How do bifocal lenses provide correction for near and distant vision?

Bifocal lenses provide correction for both near and distant vision by incorporating two distinct focal lengths into a single lens.1

These lenses are constructed using a few primary methods:
* Surface Formation: Two or three separate surfaces are formed on a single piece of glass to provide the necessary optical power for different distances.2
* Fusion: A piece of high-index glass is fused onto the front of the main lens, followed by the polishing of a single spherical surface over both materials to achieve the desired correction.2
* Historical Design: Originally, bifocals were created by dividing lenses into two parts—one for distance and one for near vision—held together within a frame.3

By integrating these different refractive powers, bifocals allow the wearer to transition between viewing distant objects and performing near-vision tasks, such as reading, without needing to switch eyeglasses.13