A better way to focus

I am informed by my optometrist I am beginning to suffer from presbyopia.

Presbyopia is an affliction that is not, despite, its name, limited to members of a particular Christian denomination with Calvinist roots. Rather, it’s the loss of ability to focus on very close objects. It’s caused by the stiffening of the eye’s internal lens after age 40, and, alas, “after age 40” is precisely the time of life in which I now find myself.

But then, I’ve had lots of experience with other “opias,” so in a way I feel like I’m completing a set.

First there was hyperopia, or farsightedness, the inability to focus on nearby objects. In hyperopia, the focal point of light entering the eye is behind the retina. A convex eyeglass lens, thicker at the center than at the edge, moves the focal point forward. I got just such a pair of glasses in kindergarten.

For a brief time in Grade 1 my vision improved and I didn’t need glasses. But somewhere around age seven, I moved on to my second opia, myopia, or nearsightedness, the inability to focus on distant objects. In myopia the focal point within the eye falls in front of the retina. For all of my growing-up years, I wore concave eyeglass lenses, thinner at the centre than at the edge (the very thick edge in my case).

In my late 20s I finally got contact lenses. But now, as presbyopia rears its graying head, I fear I may soon enter the uncharted land of bifocals.

Benjamin Franklin had the bifocals ground for himself about 1760. The upper part of bifocals provides clear distant vision, while the lower part provides clear close-up vision. Unfortunately, focusing through only specific portions of a bifocal lens causes many wearers to become dizzy or disoriented, or to experience more eye fatigue.

But now, just in time, comes news of an better way to deal with the need for bifocal glasses: smart glasses that can change focus with the flick of a switch.

The magazine New Scientist reports researchers have developed a prototype of such glasses, each lens of which consists of a five-micron layer of nematic liquid crystal sandwiched between two pieces of glass. Nematic liquid crystal molecules reorient when exposed to an electric field. By embedding concentric circles of clear electrodes in the glass, the researchers were able to turn the liquid crystal into dynamic Fresnel lens.

A normal Fresnel lens consists of concentric rings carved into a piece of glass or plastic. These rings focus light in a fashion similar to a conventional lens. The pieces of glass in the smart eyeglasses contain concentric circles of clear electrodes. When electricity is passed through them, the liquid crystal aligns itself into rings and focuses the light passing through the lens. When the current is cut off, the liquid crystal loses alignment and the effect vanishes.

The result is a pair of glasses that can go from “long-distance” to “reading” mode at the flick of a switch. Commercialization efforts are already underway: a company called PixelOptics, based in Virginia, plans to cell eyeglasses “virtually indistinguishable from other, very stylish glasses” containing the dynamic lenses within two years.

Originally PixelOptics planned to develop dynamic lenses for computer monitors, so that both near-sighted and far-sighted people could use them without having to wear their glasses. But that became impractical as monitors got thinner, so they switched their focus (sorry) to computer users instead.

Although the first commercial versions of the glasses will only allow people to switch between their normal vision and reading prescriptions, the researchers believe that by applying different voltages and changing the number of current-carrying rings within each lens they can make lenses that produce a variety of different magnifications.

Nasser Peyghambarian, a professor of optical sciences at Arizona State University, helped develop the dynamic lenses. He’s now working on a version that can dynamically refocus on whatever the wearer is looking at, probably by using an infrared laser built into the glasses’ bridge: in effect giving eyeglasses the same automatic focusing power we’ve become used to in cameras.

Of course, maybe it’s because I grew up mostly in Saskatchewan, but I see one other application they should be working on. I mean, they’ve already got electrical conductors running through the lenses. I suggest they try running just a bit more current through them than they normally would.

Presto! Instant lens defoggers.

Permanent link to this article: https://edwardwillett.com/2006/04/a-better-way-to-focus/

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