If you wear bifocal or even trifocal eyeglasses, then you will know what a hassle it can be having to tilt your head up to see things that are nearby. The areas of image softness or distortion can also be distracting, and even cause nausea or headaches in some users. Using multiple pairs of single-vision glasses gets you around these problems, but introduces the problem of... well, of carrying around and using multiple pairs of glasses. TruFocals, however, allow users to wear one pair of glasses for near-, distance- and mid-vision, without having different focal areas within the same lens at the same time. Instead, users actually focus the glasses by hand, not unlike a pair of binoculars.

TruFocals have three optical surfaces for each eye. On the front is a rigid lens, in the user’s distance prescription. Behind that is a flexible lens, and behind that (closest to the eye) is a rigid, optically-neutral lens. In the space between the flexible and neutral lenses is an optically-clear fluid. By moving a slider on the bridge of the glasses, users change the shape of the flexible lens, by pumping fluid in or out of the space behind it. This allows them to instantly refocus the glasses on the fly, as the situation warrants.

The technology is much like that which retired physics professor Joshua Silver is using in his Adspecs eyeglasses for people in developing nations, in which flexible lenses are bowed out or sucked in by the injection or withdrawal of clear fluid behind them. In the case of Silver’s glasses, however, the lens distortion is set once for each client, then sealed in place – recipients can’t change the shape of the lenses back and forth, depending on whether they want reading, distance, or mid-range glasses.

TruFocals are said to work from temperatures of -4C (25F) to 52C (125F), so their adjustability outdoors in cold winter climates is certainly limited. Some potential users might also wonder about the bother of having to reach up and move the focus slider. While the company claims that it becomes second nature, there could certainly be situations – such as where a user’s hands are occupied or dirty – in which it wouldn’t be possible.

The glasses are also only available in the one style, so if you don’t like it, you're stuck. They are said to be similar in weight to regular glasses with conventional frames.

You can buy TruFocals through the company website, for the eyebrow-raising price of US$898.

Via InventorSpot.