When it is determined that an individual is blind, it means that he or she is unable to see, which can be a total lack of sight or identified in legal terms useful for determining the level of need for government assistance. Legal blindness, in certain countries such as the U.S., refers to vision that is correctable to 20/200 maximum visual acuity (VA) or lower. The International Classification of Diseases-10 assigns a range of sight ability in reference to visual impairment, ranging from moderate to severe to blindness, which is the most profound. Being visually impaired can mean several things, the most basic is that, even with medical correction, a person cannot see well enough to function without some additional assistance. Within that, there are varying degrees of blindness and visual impairment is a general term defining the condition as a whole.
As of 2011, 284 million people suffer from blindness and visual impairment. Some are totally blind, which means that they cannot see any kind of light, or they have a VA which is very low — 10/200 (3/60 meters) or less. People classified as having moderate to severe visual impairment have low vision and can see, although not well enough to do certain things like drive or read, even after correction. Low vision VA ranges from 20/60 (6/18 meters) or lower, to a little better than 10/200 (3/60 meters).
Causes of blindness and visual impairment, particularly in the adult population, includes diabetes, cataracts, and refractive errors that go uncorrected. Corrective visual impairments, such as nearsightedness and astigmatism, and refractive errors contribute most to blindness and visual impairment worldwide. Most causes are treatable and can be prevented, including vitamin A deficiency, which accounts for many of the world's blind children. Lack of medical equipment and supplies are some of the factors affecting availability of treatment, as the World Health Organization reports in 2011 that 90% of people who are blind in the world live in poverty, though 60% of them could be effectively treated and another 20% prevented.
Living with visual impairment brings with it lots of challenges, most of which seem simple or are typically taken for granted by those who are not visually impaired. Normal everyday tasks such as grocery shopping, driving, reading a book, or taking a walk require the assistance of either a person, a guide dog, or a device. Most activities can be accomplished with a different approach. Braille, for example, allows those who are visually impaired to read and write by use of a dotted code that can be touched. Special cooking utensils, like timers with big numbers and using color coding, make meal preparation possible.