What Causes Myopia?

People who are nearsighted have what is called a refractive error.
In people with myopia, the eyeball is too long or the cornea has too much curvature, so the light entering the eye is not focused correctly.
Images focus in front of the retina, the light-sensitive part of the eye, rather than directly on the retina, causing blurred vision.
Myopia runs in families and usually appears in childhood. Usually the condition plateaus, but it can worsen with age.