ABSTRACT
An estimated 38 million people are blind by theWorld Health Organization (WHO) definition of central acuity of less than 20/400 (Resnikoff et al. 2004). But this severely underestimates the impact of ocular disease on societal productivity. Many important tasks, from reading to driving, to mending fish nets, require vision of 20/60 or better. The global estimate of those who are visually impaired or blind exceeds 135 million, most of whom are incapacitated by their disability and unable to fully participate in economic and development activities to the degree they otherwise might (Resnikoff et al. 2004). This impact is magnified by the need, by many of those who are visually impaired, for the assistance of sighted caregivers, which further deprives the economy of individuals who might otherwise contribute more effectively to development. More than half of all blindness is avoidable, and most avoidable blindness occurs among poor people in the least developed regions of the world. Not surprisingly, there is a direct correlation between per capita GDP and the prevalence of blindness (Figure 33.1) (Ho and Schwab 2001).
The single greatest cause of avoidable blindness is unoperated cataract. In most underdeveloped regions (and poor populations of wealthy countries), unoperated cataract accounts for roughly half of all blindness. A cataract is simply an opacification of the lens of the eye, which commonly increases with aging. In some populations, as in many areas of India, cataracts develop a decade or so earlier than they do in other countries. Exposure to ultra-violet light, tobacco use, frequent diarrhoea, and poor nutrition may play a role. As a result, visual impairment often forces otherwise vigorous individuals to lose their jobs. Many also suffer a loss of social standing (Frick and Foster 2003; Javitt et al. 1983).
