Causes of Myopia
Nearsighted people have a refractive error, which causes light rays to focus at a point in front of the retina rather than directly on its surface. In most cases, this error occurs as a result of the eyeball being too long or the curvature of the cornea being extreme. Sometimes it can be a combination of both factors.
Myopia also runs in families, so there is reason to believe it is partly genetic. Children who have one parent with myopia have a higher risk developing the condition. This risk compounds if both parents are nearsighted.