Epidemiologic aspects of global blindness prevention.

The number of blind persons in the world is not accurately known. However, taking into account previous estimates by the World Health Organization and adjusting to the world population of 1990, it is likely that there are at least 35 million blind people if we apply the internationally accepted definition of blindness as vision less than 3/60 ( less than 20/400 or 0.05) in the better eye. If the threshold of vision less than 6/60 ( less than 20/200 or 0.1) is applied, the above figure can be increased by roughly 50%, ie, going well beyond 50 million blind people. To this somber picture should be added the effects of aging on populations in both developed and developing countries. Longer life expectancy is going to dramatically increase the need for eye care to prevent visual loss from such conditions as cataract, glaucoma, diabetic retinopathy, and macular degenerations. Corneal blindness, resulting mainly from trachoma and other infections, is apparently showing a downward trend, but there are still foci of severe disease. Thus the need for trichiasis surgery remains, and some recently evaluated techniques offer particularly good results. On the other hand, xerophthalmia due to vitamin A deficiency is still a major public health problem, causing both visual loss and increased mortality. It should be possible, by targeting ivermectin distribution programs to high-risk populations, to gradually eliminate onchocerciasis as a cause of blindness; however, the long-term sight-saving effect of ivermectin in cases of established ocular lesions needs to be confirmed.