Monday, July 28, 2008


Vaughan & Asbury's General Ophthalmology> 17th Edition> Chapter 23. Blindness >


In this chapter we will discuss blindness as a worldwide health problem, summarizing information about its epidemiology, emphasizing the value of community-based methods to prevent or treat its causes, and outlining resources available in more developed countries for rehabilitation of the blind. All of the disorders that may cause blindness are discussed more fully in other parts of this book.

Definition of Blindness

The World Health Organization (WHO) defines visual impairment as shown in Table 1. WHO officials encourage investigators and reporting agencies in all countries to report blindness and visual disability according to the categories defined in this table.

Table 1. Categories of Visual Impairment (Adapted from International Classification of Diseases, World Health Organization, 1977).

Category of Visual Impairment

Visual Acuity (Best Corrected)

Low Vision



3/10 (0.3)




1/10 (0.1)




3/60 (finger counting at 3 m)

1/20 (0.05)



1/60 (finger counting at 1 m)

1/50 (0.02)



No light perception

Visual field

Patients with a visual field radius no greater than 10 degrees but greater than 5 degrees around central fixation should be placed in category 3 and patients with a field no greater than 5 degrees around the central fixation in category 4—even if the central acuity is not impaired.

In the United States, the most widely used definition of partial blindness is that used by the Internal Revenue Service for the purpose of determining who is eligible for tax deductions on that basis: central visual acuity 20/200 or less in the better eye with best correction, or widest diameter of visual field subtending an angle of no greater than 20 degrees. An alternative functional definition is loss of vision sufficient to prevent one from being self-supporting in an occupation, making the individual dependent on other persons, agencies, or devices in order to live.

"Industrial blindness" is said to be present when a worker can no longer pursue an occupation because of poor vision; "automobile blindness" when vision is so poor that the responsible licensing agency in that state will not issue a driver's license. The term color blindness is a misnomer since this genetically transmitted disorder is not true blindness as the term is generally understood and implies only a minor visual aberration. Loss of vision may affect only the central fields, only the peripheral fields, or only specific portions of the peripheral fields in one or both eyes. Total loss of vision in one eye is said to reduce visual capacity by only 10%, although it makes the other eye infinitely more valuable.

Prevalence of Blindness Throughout the World

WHO estimates that there are more than 50 million blind people in the world today, with at least 135 million suffering significant visual disability. Even where health statistics are most reliable, the methods of counting the blind are often crude and may be applied according to different criteria in different places and at different times within any extensive geographic area. Because of these limitations, extrapolations are often made from small sample studies to large populations. Ninety percent of the world's blind live in developing countries, mostly in Asia (approximately 20 million) and Africa (approximately 6 million), clustered largely in disadvantaged communities in rural areas and urban slums. The risk of blindness in many of these neglected communities is 10–40 times higher than in the industrially developed regions of Europe and America.

Table 2 lists some countries where fairly reliable data are available about the prevalence of blindness.

Table 2. Approximate Prevalence of Blindness (%). (Estimates Based on WHO Surveys.)1





























Saudi Arabia
















1Based on available data, 1969–1980. Some data were only rough estimates when obtained and may have changed markedly since then. In some cases, the survey criteria used did not correspond to WHO definitions. Data taken from Maitchouk IF: Data on blindness: Prevalence and causes throughout the world. In: Lim ASM, Jones BR (editors); World's major blinding conditions. Vision 1982;1:99. (International Agency for the Prevention of Blindness.)

Causes of Blindness & Methods of Prevention & Treatment

The relative importance of various causes of blindness differs according to the level of social development in the geographic area being studied. In developing countries, cataract is the leading cause, with trachoma, glaucoma, leprosy, onchocerciasis, and xerophthalmia also being important. Corneal ulceration is also a significant cause of monocular blindness in the developing world. In more developed countries, blindness is to a great extent related to the aging process. Cataract is still important despite the availability of facilities for its treatment, along with age-related macular degeneration and glaucoma. Other causes are diabetic retinopathy, herpes simplex keratitis, retinal detachment, and inherited retinal degenerative disorders.

In terms of the worldwide prevalence of blindness, the vastly greater number of people in the developing world and the greater likelihood of their being affected mean that the causes of blindness in those areas are numerically more important. Cataract is responsible for more than 22 million cases of blindness and glaucoma 6 million, while leprosy and onchocerciasis each blind approximately 1 million individuals worldwide. Interestingly, the number of individuals blind from trachoma has dropped dramatically 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. Xerophthalmia is estimated to affect 5 million children each year; 500,000 develop active corneal involvement, and half of these go blind. 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 now is the fourth greatest cause of global blindness.

WHO estimates that up to 80% of blindness in developing countries is avoidable, ie, preventable or treatable. The worldwide eradication of smallpox demonstrates what can be achieved in the area of infectious disease and the superiority of prevention over treatment. Similar efforts are being made to prevent the infectious diseases trachoma, leprosy, and onchocerciasis as well as the noninfectious xerophthalmia. The sheer numbers of individuals blinded by cataract continues to overwhelm the resources available. In all programs to reduce blindness in the developing world, cooperation between governments and nongovernmental charitable organizations has proved to be essential. The WHO Prevention of Blindness Program has established centers in about 60 developing countries to undertake collaborative studies, particularly generating epidemiologically sound information to form the basis for rational planning, implementation, and proper evaluation of programs for prevention of blindness.

In more developed countries, the causes of blindness are less amenable to prevention. In general, it is necessary to rely on recognition and treatment of the early stages of the disease. This depends on education of ophthalmologists, nonophthalmologic medical personnel, and lay people about the necessity for screening for glaucoma and diabetic retinopathy and about the importance of the early symptoms of retinal detachment, age-related macular degeneration, and herpes simplex keratitis. The inherited conditions are amenable to prevention by genetic counseling.


Cataract accounts for at least 50% of cases of blindness worldwide. As life expectancy increases, there is a continuing rise in the total number of people affected. In many parts of the developing world, the facilities available for treating cataract are grossly inadequate, hardly sufficient to cope with the new cases arising and completely inadequate for dealing with the backlog of existing cases, which is conservatively estimated to be 10 million worldwide.

It is not clearly understood why the frequency of cataract in different geographic areas varies so greatly, although exposure to ultraviolet radiation and recurrent episodes of dehydration, such as occur in severe diarrheal diseases, are thought to be important. If medical means could be found to delay the development of cataract by 10 years, it is estimated that this would reduce the number of individuals requiring surgery by 45%. Unfortunately, there is no method of preventing or retarding the growth of cataracts. Although the oral administration of antioxidants was considered promising, clinical studies have now shown conclusively that they have no effect on cataract growth. Mobile eye camps have aided in identifying patients for surgery, but surgery is no longer performed in a camp setting and there are too few well-equipped hospitals and trained surgeons in many developing countries to keep up with the load. In a number of blindness surveys, the problem of uncorrected aphakia is particularly apparent. It is now accepted that intraocular lens implantation at the time of surgery, although requiring greater expertise, is a better solution than relying on the subsequent provision of spectacles.


Trachoma causes bilateral keratoconjunctivitis, generally in childhood, that leads in adulthood to corneal scarring, which, when severe, causes blindness. About 400 million people have trachoma, most of them in Africa, the Middle East, and Asia. Trachoma can be treated with various antibiotics, including tetracyclines and erythromycin, but azithromycin is proving to be the drug of choice. It is estimated that 70 million individuals currently require treatment, but in the past 10 years, the number of individuals blind from trachoma has dropped from 6 million to 1.3 million. This is an obvious tribute to current WHO-supervised treatment programs and probably to the effectiveness of azithromycin. However, to eliminate the disease will depend on global implementation of WHO's SAFE strategy (surgery for trichiasis, antibiotic treatment, face washing, and environmental changes such as latrine building). Prevention of spread of infection will require provision of proper sanitary facilities, including clean water for drinking and washing, waste disposal, fly control, and behavioral change in hygiene.


Leprosy (Hansen's disease) affects 14 million people in the world and has a higher percentage of ocular involvement than any other systemic disease. Up to 10% of leprosy patients are blind or visually impaired from the disease. The social stigma attached to leprosy has greatly hindered its treatment, but there are now highly effective chemotherapeutic agents that in most cases eradicate the infection. Effective treatment programs using triple drug therapy (dapsone, clofazamine, and rifampin) have markedly reduced the number of cases of leprosy worldwide as well as prevented the deformity and morbidity associated with the disease.


Onchocerciasis is transmitted by bites of the blackfly, which breeds in clear running streams (hence the name river blindness). It is endemic in the greater part of tropical Africa and Central and South America. The most heavily infested zone is the Volta River basin, which extends over parts of Dahomey, Ghana, Ivory Coast, Mali, Niger, Togo, and Upper Volta. Worldwide, 15–20 million people are affected by onchocerciasis, with 20% of individuals in hyperendemic areas blinded by the disease.

The major ophthalmic manifestations of onchocerciasis are keratitis, uveitis, retinochoroiditis, and optic atrophy. The disease is prevented by insect eradication and personal protection by screening. Treatment with ivermectin is extremely effective in killing the microfilaria and sterilizing the adult females residing in nodules in the body. The effect of the mass distribution of ivermectin in areas where onchocerciasis is endemic is a public health success story. Like leprosy, onchocerciasis is definitely decreasing in its importance as a worldwide cause of blindness because of successful treatment programs.


Xerophthalmia is due to hypovitaminosis A. Clinically, there is xerosis of the conjunctiva with characteristic Bitot's spots and softening of the cornea (keratomalacia), which may lead to corneal perforation. Protein malnutrition exacerbates the condition and renders it refractory to treatment. Xerophthalmia is a common cause of blindness in infants, particularly in India, Bangladesh, Indonesia, and the Philippines. Affected infants often do not reach adulthood, dying from malnutrition, pneumonia, or diarrhea.

Xerophthalmia can be prevented by general dietary improvement or vitamin A supplementation. If the problems of distribution and administration were solved, the cost of a quantity of the vitamin sufficient to prevent blindness in 1000 infants would be only about $25.00. Measles immunization is also important in this regard because of the close association of measles epidemics with the blinding complications of xerophthalmia.

Other Causes

Glaucoma, retinal detachment, diabetic retinopathy, and herpes simplex keratitis are discussed in greater detail elsewhere in this text. The incidence of blindness due to glaucoma has decreased in recent years as a result of earlier detection, improved medical and surgical treatment, and a greater awareness and understanding of the disorder by the lay population. However, in many developing countries, glaucoma is the second most common cause of blindness after cataract. This is especially the case in West Africa, where untreated open-angle glaucoma is extremely common. In China and Southeast Asia, there appears to be a preponderance of narrow-angle glaucoma. Glaucoma now blinds 6 million individuals worldwide, and a simple easy method of detecting patients at risk still does not exist. Treatment is also a major problem because of the poor compliance of most patients for taking daily eye drops. A simple but safe surgical procedure may ultimately be the only solution for reducing the needless burden of blindness from this disease. More research in this area is essential.

Diabetic retinopathy is an increasingly more common cause of blindness everywhere in the world. Recent advances in surgical treatment (vitrectomy, laser therapy) are of some help, but many patients still suffer from proliferative retinopathy, recurrent vitreous hemorrhages, and eventual bilateral blindness. A vast research effort directed at all aspects of diabetes is in progress, and there is justification for hoping that the next generation of diabetics will benefit greatly from what is being done now.

Hereditary conditions are important causes of blindness but should gradually decrease in incidence in response to the efforts of genetic counselors to increase public awareness of the preventable nature of these disorders.

As is true also in other countries where medical care and social services are widely available, blindness in the United States is to a great extent related to the aging process, and about half of the legally blind people in this country are over age 65. The leading causes of blindness in this age group are degenerative retinal disorders, glaucoma, diabetes, and vascular diseases.

Costs of Avoiding Blindness

Some examples of what can be achieved for modest outlays of scarce funds are as follows:

1. To cure one person of trachoma in Saudi Arabia: $1.25.

2. To restore vision to one person in India blinded by cataracts: $30.00.

3. To prevent blindness due to xerophthalmia in one infant in Indonesia: 30 cents.

On the advice of WHO experts, the World Council for the Welfare of the Blind and several international professional ophthalmic societies and agencies agreed to take the initiative, which led to the establishment in 1974 of the International Agency for Prevention of Blindness (Vision International), with Sir John Wilson, a blind barrister, as president. The aim of this agency is to work with groups formed for the purpose of preventing blindness. Its theme, Foresight Prevents Blindness, was brought into prominent display when WHO celebrated the first World Health Day on April 7, 1976. Its goal was stated as follows: "In every donor country during 1976, every family should be asked—in thanksgiving for sight—to give $10.00 to save the sight of its fellow countrymen or of the millions in the third world

Rehabilitation of the Blind

Although no completely reliable statistics are available, the most widely used estimates place the legally blind population of the United States at 2.24 per thousand (ie, approximately 500,000). Approximately 50,000 become legally blind annually, and many others have enough visual loss to constitute a serious employment problem.

Blindness does not necessarily imply helplessness. Individual adjustment to marked visual impairment or total blindness varies with age at onset, temperament, education, economic resources, and many other factors. The older patient, for example, may accept blindness quite stoically, whereas for the younger patient, the vocational or social impact of blindness is often catastrophic. Blindness is accepted more easily by persons who are born blind and by persons of any age who lose their vision gradually rather than suddenly.

The aim of rehabilitation is to enable the patient to lead as nearly normal a life as possible. Approximately 5000 blind persons in the United States are rehabilitated and obtain paid employment each year. An additional larger number of blind homemakers are able to perform their household duties without assistance or are able to live independently of others.

Rehabilitation must be individualized. Many special services (see Appendix III) and increasingly complex optical and nonoptical aids are available, but they are not universally helpful. Different categories of the blind have different needs, and some blind people simply cannot benefit from a number of services or aids available. It has been said that over half of the blind people in the United States are over age 65. The elderly widowed housewife may need or want no more than mobility training in home care and a steady supply of Talking Books. A young person facing blindness in later life due to retinitis pigmentosa requires the full range of social services, including educational assessment, job rehabilitation, and psychological counseling as well as a number of sophisticated aids.

The responsibility of the physician clearly does not end with the diagnosis, prevention, and treatment of ocular disorders that might result in blindness. The physician caring for the patient who is suddenly faced with actual or imminent blindness is in a position to be of great assistance. When blindness is a possibility but is not inevitable (eg, during acute ocular inflammation), optimism and reassurance are warranted. However, it is unwise to offer false hope or to delay "breaking the news" when blindness is inevitable. If it is certain that blindness will occur, it is important to extend to the distraught patient as well as to the patient's family the warmth, understanding, encouragement, and assistance so desperately needed. The physician should be alert to the severe depressive reactions that may occur.

It is especially important to assist the patient in making the adjustment to blindness while some vision is still present. Early referral to rehabilitation agencies is essential for recently blinded adults and those with irreversible progressive visual loss. Training programs or reeducation for the many changes involved in daily living and employment are greatly simplified if the patient has the partial support provided by even limited vision.

The physician should work actively with both the patient and the family and with other professional people concerned with rendering services to the blind. The physician must know what referral sources are available and how to use them skillfully. Medical social workers, public health nurses, and counseling services and agencies serving the blind and visually handicapped are common sources of reliable information. It may be valuable to have the patient talk with a blind person who has made a satisfactory adjustment to blindness.

Mobility Training & Guide Dogs

Mobility training is most important in rehabilitation of the blind. Many state commissions for the blind offer a wide variety of mobility training courses, either directly or in cooperation with private agencies. The courses are offered on an outpatient and residential basis and have varied objectives according to the special needs of the people who apply for help. The curriculum commonly includes self-care, home functions, and mobility within the community. Several universities1 have undergraduate and postgraduate programs in mobility training for the blind.

The usefulness of guide dogs is limited by their daily care needs and the physical strength required to hold them in check. They are most useful for students and professional men and women in good health who lead fairly well-organized lives. At this time, less than 2% of blind people in the United States use guide dogs. Sonar sensor canes may ultimately be a better answer to the mobility problem even for those who are now using a dog successfully.

1Undergraduate-level programs are offered at Cleveland State University in Ohio, Florida State University in Florida, and Stephen F. Austin University in Texas. Graduate programs are available at Boston University, California State University (Los Angeles), Northern Colorado University, San Francisco State University, University of Arkansas, University of Wisconsin, and Western Michigan State University.


This remarkably effective system of reading for the blind was introduced in 1825. The braille characters consist of raised dots arranged in two columns of three. The system is so simple that a blind child can quickly learn to read braille, and proficient readers can learn to read braille as fast as they can talk. The system has been adapted to musical notation and technical and scientific uses also. An international braille code was introduced in 1951.

Braille is used less commonly now than formerly, since many blind people prefer auditory aids both for informational and recreational purposes. But the recent availability of portable data storage systems with braille-encoded input and conventional or braille form printed output has brought about a resurgence of interest. Braille continues to be essential on tags attached to items in common personal use even for people who do not wish to use it for reading.

All paper money in the Netherlands and Switzerland is braille-printed to show the denomination.

Electronic Devices

Optacon is an electronic device that converts visual images of letters into tactile forms. It is easily portable and can be used with almost any kind of reading matter. Auditory aids are becoming increasingly important (eg, talking calculators, clocks, paper money identifiers).

Financial Assistance Programs

It is unfortunate that over half of the blind people in the United States are essentially dependent on Social Security and whatever local supplemental aid may be available to them. For the younger blind population, rehabilitation programs are commonly administered at the state level by a division of the department of education specifically set up to serve blind people in the state. Some of these programs are better than others, and all physicians should support efforts to increase the effectiveness of such programs in their geographic area of influence. The programs are of wide scope and offer preliminary counseling followed by academic or vocational training as the circumstances warrant. Once a realistic vocational objective has been established, full financial support is commonly available. This single resource is probably the most crucial referral available to the ophthalmologist, particularly in the case of young patients. Counseling services are available as early as the junior high school years to ensure compliance with a curriculum consistent with measured aptitudes and interests. In many states, such rehabilitation programs as mobility training are administered under state auspices but contracted to private agencies for operational purposes.

In many countries, the blind receive no financial or other support from their governments and are either cared for by their families or left to manage by themselves in any way they can.


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