| Visual impairment | |
|---|---|
| Other names | Vision impairment, vision loss |
 | |
| A white cane, the international symbol of blindness | |
| Specialty | Ophthalmology |
| Symptoms | Decreased ability to see |
| Causes | Uncorrected refractive errors, cataracts, glaucoma |
| Diagnostic method | Eye examination |
| Treatment | Vision rehabilitation, changes in the environment, assistive devices |
| Frequency | 940 million / 13% (2015) |
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. Visual impairment is often defined as a best corrected visual acuity of worse than either 20/40 or 20/60. The term blindness is used for complete or nearly complete vision loss. Visual impairment may cause people difficulties with normal daily activities such as driving, reading, socializing, and walking.
The most common causes of visual impairment globally are uncorrected refractive errors (43%), cataracts (33%), and glaucoma (2%). Refractive errors include near sighted, far sighted, presbyopia, and astigmatism. Cataracts are the most common cause of blindness. Other disorders that may cause visual problems include age related macular degeneration, diabetic retinopathy, corneal clouding, childhood blindness, and a number of infections. Visual impairment can also be caused by problems in the brain due to stroke, premature birth, or trauma among others. These cases are known as cortical visual impairment. Screening for vision problems in children may improve future vision and educational achievement. Screening adults without symptoms is of uncertain benefit. Diagnosis is by an eye exam.
The World Health Organization (WHO) estimates that 80% of visual impairment is either preventable or curable with treatment. This includes cataracts, the infections river blindness and trachoma, glaucoma, diabetic retinopathy, uncorrected refractive errors, and some cases of childhood blindness. Many people with significant visual impairment benefit from vision rehabilitation, changes in their environment, and assistive devices.
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.
Classification
A typical Snellen chart that is frequently used for visual acuity testing.
The definition of visual impairment is reduced vision not corrected by glasses or contact lenses.
The World Health Organization uses the following classifications of
visual impairment. When the vision in the better eye with best possible
glasses correction is:
- 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 (NLP) : is considered total visual impairment, or total blindness
Blindness is defined by the World Health Organization as vision in a person's best eye with best correction of less than 20/500 or a visual field of less than 10 degrees.
This definition was set in 1972, and there is ongoing discussion as to
whether it should be altered to officially include uncorrected
refractive errors.
United Kingdom
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 (10 ft) what the normally sighted person sees at 60 metres (200 ft).
Sight impaired
- Able to see at 3 metres (10 ft), but not at 6 metres (20 ft), what the normally sighted person sees at 60 metres (200 ft)
- Less severe visual impairment is not captured by registration data, and its prevalence is difficult to quantify
Low vision
- 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". Certification is based on whether a
person can do any work for which eyesight is essential, not just one
particular job (such as their job before becoming blind).
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.
United States
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.
- 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.
- 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.
- Totally blind students learn via Braille or other non-visual media.
In 1934, the American Medical Association adopted the following definition of blindness:
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.
The United States Congress included this definition as part of the Aid to the Blind program in the Social Security Act passed in 1935. In 1972, the Aid to the Blind program and two others combined under Title XVI of the Social Security Act to form the Supplemental Security Income program which states:
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.
Health effects
Visual
impairments may take many forms and be of varying degrees. Visual
acuity alone is not always a good predictor of the degree of problems a
person may have. Someone with relatively good acuity (e.g., 20/40) can
have difficulty with daily functioning, while someone with worse acuity
(e.g., 20/200) may function reasonably well if their visual demands are
not great.
The American Medical Association 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.
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. Low vision rehabilitation
professionals, some of whom are connected to an agency for the blind,
can provide advice on lighting and contrast to maximize remaining
vision. These professionals also have access to non-visual aids, and can
instruct patients in their uses.
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. 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 to be at its highest when sight
loss is not complete, but the prognosis is unfavorable. Therefore,
early intervention is imperative for enabling successful psychological
adjustment.
Associated problems
Blindness can occur in combination with such conditions as intellectual disability, autism spectrum disorders, cerebral palsy, hearing impairments, and epilepsy. Blindness in combination with hearing loss is known as deafblindness.
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.
Cause
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%)
- Diabetic retinopathy (14.4%)
- Optic atrophy (14.1%)
- Glaucoma (5.9%)
- Congenital abnormalities (5.1%)
- Disorders of the visual cortex (4.1%)
- Cerebrovascular disease (3.2%)
- Degeneration of the macula and posterior pole (3.0%)
- Myopia (2.8%)
- Corneal disorders (2.6%)
- Malignant neoplasms of the brain and nervous system (1.5%)
- Retinal detachment (1.4%)
Cataracts
Of
these, cataract is responsible for more than 65%, or more than 22 million
cases of blindness, and glaucoma is responsible for 6 million cases.
Cataracts:
is the congenital and pediatric pathology that describes the greying or
opacity of the crystalline lens, which is most commonly caused by
intrauterine infections, metabolic disorders, and genetically
transmitted syndromes.
Cataracts are the leading cause of child and adult blindness that
doubles in prevalence with every ten years after the age of 40. Consequently, today cataracts are more common among adults than in children.
That is, people face higher chances of developing cataracts as they
age. Nonetheless, cataracts tend to have a greater financial and
emotional toll upon children as they must undergo expensive diagnosis,
long term rehabilitation, and visual assistance. Also, according to the Saudi Journal for Health Sciences, sometimes patients experience irreversible amblyopia after pediatric cataract surgery because the cataracts prevented the normal maturation of vision prior to operation.
Despite the great progress in treatment, cataracts remain a global
problem in both economically developed and developing countries.
At present, with the variant outcomes as well as the unequal access to
cataract surgery, the best way to reduce the risk of developing
cataracts is to avoid smoking and extensive exposure to sun light (i.e.
UV-B rays).
Glaucoma
Glaucoma is a congenital and pediatric eye disease characterized by increased pressure within the eye or intraocular pressure (IOP). Glaucoma causes visual field loss as well as severs the optic nerve.
Early diagnosis and treatment of glaucoma in patients is imperative
because glaucoma is triggered by non-specific levels of IOP.
Also, another challenge in accurately diagnosing glaucoma is that the
disease has four causes: 1) inflammatory ocular hypertension syndrome
(IOHS); 2) severe uveitic angle closure; 3) corticosteroid-induced; and
4) a heterogonous mechanism associated with structural change and
chronic inflammation. In addition, often pediatric glaucoma differs greatly in cause and management from the glaucoma developed by adults. Currently, the best sign of pediatric glaucoma is an IOP of 21 mm Hg or greater present within a child.
One of the most common causes of pediatric glaucoma is cataract removal
surgery, which leads to an incidence rate of about 12.2% among infants
and 58.7% among 10-year-olds.
Infections
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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.
Injuries
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) throughout
the United States. 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.
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
is Oedipus,
who gouges out his own eyes after realizing that he fulfilled the awful
prophecy spoken of him. Having crushed the Bulgarians, the Byzantine
Emperor Basil II blinded as many as 15,000 prisoners taken in the battle, before releasing them. Contemporary examples include the addition of methods such as acid throwing as a form of disfigurement.
Genetic defects
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.
Poisoning
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. Methanol is commonly found in methylated spirits, denatured ethyl alcohol, to avoid paying taxes on selling ethanol intended for human consumption. Methylated spirits are sometimes used by alcoholics as a desperate and cheap substitute for regular ethanol alcoholic beverages.
Other
- Amblyopia: is a category of vision loss or visual impairment that is caused by factors unrelated to refractive errors or coexisting ocular diseases. Amblyopia is the condition when a child's visual systems fail to mature normally because the child either suffers from a premature birth, measles, congenital nubella syndrome, vitamin A deficiency, or meningitis. If left untreated during childhood, amblyopia is currently incurable in adulthood because surgical treatment effectiveness changes as a child matures. Consequently, amblyopia is the world's leading cause of child monocular vision loss, which is the damage or loss of vision in one eye. In the best case scenario, which is very rare, properly treated amblyopia patients can regain 20/40 acuity.
- Corneal opacification
- Degenerative myopia
- Diabetic retinopathy: is one of the manifestation microvascular complications of diabetes, which is characterized by blindness or reduced acuity. That is, diabetic retinopathy describes the retinal and vitreous hemorrhages or retinal capillary blockage caused by the increase of A1C, which a measurement of blood glucose or sugar level. In fact, as A1C increases, people tend to be at greater risk of developing diabetic retinopathy than developing other microvascular complications associated with diabetes (e.g. chronic hyperglycemia, diabetic neuropathy, and diabetic nephropathy). Despite the fact that only 8% of adults 40 years and older experience vision-threatening diabetic retinopathy (e.g. nonproliferative diabetic retinopathy or NPDR and proliferative diabetic retinopathy or PDR), this eye diseased accounted for 17% of cases of blindness in 2002.
- Retinitis pigmentosa
- Retinopathy of prematurity: The most common cause of blindness in infants worldwide. In its most severe form, ROP causes retinal detachment, with attendant visual loss. Treatment is aimed mainly at prevention, via laser or Avastin therapy.
- Stargardt's disease
- Uveitis: is a group of 30 intraocular inflammatory diseases caused by infections, systemic diseases, organ-specific autoimmune processes, cancer or trauma. That is, uveitis refers to a complex category of ocular diseases that can cause blindness if either left untreated or improperly diagnosed. The current challenge of accurately diagnosing uveitis is that often the cause of a specific ocular inflammation is either unknown or multi-layered. Consequently, about 3–10% uveitis victims in developed countries, and about 25% of victims in the developing countries, become blind from incorrect diagnosis and from ineffectual prescription of drugs, antibiotics or steroids. In addition, uveitis is a diverse category of eye diseases that are subdivided as granulomatous (or tumorous) or non-granulomatous anterior, intermediate, posterior or pan uveitis. In other words, uveitis diseases tend to be classified by their anatomic location in the eye (e.g. uveal tract, retina, or lens), as well as can create complication that can cause cataracts, glaucoma, retinal damage, age-related macular degeneration or diabetic retinopathy.
- Xerophthalmia, often due to vitamin A deficiency, is estimated to affect 5 million children each year; 500,000 develop active corneal involvement, and half of these go blind.
Diagnosis
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 provides an approach to evaluating visual loss as it affects an individual's ability to perform activities of daily living.
Screening adults who have no symptoms is of uncertain benefit.
Prevention
The World Health Organization estimates that 80% of visual loss is either preventable or curable with treatment.
This includes cataracts, onchocerciasis, trachoma, glaucoma, diabetic
retinopathy, uncorrected refractive errors, and some cases of childhood
blindness. The Center for Disease Control and Prevention estimates that half of blindness in the United States is preventable.
Treatment
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.
Mobility
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.
Others read Braille (or the infrequently used Moon type), or rely on talking books and readers or reading machines, which convert printed text to speech or Braille. They use computers with special hardware such as scanners and refreshable Braille displays as well as software written specifically for the blind, such as optical character recognition applications and screen readers.
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.
Computers and mobile technology
Access technology such as screen readers, screen magnifiers and refreshable Braille displays enable the blind to use mainstream computer applications and mobile phones.
The availability of assistive technology is increasing, accompanied by
concerted efforts to ensure the accessibility of information technology
to all potential users, including the blind. Later versions of Microsoft Windows include an Accessibility Wizard & Magnifier for those with partial vision, and Microsoft Narrator, a simple screen reader. Linux distributions (as live CDs) for the blind include Vinux and Adriane Knoppix, the latter developed in part by Adriane Knopper who has a visual impairment. macOS and iOS also come with a built-in screen reader called VoiceOver, while Google TalkBack is built in to most Android devices.
The movement towards greater web accessibility is opening a far wider number of websites to adaptive technology, making the web a more inviting place for visually impaired surfers.
Experimental approaches in sensory substitution are beginning to provide access to arbitrary live views from a camera.
Modified visual output that includes large print and/or clear
simple graphics can be of benefit to users with some residual vision.
Other aids and techniques
A tactile feature on a Canadian banknote
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 Indian rupee, the size of a note increases with its value.
- On US coins, pennies and dimes, and nickels and quarters are similar in size. The larger denominations (dimes and quarters) have ridges along the sides (historically used to prevent the "shaving" of precious metals from the coins), which can now be used for identification.
- Some currencies' banknotes have a tactile feature to indicate denomination. For example, the Canadian currency 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.
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 (Braille
line), and are useful for all levels of visual handicap. OCR
scanners can, in conjunction with text-to-speech software, read the
contents of books and documents aloud via computer. Vendors also build
closed-circuit televisions that electronically magnify paper, and even
change its contrast and color, for visually impaired users.
In adults with low vision there is no conclusive evidence supporting one form of reading aid over another. In several studies stand-mounted devices allowed faster reading than hand-held or portable 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
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.
Adjusting attitude
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.
Surroundings
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
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
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.
Smell
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 area's 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.
Communication development
Visual
impairment can have profound effects on the development of infant and
child communication. The language and social development of a child or
infant can be very delayed by the inability to see the world around
them.
Social development
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 uneducated on how to communicate with other
people. This may cause the child to be avoided by peers and consequently
overprotected by family members.
Language development
With
sight, much of what is learned by a child is learned through imitation
of others, whereas 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.
Healthcare access
Visual
impairment has the ability to create consequences for health and well
being. Visual impairment is increasing, especially among older people.
It is recognized that those individuals with visual impairment are
likely to have limited access to information and healthcare facilities,
and may not receive the best care possible because not all health care
professionals are aware of specific needs related to vision.
- 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.
Epidemiology
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 age: Visual impairment is unequally distributed across
age groups. More than 82% of all people who are blind are 50 years of
age and older, although they represent only 19% of the world's
population. Due to the expected number of years lived in blindness
(blind years), childhood blindness remains a significant problem, with
an estimated 1.4 million blind children below age 15.
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.
By geography: Visual impairment is not distributed
uniformly throughout the world. More than 90% of the world's visually
impaired live in developing countries.
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
Legal definition
To
determine which people qualify for special assistance because of their
visual disabilities, various governments have specific definitions for
legal blindness. In North America and most of Europe, legal blindness is defined as visual acuity
(vision) of 20/200 (6/60) or less in the better eye with best
correction possible. This means that a legally blind individual would
have to stand 20 feet (6.1 m) from an object to see it—with corrective lenses—with
the same degree of clarity as a normally sighted person could from 200
feet (61 m). In many areas, 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.
Approximately fifteen percent of those deemed legally blind, by any
measure, have no light or form perception. The rest have some vision,
from light perception alone to relatively good acuity. Low vision is sometimes used to describe visual acuities from 20/70 to 20/200.
Literature and art
Antiquity
In Greek myth, Tiresias was a prophet famous for his clairvoyance.
According to one myth, he was blinded by the gods as punishment for
revealing their secrets, while another holds that he was blinded as
punishment after he saw Athena naked while she was bathing. In the Odyssey, the one-eyed Cyclops Polyphemus captures Odysseus, who blinds Polyphemus to escape. In Norse mythology, Loki tricks the blind god Höðr into killing his brother Baldr, the god of happiness.
The New Testament contains numerous instances of Jesus performing miracles to heal the blind. According to the Gospels, Jesus healed the two blind men of Galilee, the blind man of Bethsaida, the blind man of Jericho and the man who was born blind.
The parable of the blind men and an elephant has crossed between many religious traditions and is part of Jain, Buddhist, Sufi and Hindu lore. In various versions of the tale, a group of blind men (or men in the dark) touch an elephant
to learn what it is like. Each one feels a different part, but only one
part, such as the side or the tusk. They then compare notes and learn
that they are in complete disagreement.
"Three Blind Mice" is a medieval English nursery rhyme
about three blind mice whose tails are cut off after chasing the
farmer's wife. The work is explicitly incongruous, ending with the
comment Did you ever see such a sight in your life, As three blind mice?
Modern times
Blind Woman by Diego Velázquez
The Sense of Touch by Jusepe de Ribera depicts a blind man holding a marble head in his hands.
Poet John Milton, who went blind in mid-life, composed On His Blindness, a sonnet about coping with blindness. The work posits that [those] who best Bear [God]'s mild yoke, they serve him best.
The Dutch painter and engraver Rembrandt often depicted scenes from the apocryphal Book of Tobit, which tells the story of a blind patriarch who is healed by his son, Tobias, with the help of the archangel Raphael.
Slaver-turned-abolitionist John Newton composed the hymn Amazing Grace about a wretch who "once was lost, but now am found, Was blind, but now I see."
Blindness, in this sense, is used both metaphorically (to refer to
someone who was ignorant but later became knowledgeable) and literally,
as a reference to those healed in the Bible. In the later years of his
life, Newton himself would go blind.
H. G. Wells' story "The Country of the Blind"
explores what would happen if a sighted man found himself trapped in a
country of blind people to emphasise society's attitude to blind people
by turning the situation on its head.
Bob Dylan's anti-war song "Blowin' in the Wind" twice alludes to metaphorical blindness: How
many times can a man turn his head // and pretend that he just doesn't
see... How many times must a man look up // Before he can see the sky?
Contemporary fiction contains numerous well-known blind characters. Some of these characters can see by means of devices, such as the Marvel Comics superhero Daredevil, who can see via his super-human hearing acuity, or Star Trek's Geordi La Forge, who can see with the aid of a VISOR, a fictional device that transmits optical signals to his brain.
Sports
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, tennis, bowling, and beep baseball. The worldwide authority on sports for the blind is the International Blind Sports Federation. People with vision impairments have participated in the Paralympic Games since the 1976 Toronto summer Paralympics.
Metaphorical uses
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.
Research
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.
Other 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.
