Short-sightedness, otherwise known as Myopia currently affects 2.6 billion people worldwide (22% of the population). It is projected to increase to affect 4.9 billion people by 2025 (50% of the world population).
Perhaps most surprising is that more than 50% of adolescents in the UK are myopic.
Myopia is a condition of the eye where light entering from a distant object does not focus directly on the retina, but in front of it. This causes distant objects to be out of focus, where near objects may be clearly in focus. This is usually because the eye grows 'too long' to focus correctly.