John Markoff of the Times looks at the "Holy Grail" come to market in the eyeglass world: One pair of glasses that the wearer can easily adjust to bring near or far objects into focus. Making Eyeglasses With a Mechanically Adjustable Focus begins,

LOS ANGELES -- As a promising Caltech graduate student in applied physics, Stephen Kurtin could have taken a job offer from Intel at the dawn of the microelectronics era 40 years ago.

Instead he followed the path of a lone inventor, gaining more than 30 patents in fields including word processing software and sound systems, culminating in the pair of glasses resting on his nose, which he believes can free nearly two billion people around the world from bifocals, trifocals and progressive lenses.

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...

How they work, from the Trufocals Technology page:

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.

New See-All Eyeglasses: A Consumer's Report. Markoff tested them for a week.

Dr. Kurtin made me a pair of glasses to my prescription. (Disclosure: I paid retail.) I'm a presbyope (presbyopia is a condition faced by almost everyone over the age of 40 where the ability to focus on close objects gradually vanishes) and have struggled with bifocals and progressives for more than a decade. I have now been using the TruFocals for a week, and I'm a convert, although I have to confess I'm not using them as my only pair of glasses -- yet.

The problem they do solve brilliantly is where bifocals, computer glasses and progressives have all failed for me: going back and forth between computer screen, laptop computer display and books, magazines and newspapers.

They can be bought online, but you need a current eyeglass prescription, including the distance between your pupils. The glasses adjust by moving a slider along the bridge between the two lenses, which must be perfectly round. So wearers all look like John Lennon. Harry Potter and a Devo concert have also been evoked to describe the fashion result of the eyewear's necessary shape. I'm tempted to call them "spectacles."

Smart commenters on Markoff's review add to the story. One notes that the next step is autofocus, like a camera: Make the glasses automatically adjust to what you're looking at. (This sounds dizzying, unless it could seamlessly offer the universal focus of younger eyes.)

TruFocals cost $895 at Stephen Kurtin's site, but that will probably come down eventually.

I have always been nearsighted. I got contact lenses at 14 and wore them for decades, until I needed to wear reading glasses on top of them, which seemed silly, or take them out, which was beyond tedious. (I can see clearly for up to about 18 inches, depending on tuype size.) I got glasses, and asked my optometrist for computer glasses as well -- in focus at arm's length. I swap among those, the all-purpose distance glasses, and no glasses at all for reading books, magazines and newspapers.

I am used to leaving my short-range glasses at my computer, and mainly donning and doffing the other pair. I don't know whether adjusting one pair of glasses would eventually become second-nature or just annoying. My current eyeglass shuffle is a workaround I'd certainly abandon for the right upgrade.

Related: Inventor's 2020 vision: to help 1bn of the world's poorest see better
"Professor pioneers DIY adjustable glasses that do not need an optician." Dr. Joshua Silver, founder of Oxford University's Centre for Vision in the Developing World, has distributed tens of thousands of adjustable glasses to the poor. These are adjusted once, on the spot, rather than having user-controlled variable adjustment.