Liquid crystal smart glasses switch focus with a tap, eliminating bifocal zones

People who develop presbyopia know the daily juggle between reading and distance vision. The eyes change with age, and close work stops being crisp without help.

Bifocals have been the go to fix for centuries. Benjamin Franklin described his own split lenses in a famous letter written in 1784, and the core idea has stayed much the same since.

The latest push to improve everyday eyewear comes from Professor Yi Hsin Lin at National Yang Ming Chiao Tung University in Taiwan (NYCU).

Her team reported electronically adjustable eyeglasses that switch between near and far correction with a quick tap on the frame.

Bifocals need change

Traditional bifocals ask the wearer to move their head or eyes to find the correct zone. That constant adjustment can strain the neck and make tasks that need quick shifts of focus feel clumsy.

People who work with small parts near the top of their field of view face another snag. The near vision segment sits low in the lens, so the sweet spot is not where the work is.

How the new lenses work

At the heart of the prototype is liquid crystal (LC). These materials have molecules that can be reoriented by tiny electric fields, which changes how the lens bends light.

The team shaped that reorientation into a gradient index profile, often shortened to GRIN. Instead of a curved piece of glass, a flat cell creates a smooth change in refractive power across the lens.

They also designed the optics to be independent of polarization, so the lens maintains its behavior for light waves of different orientations. That matters for clear vision in normal, mixed light.

In their words, “we present here electrically switchable spectacles based on LC GRIN lenses,” wrote Lin. The device builds optical power without moving parts and with modest energy use.

What the prototype shows

The current active viewing area is about 0.4 inches across. That is smaller than a full conventional lens, which tells you this is early stage hardware backed by careful physics.

The authors mapped how the lens responds as voltage and alignment change, and they modeled how to limit color fringing across the viewing zone. Those steps are basic for a path to manufacturing.

“This concept has existed since the 1970s, but no one could make it practical for everyday eyewear,” said Professor Lin. The group set out the electronics and lens physics needed to shrink switching times as designs mature.

The frame hides slim electrodes and a small battery. A tap cues the field pattern that nudges the molecules into a new alignment and shifts the optical power.

Who might benefit first

Jobs that bounce between close and far tasks could gain the most. Consider someone checking fine marks on a board then glancing across a room to confirm alignment.

Another early fit is anyone who dislikes the edge distortions of progressive lenses. A clean, switchable field avoids the corridor effect that some users find distracting.

Comparing bifocals

Variable focus eyewear is not new. Low cost, fluid filled glasses pioneered by Joshua Silver at Oxford can be tuned by pumping liquid to change curvature, which has helped many people in settings with limited access to eye care.

Liquid crystal systems work differently. They tune refractive power by changing orientation inside a thin cell, so there are no moving surfaces and power draw can be low.

A recent review notes that LC lenses can be compact and stable while still providing adjustable focus. It also flags the tradeoffs designers must juggle, such as response speed, optical power range, and image quality.

LC GRIN lenses tackle image quality in a direct way. The gradient profile avoids the diffraction artifacts that limited earlier LC Fresnel designs and moves closer to the performance of standard glass.

Why this matters beyond reading

Most people will deal with age related near vision loss at some point. A pair of glasses that can switch correction without zones could reduce neck strain and speed small focus changes in daily life.

There is also a straight line to digital devices. Wearables and headsets need compact optics that refocus fast, and a cell that shifts power by voltage alone is an appealing building block.

Future research on bifocals

Two hurdles are clear from the lab report. The active viewing area needs to widen, and the electronics must settle focus more quickly for real world comfort.

The physics is now charted, and the ingredients are familiar to display makers. If engineers can broaden the clear zone and keep costs reasonable, switchable prescription eyewear could move from demo to store shelf.

The study is published in Physical Review Applied.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–