Visual impairment, also known as vision impairment, is a medical definition primarily measured based on an individual's better eye visual acuity; in the absence of treatment such as correctable eyewear, assistive devices, and medical treatment– visual impairment may cause the individual difficulties with normal daily tasks including reading and walking. Low vision is a functional definition of visual impairment that is chronic, uncorrectable with treatment or correctable lenses, and impacts daily living. As such low vision can be used as a disability metric and varies based on an individual's experience, environmental demands, accommodations, and access to services. The American Academy of Ophthalmology defines visual impairment as the best-corrected visual acuity of less than 20/40 in the better eye, and the World Health Organization defines it as a presenting acuity of less than 6/12 in the better eye. The term blindness is used for complete or nearly complete vision loss. In addition to the various permanent conditions, fleeting temporary vision impairment,
amaurosis fugax
Amaurosis fugax (Greek ''amaurosis'' meaning ''darkening'', ''dark'', or ''obscure'', Latin '' fugax'' meaning ''fleeting'') is a painless temporary loss of vision in one or both eyes.
Signs and symptoms
The experience of amaurosis fugax is clas ...
, may occur, and may indicate serious medical problems.
The most common causes of visual impairment globally are uncorrected
refractive errors
Refractive error, also known as refraction error, is a problem with focusing light accurately on the retina due to the shape of the eye and or cornea. The most common types of refractive error are near-sightedness, far-sightedness, astigmatism, ...
(43%),
cataract
A cataract is a cloudy area in the lens of the eye that leads to a decrease in vision. Cataracts often develop slowly and can affect one or both eyes. Symptoms may include faded colors, blurry or double vision, halos around light, trouble w ...
s (33%), and
glaucoma
Glaucoma is a group of eye diseases that result in damage to the optic nerve (or retina) and cause vision loss. The most common type is open-angle (wide angle, chronic simple) glaucoma, in which the drainage angle for fluid within the eye rem ...
(2%). Refractive errors include
near-sightedness
Near-sightedness, also known as myopia and short-sightedness, is an eye disease where light focuses in front of, instead of on, the retina. As a result, distant objects appear blurry while close objects appear normal. Other symptoms may include ...
,
far-sightedness
Far-sightedness, also known as long-sightedness, hypermetropia, or hyperopia, is a condition of the eye where distant objects are seen clearly but near objects appear blurred. This blurred effect is due to incoming light being focused behind, i ...
,
presbyopia
Presbyopia is physiological insufficiency of accommodation associated with the aging of the eye that results in progressively worsening ability to focus clearly on close objects. Also known as age-related farsightedness (or age-related long si ...
, and
astigmatism
Astigmatism is a type of refractive error due to rotational asymmetry in the eye's refractive power. This results in distorted or blurred vision at any distance. Other symptoms can include eyestrain, headaches, and trouble driving at nig ...
. Cataracts are the most common cause of blindness. Other disorders that may cause visual problems include
age-related macular degeneration
Macular degeneration, also known as age-related macular degeneration (AMD or ARMD), is a medical condition which may result in blurred or no vision in the center of the visual field. Early on there are often no symptoms. Over time, however, som ...
,
diabetic retinopathy
Diabetic retinopathy (also known as diabetic eye disease), is a medical condition in which damage occurs to the retina due to diabetes mellitus. It is a leading cause of blindness in developed countries.
Diabetic retinopathy affects up to 80 perc ...
childhood blindness
Childhood blindness is an important contribution to the national prevalence of the disability of blindness. Blindness in children can be defined as a visual acuity of <3/60 in the eye with better vision of a child under 16 years of age. This gene ...
, and a number of
infection
An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable dise ...
s. Visual impairment can also be caused by problems in the
brain
A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a v ...
due to
stroke
A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop functionin ...
,
premature birth
Preterm birth, also known as premature birth, is the birth of a baby at fewer than 37 weeks gestational age, as opposed to full-term delivery at approximately 40 weeks. Extreme preterm is less than 28 weeks, very early preterm birth is between 2 ...
, or trauma, among others. These cases are known as
cortical visual impairment Cortical visual impairment (CVI) is a form of visual impairment that is caused by a brain problem rather than an eye problem. (The latter is sometimes termed "ocular visual impairment" when discussed in contrast to cortical visual impairment.) Some ...
. 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
An eye examination is a series of tests performed to assess vision and ability to focus on and discern objects. It also includes other tests and examinations pertaining to the eyes. Eye examinations are primarily performed by an optometrist, oph ...
.
The
World Health Organization
The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of h ...
(WHO) estimates that 80% of visual impairment is either preventable or curable with treatment. This includes cataracts, the infections
river blindness
Onchocerciasis, also known as river blindness, is a disease caused by infection with the parasitic worm ''Onchocerca volvulus''. Symptoms include severe itching, bumps under the skin, and blindness. It is the second-most common cause of blindne ...
and
trachoma
Trachoma is an infectious disease caused by bacterium ''Chlamydia trachomatis''. The infection causes a roughening of the inner surface of the eyelids. This roughening can lead to pain in the eyes, breakdown of the outer surface or cornea of ...
, glaucoma, diabetic retinopathy, uncorrected refractive errors, and some cases of childhood blindness. Many people with significant visual impairment benefit from
vision rehabilitation Vision rehabilitation (often called vision rehab) is a term for a medical rehabilitation to improve vision or low vision. In other words, it is the process of restoring functional ability and improving quality of life and independence in an individ ...
, changes in their environment, and assistive devices.
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
A developing country is a sovereign state with a lesser developed industrial base and a lower Human Development Index (HDI) relative to other countries. However, this definition is not universally agreed upon. There is also no clear agreem ...
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
In 2010, the WHO definition for visual impairment was changed and now follows the ICD-11. The previous definition which used "best corrected visual acuity" was changed to "presenting visual acuity". This change was made as newer studies showed that best-corrected vision overlooks a larger proportion of the population who has visual impairment due to uncorrected refractive errors, and/or lack of access to medical or surgical treatment.
Distance vision impairment:
* Category 0: No or mild visual impairment –presenting visual acuity better than 6/18
* Category 1: Moderate visual impairment –presenting visual acuity worse than 6/18 and better than 6/60
* Category 2: Severe visual impairment –presenting visual acuity worse than 6/60 and better than 3/60
* Category 3: Blindness –presenting visual acuity worse than 3/60 and better than 1/60
* Category 4: Blindness—presenting visual acuity worse than 1/60 with light perception
* Category 5: Blindness—irreversible blindness with no light perception
Near vision impairment:
* Near visual acuity worse than N6 or M.08 at 40 cm.
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 what the normally sighted person sees at .
Sight impaired
* Able to see at , but not at , what the normally sighted person sees at
* 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
Visual acuity (VA) commonly refers to the clarity of vision, but technically rates an examinee's ability to recognize small details with precision. Visual acuity is dependent on optical and neural factors, i.e. (1) the sharpness of the retinal ...
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
In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints lie on the circle. It can also be defined as the longest chord of the circle. Both definitions are also valid for ...
) 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
Braille (Pronounced: ) is a tactile writing system used by people who are visually impaired, including people who are Blindness, blind, Deafblindness, deafblind or who have low vision. It can be read either on Paper embossing, embossed paper ...
.
* ''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
The American Medical Association (AMA) is a professional association and lobbying group of physicians and medical students. Founded in 1847, it is headquartered in Chicago, Illinois. Membership was approximately 240,000 in 2016.
The AMA's state ...
adopted the following definition of blindness:
The
United States Congress
The United States Congress is the legislature of the federal government of the United States. It is bicameral, composed of a lower body, the House of Representatives, and an upper body, the Senate. It meets in the U.S. Capitol in Washing ...
included this definition as part of the Aid to the Blind program in the
Social Security Act
The Social Security Act of 1935 is a law enacted by the 74th United States Congress and signed into law by US President Franklin D. Roosevelt. The law created the Social Security program as well as insurance against unemployment. The law was pa ...
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
Supplemental Security Income (SSI) is a means-tested program that provides cash payments to disabled children, disabled adults, and individuals aged 65 or older who are citizens or nationals of the United States. SSI was created by the Social Se ...
program which states:
Temporary vision impairment
Vision impairment for a few seconds, or minutes, may occur due to any of a variety of causes, some serious and requiring medical attention.
Health effects
General functioning
Visual impairments may take many forms and be of varying degrees. Visual acuity alone is not always a good predictor of an individual's function. 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 they have low visual demands. It is also important to note that best-corrected visual acuity differs from presenting visual acuity; a person with a "normal" best corrected acuity can have "poor" presenting acuity (e.g. individual who has uncorrected refractive error). Thus, measuring an individual's general functioning depends on one's situational and contextual factors, as well as access to treatment.
The
American Medical Association
The American Medical Association (AMA) is a professional association and lobbying group of physicians and medical students. Founded in 1847, it is headquartered in Chicago, Illinois. Membership was approximately 240,000 in 2016.
The AMA's state ...
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.
Mobility
Older adults with visual impairment are at an increased risk of physical inactivity, slower gait speeds, and fear of falls.
Physical activity is a useful predictor of overall well-being, and routine physical activity reduces the risk of developing chronic diseases and disability. Older adults with visual impairment (including glaucoma, age-related macular degeneration, and diabetic retinopathy) have decreased physical activity as measured with self-reports and accelerometers. The US
National Health and Nutrition Examination Survey
The National Health and Nutrition Examination Survey (NHANES) is a survey research program conducted by the National Center for Health Statistics (NCHS) to assess the health and nutritional status of adults and children in the United States, and to ...
(NHANES) showed that people with corrected visual acuity of less than 20/40 spent significantly less time in moderate to vigorous physical activity. Age-related macular degeneration is also associated with a 50% decrease in physical activity–however physical activity is protective against age-related macular degeneration progression.
In terms of mobility, those with visual impairment have a slower gait speed than those without visual impairment; however, the rate of decline remains proportional with increasing age in both groups. Additionally, the visually impaired also have greater difficulty walking a quarter mile (400 m) and walking up stairs, as compared to those with normal vision.
Cognitive
Older adults with vision loss are at an increased risk of memory loss, cognitive impairment, and cognitive decline.
Social and psychological
Studies demonstrate an association between older adults with visual impairment and a poor mental health; discrimination was identified as one of the causes of this association. Older adults with visual impairment have a 1.5-fold risk of reporting perceived discrimination and of these individuals, there was a 2-fold risk of loneliness and 4-fold risk of reporting a lower quality of life. Among adults with visual impairment, the prevalence of moderate loneliness is 28.7% (18.2% in general population) and prevalence of severe loneliness is 19.7% (2.7% in general population). The risk of depression and anxiety are also increased in the visually impaired; 32.2% report depressive symptoms (12.01% in general population), and 15.61% report anxiety symptoms (10.69% in general population).
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 impairment 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.
cerebral palsy
Cerebral palsy (CP) is a group of movement disorders that appear in early childhood. Signs and symptoms vary among people and over time, but include poor coordination, stiff muscles, weak muscles, and tremors. There may be problems with sensa ...
,
hearing impairment
Hearing loss is a partial or total inability to hear. Hearing loss may be present at birth or acquired at any time afterwards. Hearing loss may occur in one or both ears. In children, hearing problems can affect the ability to acquire spoken l ...
s, and
epilepsy
Epilepsy is a group of non-communicable neurological disorders characterized by recurrent epileptic seizures. Epileptic seizures can vary from brief and nearly undetectable periods to long periods of vigorous shaking due to abnormal electrical ...
. Blindness in combination with hearing loss is known as
deafblindness
Deafblindness is the condition of little or no useful hearing and little or no useful sight. Different degrees of vision loss and auditory loss occur within each individual. Because of this inherent diversity, each deafblind individual's needs re ...
.
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
A circadian rhythm (), or circadian cycle, is a natural, internal process that regulates the sleep–wake cycle and repeats roughly every 24 hours. It can refer to any process that originates within an organism (i.e., Endogeny (biology), endogeno ...
, normally slightly longer than 24 hours, is not entrained (synchronized) to the lightdark cycle.
Cause
The most common causes of visual impairment globally in 2010 were:
# Refractive error (42%)
# Cataract (33%)
#
Glaucoma
Glaucoma is a group of eye diseases that result in damage to the optic nerve (or retina) and cause vision loss. The most common type is open-angle (wide angle, chronic simple) glaucoma, in which the drainage angle for fluid within the eye rem ...
(2%)
#
Age-related macular degeneration
Macular degeneration, also known as age-related macular degeneration (AMD or ARMD), is a medical condition which may result in blurred or no vision in the center of the visual field. Early on there are often no symptoms. Over time, however, som ...
(1%)
#
Corneal opacification
The human cornea is a transparent membrane which allows light to pass through it. The word corneal opacification literally means loss of normal transparency of cornea. The term corneal opacity is used particularly for the loss of transparency of c ...
Childhood blindness
Childhood blindness is an important contribution to the national prevalence of the disability of blindness. Blindness in children can be defined as a visual acuity of <3/60 in the eye with better vision of a child under 16 years of age. This gene ...
# Trachoma (1%)
# Undetermined (18%)
The most common causes of blindness worldwide 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
A developing country is a sovereign state with a lesser developed industrial base and a lower Human Development Index (HDI) relative to other countries. However, this definition is not universally agreed upon. There is also no clear agreem ...
. 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
Cataracts
A cataract is a cloudy area in the lens of the eye that leads to a decrease in vision. Cataracts often develop slowly and can affect one or both eyes. Symptoms may include faded colors, blurry or double vision, halos around light, trouble w ...
are the greying or opacity of the crystalline lens, which can be caused in children 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
Glaucoma is a group of eye diseases that result in damage to the optic nerve (or retina) and cause vision loss. The most common type is open-angle (wide angle, chronic simple) glaucoma, in which the drainage angle for fluid within the eye rem ...
is an eye disease often characterized by increased pressure within the eye or intraocular pressure (IOP).<>. Glaucoma causes visual field loss as well as severs the optic nerve.Glaucoma Research Foundation. "High Eye Pressure and Glaucoma." Glaucoma Research Foundation. N.p., 5 Sept. 2013. Web.<>. 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
Primary juvenile glaucoma is glaucoma that develops due to ocular hypertension and is evident either at birth or within the first few years of life. It is caused due to abnormalities in the anterior chamber angle development that obstruct aqueous o ...
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
Childhood blindness can be caused by conditions related to pregnancy, such as congenital rubella syndrome and
retinopathy of prematurity
Retinopathy of prematurity (ROP), also called retrolental fibroplasia (RLF) and Terry syndrome, is a disease of the eye affecting prematurely born babies generally having received neonatal intensive care, in which oxygen therapy is used due to ...
. Leprosy and onchocerciasis each blind approximately 1 million individuals in the developing world.
The number of individuals blind from
trachoma
Trachoma is an infectious disease caused by bacterium ''Chlamydia trachomatis''. The infection causes a roughening of the inner surface of the eyelids. This roughening can lead to pain in the eyes, breakdown of the outer surface or cornea of ...
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
Eye injuries
Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and conv ...
, most often occurring in people under 30, are the leading cause of monocular blindness (vision loss in one eye) throughout the
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
. 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
Cortical blindness is the total or partial loss of vision in a normal-appearing eye caused by damage to the brain's occipital cortex. Cortical blindness can be acquired or congenital, and may also be transient in certain instances. Acquired cortic ...
brain
A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a v ...
that prevent the brain from correctly receiving or interpreting signals from the
optic nerve
In neuroanatomy, the optic nerve, also known as the second cranial nerve, cranial nerve II, or simply CN II, is a paired cranial nerve that transmits visual system, visual information from the retina to the brain. In humans, the optic nerve i ...
. 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
Oedipus (, ; grc-gre, Οἰδίπους "swollen foot") was a mythical Greek king of Thebes. A tragic hero in Greek mythology, Oedipus accidentally fulfilled a prophecy that he would end up killing his father and marrying his mother, thereby ...
, 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
Basil II Porphyrogenitus ( gr, Βασίλειος Πορφυρογέννητος ;) and, most often, the Purple-born ( gr, ὁ πορφυρογέννητος, translit=ho porphyrogennetos).. 958 – 15 December 1025), nicknamed the Bulgar S ...
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
An acid attack, also called acid throwing, vitriol attack, or vitriolage, is a form of violent assault involving the act of throwing acid or a similarly corrosive substance onto the body of another "with the intention to disfigure, maim, tortu ...
People with albinism often have vision loss to the extent that many are legally blind, though few of them actually cannot see.
Leber congenital amaurosis
Leber congenital amaurosis (LCA) is a rare inherited eye disease that appears at birth or in the first few months of life.
It affects about 1 in 40,000 newborns. LCA was first described by Theodor Leber in the 19th century. It should not be co ...
can cause total blindness or severe sight loss from birth or early childhood. Retinitis pigmentosa is characterized by decreased peripheral vision and trouble seeing at night.
Advances in mapping of the human genome have identified other genetic causes of low vision or blindness. Two such examples are
Bardet–Biedl syndrome
Bardet–Biedl syndrome (BBS) is a ciliopathic human genetic disorder that produces many effects and affects many body systems. It is characterized by rod/cone dystrophy, polydactyly, central obesity, hypogonadism, and kidney dysfunction in som ...
.
Poisoning
Rarely, blindness is caused by the intake of certain chemicals. A well-known example is
methanol
Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical and the simplest aliphatic alcohol, with the formula C H3 O H (a methyl group linked to a hydroxyl group, often abbreviated as MeOH). It is a ...
, which is only mildly toxic and minimally intoxicating, and breaks down into the substances
formaldehyde
Formaldehyde ( , ) (systematic name methanal) is a naturally occurring organic compound with the formula and structure . The pure compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde (refer to section F ...
and
formic acid
Formic acid (), systematically named methanoic acid, is the simplest carboxylic acid, and has the chemical formula HCOOH and structure . It is an important intermediate in chemical synthesis and occurs naturally, most notably in some ants. Es ...
which in turn can cause blindness, an array of other health complications, and death. When competing with
ethanol
Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an Alcohol (chemistry), alcohol with the chemical formula . Its formula can be also written as or (an ethyl ...
for metabolism, ethanol is metabolized first, and the onset of toxicity is delayed. Methanol is commonly found in
methylated spirits
Denatured alcohol (also called methylated spirits in Australia, Canada, Ireland, New Zealand, South Africa, and the United Kingdom; wood spirit; and denatured rectified spirit) is ethanol that has additives to make it poisonous, bad-tasting, fou ...
Amblyopia
Amblyopia, also called lazy eye, is a disorder of sight in which the brain fails to fully process input from one eye and over time favors the other eye. It results in decreased vision in an eye that typically appears normal in other aspects. Amb ...
: 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 has been born premature, measles, congenital rubella 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
The human cornea is a transparent membrane which allows light to pass through it. The word corneal opacification literally means loss of normal transparency of cornea. The term corneal opacity is used particularly for the loss of transparency of c ...
*
Degenerative myopia
Near-sightedness, also known as myopia and short-sightedness, is an eye disease where light focuses in front of, instead of on, the retina. As a result, distant objects appear blurred vision, blurry while close objects appear normal. Other sympt ...
* 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 disease accounted for 17% of cases of blindness in 2002.
* Retinitis pigmentosa
*
Retinopathy of prematurity
Retinopathy of prematurity (ROP), also called retrolental fibroplasia (RLF) and Terry syndrome, is a disease of the eye affecting prematurely born babies generally having received neonatal intensive care, in which oxygen therapy is used due to ...
: 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
Stargardt disease is the most common inherited single-gene retinal disease. In terms of the first description of the disease, it follows an autosomal recessive inheritance pattern, which has been later linked to bi-allelic ABCA4 gene variants ...
* 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% of those with uveitis in developed countries, and about 25% of those with uveitis 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
Xerophthalmia (from Ancient Greek "xērós" (ξηρός) meaning "dry" and "ophthalmos" (οφθαλμός) meaning "eye") is a medical condition in which the eye fails to produce tears. It may be caused by vitamin A deficiency, which is someti ...
, often due to
vitamin A deficiency
Vitamin A deficiency (VAD) or hypovitaminosis A is a lack of vitamin A in blood and tissues. It is common in poorer countries, especially among children and women of reproductive age, but is rarely seen in more developed countries. Nyctalopia (ni ...
, 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
The American Medical Association (AMA) is a professional association and lobbying group of physicians and medical students. Founded in 1847, it is headquartered in Chicago, Illinois. Membership was approximately 240,000 in 2016.
The AMA's state ...
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.
Management
Mobility
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
A white cane is a device used by many people who are blind or visually impaired. A white cane primarily allows its user to scan their surroundings for obstacles or orientation marks, but is also helpful for onlookers in identifying the user as b ...
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 blind people in many cities.
Tactile paving
Tactile paving (also called tenji blocks, truncated domes, detectable warnings, tactile tiles, tactile ground surface indicators, tactile walking surface indicators, or detectable warning surfaces) is a system of textured ground surface indicat ...
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
Right of way is the legal right, established by grant from a landowner or long usage (i.e. by prescription), to pass along a specific route through property belonging to another.
A similar ''right of access'' also exists on land held by a gov ...
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
Large-print (also large-type or large-font) refers to the formatting of a book or other text document in which the typeface (or font) are considerably larger than usual to accommodate people who have low vision. Frequently the medium is also increa ...
, which is easier for them to read without such devices. A variety of
magnifying glass
A magnifying glass is a convex lens that is used to produce a magnified image of an object. The lens is usually mounted in a frame with a handle. A magnifying glass can be used to focus light, such as to concentrate the sun's radiation to crea ...
es, some handheld, and some on desktops, can make reading easier for them.
Others read
braille
Braille (Pronounced: ) is a tactile writing system used by people who are visually impaired, including people who are Blindness, blind, Deafblindness, deafblind or who have low vision. It can be read either on Paper embossing, embossed paper ...
(or the infrequently used
Moon type
The Moon System of Embossed Reading (commonly known as the Moon writing, Moon alphabet, Moon script, Moon type, or Moon code) is a writing system for the blind, using embossed symbols mostly derived from the Latin script (but simplified). It is ...
braille
Braille (Pronounced: ) is a tactile writing system used by people who are visually impaired, including people who are Blindness, blind, Deafblindness, deafblind or who have low vision. It can be read either on Paper embossing, embossed paper ...
. They use computers with special hardware such as
scanners
''Scanners'' is a 1981 Canadian science fiction horror film written and directed by David Cronenberg and starring Stephen Lack, Jennifer O'Neill, Michael Ironside, and Patrick McGoohan. In the film, "scanners" are psychics with unusual telepathic ...
and
refreshable braille display
A refreshable braille display or braille terminal is an electro-mechanical device for displaying braille characters, usually by means of round-tipped pins raised through holes in a flat surface. Visually impaired computer users who cannot use a s ...
s as well as software written specifically for the blind, such as
optical character recognition
Optical character recognition or optical character reader (OCR) is the electronic or mechanical conversion of images of typed, handwritten or printed text into machine-encoded text, whether from a scanned document, a photo of a document, a scen ...
applications and
screen reader
A screen reader is a form of assistive technology (AT) that renders text and image content as speech or braille output. Screen readers are essential to people who are blindness, blind, and are useful to people who are visual impairment, visually ...
National Library for the Blind
The National Library for the Blind (NLB) was a public library in the United Kingdom, founded 1882, which aimed to ensure that people with sight problems have the same access to library services as sighted people. NLB was taken over by the Royal Na ...
or the
RNIB
The Royal National Institute of Blind People (RNIB) is a UK charity offering information, support and advice to almost two million people in the UK with sight loss.
History
The RNIB was founded by Thomas Rhodes Armitage, a doctor who had eye ...
in the United Kingdom.
Closed-circuit television
Closed-circuit television (CCTV), also known as video surveillance, is the use of video cameras to transmit a signal to a specific place, on a limited set of monitors. It differs from broadcast television in that the signal is not openly t ...
s, equipment that enlarges and contrasts textual items, are a more
high-tech
High technology (high tech), also known as advanced technology (advanced tech) or exotechnology, is technology that is at the cutting edge: the highest form of technology available. It can be defined as either the most complex or the newest te ...
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 reader
A screen reader is a form of assistive technology (AT) that renders text and image content as speech or braille output. Screen readers are essential to people who are blindness, blind, and are useful to people who are visual impairment, visually ...
s,
screen magnifier
A screen magnifier is software that interfaces with a computer's graphical output to present enlarged screen content. By enlarging part (or all) of a screen, people with visual impairments can better see words and images. This type of assistive te ...
s and
refreshable braille display
A refreshable braille display or braille terminal is an electro-mechanical device for displaying braille characters, usually by means of round-tipped pins raised through holes in a flat surface. Visually impaired computer users who cannot use a s ...
s enable the blind to use mainstream computer applications and
mobile phone
A mobile phone, cellular phone, cell phone, cellphone, handphone, hand phone or pocket phone, sometimes shortened to simply mobile, cell, or just phone, is a portable telephone that can make and receive calls over a radio frequency link whil ...
s. 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
Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for serv ...
include an Accessibility Wizard & Magnifier for those with partial vision, and
Microsoft Narrator
Narrator is a screen reader in Microsoft Windows. Developed by Professor Paul Blenkhorn in 2000, the utility made the Windows operating system more accessible for blind and visually impaired users.
Overview
Narrator is included with every copy of ...
, a simple screen reader.
Linux distribution
A Linux distribution (often abbreviated as distro) is an operating system made from a software collection that includes the Linux kernel and, often, a package management system. Linux users usually obtain their operating system by downloading one ...
s (as
live CD
A live CD (also live DVD, live disc, or live operating system) is a complete bootable computer installation including operating system which runs directly from a CD-ROM or similar storage device into a computer's memory, rather than loading fro ...
s) for the blind include
Vinux
Vinux is a Linux distribution which has been specially designed for blind and partially sighted users. Specifically it is a remastered version of the Ubuntu distribution and provides users with two screen readers, two full-screen magnifiers, ...
and
Adriane Knoppix
KNOPPIX ( ) is an operating system based on Debian designed to be run directly from a CD / DVD (Live CD) or a USB flash drive (Live USB), one of the first live operating system distributions (just after Yggdrasil Linux). Knoppix was developed b ...
, 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
Google Talkback is an accessibility service for the Android operating system that helps blind and visually impaired users to interact with their devices. It uses spoken words, vibration and other audible feedback to allow the user to know what is ...
is built in to most Android devices.
The movement towards greater web accessibility is opening a far wider number of websites to
adaptive technology
Assistive technology (AT) is a term for assistive, adaptive, and rehabilitative devices for people with disabilities and the elderly. Disabled people often have difficulty performing activities of daily living (ADLs) independently, or even with ...
, making the web a more inviting place for visually impaired surfers.
Experimental approaches in
sensory substitution Sensory substitution is a change of the characteristics of one sensory modality into stimuli of another sensory modality.
A sensory substitution system consists of three parts: a sensor, a coupling system, and a stimulator. The sensor records stimu ...
are beginning to provide access to arbitrary live views from a
camera
A camera is an Optics, optical instrument that can capture an image. Most cameras can capture 2D images, with some more advanced models being able to capture 3D images. At a basic level, most cameras consist of sealed boxes (the camera body), ...
.
Modified visual output that includes large print and/or clear simple graphics can be of benefit to users with some residual vision.Gregor, P., Newell, A.F., Zajicek, M. (2002). Designing for Dynamic Diversity – interfaces for older people. Proceedings of the fifth international ACM conference on Assistive technologies. Edinburgh, Scotland. Session: Solutions for aging. Pages 151–156.
Other aids and techniques
Blind people may use talking equipment such as
thermometer
A thermometer is a device that temperature measurement, measures temperature or a temperature gradient (the degree of hotness or coldness of an object). A thermometer has two important elements: (1) a temperature sensor (e.g. the bulb of a merc ...
s, watches, clocks,
scales
Scale or scales may refer to:
Mathematics
* Scale (descriptive set theory), an object defined on a set of points
* Scale (ratio), the ratio of a linear dimension of a model to the corresponding dimension of the original
* Scale factor, a number w ...
,
calculator
An electronic calculator is typically a portable electronic device used to perform calculations, ranging from basic arithmetic to complex mathematics.
The first solid-state electronic calculator was created in the early 1960s. Pocket-sized ...
s, and
compass
A compass is a device that shows the cardinal directions used for navigation and geographic orientation. It commonly consists of a magnetized needle or other element, such as a compass card or compass rose, which can pivot to align itself with ...
es. 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
coin
A coin is a small, flat (usually depending on the country or value), round piece of metal or plastic used primarily as a medium of exchange or legal tender. They are standardized in weight, and produced in large quantities at a mint in order t ...
s and
banknote
A banknote—also called a bill (North American English), paper money, or simply a note—is a type of negotiable instrument, negotiable promissory note, made by a bank or other licensed authority, payable to the bearer on demand.
Banknotes w ...
s so that the value can be determined by touch. For example:
** In some currencies, such as the
euro
The euro ( symbol: €; code: EUR) is the official currency of 19 out of the member states of the European Union (EU). This group of states is known as the eurozone or, officially, the euro area, and includes about 340 million citizens . ...
, the
pound sterling
Sterling (abbreviation: stg; Other spelling styles, such as STG and Stg, are also seen. ISO code: GBP) is the currency of the United Kingdom and nine of its associated territories. The pound ( sign: £) is the main unit of sterling, and t ...
and the
Indian rupee
The Indian rupee ( symbol: ₹; code: INR) is the official currency in the republic of India. The rupee is subdivided into 100 ''paise'' (singular: ''paisa''), though as of 2022, coins of denomination of 1 rupee are the lowest value in use wh ...
, 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
Braille (Pronounced: ) is a tactile writing system used by people who are visually impaired, including people who are Blindness, blind, Deafblindness, deafblind or who have low vision. It can be read either on Paper embossing, embossed paper ...
.
** 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
Large-print (also large-type or large-font) refers to the formatting of a book or other text document in which the typeface (or font) are considerably larger than usual to accommodate people who have low vision. Frequently the medium is also increa ...
reading materials and e-book readers that provide large
font
In metal typesetting, a font is a particular size, weight and style of a typeface. Each font is a matched set of type, with a piece (a "sort") for each glyph. A typeface consists of a range of such fonts that shared an overall design.
In mod ...
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 impairment. 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. For more information, consult
assistive technology
Assistive technology (AT) is a term for assistive, adaptive, and rehabilitative devices for people with disabilities and the elderly. Disabled people often have difficulty performing activities of daily living (ADLs) independently, or even with ...
.
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 many 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.
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.World Health Organization
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
North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...
and most of
Europe
Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
, legal blindness is defined as
visual acuity
Visual acuity (VA) commonly refers to the clarity of vision, but technically rates an examinee's ability to recognize small details with precision. Visual acuity is dependent on optical and neural factors, i.e. (1) the sharpness of the retinal ...
(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 from an object to see it—with corrective lenses—with the same degree of clarity as a normally sighted person could from . In many areas, people with average acuity who nonetheless have a
visual field
The visual field is the "spatial array of visual sensations available to observation in introspectionist psychological experiments". Or simply, visual field can be defined as the entire area that can be seen when an eye is fixed straight at a point ...
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.
Peru
, image_flag = Flag of Peru.svg
, image_coat = Escudo nacional del Perú.svg
, other_symbol = Great Seal of the State
, other_symbol_type = Seal (emblem), National seal
, national_motto = "Fi ...
depicted the blind in their ceramics.
In Greek myth,
Tiresias
In Greek mythology, Tiresias (; grc, Τειρεσίας, Teiresías) was a blind prophet of Apollo in Thebes, famous for clairvoyance and for being transformed into a woman for seven years. He was the son of the shepherd Everes and the nymph ...
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
Athena or Athene, often given the epithet Pallas, is an ancient Greek goddess associated with wisdom, warfare, and handicraft who was later syncretized with the Roman goddess Minerva. Athena was regarded as the patron and protectress of ...
naked while she was bathing. In the Odyssey, the one-eyed Cyclops
Polyphemus
Polyphemus (; grc-gre, Πολύφημος, Polyphēmos, ; la, Polyphēmus ) is the one-eyed giant son of Poseidon and Thoosa in Greek mythology, one of the Cyclopes described in Homer's ''Odyssey''. His name means "abounding in songs and lege ...
captures
Odysseus
Odysseus ( ; grc-gre, Ὀδυσσεύς, Ὀδυσεύς, OdysseúsOdyseús, ), also known by the Latin variant Ulysses ( , ; lat, UlyssesUlixes), is a legendary Greek king of Ithaca and the hero of Homer's epic poem the ''Odyssey''. Odysse ...
, who blinds Polyphemus to escape. In Norse mythology,
Loki
Loki is a god in Norse mythology. According to some sources, Loki is the son of Fárbauti (a jötunn) and Laufey (mentioned as a goddess), and the brother of Helblindi and Býleistr. Loki is married to Sigyn and they have two sons, Narfi or Na ...
tricks the blind god Höðr into killing his brother
Baldr
Baldr (also Balder, Baldur) is a god in Germanic mythology. In Norse mythology, Baldr (Old Norse: ) is a son of the god Odin and the goddess Frigg, and has numerous brothers, such as Thor and Váli. In wider Germanic mythology, the god was kno ...
, the god of happiness.
The
New Testament
The New Testament grc, Ἡ Καινὴ Διαθήκη, transl. ; la, Novum Testamentum. (NT) is the second division of the Christian biblical canon. It discusses the teachings and person of Jesus, as well as events in first-century Christ ...
blind men and an elephant
The parable of the blind men and an elephant is a story of a group of blind men who have never come across an elephant before and who learn and imagine what the elephant is like by touching it. Each blind man feels a different part of the elepha ...
has crossed between many religious traditions and is part of
Jain
Jainism ( ), also known as Jain Dharma, is an Indian religion. Jainism traces its spiritual ideas and history through the succession of twenty-four tirthankaras (supreme preachers of ''Dharma''), with the first in the current time cycle being ...
,
Buddhist
Buddhism ( , ), also known as Buddha Dharma and Dharmavinaya (), is an Indian religion or philosophical tradition based on teachings attributed to the Buddha. It originated in northern India as a -movement in the 5th century BCE, and ...
,
Sufi
Sufism ( ar, ''aṣ-ṣūfiyya''), also known as Tasawwuf ( ''at-taṣawwuf''), is a mystic body of religious practice, found mainly within Sunni Islam but also within Shia Islam, which is characterized by a focus on Islamic spirituality, ...
and
Hindu
Hindus (; ) are people who religiously adhere to Hinduism.Jeffery D. Long (2007), A Vision for Hinduism, IB Tauris, , pages 35–37 Historically, the term has also been used as a geographical, cultural, and later religious identifier for ...
lore. In various versions of the tale, a group of blind men (or men in the dark) touch an
elephant
Elephants are the largest existing land animals. Three living species are currently recognised: the African bush elephant, the African forest elephant, and the Asian elephant. They are the only surviving members of the family Elephantidae an ...
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
"Three Blind Mice" is an English-language nursery rhyme and musical round.I. Opie and P. Opie, ''The Oxford Dictionary of Nursery Rhymes'' (Oxford: Oxford University Press, 1951, 2nd edn., 1997), p. 306. It has a Roud Folk Song Index number o ...
" is a medieval
English
English usually refers to:
* English language
* English people
English may also refer to:
Peoples, culture, and language
* ''English'', an adjective for something of, from, or related to England
** English national ide ...
nursery rhyme
A nursery rhyme is a traditional poem or song for children in Britain and many other countries, but usage of the term dates only from the late 18th/early 19th century. The term Mother Goose rhymes is interchangeable with nursery rhymes.
From t ...
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
Poet
John Milton
John Milton (9 December 1608 – 8 November 1674) was an English poet and intellectual. His 1667 epic poem '' Paradise Lost'', written in blank verse and including over ten chapters, was written in a time of immense religious flux and political ...
, who went blind in mid-life, composed "
On His Blindness
"When I Consider How My Light is Spent" (Also known as "On His Blindness") is one of the best known of the sonnets of John Milton (1608–1674). The last three lines are particularly well known; they conclude with "They also serve who only stand a ...
", a sonnet about coping with blindness. The work posits that ''
hose
A hose is a flexible hollow tube designed to carry fluids from one location to another. Hoses are also sometimes called ''pipes'' (the word ''pipe'' usually refers to a rigid tube, whereas a hose is usually a flexible one), or more generally '' ...
who best Bear ods mild yoke, they serve him best.''
The Dutch painter and engraver
Rembrandt
Rembrandt Harmenszoon van Rijn (, ; 15 July 1606 – 4 October 1669), usually simply known as Rembrandt, was a Dutch Golden Age painter, printmaker and draughtsman. An innovative and prolific master in three media, he is generally consid ...
often depicted scenes from the apocryphal
Book of Tobit
The Book of Tobit () ''Tōbith'' or ''Tōbit'' ( and spellings are also attested) itself from he, טובי ''Tovi'' "my good"; Book of Tobias in the Vulgate from the Greek ''Tōbias'', itself from the Hebrew ''Tovyah'' " Yah is good", also k ...
, which tells the story of a blind patriarch who is healed by his son, Tobias, with the help of the archangel
Raphael
Raffaello Sanzio da Urbino, better known as Raphael (; or ; March 28 or April 6, 1483April 6, 1520), was an Italian painter and architect of the High Renaissance. List of works by Raphael, His work is admired for its clarity of form, ease of ...
.
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.
The Country of the Blind
"The Country of the Blind" is a short story by English writer H. G. Wells. It was first published in the April 1904 issue of ''The Strand Magazine'' and included in a 1911 collection of Wells's short stories, ''The Country of the Blind and Ot ...
" 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
Bob Dylan (legally Robert Dylan, born Robert Allen Zimmerman, May 24, 1941) is an American singer-songwriter. Often regarded as one of the greatest songwriters of all time, Dylan has been a major figure in popular culture during a career sp ...
'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
Marvel Comics is an American comic book publishing, publisher and the flagship property of Marvel Entertainment, a divsion of The Walt Disney Company since September 1, 2009. Evolving from Timely Comics in 1939, ''Magazine Management/Atlas Co ...
superhero
Daredevil
Daredevil may refer to:
* A stunt performer
Arts and media Comics
* Daredevil (Lev Gleason Publications), a fictional 1940s superhero popularized by writer-artist Charles Biro
* Daredevil (Marvel Comics character), a Marvel comic book superher ...
, who can see via his super-human hearing acuity, or ''
Star Trek
''Star Trek'' is an American science fiction media franchise created by Gene Roddenberry, which began with the eponymous 1960s television series and quickly became a worldwide pop-culture phenomenon. The franchise has expanded into vari ...
'' 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
Athletics may refer to:
Sports
* Sport of athletics, a collection of sporting events that involve competitive running, jumping, throwing, and walking
** Track and field, a sub-category of the above sport
* Athletics (physical culture), competiti ...
. Some sports have been invented or adapted for the blind, such as goalball,
association football
Association football, more commonly known as football or soccer, is a team sport played between two teams of 11 players who primarily use their feet to propel the ball around a rectangular field called a pitch. The objective of the game is ...
,
cricket
Cricket is a bat-and-ball game played between two teams of eleven players on a field at the centre of which is a pitch with a wicket at each end, each comprising two bails balanced on three stumps. The batting side scores runs by striki ...
,
golf
Golf is a club-and-ball sport in which players use various clubs to hit balls into a series of holes on a course in as few strokes as possible.
Golf, unlike most ball games, cannot and does not use a standardized playing area, and coping wi ...
,
tennis
Tennis is a racket sport that is played either individually against a single opponent ( singles) or between two teams of two players each ( doubles). Each player uses a tennis racket that is strung with cord to strike a hollow rubber ball ...
,
bowling
Bowling is a target sport and recreational activity in which a player rolls a ball toward pins (in pin bowling) or another target (in target bowling). The term ''bowling'' usually refers to pin bowling (most commonly ten-pin bowling), though ...
, and
beep baseball
Beep baseball is a form of baseball which can be played by people who are visually impaired, using a ball that beeps.
National Beep Baseball Association
The National Beep Baseball Association (NBBA) was organized in the United States in 1976 for a ...
. The worldwide authority on sports for the blind is the
International Blind Sports Federation
The International Blind Sports Federation () is a non-profit organisation founded 1981 in Paris, France. It was formerly known as the International Blind Sports Association. IBSA's mission is to promote the full integration of blind and parti ...
. People with vision impairments have participated in the
Paralympic Games
The Paralympic Games or Paralympics, also known as the ''Games of the Paralympiad'', is a periodic series of international multisport events involving athletes with a range of physical disabilities, including impaired muscle power and impaire ...
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 Observer bias is one of the types of detection bias and is defined as any kind of systematic divergence from accurate facts during observation and the recording of data and information in studies. The definition can be further expanded upon to incl ...
. The expression "
blind leading the blind
"The blind leading the blind" is an idiom and a metaphor in the form of a parallel phrase, it is used to describe a situation where a person who knows nothing is getting advice and help from another person who knows almost nothing.
History
Th ...
" 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).
Research
A 2008 study tested the effect of using
gene therapy
Gene therapy is a medical field which focuses on the genetic modification of cells to produce a therapeutic effect or the treatment of disease by repairing or reconstructing defective genetic material. The first attempt at modifying human DN ...
to help restore the sight of patients with a rare form of inherited blindness, known as
Leber's congenital amaurosis
Leber congenital amaurosis (LCA) is a rare inherited eye disease that appears at birth or in the first few months of life.
It affects about 1 in 40,000 newborns. LCA was first described by Theodor Leber in the 19th century. It should not be co ...
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
Retinal pigment epithelium-specific 65 kDa protein, also known as retinoid isomerohydrolase, is an enzyme of the vertebrate visual cycle that is encoded in humans by the ''RPE65'' gene. RPE65 is expressed in the retinal pigment epithelium (RPE, a ...
directly into the eyes of affected patients. All three patients, aged 19, 22 and 25, responded well to the treatment and reported improved vision following the procedure.
Two experimental treatments for retinal problems include a cybernetic replacement and transplant of fetal retinal cells.
There is no high-quality evidence on the effect of assistive technologies on educational outcomes and quality of life in children with low vision , nor is there evidence on magnifying reading aids in children. Low-vision rehabilitation does not appear to have an important impact on health-related quality of life, though some low-vision rehabilitation interventions, particularly psychological therapies and methods of enhancing vision, may improve vision-related quality of life in people with sight loss.
Other animals
Statements that certain species of
mammal
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
s 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
Rabbits, also known as bunnies or bunny rabbits, are small mammals in the family Leporidae (which also contains the hares) of the order Lagomorpha (which also contains the pikas). ''Oryctolagus cuniculus'' includes the European rabbit speci ...
. 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
The blind mole-rats, also known as the fossorial or subterranean mole rats, are a subfamily (Spalacinae) of rodents in the family Spalacidae, found in eastern Europe and western & central Asia. The hystricognath mole-rats of the family Bathyergi ...
, 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
''The'' () is a grammatical article in English, denoting persons or things already mentioned, under discussion, implied or otherwise presumed familiar to listeners, readers, or speakers. It is the definite article in English. ''The'' is the ...
'', is about a teenage girl, Helen, who trains her blind dog to follow and trust a seeing-eye dog.
See also
*
Accessible Books Consortium
The Accessible Books Consortium (ABC) is a public-private partnership which was launched in 2014 by the World Intellectual Property Organization. The ABC was created with the intent of being "one possible initiative, amongst others, to implement t ...
*
Acute visual loss
Acute visual loss is a rapid loss of the ability to see. It is caused by many ocular conditions like retinal detachment, glaucoma, macular degeneration, and giant cell arteritis, etc.
Main causes
Retinal detachment
Retinal detachment should ...
*
Blindness and education
The subject of blindness and education has included evolving approaches and public perceptions of how best to address the special needs of blind students. The practice of institutionalizing the blind in asylums has a history extending back over a ...
Nyctalopia
Nyctalopia (; ), also called night-blindness, is a condition making it difficult or impossible to see in relatively low light. It is a symptom of several eye diseases. Night blindness may exist from birth, or be caused by injury or malnutrition ( ...
*
Recovery from blindness
Recovery from blindness is the phenomenon of a blind person gaining the ability to see, usually as a result of medical treatment. As a thought experiment, the phenomenon is usually referred to as Molyneux's problem. It is often stated that the fir ...
*
Stereoblindness Stereoblindness (also stereo blindness) is the inability to see in 3D using stereopsis, or stereo vision, resulting in an inability to perceive stereoscopic depth by combining and comparing images from the two eyes.
Individuals with only one funct ...
Tactile graphic
Tactile graphics, including tactile pictures, tactile diagrams, tactile maps, and tactile graphs, are images that use raised surfaces so that a visually impaired person can feel them. They are used to convey non-textual information such as maps, pa ...
*
Tangible symbol systems
Tangible symbols are a type of augmentative and alternative communication (AAC) that uses objects or pictures that share a perceptual relationship with the items they represent as symbols. A tangible symbol's relation to the item it represents is ...
Visual impairment due to intracranial pressure
Spaceflight-associated neuro-ocular syndrome (SANS), previously known as ''Spaceflight-induced visual impairment'', is hypothesized to be a result of increased intracranial pressure. The study of visual changes and intracranial pressure (ICP) in ...
*
World Blind Union
The World Blind Union (WBU) is an international organization representing the estimated 2.2 billion people worldwide who are blind or partially sighted. It consists of other organizations, not individuals.
History, scope, and organization
The Wor ...