Victoria Sheffield is the Executive Director of the International Eye Foundation and has 40 years of experience in ophthalmology and international blindness prevention. She is a recognized leader in the field of blindness prevention and has worked with the World Health Organization (WHO) Programme for Prevention of Blindness in Geneva where she designed and produced public education materials.

Over 90% of the world's blind people live in developing countries. This is mainly the result of extreme poverty, lack of drinkable water, poor hygiene and sanitation (trachoma and other infections), malnutrition (vitamin A deficiency), parasites (onchocerciasis), and poor access to quality ophthalmic services. Fortunately, blindness rates from these particular diseases are falling, primarily in response to comprehensive eye care programs provided by a wide range of organizations, and medicines given free of charge by pharmaceutical manufacturers.

However, cataract is still responsible for half the world's blindness (47.8%). Additionally, diseases found in the US and other developed countries such as glaucoma, complications from diabetes (diabetic retinopathy), and age-related macular degeneration (AMD), are also now emerging in the developing world.

Meeting these challenges requires far more trained ophthalmic personnel, better distribution of eye care providers outside urban areas, and sustainable hospitals that provide quality care and service at affordable prices for all, especially the poor. Member organizations of the International Agency for Prevention of Blindness in collaboration with the World Health Organization are implementing Vision 2020: the Right to Sight to strengthen collaboration and mobilize resources to meet these challenges.

Introduction by Victoria Sheffield, Executive Director, International Eye Foundation. The Foundation's Mission: The International Eye Foundation (IEF) is dedicated to preventing blindness worldwide by eliminating the causes of avoidable blindness: cataract, trachoma, "river blindness," and childhood blindness; reducing the cost of eye care; and creating a network of highly efficient, productive and self-sustaining eye hospitals that treat all persons including the poor.

How Many People in the World are Blind or Have Low Vision?

In 2010, the World Health Organization (WHO) estimated that 285 million people worldwide were visually impaired; of that total, 39 million people were blind and 246 million people had moderate to severe visual impairment. (Note: WHO uses the term 'visual impairment' to include both 'low vision' and 'blindness.')

These totals were significantly lower than the 314 million people worldwide that WHO estimated were visually impaired in May 2009, of which 45 million were blind. According to the International Agency for the Prevention for Blindness (IAPB), this reduction reflected the investment of governments and their international development partners in prevention of blindness activities and programs.

These figures do not include people with refractive errors that can be corrected. Refractive errors/disorders are conditions which prevent the eye from focusing light images on to the retina. Most refractive errors, which include myopia (nearsightedness), hyperopia (farsightedness), and astigmatism (a distorted curvature of the front surface of the eye), can be corrected to 20/20 i.e., normal vision, by wearing eyeglasses or contact lenses. See also the discussion of eye conditions on this web site.

The prevalence of eye diseases in the United States can be seen in this table from the National Eye Institute.

The World Health Organization (WHO) Definitions of Blindness and Low Vision

The World Health Organization (WHO) uses the following definitions:

Definition of Blindness

Blindness is defined as visual acuity worse than 3/60 meters (10/200 or 20/400 in US terms), or a visual field of less than 10 degrees in the better eye with best possible correction. (Note: Since most parts of the world use the metric system, the World Health Organization uses meters in its definitions.)

Definition of Low Vision

Low vision (previously referred to as "partial sight"), is a significant reduction of visual function that cannot be fully corrected by ordinary eyeglasses, contact lenses, medical treatment and/or surgery.

A person with low vision will have some sight but it will be reduced and will usually interfere with everyday activities, such as cooking, reading and writing. If the visual field is reduced, the person may have difficulty seeing well enough to walk alone or drive a car. The World Health Organization defines low vision as visual acuity or worse than 6/18 (US 20/60), but better than 3/60 (10/200 in US terms), or a visual field of less than 20 degrees in the better eye with best correction.

Definition of Best Possible Correction

Best possible correction is the best visual acuity achieved with spectacles, contact lenses, and/or surgery. However, when the best possible correction cannot achieve 20/20 or 6/6, the person is said to have "low vision". Low vision causes a significant reduction in visual function that affects daily activities. These people may need additional "low vision aids" such as a special magnifier.

Definition of Normal Vision

Normal vision is defined as a distance visual acuity of 6/6 where the metric system is used. (or as 20/20 in US terms) with a full visual field of 180 degrees. In the United States, visual acuity is measured at a distance of 20 feet. In Europe and the rest of the world visual acuity is measured at a distance of 6 meters. Distance visual acuity is the most central part of vision that is used to see objects at a distance. "6/6 or 20/20" means that a person can see a specific line of letters when they are standing or seated 6 meters or 20 feet away from an eye chart.

The World Health Organization (WHO) Categories of Vision Impairment

The following chart produced by the World Health Organization's Programme for Prevention of Blindness illustrates the different categories of vision impairment:

Category of Visual Impairment	Visual Acuity with BEST POSSIBLE Correction
	Maximum less than:	Minimum equal to or better than:
1	6/18 3/10 (0.3) 20/70	6/60 1/10 (0.1) 20/200
2	6/60 1/10 (0.1) 20/200	3/60 1/20 (0.05) 20/400
3	3/60 1/20 (0.05) 20/400	1/60 (finger-counting at 1 metre) 1/50 (0.02) 5/300 (12/1200)
4	1/60 (finger-counting at 1 metre) 1/50 (0.02) 5/300 (12/1200)
5	No light perception
9	Undetermined or unspecified

Adapted from International Statistical Classification of Diseases and Related Health Problems, Tenth Revision, Geneva, World Health Organization, 1992

Categories of visual impairment 1 and 2 are referred to as "low vision"; categories 3, 4, and 5 as "blindness"; and category 9 as "unqualified visual loss." If the extent of the visual field is taken into account, patients with a field 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 central fixation should be placed in category 4, even if visual acuity is not impaired.

Primary Causes of Blindness Throughout the World

World Health Organization (WHO) data, based on the 2002 global population survey, shows that blindness resulting from infectious diseases is decreasing. However, blindness from conditions relating to aging is increasing.

According to the State of the World's Sight, VISION 2020: the Right to Sight 1999-2005 published by the World Health Organization in collaboration with the International Agency for the Prevention of Blindness, the major causes of blindness worldwide are cataracts, glaucoma, trachoma, xerophthalmia, age-related macular degeneration, and diabetic retinopathy:

Cataracts

Approximately 17.6 million people are blind from cataract, a clouding of the lens inside the eye due primarily to aging. It is the leading cause of treatable blindness in developing countries where cataract surgical services are limited.

Glaucoma

Glaucoma, with an estimated 4.5 million people blind, is the second leading cause of blindness worldwide. The US National Eye Institute reports that g laucoma, which affects 2.2 million people in the US, is the most common cause of blindness among Hispanics in the United States and among African Americans. Glaucoma runs in families, and many people are unaware they have this disease because there are no signs or symptoms until a lot of sight is lost. Most cases of glaucoma can be controlled before sight is lost, and this is why examination and early detection are so important.

Trachoma

The WHO estimates there are 84 million people infected with trachoma of whom 1.3 million are blind. This highly infectious disease is caused by the organism Chlamydia trachomatis and is found primarily in 55 countries in Africa, the Middle East, Central Asia, India and South-East Asia. Rates are being slowly reduced due to improved access to unpolluted water, good hygiene, and antibiotic treatments.

Xerophthalmia

Xeropohthalmia is the blinding complication of vitamin A deficiency, is seen most often in malnourished children. Globally, an estimated 750 million people have vitamin A deficiency. An estimated 2.7 million, mostly children, are blind of whom 60% will die. Prevention through nutrition education, promotion of home gardens, and the distribution of vitamin A supplements can prevent xerophthalmia, save sight, and prevent early death.

Age-related Macular Degeneration (AMD)

Due to the growing number of people over 70 years of age, AMD ranks third as a cause of global vision impairment, with a estimated 3.2 million blind from this condition. It is the primary cause of visual impairment in industrialized nations, such as the USA.

Diabetic Retinopathy

The blinding complication of diabetes is diabetic retinopathy accounting for an estimated 1.8 million blind people worldwide. It is the leading cause of blindness among working age adults. Keeping diabetes under control through diet and medical treatment is the best way to prevent eye complications. In severe cases, treatment includes laser and/or surgery.

Other major causes of blindness

Other major causes of blindness worldwide include ocular injuries, onchocerciasis (river blindness) caused by a parasitic worm carried by the black fly, and Hanson's Disease (leprosy).

WHO estimates that cataract, glaucoma, and macula degeneration — all linked to aging — are responsible for up to 75% of the world's blindness. By the year 2020, the UN estimates there will be a global elderly population of 698 million which could significantly raise levels of vision impairment worldwide — hence the importance attached to the Global Initiative for the Elimination of Avoidable Blindness — Vision 2020.

Aging Issues Worldwide

A number of organizations focused on issues of aging are now establishing collaborative projects to compare the situation of older people in different parts of the world and to look at the ways in which provisions are being made to ensure healthy and productive aging.

The United Nations provides a chart that shows the number of people in a great number of countries that are either under 15 years of age or over 60. The growth of the aging population poses many challenges for both individuals and governments around the world.

Other International Organizations

For information on other organizations, see VisionAWARE's directory of international vision service organizations.