Time for Visionary VR Tech to Focus on Vision
Virtual Reality has immersed us in captivating alternate worlds and intense gaming experiences. However, VR has much to look into, including VR-induced cybersickness, why children should not use VR headsets, and the contradictions VR displays present to our eyes.
The global market for Virtual Reality (VR) and Augmented Reality (AR) is expected to reach $94.4 billion by 2023, according to ReportLinker, a technology company that provides industry data on the topic. Of the two areas (VR and AR), VR held 60% of the market share in 2017.[i] VR can create an immersive experience that can fascinate users who are transported to another world. Time spent in a VR headset is an issue for youngsters, however. VR is a new technology, so the effect of the long-term use on eyesight is unknown. VR is not recommended for kids age 12 and younger, as VR headsets are made to fit the pupillary distance of an adult, not a child. Excessive use of VR may also affect the way the eyes grow and lead to myopia or near-sightedness. Another side effect that VR is working to overcome is “cybersickness,” where nausea akin to motion sickness can be induced when using VR headsets, although not all VR headsets and not all people using them experience the same intensity of cybersickness. What challenges does VR face, and how can the VR industry overcome them?
The Effect of VR Headsets on Eyesight
The Canadian Association of Optometrists states “Most VR headset manufacturers have put in place warnings for children. This is important because a child’s visual system continues to develop throughout childhood, and VR systems are set to the pupillary distance of the average adult, not child. Extended exposure to the awkward visual posture created by VR headsets can alter the development of focusing, tracking, and depth perception.”[ii] An increase in the incidence of myopia in the general population has been linked to the advent of the extensive use of smartphones, but no studies have definitively shown that using VR increases the propensity to develop myopia or any other permanent damage.
Nevertheless, makers of VR headsets include warnings of risk to eyesight. Myopia has long been associated with near-work tasks that prevent one’s eyes from naturally focusing at different distances in natural light. Microscopes are a lot like VR headsets, in that they involve close-up viewing through binocular lenses. A study associated the occupational use of microscopes with myopia in adults.[iii] VR headsets are not often used in an occupational setting, however, which implies near constant use for 40 hours a week or more. AR headsets do allow natural vision but provide an overlay of virtual objects or information, much like a heads-up display in a cockpit.
Presently, known optical issues specific to VR headsets include eye strain and dry eyes, since people caught up in an active or tense situation in a game do not blink as often as they should. Dry eyes can lead to extreme pain. Over a prolonged period of VR immersion, many users forget to take a break to rest their eyes to avoid eye strain. VR is fun, engaging, and immersive. It’s understandable that playing for a couple of hours without stopping is the norm, not the exception. But VR induces an eyesight-focusing situation that does not often occur in the real world, mainly because a VR headset fixes the display close to the eyes. No one knows if this is an actual health problem yet, but it’s important to be at least aware of what’s happening.
For thousands of years, our eyes have naturally converged to focus on objects located at different distances. However, the visual presentation in a VR headset forces an unnatural action for the eyes. In a VR headset, a separate image for each eye is projected on fixed, bright displays physically located close to the eyes. VR displays induce a sense of depth and a 3D quality by introducing a lateral relative offset of the objects in each image, which is like creating a slight double vision effect if you were to overlap the two images on one display. The higher the lateral disparity between the images, the nearer the object seems. In the real world, our eyes both converge and focus on the same point. In VR, objects that appear to be moving around at a distance are just a few centimeters from the eyes, which messes up the natural convergence action.
Vergence and Accommodation Coupling
Eyesight is complicated. To perceive an object, you first point your eyes in the direction of that object (convergence) and then your eyes’ lenses focus on it (accommodation). In industry lingo, vergence and accommodation coupling work together to create a meaningful image for you. In a VR headset, the eyes remain focused at a fixed distance even though they converge on objects that are seemingly located further away. In a VR headset, your eyes adjust to changes in convergence as objects move around, but unlike natural vision, your eyes never change focus, or accommodation. As a result, VR headsets force users to make exaggerated convergent eye movements when they look at virtual “near” objects. The eyes are forced to accommodate a situation that is not the normal mode of operation in the real world and can result in discomfort for minutes or hours. The long-term effects of VR headset use, especially on children, are not known.
In a paper presented in a scientific report from the U.S. National Institutes of Health, Ocular effects of virtual reality headset wear in young adults, Turnbull and Phillips describe how the focal distance in VR is different than in natural environments, which affects vergence eye movements. “To prevent double vision as gaze shifts between objects, users make both version and vergence eye movements, which minimise retinal disparity of the object between eyes, and permit the object of interest to be perceived binocularly. In real-world viewing of objects, vergence eye movements are associated with changes in accommodation to focus the eyes at the depth of the object. However, in VR, the focal distance of all objects on the screen is constant, and the eyes must converge without changing accommodation to maintain a clear retinal image. Thus, wearing a VR HMD creates a dissociation between convergence and accommodative demands, which may contribute to visual discomfort.”[iv] Twirling around in a swivel chair also induces dizziness and an off-kilter center of balance that can be uncomfortable if you spin too fast or for too long. There aren’t any studies that tell us whether spinning around in a swivel chair for hours at a time is detrimental to one’s health in the long term, but it is certain that such sustained activity is unnatural in the evolution of the human race.
Users who experience discomfort while using VR headsets have also experienced “cybersickness,” which is a feeling of nausea much like motion sickness. Cybersickness occurs when visual information doesn’t match the user’s body position, sending false signals to the senses, such as when the VR headset immerses the user in a moving landscape when in reality the user is sitting still. A VR experience full of sharp turns, rapid acceleration, and falling would be sufficient for most to induce cybersickness. A time-lag between physical movement and perceived movement can also create sickness. Cybersickness results in a short-term (a few minutes) to long-term (a few hours) illness characterized by dizziness, vertigo, disorientation, headache, and nausea. Cybersickness that lasts for hours can potentially be a real-life problem, for instance, leading to hours of impaired balance or driving. Game developers have found that adding a virtual stationary object in the game can help reduce cybersickness. Stationary objects in the frame can be as simple as adding a front-seat bar in a roller coaster or a virtual nose.[v] VR games that do not require a lot of head movement contribute less to cybersickness, as well. Displays with images that move with you as they do in the natural world are an improvement. VR headset displays that move the entire visual field when the wearer moves their head can induce sickness, because the experience is little more than strapping a television to your face. Light-field technology can reduce cybersickness since it creates images where people can look around as the image stays fixed while the wearer moves through the virtual world. Light-field technology imparts imagery that is more true-to-life in terms of what influences depth perception, shadows, and motion parallax (i.e., objects closer to you move faster than those farther away from you).
VR is still in its technological infancy. Any technology that makes people feel sick needs improvement. VR makers are well aware of the problem, although no one knows the exact mechanics of the cause as to why some are more prone to cybersickness than others. We can mitigate cybersickness with high-performance hardware and with VR games that avoid sending false or conflicting sensory signals about physical movement to the brain. Eliminating the headset in VR is not a possibility yet, although a real-life “holodeck” as imagined by Star Trek Next Generation creators would solve the vergence and accommodation coupling issue discussed above. Displays that are less exhausting for the eyes as backlit LCDs might also improve the VR experience. Without information on the effects of long-term use of VR headsets, the best action for VR use today is to limit the use of VR to 30 minutes per session, take regular breaks, and avoid any VR use for children under the age of twelve unless the VR is specifically designed and intended for children.
[i] Global Industry Analysts. “Market Research.” Reportlinker Insight, Global Industry Analysts, June 2018, www.reportlinker.com/p05479743/Augmented-Reality-and-Virtual-Reality-Market-by-Devices-by-Component-by-Application-by-Geography-Global-Market-Size-Share-Development-Growth-and-Demand-Forecast.html.
[ii] “Are Virtual Reality Headsets Dangerous for Our Eyes?” The Canadian Association of Optometrists, 23 May 2017, opto.ca/health-library/are-virtual-reality-headsets-dangerous-for-our-eyes.
[iii] McBrien, N A, and D W Adams. “A Longitudinal Investigation of Adult-Onset and Adult-Progression of Myopia in an Occupational Group. Refractive and Biometric Findings.” Current Neurology and Neuroscience Reports., U.S. National Library of Medicine, Feb. 1997, www.ncbi.nlm.nih.gov/pubmed/9040464/.
[iv] Turnbull, Philip R. K., and John R. Phillips. “Ocular Effects of Virtual Reality Headset Wear in Young Adults.” Current Neurology and Neuroscience Reports., U.S. National Library of Medicine, Nov. 23 2017, www.ncbi.nlm.nih.gov/pmc/articles/PMC5701049/#CR2.
[v] Kanarbik, Kevin, and Al William Tammsaar. “Best Ways of Producing Cybersickness in VR.” Introduction to Computational Neuroscience, University of Tartu, Estonia, 2015, interview with Madis Vasser.
Lynnette Reese is Editor-in-Chief, Embedded Intel Solutions and Embedded Systems Engineering, and has been working in various roles as an electrical engineer for over two decades. She is interested in open source software and hardware, the maker movement, and in increasing the number of women working in STEM so she has a greater chance of talking about something other than football at the water cooler.