I think GP is mistaken about two physical lenses being needed (until it's the future and we're all wearing expensive smart glasses, in which case you do want an

I think GP is mistaken about two physical lenses being needed (until it's the future and we're all wearing expensive smart glasses, in which case you do want an additional interchangeable lens for this purpose). When designing the system, it can be thought of as a lens that corrects for refractive error of the relaxed eye (moving the eye's far point to infinity) stacked on top of another lens that makes light coming from an object parallel (producing an image of the object at infinity for the first lens and eye to receive); to implement it, you only need one lens with the combined power of the two. Edit: GP might also be talking about eyeglasses with adjustable focus, which apparently are already available. https://en.wikipedia.org/wiki/Adjustable-focus_eyeglasses https://en.wikipedia.org/wiki/Adjustable-focus_eyeglasses