What type of lens would be used to correct nearsightedness?

A concave lens is used to correct nearsightedness, also known as myopia. This condition occurs when the eye is too long relative to its focusing power, causing distant objects to appear blurry while close objects can be seen clearly. A concave lens diverges light rays before they enter the eye, effectively extending the focal length. This allows the light to focus further back inside the eye onto the retina, thereby improving the clarity of distant vision.

In contrast, a convex lens, which is thicker in the center and thinner at the edges, is typically used to correct farsightedness (hyperopia) where distant objects are seen clearly but near objects are blurry. A flat lens does not perform any significant optical correction and is not typically used for vision correction. Biconvex lenses are also primarily for farsightedness or magnification rather than for nearsightedness. Thus, the selection of a concave lens is specifically tailored to address the needs associated with myopia.