Nearsightedness, medically known as myopia, is the most common cause of poor eyesight, especially in younger adults. It refers to being able to see well at close range, but not at a distance. It is the opposite of farsightedness (hyperopia). Focusing ability can start to decline in childhood and continue to slide through the teenage years, usually stabilizing in the early 20s. After that, most people find they don't need to change their glasses or contact lens prescriptions very often, if at all.
Myopia affects about 30% of the population of Canada. We know that some ethnic groups are more prone than others. People of Chinese, Japanese, and Southeast Asian descent are especially likely to be myopic.