Nearsightedness (Myopia)

Myopia (nearsightedness) occurs when the eye lens has too short a focal length, from a thickened lens or an eyeball longer than normal; these people struggle to relax the eye enough (rather than strain it), so parallel rays from a distant object are brought to a focus before they reach the retina, blurring distant vision, though nearer objects (up to the person's own reduced far point $x$) remain in focus. The correcting lens must make the virtual image of an object at infinity form instead at distance $x$ from the eye; using the lens equation with $u=-\infty$, $v=-x$ gives $\boxed{f=-x}$ -- a diverging (concave) lens, negative focal length, which spreads the incoming parallel rays out slightly …