TruFocal specs have manual focus slider

A new breed of spectacles allows you to adjust their focus from close-up to distance at the flick of a finger.

The geek-chic glasses - dubbed TruFocals by their inventor Stephen Kurtin - have a slider on the bridge that lets wearers change the focus manually.

Each "lens" is actually a set of two lenses, one flexible and one firm. The flexible lens nearer the eye has a transparent membrane attached to a clear rigid surface. The pocket between them holds a small quantity of clear fluid. As you move the slider on the bridge, it pushes the fluid and alters the shape of the flexible lens.

Vision of the past

According to TruFocal, changing the shape changes the correction, "mimicking the way the lenses in your eyes used to perform when you were younger".

The company claims that their glasses can correct for nearsightedness, farsightedness, astigmatism, and even prismatic imbalance, without the sudden shifts in sharpness you get with bi-focal or multi-focal spectacles.

However, the variable thickness fluid sac technology requires that TruFocal spectacles be round, giving a Harry Potter look to even the most astigmatic wearer.

TruFocal says that glasses, which cost around £550 a pair, weigh 'about the same' as a traditional pair of glasses with conventional lenses. More info at www.trufocals.com.