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Blindness and severe visual impairment occur everywhere in the world and at all social levels. They are least prevalent in the economically advanced nations and most prevalent in the emerging nations. But whatever their prevalence, these ancient scourges of mankind are enveloped in a mystique that often defies rational analysis and that promotes many social misconceptions to the detriment of both blind people and society. How any social group—from nuclear family to complex modern nation—treats its blind and severely visually impaired provides meaningful cues as to how it perceives the individual, impaired or not, in that social group. For this reason changes in the treatment of these severely limiting chronic conditions can be considered a sensitive barometer of social change at any level of society.

Estimates of prevalence. World-wide estimates of any chronic condition, including blindness, are notoriously unreliable because of differences of definitions and reporting procedures. There is some agreement throughout the world on what basically constitutes blindness: in the United States it is generally defined as a central visual acuity of 20/200 or less in the better eye (with correcting lenses); 6/60 acuity is the comparable standard used in Britain and by other members of the Commonwealth; and 3/60 has been recommended by some international groups. But beyond this basic agreement, there are endless variations of interpretations, additional conditions, and varying reporting procedures that make comparable statistics from one administrative unit to another unobtainable. Still, some estimates must be made because of the severity of blindness as a limiting chronic condition and the consequent need for medical and social services. The World Health Organization (WHO) estimated that in 1962 there were ten million blind persons in the world, or a rate of 3.2 per thousand, and in 1965 the estimate was fourteen million (Wilson 1965).

As to reporting procedures, the United Kingdom has a central registry in the Ministry of Health that is maintained by local health districts and consolidated at the national level; thus its estimate of 2.07 per thousand is considered fairly reliable. Canada has a reporting procedure similar to the United Kingdom’s. The U.S.S.R. and Sweden report through local chapters of a national society for the blind that is supported by the government but that remains private; these estimates are probably less reliable than those of the United Kingdom but are still very useful. In the United States the usual bureaucratic maze exists, with 8 states having mandatory reporting, about 40 having central registers of the blind, and only 13 reporting through uniform procedures to the National Institute of Neurological Diseases and Blindness (according to an unpublished survey conducted by the American Foundation for the Blind). In addition, the United States Public Health Service periodically conducts nationwide household interview surveys on health conditions and impairments, including severe visual impairment (generally defining blindness as the inability to read newsprint with glasses); this agency estimates the national prevalence of severe visual impairments to be 1.98 per thousand, based on data from the household interview sample for July 1959 through June 1961 (U.S. Public Health Service 1962). In the emerging countries regular reporting procedures are rare and tend to be unreliable. They resort to occasional sample surveys, such as those undertaken in the 1960s in India and some of the countries of the Arabian Peninsula (Wilson 1965). A notable example of a thorough clinical screening is one that was under way in Egypt in 1965 (Around the World 1965).

Two factors are major influences on trends of blindness in the world today: increasing survival rates of the aged and of children. In the industrialized countries like the United Kingdom and the United States, two-thirds of the blind and severely visually impaired are estimated to be over 65. In underdeveloped countries survival rates of the aged are far below those reported for industrialized countries, and hence the prevalence of types of blindness associated with aging is also lower. Survival rates among children have made spectacular advances in all countries, particularly the emerging nations like India. One estimate for Africa and the Middle East has been that one per cent of all children there will be blind during childhood (Wilson 1965); the comparable estimate for children under five in the United States is .01 per cent (U.S. National Institutes … 1965).

Blindness as a social problem . While the numbers of blind and severely visually impaired persons are relatively small, the social implications of their existence are enormous, because they have always imposed peculiar strains on the social structure of the society of which they are a part. The blind person in every culture is a man set apart, who by reason of his impairment cannot move about, work, or read as can the majority of his sighted peers. Thus the expectations of his sighted peers set limits on his activities. If, as in some primitive societies, his impairment is considered a special mark of attention from the deity, he is favored. However, in most societies he is seen primarily as a public health problem. In the more economically advanced nations where society is work-oriented and where the major emphasis is on the employability of all citizens, including the sensory impaired, the blind person is an economic and a psychosocial problem.

While the emphasis may differ from society to society, several social correlates of visual impairment exist universally in greater or lesser degree: the religious–mystic element that attributes guilt or favor to impairment, the medical or public health problem, and the psychosocial aspects. To ignore any of these correlates in analyzing the impact of blindness on a culture would result in oversimplification of the problems that blindness and severe visual impairment introduce in society and in an impaired person.

In the United States the complex social problem of caring for the visually handicapped is generally placed in the context of two cultural themes: the work orientation that requires each person to be a contributing, functioning member; and Judaeo-Christian concepts of individual worth and dignity. The ideal, then, in the United States is that the blind or severely visually impaired person be encouraged and helped to become a contributing member of society within the limitations imposed upon him by his sensory loss and that this be done in such a way as to insure his sense of personal worth and his individual dignity. However, the fulfillment of this ideal becomes complicated by the rigorous demands made by a highly mobile and competitive society on its visually impaired members. Thus, in such a society several important program aspects become necessary: personal reorientation and adjustment of the newly blind; vocational training and placement services for both the born blind and the newly blind; instrumentation to aid the blind of all ages to get around and to read with a minimum of help from another person; and, finally, provisions for meeting the financial needs of blind persons who are not able to support themselves. In the United States so-called “work for the blind” programs and research and development programs are concerned with providing comprehensive services to meet these needs.

Most European nations have instituted some prevocational or adjustment training centers as well as vocational training centers. In Finland a very thorough medical and psychosocial examination lasting one week is made before adjustment and/or vocational programs are prescribed (Graham & Clark 1964). Although few European nations have services as thorough as those of Finland, most do provide at least medical care and vocational training for newly blind persons. In Poland a special training course on mobility is given using the “long cane,” which was first employed in training American war-blinded veterans. In the U.S.S.R. special training courses are given the foremen of state industrial concerns where large numbers of blind workers are employed. As compared with programs in the United States and Europe, those in the emerging countries are far more general and traditional; schools for blind children and homes for the aged are ordinarily the only existing services. Of course, there are a few exceptions: for example, Israel provides courses in modern technology, and in Japan the blind are traditionally taught to be masseurs and musicians.

In general, programs for the blind and severely visually impaired throughout the world are limited by two major factors: the ideological and economic emphasis of each country and the extent of its resources. For example, in work-oriented countries like the United States and the U.S.S.R., considerable effort is expended to make the blind person a contributing member of society through employment. In the U.S.S.R. experimental vocational programs are instituted in the R.S.F.S.R. Academy of Sciences, and those that are validated become required courses throughout the Soviet Union. In contrast, American vocational programs at the secondary school level, like American education in general, are not centrally controlled and differ a great deal with the locale (Graham & Clark 1964). In Europe several countries have laws requiring the employment of handicapped persons, a model of which is the British Disabled Persons (Employment) Act of 1944. However, in general, except for the British law, such statutes are not rigorously enforced; and employment is less emphasized than programs to meet the financial needs of the blind, especially in the more welfare-minded countries. In less affluent countries the daily needs of the adult blind are less often met; but in all countries, rich and poor, considerable effort is made to educate the young blind population.

Demographic data for the United States . In 1963 the number of legally blind persons in the United States (those having clinically verified central visual acuity of 20/200 in the better eye or a peripheral field of 20 degrees or less) was estimated at about 400,000, or a prevalence of about 2 per thousand. About 10 per cent of these were estimated to be totally blind; the rest have some useful vision. Well over half of the legally blind are 65 years of age or older, and, following national population trends, there are more aged women than men; 7 per cent of the legally blind are under 20 years of age. Compared to national norms, the legally blind have less education and are in the lower income brackets. The principal causes of blindness among the group are cataracts, glaucoma, and diabetes, which account for 40 per cent of all blindness and none of which are infectious (Schloss 1963, pp. 111–116; Hurlin 1962, pp. 2–10). Congenital blindness among children is often associated with prematurity.

A more liberal set of criteria for defining blindness is applied to those who function as blind people, particularly as far as being able to read is concerned. By these criteria almost one million Americans, or 5.6 per thousand of the U.S. population, are considered to be blind or severely visually impaired (U.S. Public Health Service 1962). Two-thirds of the “functionally blind” are over 65, with a somewhat greater number of females than males; about 15 per cent are under 24. They are probably nearer the national norms on education and income than the smaller legally blind group. Cataracts are reported by almost half of the aged as the cause of their visual impairment.

The legally blind are likely to be known to agencies serving the blind and to research projects, since they have become known to some reporting agency as being within the eligibility requirements for services for the blind. However, among the larger group of the functionally blind there are a large number of “hidden” blind who have not sought services from agencies for the blind. This hidden group (according to preliminary research results) is composed of several categories of blind people: those who are affluent enough to care for themselves, those who are ignorant of available services, isolates (“rocking-chair cases”) who desire no care, and a much larger group of persons who are able to function as sighted people in many tasks and activities (Josephson 1963).

Service and research programs. These demographic data, inexact as they are, influence services and research. It is clear that the low prevalence of blindness and its being a function of general population characteristics mean that blind people are widely scattered in relatively small numbers throughout the country, with urban centers having the largest and most readily accessible populations. Consequently, the urban blind are most likely to have services provided for them and to participate in research projects. However, research shows that the rural blind function relatively effectively in their home communities as long as they have resided there over a long period of time and do not have to leave familiar territory often (McPhee & Magleby 1963).

If current population trends persist, the numbers of severely impaired persons aged 20 or less and aged 65 and over will increase by about 40 per cent over the next 10 to 15 years. This suggests that the proper educational training of young blind people is a particularly acute problem and that prevention and early detection campaigns for both the young and the aged will have to be stepped up.

Research also shows that more effective techniques are needed for diagnosing the pseudoretardation of the blind child who is understimulated both at home and at school; unless we develop more successful techniques for finding these cases, increasing numbers of such children (many of whom are premature at birth) will be mistakenly assigned to institutional care of a custodial nature only. The evidence strongly suggests that when blind children are properly stimulated through their remaining senses and put in an atmosphere favorable to learning they develop in much the same way as their sighted peers (Hallenbeck 1954, pp. 301–307; Imamura 1965; Norris et al. 1957; Parmelee et al. 1962). There is an obvious need for new instructional materials in keeping with advances for teaching sighted children. Furthermore, severely visually impaired children need to be given systematic travel or mobility training before they reach maturity, rather than receive it later in adult rehabilitation training centers, as so often happens now (American Foundation for the Blind 1960).

For the adult blind, research on new vocational opportunities is needed. In the United States economy, which sustains a steady unemployment level of about 5 per cent of the working force, the non-professional blind worker is very likely to be a marginal worker. Moreover, it would appear that in the future more opportunities in highly professional jobs and fewer in industrial and semiskilled jobs will be available in competitive employment. In the United States, where there are approximately seventy workshops employing the visually impaired, the trend is toward more “terminal” employment in workshops and less training for competitive employment; this change of emphasis is implicit in the 1965 amendments to the Vocational Rehabilitation Act (U.S. National Institutes … 1965). According to National Industries for the Blind, in the period 1964–1966 less than one thousand workers each year have passed from workshop employment to competitive employment in the United States. To increase the effectiveness of the adult blind person, technological research will have to be expanded so as to offer instrumentation that will permit the blind man to travel better, to undertake increasingly more complex jobs, and to have direct access to the printed word. Present research and development projects in the United States, the United Kingdom, and the Soviet Union offer some promise even at present levels of financial support (International Congress … 1963).

Older blind persons, ever increasing in numbers, need assistance with three major problems: maintaining a reasonable income, acquiring more meaningful patterns of daily existence, and maintaining reasonably good health. Welfare programs based on means tests too often compromise individual dignity; an insurance program against sensory deprivation, much like the American social security system, should be considered. To help the aged blind in adjusting to new patterns of living, individual counseling is needed. The problems of health are largely geriatric and well known, except for the problem of the blind person’s emotional resistance to medical advances, such as cataract surgery, and to low-vision aids; this resistance needs to be broken down among older people who stand to benefit from such programs (Miller 1964).

Through all of these unsolved problems of the severely visually impaired runs the thread of public attitudes that commonly support the exclusion of blind people from jobs and schools and thereby adversely affect their acceptance as functioning members of society. Most societies still consider their blind populations as health and welfare problems only. Recent research by Lukoff and Whiteman (e.g., 1963) has found that attitudes toward blindness are multidimensional and generally susceptible to modification through exposure to blind persons and better knowledge of them. With a focus contrary to that of conventional theory of attitude formation and change, Cutsforth (1933) and others in the last thirty years have stressed the vital importance of a healthy self-image on the part of the blind person if stereotypes are to be overcome. Following this tradition, Lukoff and Whiteman found that in large part the formation of public attitudes depends on three factors that are involved in the blind person’s adjustment to his blindness: his self-image; his status set, that is, “the way a person orients himself toward the several positions he occupies that also identify him to other persons”; and his role set, which is “arranged along a continuum of independence–dependence.”

New opportunities for the blind. In general, the most advanced research on blindness has been done in the United States, with the exception of certain experimental programs for vocational training conducted by the U.S.S.R. However, even in the United States a great deal more needs to be done to eliminate the age-old subcultures of “the blind,” who are in effect a minority of the severely visually impaired population. It is apparent from the discriminatory practices, such as labeling “the blind” with arm brassards in some Scandinavian and western European countries or tolerating them as fakirs and beggars in the Far East, that generally enlightened national health and welfare plans are not sufficient, at least by American standards, to insure the full participation of blind and severely impaired people in the society in which they live.

There is some hope that research and the further development of services will improve the lot of blind people throughout the world. Among the emerging nations the emphasis for some time will undoubtedly be medical: the prevention of blinding eye diseases, such as trachoma, by public health measures and the early detection and treatment of such conditions as glaucoma. Among the more developed nations, both psychosocial and technological research offer promise. It is generally conceded now by both ophthalmologists and educational specialists that residual vision should be used to its fullest capacity, not “saved.” In the United States today there are about thirty “near-vision” clinics, partially supported by federal government grants; and double this number are planned if, on evaluation, the near-vision clinic proves an effective means of introducing visual aids and training severely visually impaired persons to use them. This encouragement to use residual vision opens up new experimental opportunities for many people: more can be taught to read, and more can be taught to get around unaided.

The experience with the war-blind in many countries, particularly the United States and the U.S.S.R., has led to many achievements hitherto not considered possible for the blind and severely visually impaired. In the U.S.S.R. the widespread employment of the war-blind as skilled workers, even though they receive pensions, has helped negate the argument that pensions destroy initiative (see Zimin 1962). Almost half of all American war-blind are employed (or twice the percentage of civilian blind), although they receive generous compensation for their losses and injuries; their average household income is well above the national average. In general, the American blinded veterans (average age 46) show very few differences from their sighted peers: largely they own their own homes, are heads of their households, are in middle-to-high socioeconomic brackets, are well educated, read heavily, are active in civic affairs, are generally healthy in spite of their impairments, and enjoy themselves in cultural and recreational activities like their neighbors. The extensive training, equipment, and economic flooring given them has paid off in terms of realizing their potentialities as human beings and as contributing members of society (Graham 1965).

The other group in the United States that has contributed to the successful challenging of the traditional stereotype of blindness (that is, characterized by hopelessness, indigence, and disease) has been the group of premature children blinded or visually impaired by oxygen poisoning in incubators, resulting in retrolental fibroplasia (RLF). The RLF children, numbering perhaps eight thousand to ten thousand since the mid-1940s, are proving conclusively that, given the proper equipment and training, as well as favorable attitudes toward their endeavors by educators, parents, and peers, they can compete successfully in their academic work and personal lives (Norris et al. 1957). Indeed, each year sees more RLF and other blind children enrolled in the public day schools, and schools for the blind are paying far more attention to multiply handicapped blind children, who hitherto have been too often committed to institutions for custodial care. In the last few years the United States and the U.S.S.R. have begun a concerted effort to aid blind children to travel and to acquire access to the printed word. Indeed, increasingly the emphasis is on the realization of the potentialities and abilities of blind and severely visually impaired people, particularly children, rather than on their limitations and problems.

There is some hope that through research it will be possible to find ways to eliminate the main social causes of discrimination against blind people, whether or not medical advances to cut their numbers are realized. That effort must be multi-disciplinary and long-range in nature if it is to succeed (Graham 1960; National Committee … 1964). From the present modest beginnings, more research on visual impairment can be expected if research funds continue at present levels. In time the emerging countries can expect to benefit from this research and experience, which has been so notable in the past few years.

Milton D. Graham

[See alsoHealth; Illness; Medical care; Planning, social, article onwelfare planning; Vision, article Onvisual defects; Vocational rehabilitation.]


Amendments to Vocational Rehabilitation Act. 1965 Rehabilitation Record 6, no. 6:5–15.

American Association of Workers for the BlindBlindness. → Published annually since 1964.

American Foundation for the Blind 1960 Services for Blind Persons in the United States. New York: The Foundation.

American Foundation for the Blind 1961 Report of Proceedings of Conference on Research Needs in Braille, September 13–15, 1961. New York: The Foundation.

American Foundation for the Blind 1962 Proceedings of the Mobility Research Conference. Edited by James W. Linsner. New York: The Foundation.

Around the World. 1965 Sight-saving Review 35, no. 2: 112–114.

Ashcroft, Samuel C.; and Henderson, Freda 1963 Programmed Instruction in Braille. Pittsburgh: Stanwix House.

Barnett, M. Robert 1960 Science Still Seeking True Electronic Substitute for Sight. UNESCO Courier 13, no. 6:7–9.

Cutsforth, Thomas D. 1933 The Blind in School and Society. New York: Appleton.

Graham, Milton D. 1960 Social Research on Blindness. New York: American Foundation for the Blind.

Graham, Milton D. 1965 Wanted: A Readiness Test for Mobility Training. Pages 133–161 in American Foundation for the Blind, Proceedings of the Rotterdam Mobility Research Conference. New York: The Foundation.

Graham, Milton D.; and Clark, Leslie L. (editors) 1964 Recent European Research on Blindness and Severe Visual Impairment. New York: American Foundation for the Blind. → See especially pages 3–29.

Hallenbeck, Jane 1954 Pseudo-retardation in Retrolental Fibroplasia. New Outlook for the Blind 48:301–307.

Hurlin, Ralph G. 1962 Estimated Prevalence of Blindness in the United States and in Individual States, 1960. Sight-saving Review 32:4–12.

Imamura, Sadako 1965 Mother and Blind Child. Research Series No. 14. New York: American Foundation for the Blind.

International Congress on Technology and Blindness 1963 Proceedings. Edited by Leslie L. Clark. New York: American Foundation for the Blind.

Josephson, Eric 1963 An Epidemiological Survey of Visual Impairment. Unpublished manuscript, American Foundation for the Blind.

Lairy, Gabrielle C.; and Netchine, S. 1962 The Electroencephalogram in Partially Sighted Children Related to Clinical and Psychological Data. American Foundation for the Blind, Research Bulletin 2:38–56.

Lukoff, Irving F.; and Whiteman, Martin 1963 Attitudes and Blindness: Components, Correlates and Effects. Unpublished manuscript, Univ. of Pittsburgh.

McPhee, William M.; and Magleby, F. Legrand 1963 Activities and Problems of the Rural Blind in Utah. Salt Lake City: Univ. of Utah.

Miller, Irving 1964 Resistance to Cataract Surgery. New York: American Foundation for the Blind.

National Committee for Research on Ophthalmology and Blindness 1964 Symposium on Research in Blindness and Severe Visual Impairment: Proceedings. New York: American Foundation for the Blind.

New Pathways for the Blind. 1960 UNESCO Courier 13, no. 6. → The whole issue is devoted to the topic.

Norris, Miriam; Spaulding, Patricia J.; and Brodie, Fern H. 1957 Blindness in Children. Univ. of Chicago Press.

Parmelee, Arthur H. Jr.; Fiske, Claude E.; and Wright, Rogers H. 1962 The Development of Ten Children With Blindness as a Result of Retrolental Fibroplasia. American Foundation for the Blind, Research Bulletin 1:64–88.

Schloss, Irvin P. 1963 Implications of Altering the Definition of Blindness. American Foundation for the Blind, Research Bulletin 3:111–116.

U.S. National Institutes of Health 1965 1963 Statistical Report: Annual Tabulations of Model Reporting Area for Blindness Statistics. Public Health Service Publication No. 1312. Washington: Government Printing Office.

U.S. Public Health Service 1962 Selected Impairments by Etiology and Activity Limitation: United States, July 1959—June 1961. Health Statistics from U.S. National Health Survey, Series B-35. Washington: Government Printing Office.

Wilson, John 1965 The Blind in a Changing World. American Association of Workers for the Blind, Blindness [1965]: 87–92.

World Blindness Rate. 1965 National Society for the Prevention of Blindness, Prevention of Blindness News [1965] Winter: 6 only.

Zimin, Boris 1962 Employment and Vocational Training of the Blind in the USSR. New Outlook for the Blind 56:363–366.

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blindness Surprisingly, blindness rarely means total absence of light perception. Most definitions of blindness are based on measurement of visual acuity (the ability to read letters at a certain distance) and assessment of the ability of the person to carry out tasks needing vision. In the UK, the National Assistance Act 1948 states that a person can be certified as blind if they are ‘so blind that they cannot do any work for which eyesight is essential’. This rather circular definition refers to ‘any work’ and not just the person's normal job or one for which he has been specially trained.

Visual acuity is usually tested by asking the patient to read letters of various sizes on a chart viewed from a distance of 6 m or 20 feet (the Snellen method). Acuity is expressed as a fraction, the number on top referring to the distance at which a normal person can read a particular size of letter and the lower number the distance at which the subject being tested can read that size of letter. Hence ‘normal’ visual acuity is 6/6 (European) or 20/20 (American). A person should be certified blind if the visual acuity (while wearing corrective glasses) is 3/60 or below (when a letter that can be recognized from 60 metres by a normal person can be identified only from 3 metres or closer). A person should also be certified blind if their acuity is between 3/60 and 6/60 but they have completely lost the peripheral part of their visual field, hence restricting their vision to the central part of the field. Indeed, if the more useful lower part of the visual field is lost then someone with better than 6/60 acuity can be certified blind.

There is no legal definition of partial sight in the UK, but a person can be certified as partially sighted if they are ‘substantially and permanently handicapped by defective vision caused by congenital defect or illness or injury’. All certification must be done by a consultant ophthalmologist. The help from Social Services should be the same for both legally blind and partially sighted groups but Social Security benefits and tax concessions differ.

Definitions of blindness are not the same around the world and the vast majority depend on measured visual acuity with no allowance for any functional deficits. Consequently comparison of the incidence of blindness world-wide is inexact. The World Health Organisation has proposed categories of visual impairment but these have not yet been widely adopted.

The common causes of blindness vary in different countries according to the general levels of economic and physical health. The high rate of blindness in developing countries is mainly due to malnutrition and infectious diseases, coupled with the scarcity of medical care. Moorfields Eye Hospital was founded in London in 1805 to treat the ‘Egyptian ophthalmia’, a mixture of trachoma and purulent ophthalmitis brought back by British troops from Aboukir after their withdrawal from Egypt in 1803. The disease quickly spread throughout the country when the disbanded soldiers returned to their homes, taking the infection with them. Nowadays the condition is treatable with tetracycline eye ointment and tetracycline taken orally.

Causes of blindness

Lack of vitamin A has a direct effect on the eye, causing clouding and softening of the cornea (keratomalacia), but also increases the risk and severity of infections, so that measles can be a blinding or even fatal disease in children who are deficient in vitamin A. Night-blindness due to lack of vitamin A may occur in famines, and cure of this condition by eating liver, which is rich in vitamin A, has been known for over 3000 years.

Another cause of night-blindness is pigmentary degeneration of the retina (retinitis pigmentosa) which, combined with partial loss of the visual field, eventually contracting down to ‘tunnel vision’, can be most disabling. This condition is mainly inherited as an autosomal recessive condition (showing itself only when both parents carry the mutant gene), but other forms occur. A high proportion of the population of the Atlantic island Tristan da Cunha was recently discovered to be affected when they were evacuated because of volcanic activity. The disorder is progressive and untreatable.

Trachoma, an infectious disease, affects some 500 million people world-wide, of whom 7 million are blind and 10 million visually impaired. The infectious agents are bacteria known as Chlamydia.

River blindness (onchocerciasis) is the next commonest infection, where microfilarial parasites, spread by black flies, which breed in the tropical, sub-Saharan belt across the whole of Africa and at similar latitudes in Mexico, Brazil, and Ecuador, invade the retina and the supporting, vascularized middle layer of the eyeball, the choroid. Treatment was revolutionized in 1987 when ivermectin, already used in veterinary medicine, was registered for human therapy.

From 1976 the total number of people registered blind in Britain has risen, but this rise is limited to those over 75 years old. Fifty per cent of all 75–85-year-olds registered with impaired vision in this country suffer from age-related macular degeneration (ARMD). Cataracts are now second as a cause of blindness, at around 40%, but these are essentially treatable by surgery except in those cases where extraction of the cataract reveals underlying, untreatable ARMD.

Damage to the retina caused by glaucoma (increased pressure in the eyeball) and by diabetes (diabetic retinopathy) make up almost all the remaining causes of blindness. Glaucoma is insidious in onset: acuity in the central visual field is not seriously affected and a diagnosis may not be made until much of the peripheral retina has been destroyed. Diabetic retinopathy is most prevalent and severe in long-standing insulin-dependent diabetes. This emphasizes the importance of striving for optimal diabetic control. Routine screening checks for both glaucoma and diabetic retinopathy are essential, but manpower and economic considerations have led to much of this work being transferred to orthoptists and optometrists. Retinal detachment (separation of the retina from the pigment epithelium behind it) is a rarer cause of blindness.

There is a long history of visual upsets from staring directly at the sun. The high energy optically concentrated at the central part of the retina for only seconds can produce prolonged after-images and even permanent loss of central vision. This is an occupational hazard for astronomers, and for members of the public who sun-gaze in a misguided attempt to strengthen their eyes or when under the influence of hallucinogenic drugs. There is a particular hazard during solar eclipses because the reduced total amount of light makes it easier to hold fixation on the sun, but the intensity on the remaining illuminated part of the retina is just as high (and just as damaging) as when there is no eclipse: hence the term ‘eclipse blindness’.

Possibilities for treatment

Given the immense social importance of vision, there is intense effort to develop new treatments for blinding conditions. These are focusing not only on the conventional approach of developing new vaccines to prevent infection and new drugs to treat specific conditions, but also on more innovative approaches. For instance, attempts have been made to implant an array of electrodes over the surface of the visual cortex, coupled to a video camera or an optical letter reader, in the hope of bypassing the eye and providing visual sensation by direct stimulation of the cortex. Unfortunately, such stimulation produces only the sensation of tiny pin-points of light, which appear to move with movements of the eyes. A more promising approach is the implantation of a thin sheet of light-sensitive electrodes into the retina, to take the place of degenerated receptors and provide direct stimulation to the fibres of the optic nerve.

Cortical blindness

Damage to the visual cortex in the occipital lobe of the cerebral hemispheres can also cause blindness — cortical blindness. When fixation is maintained on a point in space, a particular region of the visual field is blind (a ‘scotoma’) whether either eye is open, or both (because the cortex receives signals from corresponding regions of the two retinae). Cortical blindness can occur, for example, after a stroke affecting the posterior cerebral artery, which supplies blood to that part of the brain. If extensive damage occurs in one hemisphere, the opposite side of the visual field becomes blind (hemianopia). Often, a small region around the fixation point is spared. This ‘macular sparing’ is thought to be due to the fact that so much of the visual cortex is devoted to the central part of the retina that some part of this region has a high chance of surviving. Interestingly, even when the occipital visual cortex is bilaterally destroyed, resulting in total blindness with no light perception, the patient does not feel enveloped in darkness: rather, the outside world simply does not exist visually (as for the world behind our heads). This contrasts with blindness resulting from retinal damage (for instance from total bilateral retinal detachment), when the patient complains of being in complete darkness. Indeed, the cortically blind patients are subjectively unaware of their disability — blind to their blindness.

When damage is restricted to the primary visual cortex (not extending into the surrounding cortical areas) some patients are still able to detect certain forms of visual stimulation (especially moving objects and sudden changes in brightness) in the ‘blind’ part of the visual field. Amazingly, if the stimulus is not very intense or rapidly moving, they are often unaware of their residual visual capacity, but can reliably ‘guess’ whether, for instance, the stimulus has moved, and even in which direction. This bizarre dissociation of vision from consciousness is known as ‘blindsight’. Recent research even suggests that the facial expression of faces ‘seen’ in the blind part of the field can be recognized. Blindsight is not magic! Even when the primary visual cortex is damaged, information from the eyes still reaches parts of the midbrain and other visual parts of the cerebral cortex. These secondary pathways presumably mediate the impoverished visual performance.

If a stroke or injury leaves the primary visual cortex intact but destroys visual areas further forward in the occipital lobe of the cerebral hemispheres, remarkable disorders of visual perception, without frank blindness, can occur. These include the inability to see movement, even though stationary objects are quite normally perceived (akinetopsia), and a lack of perceived colour, despite normal perception of shape and movement (achromatopsia). These observations are entirely compatible with evidence from experiments in animals in which the activity of nerve cells has been recorded with microelectrodes, as well as with studies using positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) to detect activity in the normal human brain caused by different forms of visual stimulation. These experimental approaches have shown that the primary visual cortex is surrounded by a patchwork of other areas in which neurons are devoted to the analysis of one aspect or another of the visual image — motion in some areas, colour in others, etc.

Damage further forward, in the lower part of the temporal lobe, can precipitate even more curious failures of perceptual interpretation, generally known as visual agnosias (from the Greek for lack of knowledge). Not uncommon, especially after damage on the right side, is prosopagnosia — an inability to recognize faces, sometimes even of family members, although other aspects of object identification (even knowing that a face is a face) are intact. In extreme cases, the poor patient has great difficulty in recognizing a wide variety of everyday objects (until he or she touches them), even though all basic aspects of vision (acuity, colour vision, detection of movement, etc.) are unaffected.

Injury to the rear part of the corpus callosum — the great cable of millions of nerve fibres that links the two hemispheres — or to regions at the junction of the occipital and temporal lobes can cause specific disorders of visual integration (associational disturbances), such as word blindness (alexia).

Provision for the visually disabled

The reaction of the public to handicapped and disabled people remains capricious, and often prejudiced. The deaf have long been figures of fun: they are often ignored and easily retreat into solitude. However, the blind generally receive more sympathy, even admiration. Social Services for the blind unfortunately are not uniformly good throughout the UK. However, some national organizations such as the Royal National Institute for the Blind and Guide Dogs for the Blind give great help and provide funds for research into blindness as well. In 1835 Louis Braille introduced his system of raised writing, where projecting dots represent a letter or number and are interpreted by touch, but it took 30 years to gain acceptance. In this electronic age there are many devices which can make an enormous difference to the blind person's quality of life. One is a computer that reads out text audibly as it appears on screen. This can be set to speeds as fast as the subject can comprehend the speech. A braille printer and labelling machine help, for example, to identify foodstuffs in the kitchen or deep-freeze, or to catalogue a CD library. Microwave units can respond to and speak instructions and will defrost different foods correctly once they have been weighed. For contact with the outside world there are talking newspapers, which can be sent by compressed e-mail, or put on to the Internet. A CD-ROM of all British daily newspapers is available weekly. Never has so much been available for blind people who can afford it.

Peter Fells, and Colin Blakemore


Cullinon, T. R. (1987). The epidemiology of blindness. In Clinical ophthalmology, (ed. S. Miller), p. 571. Wright, Bristol.
Walsh, F. B. and and Hoyt, W. F. (1969). Clinical neuro-ophthalmology, Vol. 1, (3rd edn), pp. 87–120. Williams and Wilkins, Baltimore.

See also blind spot; eyes; optometry; orthoptics; vision.

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74. Blindness

  1. Agib dervish who lost an eye. [Arab. Lit.: Arabian Nights ]
  2. Anchises blinded by lightning. [Gk. Myth.: Walsh Classical, 22]
  3. Blind Pew David, the blind beggar. [Br. Lit.: Treasure Island ]
  4. Braille, Louis (18091852) teacher of blind; devised raised printing which is read by touch. [Fr. Hist.: NCE, 354]
  5. Cratus Titan who blinded Prometheus. [Gk. Myth.: Kravitz, 6768]
  6. Demodocus blind bard rewarded by Odysseus. [Gk. Lit.: Odyssey VIII]
  7. Ephialtes giant deprived of his left eye by Apollo and of his right eye by Hercules. [Gk. Myth.: Brewer Dictionary, 333]
  8. Gloucester cruelly blinded by those he served. [Br. Lit.: King Lear ]
  9. the Graeae share one eye among them. [Gk. Myth.: Gayley, 208210]
  10. Heldar, Dick artist who gradually goes blind and is abandoned by his sweetheart. [Br. Lit.: The Light that Failed in Benét, 586]
  11. Homer sightless writer of Iliad and Odyssey. [Gr. Hist.: Wallechinsky, 13]
  12. Justice personified as a blindfolded goddess, token of impartiality. [Rom. Tradition: Jobes II, 898]
  13. Keller, Helen (18801968) Achieved greatness despite blindness and deafness. [Am. Hist.: Wallechinsky, 13]
  14. Lucy, St. vision restored after gouging out of eyes. [Christian Hagiog.: Brewster, 2021]
  15. mole said to lack eyes. [Medieval Animal Symbolism: White, 9596]
  16. Nydia beautiful flower girl lacks vision but sees love. [Br. Lit.: The Last Days of Pompeii, Magill I, 490492]
  17. Odilia, St. recovered vision; shrine, pilgrimage for visually afflicted. [Christian Hagiog.: Attwater, 257]
  18. Oedipus blinded self on learning he had married his mother. [Gk. Lit.: Oedipus Rex ]
  19. Paul, St. blinded by God on road to Damascus. [N.T.: Acts 9:119]
  20. Peeping Tom stricken blind for peeping as the naked Lady Godiva rode by. [Br. Legend: Brewer Dictionary ]
  21. Plutus blind god of Wealth. [Gk. Lit.: Plutus ]
  22. Polyphemus Cyclops blinded by Odysseus. [Gk. Myth.: Odyssey ]
  23. Rochester, Edward blinded when his home burns down, depends on the care of Jane Eyre. [Br. Lit.: Charlotte Bronte Jane Eyre ]
  24. Samson Israelite hero treacherously blinded by Philistines. [O.T.: Judges 16:421]
  25. Stagg sightless roomkeeper. [Br. Lit.: Barnaby Rudge ]
  26. three blind mice sightless rodents; lost tails to farmers wife. [Nurs. Rhyme: Opie, 306]
  27. Tiresias made sightless by Athena for viewing her nakedness. [Gk. Myth.: Brewer Dictionary, 1086]
  28. Tobit sparrow guano falls into his eyes while sleeping. [Apocrypha: Tobit 2:10]
  29. Zedekiah eyes put out for revolting against Nebuchadnezzar. [O.T.: II Kings 25:7]

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blindness, partial or complete loss of sight. Blindness may be caused by injury, by lesions of the brain or optic nerve, by disease of the cornea or retina, by pathological changes originating in systemic disorders (e.g., diabetes) and by cataract, glaucoma, or retinal detachment. Blindness caused by infectious diseases, such as trachoma, and by dietary deficiencies is common in underdeveloped countries where medical care is inadequate. River blindness, caused by a parasitic worm transmitted by black flies, results in severe itching and disfiguring lesions. Infection of the eye area can destroy vision. An estimated 18 million people in Africa, Latin America, South America, and Yemen are infected with the parasite; 1 million of those infected are expected to become blind or severely impaired. Until recently, pesticides have been used to eradicate the flies. Two new drugs, ivermectin and amocarzine, have proved effective when used together. Most infectious diseases of the eye can be prevented or cured.

A major cause of congenital blindness in the United States, ophthalmia neonatorum, which is caused by gonorrhea organisms in the maternal birth canal, is now prevented by placing silver nitrate solution in all newborn infants' eyes. Retinitis pigmentosis, a hereditary and degenerative eye disease, affects 100,000 people in the United States. An early sign is night blindness which progresses to total blindness. Color blindness, an hereditary problem, is an inability to distinguish colors, most commonly red and green. Snow blindness is a temporary condition resulting from a burn of the cornea caused by the reflection of sunlight on snow. Night blindness results from a deficiency of vitamin A. See eye.

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48. Blindness

See also 148. EYES .

ablepsia, ablepsy
a lack or loss of sight. ableptical, adj.
a condition of partial or total blindness, caused by a disease of the optie nerve. amaurotic , adj.
amblyopia, amblyopy
obscurity of vision, occurring without any organic change in the eyes; the first stage of amaurosis. amblyopic, adj.
anopsy, anopsia, anoöpsia
Medicine. the condition of snow blindness.
Obsolete, the state of having defective eyesight; purblindness.
Obsolete, the process of blinding.
a disease of the eyes, in which the eyeball hardens and becomes tense, often resulting in blindness. glaucomatous , adj.
the loss of sight in daylight. hemeralopic , adj.
a writing frame designed for use by blind people.
the loss of sight in darkness. nyctalopic , adj.
a device combining a selenium cell and telephone apparatus that converts light energy into sound energy, used to enable blind people to sense light through the hearing and thus read printed matter.
an instrument for writing when unable to see.
scotoma, scotomy
a blind spot or blind area in the field of vision.
the totality of medical knowledge concerning the causes, treatment, and prevention of blindness.
a person who devotes himself to helping the blind.
blindness. typhlotic , adj.

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Is There Hope in the Darkness?

What Causes Blindness?

How Do People with Vision Loss and Blindness Adapt?


Blindness is the absence of all or most vision.


for searching the Internet and other reference sources






Corrine tried to imagine how she would describe a bird to her sister Amy, who might never be able to see one. She could say that it is small, that it has feathers, and that it sings. At least those are the things her sister can feel and hear. But how could she describe the red of a male cardinal and distinguish it from the reddish-brown of a female cardinal, when Amy might never see anything at all? And what about all the other things Conines sister might not see: the television shows and the movies, the picture books Corrine saved to give her, the blue sky, the faces of their mom and dad.

Corrine s sister Amy was born prematurely. The doctors told Amys family that she had retinopathy (ret-i-NOP-a-thee) of prematurity. This condition results when the blood vessels in the eyes of a premature baby grow abnormally and cause bleeding and scarring. It may result in total or partial blindness.

More than 1 million people in the United States are blind, which means they cannot see at all or their vision is very poor. Another 14 million people have severe visual impairments that cannot be corrected with eyeglasses, according to the group Research to Prevent Blindness, Inc. Many diseases and injuries can cause blindness. There are treatments that can restore partial or complete eyesight for some people with blindness. Others, however, will remain blind for the rest of their lives.

Is There Hope in the Darkness?

Conines sister Amy might not lose her vision. Doctors now can use a probe to freeze parts of the eye and prevent permanent damage from retinopathy of prematurity. Thousands of other people with potentially vision-threatening conditions, such as strabismus*, glaucoma*, and cataracts*, also can benefit from treatments, especially if the disorders are detected early. Others whose conditions cannot be reversed or improved may benefit from special devices like voice-recognition software for computers and from programs that train guide dogs to assist with daily tasks like walking, going to school, and working.

* strabismus
is a condition that causes the eyes to cross or not work together correctly, which may lead to permanent loss of vision in one eye.
* glaucoma
is a group of disorders that cause pressure to build in the eye, which may result in vision loss.
* cataracts
result from cloudiness of the lenses in the eyes that usually develops as a person ages. They often impair vision.

What Causes Blindness?

Many conditions may cause blindness. The most common cause of vision loss in infants and young children is amblyopia (am-ble-O-pe-a).


Amblyopia is the loss of vision in one eye that results when the eyes are misaligned or not working together correctly in a condition known as strabismus (stra-BIZ-mus). About 3 to 5 percent of children have strabismus, which usually is present from birth or develops during infancy. In most cases, there is no known cause for the condition, which often makes a person look cross-eyed. With early diagnosis and treatment, the eye that is not pointing straight can be trained to develop normal vision. For some people, surgery is needed to align the eye correctly.


Trachoma is a chronic infection of the eye by Chlamydia trachomatis bacteria. The bacteria infect the linings of the eyelid, causing them to become thick and rough. If the condition is untreated or if the infection returns, the eyelashes can turn inward and cause small scars on the eyes surfaces. Eventually, blindness results. Trachoma is the leading cause of preventable blindness in the world.

Trachoma is spread through contact with the discharge from the eyes of infected persons. For example, if infected people rub their eyes and then shake another persons hands, the bacteria that cause trachoma can be spread. Also, using the handkerchief or towel of an infected person can spread the bacteria.

Today, about 10 percent of the worlds population live in areas where trachoma is a problem, including Africa, Asia, Australia, Latin America, and some poorer areas of the United States.

Treatment can stop trachoma before it blinds people. Antibiotic ointments or oral antibiotics are used to treat the disease. The World Health Organization (WHO) has established a WHO Alliance for the Global Elimination of Trachoma. WHO hopes to achieve its goal by the year 2020 through prevention, antibiotics, and surgery to repair eyelids.


Some children are born with cataracts, which cloud the lens in the eye and prevent images from being seen clearly or at all. People also develop cataracts as they age, which makes it one of the most common causes of reduced vision. More than 400,000 new cases of cataracts develop each year in the United States. Surgery to remove cataracts is common for adults and for those few children with them. This restores vision in more than 90 percent of cases.


Diabetes may lead to vision loss if diabetic retinopathy develops. Diabetic retinopathy, one of the leading causes of blindness in adults, results in vision loss if blood vessels supplying the eyes retina* are damaged by the disease. The blood vessels sometimes leak or break open to damage the retina. More vessels also may grow and start to cover the retina or grow into the fluid that fills the eyeball, further reducing vision.

* retina
is the area at the inside rear of the eyeball that acts like film in a camera to capture the image a person sees.

Researchers estimate that as many as 10 million to 15 million people have diabetes in the United States and 700,000 are at risk of developing diabetic retinopathy. Almost all people with diabetes can show signs of damage to their retina after two or three decades of living with the disease, but not all of them lose their vision. There are no symptoms of diabetic retinopathy at first. As the damage increases, vision becomes blurred. Doctors can see the damage with a device that looks at the retina, which is why annual vision exams are so important for people with diabetes.

The best treatment for diabetic retinopathy is prevention, which means managing diabetes (and high blood pressure, if present) with proper nutrition, exercise, and medications. In some cases, laser treatment may be used to prevent worsening of diabetic retinopathy. People with diabetes also are at higher risk for cataracts and glaucoma.


Glaucoma is a disorder that causes fluid pressure to build up inside the eye, which may cause optic nerve* damage. It may go undetected for many years before its effects on vision are noticed. It is one of the leading causes of blindness in the United States, with elderly people and people of African ancestry at increased risk.

* optic nerve
is the nerve that sends messages, or conducts impulses, from the eyes to the brain, making it possible to see. The optic nerve is also referred to as the second cranial nerve.

Macular degeneration

Macular degeneration is similar to diabetic retinopathy. Changes in the blood vessels supplying the central portion of the retina, known as the macula, cause the vessels to leak and to damage cells that are needed for the central part of the field of vision. Peripheral or side vision usually remains, but without treatment, the damaged field of vision may expand. Doctors sometimes recommend laser surgery to treat the leaking blood vessels when people are in the early stages of macular degeneration in order to prevent or slow progressive vision loss. Others compensate for vision loss by using magnifying devices.


Ocular (OK-yoo-lar) herpes may cause vision loss as a result of herpesvirus infections, usually the herpes simplex virus that causes cold sores or the herpes zoster virus that causes chickenpox and shingles. The U.S. National Eye Institute estimates that ocular herpes affects approximately 400,000 people in the United States.

Infection of the eyes by the Chlamydia trachomatis organism is a leading cause of blindness in developing nations. The eyes of newborn babies may become infected during childbirth if the mother has chlamydia.

A Best Friend

Dorothy Harrison Eustis was an American living in Europe when she first saw German shepherd dogs used as guides for people with blindness. The dogs were part of a program to help former soldiers who had been blinded in World War I.

She was impressed. The dogs allowed the retired soldiers to live more independently. With the dogs as their guides, the blind men could walk through and across crowded streets. As Mrs. Eustis wrote in 1927 about one such man, No longer a care and a responsibility to his family and friends, he can take up his life where he left it off; no longer dependent on a member of the family, he can come and go as he pleases. ...

Mrs. Eustis returned to the United States in 1929 and founded the first school to train guide dogs in Nashville, Tennessee. Called the Seeing Eye, the school moved to Morristown, New Jersey, in 1931, where it remains.

German shepherds often are used as guide dogs, although Labrador retrievers, boxers, and even mixed breeds also are used. The dogs begin their training at about 18 months of age with a sighted trainer. Then the dog is matched with a blind person, who spends three or four weeks working with the trainer and the dog.

The dogs learn when to stop and when to go at street corners based on commands from their owners. They do not read traffic signs or lights in part because dogs are color blind. The owner listens to traffic sounds and tells the dog to go when it sounds as if traffic has stopped. But the dog is trained not to go if there is danger. Dogs also steer owners away from people and from objects in their path.


About 3 percent of cases of blindness occur from accidents or other injuries that damage the eyes.

Helen Keller

Helen Keller (1880-1968) became a writer and activist despite losing her sight and her hearing when she was not even 2 years old. She learned to communicate after she was taught to associate the movements of another persons hands with letters, words, and the objects around her.

During the 1930s, Helen Keller lobbied the U.S. Congress to provide federally funded reading services for people who are blind. Her efforts resulted in the inclusion of Title X in the 1935 Social Security Act, establishing federal grant assistance for the blind.

The story of Helen Kellers life, and the role of her teacher, Anne Sullivan, was made into the movie The Miracle Worker (1962), which won Academy Awards for actors Patty Duke and Anne Bancroft. It is available in many video stores and is often broadcast on television.

How Do People with Vision Loss and Blindness Adapt?

Millions of people with severe vision loss, including more than 1 million people who are blind, can do many of the same things that people with normal vision do. People with partial sight can use powerful eyeglasses and magnifying devices to improve their ability to read and to see objects. People with blindness also can:

  • listen to books, newspapers, and magazines on tape
  • use computers that read text aloud and respond to spoken commands
  • read Braille, a system that translates words into raised patterns of dots that are read by touching them
  • use guide dogs to increase their mobility
  • take many of the same classes, jobs, and roles as people with sight
  • become parents and teachers
  • become famous entertainers (if theyre talented), like singers Stevie Wonder and Ray Charles.

See also


Chlamydial Infections







The U.S. National Eye Institute, 2020 Vision Place, Bethesda, MD 20892-3655. The National Eye Institute is one of the U.S. National Institutes of Health (NIH). Its website has a search engine that locates information about blindness and vision problems, and its resource list provides links to over 40 other organizations that provide information to the public about eyes and vision. Telephone 301-496-5248

American Council of the Blind, 1155 15 Street NW, Suite 720, Washington, DC 20005. The American Council of the Blind has a monthly radio program called ACB Reports, a monthly magazine called the Braille Forum, a jobs bank, and Speech Friendly Software at its website. Telephone 800-424-8666

American Foundation for the Blind, 11 Penn Plaza, Suite 300, New York, NY 10001. The American Foundation for the Blind houses the Helen Keller Archive and publishes many print books, talking books, and a Journal of Visual Impairment and Blindness. Telephone 212-502-7661 or 212-502-7662 (TDD)

Lighthouse International, 111 East 59 Street, New York, NY 10022-1202. The Lighthouse offers information, products, and publications about vision and blindness. It includes a Lighthouse National Center for Vision and Child Development, and posts a story called My Friend Jodi Is Blind at its website. Telephone 800-829-0500 or 212-821-9713 (TTY)

The U.S. and the World

1.1 million people in the United States are legally blind

42 million people are blind worldwide

100 million people in the United States need eyeglasses to see clearly, and 14 million have eye problems that cannot be corrected with glasses

Only 3 percent of cases of blindness results from injuries. The remainder occur as a result of eye diseases

Blindness and eye disabilities may double by the year 2020, because post-war baby boomers are aging and many eye disorders are more likely to occur in old age.

National Federation of the Blind, 1800 Johnson Street, Baltimore, MD 21230. The National Federation of the Blind offers many resources for blind children and blind adults. Its website posts an informative fact sheet called Questions from Kids about Blindness and a newsletter called Student Slate: The Voice of Organized Blind Students in America. Telephone 410-659-9314

Research to Prevent Blindness, Inc., 645 Madison Avenue, New York, NY 10022-1010. This is a research organization for scientists, ophthalmologists, and the public. Telephone 800-621-0026

The Seeing Eye, Inc., P.O. Box 375, Morristown, NJ 07963-0375. This is the pioneer guide dog school in the United States. Its speech-friendly website provides an excellent overview of its history and of guide dog training. It publishes several videos and a Seeing Eye Guide. Telephone 973-539-4425

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blindness (blynd-nis) n. the inability to see. For administrative purposes, the term covers both total blindness and certain degrees of visual impairment (see blind register). The commonest causes of blindness worldwide are trachoma, onchocerciasis, and vitamin A deficiency, and in Great Britain age-related macular degeneration, glaucoma, cataract, myopic retinal degeneration, and diabetic retinopathy. See also colour blindness, day blindness, night blindness, snow blindness.

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blindness Severe impairment (or absence of) vision. It may be due to heredity, accident, disease, or old age. Worldwide, the commonest cause of blindness is trachoma. In developed countries, it is most often due to severe diabetes, glaucoma, cataract or degenerative changes associated with ageing.

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