Middle age is often accompanied by the onset of presbyopia, a condition whereby the eye's crystalline lens loses some of the youthful elasticity that enabled it to focus on nearby objects. The remedy for most people has been reading glasses or, for those already wearing prescription lenses, bifocals. For the handful of humans who work in the topsy-turvy environs of the space station or a spacecraft, presbyopia can be a bit more problematic because reading can take place at any number of odd angles, not to mention in microgravity, which tends to degrade vision.

Add to this the fact that many astronauts today are either at or approaching the age when presbyopia sets in, and it is not surprising that NASA is evaluating a new type of adjustable eyeglass lens called TruFocals for use during training and on missions. For the past six months NASA has been taking TruFocals (made by Van Nuys, Calif.–based Zoom Focus Eyewear, LLC) through a detailed certification process to ensure they are not only a better option than other types of eyeglasses but that the materials used to make them will not pose a hazard to astronauts in their enclosed work environs, says C. Robert Gibson, a senior optometrist at the NASA Johnson Space Center in Houston. One test includes burning the TruFocals to determine whether they emit any harmful gases.

Astronauts have a very demanding training regimen, often working in conditions designed to simulate the International Space Station (ISS), the space shuttle or Russian Soyuz spacecraft—all of which require the ability to work on highly detailed equipment as well as read checklists and instrument panels in low light. Whereas astronauts in the earliest days of the space program were eagle-eyed young pilots, NASA loosened the vision requirements for subsequent generations of space travelers as the demand for non-pilot mission specialist astronauts grew, says Gibson, who wears TruFocals himself. This means a lot more astronauts are wearing correctives lenses of some sort.

Each TruFocals lens—about three millimeters thick—actually consists of two magnetically attached lenses. The lens closer to the eye is flexible, with a transparent distensible (expandable) membrane attached to a clear rigid surface. The space between the membrane and the clear rigid surface holds a small amount of clear silicon fluid. A sliding lever on the bridge of the eyeglasses is used to push the fluid forward to alter the shape of the membrane and, by extension, the flexible lens. TruFocals for people with more advanced presbyopia contain more fluid than those made for people with a milder form of the condition. The second, outer lens features the wearer's normal prescription.

Changing the shape of the flexible lens changes its focus, a job that was performed by the eye's natural lenses prior to the onset of presbyopia. With the condition, "the crystalline lens in your eye is losing its ability to focus, and you can't get it to reading distance," says TruFocals inventor and Zoom Focus chief technologist Stephen Kurtin. TruFocals, which cost about $900 per pair, became commercially available last year.

Although Zoom Focus would like to offer its adjustable-focus glasses in a variety of styles, round lenses are required to get the best performance, Kurtin says. This Harry Potteresque look has gotten a mixed reaction, he adds, "Some people say they're cool, and some say they're butt ugly." At least they come in a variety of colors.

NASA's primary interest in adjustable eyeglasses has been as a replacement for the normal reading glasses, bifocals or progressive lenses that astronauts take with them into space. The small corrective zone on these conventional eyeglasses is fine for the normal reading posture (with the eyes looking through the lower portion of the lens) but is much less helpful when monitoring overhead readouts, for example. The agency is also studying the long-term effects of time spent in microgravity, which causes bodily fluids to gravitate to the upper body and has been known to cause degradation of vision in some astronauts. Once more is understood about how prolonged space travel affects vision and why, NASA will be in a better position to address the problem, either with the help of adjustable-lens glasses or some other means, according to Gibson.

Gibson is optimistic that NASA will soon wrap up its evaluation and that TruFocals will be cleared in time for astronauts to wear them on the next space mission, whether that is on board one of the remaining shuttle flights or a Soyuz. He is also keeping other options open, including eyeglass lenses made by PixelOptics, Inc., in Roanoke, Va. PixelOptics's emPower! lenses feature an embedded corrective electronic reading zone that acts like a virtual bifocal. This reading zone can be turned off or on based on head position, thanks to a built-in accelerometer. Gibson points out, however, that a lot more work has to be done evaluating PixelOptics's technology to determine whether it might be a good fit for NASA.

One of the strengths of the TruFocals approach is that they deliver a sharp image across the entire lens, as opposed to the limited field of view provided by bifocals or progressive lenses, says Mark Bullimore, a professor at The Ohio State University College of Optometry. Although Bullimore has not evaluated TruFocals in person, he notes that an expanded field of view could also reduce eye, neck and back strain for people with presbyopia. "A lot of the strain they feel comes from them constantly having to point their chin at what they're looking at," he adds.

In general, the emergence of adjustable lens technology, including those made by Adlens, Ltd., and the not-for-profit Adaptive Eyewear for the developing world, is a promising sign for those unsatisfied with or without access to conventional means for correcting presbyopia. "I'd like to see the technology succeed because I think it's a nice option for people to have," Bullimore says.