporary fiction contains numerous well-known blind characters .
Some of these characters can "see" by means of fictitious devices,
such as the
Blind and partially sighted people participate in sports, such as
swimming , snow skiing and athletics . Some sports have been invented
or adapted for the blind, such as goalball , association football ,
cricket , golf , and tennis . The worldwide authority on sports for
the blind is the
International Blind Sports Federation . People with
vision impairments have participated in the
The word "blind" (adjective and verb) is often used to signify a lack of knowledge of something. For example, a blind date is a date in which the people involved have not previously met; a blind experiment is one in which information is kept from either the experimenter or the participant to mitigate the placebo effect or observer bias . The expression "blind leading the blind" refers to incapable people leading other incapable people. Being blind to something means not understanding or being aware of it. A "blind spot " is an area where someone cannot see: for example, where a car driver cannot see because parts of his car's bodywork are in the way; metaphorically, a topic on which an individual is unaware of their own biases, and therefore of the resulting distortions of their own judgements (see Bias blind spot ).
Main article: Visual prosthesis
A 2008 study tested the effect of using gene therapy to help restore the sight of patients with a rare form of inherited blindness, known as Leber\'s congenital amaurosis or LCA. Leber's 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, 22 and 25, responded well to the treatment and reported improved vision following the procedure. Due to the age of the patients and the degenerative nature of LCA, the improvement of vision in gene therapy patients is encouraging for researchers. It is hoped that gene therapy may be even more effective in younger LCA patients who have experienced limited vision loss, as well as in other blind or partially blind individuals.
Two experimental treatments for retinal problems include a cybernetic replacement and transplant of fetal retinal cells.
Main article: Blind 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; however, 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.
The theme of blind animals has been a powerful one in literature. Peter Shaffer 's Tony Award-winning play, Equus , tells the story of a boy who blinds six horses. Theodore Taylor 's classic young adult novel, The Trouble With Tuck , is about a teenage girl, Helen, who trains her blind dog to follow and trust a seeing-eye dog.
* Disability portal
Blindness and education
* ^ A B C D "Change the Definition of Blindness" (PDF). World
Health Organization. Archived (PDF) from the original on 14 July 2015.
Retrieved 23 May 2015.
* ^ A B C D E F G H "
CLASSIFICATION V · T · D
* ICD -10 : H54.0, H54.1, H54.4 * ICD