Hugh Pickens writes "The NY Times reports that inventor Stephen Kurtin has developed glasses with a mechanically adjustable focus that he believes can free nearly two billion people around the world from bifocals, trifocals and progressive lenses. Kurtin has spent almost 20 years on his quest to create a better pair of spectacles for people who suffer from presbyopia — the condition that affects almost everyone over the age of 40 as they progressively lose the ability to focus on close objects. The glasses have a tiny adjustable slider on the bridge of the frame that makes it possible to focus alternately on the page of a book, a computer screen, or a mountain range in the distance. 'For more than 140 years, adjustable focus has been recognized as the Holy Grail for presbyopes,' says Kurtin. 'It's a blazingly difficult problem.' 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."