Augmented reality technology enables goggle-like devices - akin to Google Glass - that you wear on your head to superimpose computer-generated images onto your direct view of the physical world.
A major limitation of this kind of augmented reality (AR) technology is that moving back and forth between a 2-D image on the screen and a 3-D world in front of you causes eye strain, unless you're looking at something far away.
Now, a new device developed by researchers at the University of Arizona in Tucson and the University of Connecticut in Storrs is making AR technology easier on the eyes for short-distance applications, too, by superimposing 3-D images instead of 2-D.
"Minimising visual discomfort involved in wearing AR displays remains an unresolved challenge. This work is making a significant step forward in addressing this important issue," said first author Hong Hua of the University of Arizona.
"A lightweight, compact and high-performance Google Glass-like device - called an optical see-through head-mounted display (OST-HMD) - could potentially be a transformative technology to redefine the way we perceive and interact with digital information," Hua said.
For example, it could one day allow a doctor to see computed tomography (CT) images overlaid on a patient's abdomen during surgery or provide a new way to train soldiers by incorporating 3-D virtual objects into real-life environments.
AR goggles for long-distance viewing don't always cause eye strain; some of these eye-friendly designs are actively used for military applications.
But short-distance designs - in which you would focus simultaneously on a 2-D screen and a 3-D world immediately around you - do cause visual discomfort, due to the so-called accommodation-convergence mismatch problem.
The device developed by Hua and her colleague Bahram Javidi of the University of Connecticut solves this problem for OST-HMDs by superimposing a 3-D image, rather than the standard 2-D image, onto the 3-D view of the real world.
To create the 3-D image, the researchers developed a technology called microscopic integral imaging display. In this technique, a tiny, high-resolution screen produces views from different perspectives of the 3-D image you want to superimpose.
The views then combine to reconstruct a 3-D scene that's sent through a specially shaped optical lens - called a freeform eyepiece - and into the eye. The lens, based on an emerging technology known as freeform optics, also allows you to directly see the real-life scene before you.
There's no conflict in how your eyes focus, giving you a much more comfortable version of augmented reality, Hua said.
The research is published in The Optical Society's (OSA) open-access journal Optics Express.