How Victorian-Era Tech Can Make Virtual Reality Clearer

By all indicators, 2016 is shaping up to be the year of virtual reality. Facebook, Google, Sony and others are all slated to release VR headsets this year in a bid to corner the market of this perennially futuristic technology. Although virtual reality is being sold to us as the future of everything from tourism to sex, the VR tech itself has a long way to go before it's ready for mass consumption.

Aside from locomotion, one of the most significant technical problems plaguing VR devices have to do with their optics. A prime example is something called the "vergence accommodation conflict," which has to do with a discrepancy between the way muscles in our eyes focus on objects and the visual cues that are then sent to the brain. So in an effort to counteract this conflict, a team of researchers from Dartmouth College and Stanford University turned to a low-tech solution for a high-tech problem—the monocle.

In the same way that a camera can be adjusted to focus on objects at different distances, the human eye has several muscles that are constantly adjusting themselves to allow us to see clearly across a range of depths. One set of these muscles works to ensure that both of our eyes are looking at the same object, which ensures we don't have double vision—this is called vergence. A different muscle in the eye adjusts itself to make sure the object we're looking at is in focus—this is known as accommodation.

The vergence accommodation conflict arises when we are able to account for one of these muscle movements without pairing it with the other—vergence without accommodation, or vice versa. This conflict is a common problem across VR platforms because current VR sets only invoke a vergence response in our eyes. We can focus on one object without having double vision, but our eyes can't properly focus on this object.

According to the researchers, this is because the images appear on the VR screen which is a fixed distance away from the user's eyes, even though the images rendered on that screen are depicted at various depths. This causes the eye's muscles to fix their focal length on the screen, rather than the objects depicted on the screen which may be placed at varying depths. The conflict between vergence and accommodation is always present for the user, but the discrepancy becomes more pronounced the closer the object is to the user.

The vergence accommodation conflict can result in eye strain and a reduction in vision clarity, leading to a significantly impoverished VR experience for the user. The researchers had to figure out a way to allow each eye to adjust its focus independently of the other, just as it would in real life. The technique they arrived at is called monovision, which has its roots in the monocle, a Victorian-era innovation which allowed its wearers to enhance their vision in only one eye.

Today the technique is much more sophisticated and is generally carried out by way of surgery or spectacles, but the result is the same. People with monovision corrected vision have one eye that is focused at a fixed near distance and another eye that is focused at fixed far distance. According to the team, this allows those treated with monovision to see more clearly over a range of distances via whichever eye is closest to the correct focal length.

The Dartmouth and Stanford researchers applied this insight to an Oculus and Google Cardboard VR headset by adding a pair of focus tunable liquid lenses to the set up. The resulting contraption is elegant in its simplicity: it's just a 3D-printed custom mount that houses the adjustable liquid lenses and can be attached directly to the viewing area of the headset. These lenses can then be set to two different fixed optical lengths (one far, one near) for the duration of a VR experience, or manually adjusted in real time by the user as needed.

The end result is the user is able to mitigate the vergence accommodation conflict by using the team's lenses to manually accomplish the adjustments our eyes do naturally when they're not a few inches away from a VR screen.

While the manually adjusted lenses are a start, this innovation could really blossom in conjunction with eye tracking software, which would allow the lenses to automatically adapt their focal lengths in real time without the user needing to manually adjust them. By tracking the user's eye motions, the software would be able to tell which object the eye is trying to focus on and its distance from the eye as rendered in the virtual environment. The eye tracking software could then make adjustments to the focal length of each eye's tunable lenses in real time as the user looks around the environment.

"In VR, monovision has the potential to reduce the vergence accommodation conflict one eye at a time," the team explained via email. "Lenses of differing powers can be placed in front of the two eyes, thus giving the VR display two optical distances, rather than one. When a simulated object is placed close by, the eye with the near lens will have a reduced conflict while the conflict will still be present in the eye with the far lens, and vice versa."

According to the researchers, they wanted to see if accounting for this vergence accommodation conflict one eye at a time was more comfortable than not trying to adjust for it at all, as is the case with an unmodified VR headset right out of the box. Based on the feedback the team received from users who tried their modified Oculus headsets, monovision corrected VR is a definite improvement.

Although users recorded a definite improvement in their VR experience and no modification of VR games is necessary to make use of these lenses, it might be awhile before you can add them to your VR rig. According to the team, there isn't enough data on the long-term comfort of monovision and more research needs to be done on how long term monovision exposure affects users with normal eyesight.

Still, the researchers remains optimistic that their VR lenses could be commercially viable in the future.

"Practical optical solutions for virtual reality are crucial to moving this technology to increasingly more comfortable and immersive experiences, said Emily Cooper, research assistant professor in Dartmouth's Department of Psychological and Brain Sciences. "Our work shows that monovision has the potential to be one such solution."