How Do Eyes Respond To Virtual Reality Headsets?
Famous science fiction author Arthur C. Clarke once said that “Any sufficiently advanced technology is indistinguishable from magic,” and in the case of VR headsets, he is absolutely correct. Complex, yet light-weight devices like the Oculus Rift, or the HTV Vive can be plugged into your PC, strapped to your head, and seemingly teleport you to somewhere completely different. Using motion tracking technology, you can turn your head to look around a simulated 3D environment, with a level of sensory immersion never before achieved by video games, or any form of media for that matter. But how do these headsets trick your eyes into thinking that the screen just centimeters away is really a place or object meters, or even kilometers away? And how do your eyes react to being tricked this way?
The technology and magic of VR headsets takes advantage of the ways that your eyes focus on and perceive the world around us. But because these devices can't completely simulate a real world environment, and are limited to just a small space just in front of your eyes, compromises have to be made. In fact, your eyes are going to have to work pretty hard in order to fully enjoy everything that VR has to offer.
No matter how far an object appears to be in VR, whether it's an object right in front of your face, a person across the room, or a beautiful mountain range in the distance, your eyes are only ever focusing on lenses that are centimeters away. Normally, your eyes work together to focus on a near by object by “crossing paths” so to speak. If you hold your finger just in front of your nose and focus on it, you'll appear rather cross-eyed while doing so.
VR takes full advantage of this mechanism by displaying different images to each eye, causing them to angle appropriately in respect to one another in order to simulate distance. A close virtual object will make you cross your eyes to see it clearly, while a far virtual object will allow your eyes to gaze almost parallel to one another.
But that's not the only way your eyes focus. Changes within your eyes are made to accurately focus incoming light onto your retina depending on how far away that light is coming from. This can be demonstrated once again by holding a finger in front of your face. This time, however, close one eye, and look directly at your fingertip. You'll notice that everything in the distance is blurry, and when focusing on distant items, your finger becomes blurry instead. This method of focus is something that VR is not able to simulate, and while you may not notice it immediately after putting on a headset, it will slowly take a toll on your eyes, and you may begin to feel fatigued over time. Close virtual objects will have a greater impact that medium or far objects will, though.
Not all of the distance-cues are interpreted by your eyes alone. Some tricks are meant to affect your brain. Distinguishing between near and far distances is also done through parallax, which has to do with the displacement or movement of an object along a line of sight. If that sounds confusing, it's because parallax is much easier to demonstrate than to explain.
Next time you're riding in the car, or on the train, take notice of how how much quicker items close by seem to be moving past than items off in the distance. A mail box or street sign is only visible for a brief moment, yet the buildings that make up the distant city skyline barely seem to move at all. By using this concept to their advantage, VR developers can make items seem very far away, or very near by. And the best part is, since this is tricking your brain, and not your eyes, it's not going to contribute to eye fatigue over time.
Although the inner ear gets most of the credit for allowing us to balance upright on two legs, our eyes play a major role, as well. A convincing virtual reality game that gives your eyes the impression that you're rotating, tilting, or otherwise moving can send confusing messages to your brain. It's not uncommon for these situations to cause people to feel off balanced, or even a bit nauseous.
So how do VR headsets create such an immersive environment using flat LCD panels? The key ingredient are fresnel lenses. Unlike normal lenses found in eye glasses or magnifying glasses that used curved surfaces to bend and refract light, fresnel lenses are completely flat. They use concentric rings that are very precisely angled to refract light towards a specific point, in this case, your eye.
Imagine a large bullseye, with many, many rings, and a light source behind it. The light that passes through the very center of the lens wont be refracted at all, and will continue moving in the direction it's currently traveling. Moving outward one ring, and the light will now bend, but only slightly. Its going to meet up with the center beam just several centimeters away. Each subsequent ring will bend the light more and more, so that each ring focuses on the exact same point.
The advantage here is that the lens allows a flat display to appear rounded, like the inside of a sphere, making it much easier to trick you into thinking you're actually in the environment you're seeing, and not looking at it through a window. The down side is that the lenses need to be very accurately aligned with your eyes, so that the light is focused directly on your iris. If the lenses are off, even just a little, the image will appear blurry, and disorienting.
One last point of caution is in regards to the so-called blue light controversy. Nearly all electronic devices, including televisions, computers, mobile phones, and even VR headsets emit light that is more blue than natural sunlight. Blue light is near the end of the colour spectrum, and carries more energy than the other colours. While there's no concrete evidence, it is suspected that over time, blue light contributes to eye damage, cataracts, and macular degeneration. Special glasses are available that are designed to filter out blue light, alleviating the stress on your eyes, and are great for people who spend a lot of time working in from of digital displays.
The most important thing to take away from all of this is, that despite all of the issues and problems listed above, there is no evidence of long-term damage risk to your eyes with the use of a VR headset. The type of eyestrain that you're at risk of having is similar to that of people who work in an office at a computer, focusing on near objects and digital displays all day. Fatigue may happen, but it's avoidable with routine eye exercises, and causes no permanent, long term damage.
If you begin get a headache or eyestrain, take a short break to allow your eyes to rest. A five minute break every 30 minutes will allow your eyes to focus on something further away, giving them an opportunity to relax. Eye muscles are like any other muscles in your body. If you work out too hard at the gym one day, you might be sore for a day or two afterwards, but unlikely that any serious damage has occurred. Even so, continued daily use can create constant sense of fatigue. Like anything good in life, it's important to consume in moderation.
Author: John Dreyer Optometrist Bsc(Hons), MCOPTOM, DipCLP
Created: 1 Jul 2016, Last modified: 10 Feb 2020