Epidemiology of visual impairment and blindness

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According to the World Health Organization Programme for Prevention of Blindness, 27 to 35 million persons have binocular vision of 0.05 or below, and 41 to 52 million have vision below 0.1 among a world population of 5300 million. More than 90% of the world's blind population lives in developing countries. With the greater population growth and the increase in life expectancy in developing countries, prevention of blindness becomes more acute and more difficult there as time goes on. The blindness rate increases greatly with increased age. Cataract is by far the most frequent cause of blindness. It is not preventable despite many good epidemiologic works. The insufficient distribution of eye care services in developing countries increases the backlog of cataract patients. Improving the methods of cataract surgery to include extracapsular cataract extraction and intraocular lens implantation adds to this backlog. Trachoma is still an important cause of blindness in some hyperendemic areas of the world but has lost importance in most areas. However, chlamydial infection still is an important sexually transmitted disease, even in developed countries. Onchocerciasis, ie, river blindness, which is caused by a kind of filaria, is the major cause of blindness in West Africa and Central America, where 85 million are at risk. The Onchocerciasis Control Programme, inaugurated in 1974, successfully controlled the vector (Simulium species) in the endemic area, and the addition of the powerful drug ivermectin is giving us hope of eradicating blindness due to onchocerciasis in the next century. According to information presented at the recent symposium on childhood blindness, of 1800 million children below 15 years of age in the world, 1.5 million are blind. Vitamin A deficiency is still an important cause of blindness in children in some developing countries. Blindness is more prone to occur in low-birth-weight babies. In developed countries, diabetic retinopathy is the most important cause of adult blindness. The control of diabetes itself, and hopefully its prevention, is the final goal for preventing blindness caused by this condition. Glaucoma, despite the progress made in medical and surgical treatment, and macular degeneration remain important causes of blindness.

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