http://trufocals.com/

Each "lens" is actually a set of two lenses, one flexible and one
firm. The flexible lens (near the eye) has a transparent distensible membrane
attached to a clear rigid surface. The pocket between them holds a small
quantity of crystal clear fluid. As you move the slider on the bridge, it pushes
the fluid and alters the shape of the flexible lens. Changing the shape changes
the correction. This mimics the way the lenses in your eyes used to perform when
you were younger.

John Markoff's review

Thanks to Dutcher.