It looks like I won't be getting bifocals, if I can geek myself up enough...
a Virginia research firm, PixelOptics, has developedsmart glasses which sandwich liquid crystal between layers of glass to realign and refocus for you.
They describe the structure of these new corrective lenses as a sort of mimic-Fresnel lens, with "concentric circles of clear electrodes on the pieces of glass containing the crystal. Activating these electrodes causes the liquid crystal to align into rings and focus light passing through the lens."
They'll eventually be able to program it according to your eye position and muscle contractions, via a laser scan, but that's still in very early development. Until then, I wonder if they expect the wearer to push a button to change the range. Any way you look at it, it still sounds spiffy.
And the picture they show, of the prototype, is quite the spectacle.