Although the prevalence of blindness worldwide is not precisely known, new global estimates from 2002 World Health Organization (WHO) show at least 37 million people are blind and another 124 million people have low vision. This figure is based on the standard international definition of blindness: a visual acuity (VA) of less than 3/60 or corresponding visual field loss in the better eye with best possible correction, and a VA of <6/18 (but greater than 3/60 or a field loss of less than 20%) constituting “low vision.” Because of the essential nature of vision for most endeavors, the frequency of blindness also reflects a global loss in disability-adjusted life years, and is considered by WHO to be a key barrier to development worldwide. The causes of blindness and visual loss, most preventable through primary intervention or secondary therapy, include a small core of major diseases including: cataract (47.8%), glaucoma (12.3%), diabetic retinopathy (4.8%), macular degeneration (8.7%), trachoma (3.6%), onchocerciasis (0.8%), and corneal opacities (5.1%) (Fig. 68-1). However the fraction of the blindness burden for each disease differs substantially from region to region (Fig. 68-2).
Causes of blindness. (Source: Resnikoff S, Pascolini D, Etya'ale D, et al. Global data on visual impairment in the year 2002. Bull World Health Organization; November 2004:82 (11).)
Visual impairment by region. (Source: WHO Fact Sheet N°282, November 2004.)
The total disease burden of blindness varies along a variety of demographic factors. First, blindness rates vary geographically (Fig. 68-3) with the largest impact occurring in regions least able to afford the loss in human resources or address economic costs of treatment. More than 90% of the world's visually impaired are found in developing countries. Furthermore, WHO estimates that some 75% of all worldwide blindness is avoidable through prevention or treatment. Age also remains the primary risk factor associated with most blinding disorders, regardless of etiology (Fig. 68-3) with more than 82% of all blindness occurring in the 50+ age group (though they constitute only 19% of the world population). This age-related distribution has been further deepened by an aging world where populations over 50 years of age increased by 30% (versus an overall population increase of 18.5%) from the last global blindness estimates of 1990. Indeed, that the blindness rate remained stable despite the aging effect over this time (38 million estimated blind in 1990) signifies a lower than projected blindness rate (With age increases the projection was 52 million blind in 2002.). This decrease has been attributed to a variety of factors, including increase in public awareness and accessibility of services, to successful elimination efforts for blindness in Gambia, India, Morocco, Nepal, Sri Lanka, Thailand, and other nations with previously high endemic blindness rates. Finally, blindness and visual impairment are unequally distributed between men and women, with females having a significantly higher risk of visual impairment (a female:male ratio ranging from 1.5 to 2.2 worldwide).1
Some visual disorders, while not major causes of blindness worldwide, represent significant medical cost, and, without treatment, significant loss of daily life functions, as ...