Editing Corrective lens (section)

===Adjustable focus===
The power or focal length of [[Adjustable-focus eyeglasses|adjustable or variable focus]] can be changed to suit the needs of the wearer.  A typical application of such a lens is to refocus the correction allowing clear vision at any distance. Unlike with bifocals, near-vision correction is achieved over the entire [[field of view]], in any direction.  Switching between distance and near vision is accomplished by re-adjusting the lens, instead of by tilting and/or rotating the head.  The need for constant adjustment when the person's attention switches to an object at a different distance is a design challenge of such a lens.  Manual adjustment is more cumbersome than bifocals or similar lenses.  Automated systems require electronic systems, power supplies, and sensors that increase the cost, size, and weight of the correction.