Myopia (also known as near-sightedness or short-sightedness) is a visual defect suffered by myopic or short-sighted people, who can clearly see close objects, but can’t properly focus far distance ones.
The myopic eye focuses objects in front of the retina, and this is either caused by a relative increase of the eye length (axial myopia), which is the most frequent cause, or by an increase of the refraction of its internal elements (refractive myopia).
Axial myopia is the most frequent type, and it generally starts in childhood or puberty and tends to increase up until the age of 20-24. It may happen that children who suffer from myopia do not realize of their condition, as they have never been able to see clearly before (they might think that they cannot see clearly because objects are too far away). They often squeeze their eyes a little bit in order to see better.