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.
I should probably disclose that as a twentysomething with the good fortune to still have both my health and my youth, not to mention only a mild prescription for astigmatism, the ability to adjust the focus of my glasses between typing this post, walking to the theater down the street, and watching "Star Trek" on the big screen just isn't necessary.
Yet I cannot deny--especially as that rare breed of women who can't stand to carry a purse and therefore fit everything in their pockets--how annoying it must be to lug around two or three pairs of glasses, not to mention change them from one activity to the next. I've seen my parents do this for a few years now, and I rue the day my own vision requires constant focus-shifting.
So it was with great interest that I read John Markoff's review of TruFocals in The New York Times. He forked over the retail price of $895 for a pair last week and has been wearing them since. Markoff doesn't yet buy the claim that users will adjust the focus on the bridge of the glasses without even realizing it, but I say give it time. (I didn't realize I push my glasses up my nose until I started wearing contacts and was pushing my pointer finger against nothing; fidgeting with one's bridge will simply be the latest version of this.)
The idea of TruFocals gives me great hope. When I reach my own bifocal years, I may not have to peer over the tops of my glasses in that hawkish hunch that has become the undeniable signal of having hit That Age. I'll just look a bit more like a fidgety Harry Potter than I do now. And I doubt I'll be the only one.