When hearing that 3D film has existed in some form or the other since the 1920s, most people are remarkably surprised. After all, it was only 8 years ago when the 3D film industry imploded and was met with unprecedented success for the first in media with the release of Avatar.
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Nowadays, 3D film has become something of the norm in the American film industry, especially in the action-packed DC or Marvel movies. Scientifically, however, there are aspects of 3D displays that have left humans in the dark. The most prevalent and relatable one perhaps is the eye irritation that comes with viewing 3D media.
You may have experienced this for yourself. After half an hour of watching a 3D movie, you may have had to take off the custom glasses, close your eyes and take a break from the screen that had left your eyes dry and irritated. If you’ve ever felt that this problem stemmed from a medical issue with your own eyes, do not worry! This issue is in fact, not unique to just one person, and there exists a scientific phenomenon that explains why eye fatigue occurs in humans when watching artificial 3D displays. This phenomenon is called vergence & accommodation, and it’s one of the many natural mechanisms governing our ocular functions. Vergence is the simultaneous movement of the pupils towards or away from one another during focusing. Accommodationis the ability of the eye to change its focus from distant to near objects, or vice-versa. Our eyes are able to accomplish this by the lens changing its shape.
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But why do our eyes hurt after looking at artificial 3D visualization? To start off, when we look at a 3D object in real life we’re really looking at two images because of we, quite simply, have two eyes. This is called a stereoscopic view. One eye sees one image, and the other eye sees the same image from a different angle. These two images capture slightly different viewpoints of the same object, and the occipital lobe in our brain is able to compute the disparity between them. This distinction of distance is specifically called convergence.
An example of a stereoscopic view. (Image Source: Hypergrid Business)
However in 3D movies, every scene is shot with two cameras, in order to provide the two images that our eyes need to create the 3-dimensional view in the brain. As you can see in the picture below, these images are often polarized — either a vertical or a horizontal polarization. Our eyes filter different polarizations, so two distinct images enter each eye. In real life, our retinae “verge” and “accommodate” to the 3D object — rotate so the object is always at the focal point and accommodate to change focus from distant to near objects. In films, however, there is a vergence-accommodation conflict. The retinae must focus at one distance because that is where light is being emitted from the screen, but they must verge at another distance — where the 3D object is being projected, either behind or in front of the screen.
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While the physiology behind this concept may be confusing, it helps to put this into a simplified terms: Vergence is the ability of our eyes to focus, while accommodation is the ability to change focus. In 3D films, the actual image and the light of the image are being emitted at different points on the screen. This disparity creates a confusion for the vergence and accommodation functions as they’re being processed in our brain.
As Martin Banks, a researcher in the ocular vision at the University of California, Berkeley, explained in his Journal of Vision article, The Zone of Comfort: Predicting Visual Discomfort with Stereo Displays:
“When watching stereo 3D displays, the eyes must focus — that is, accommodate — to the distance of the screen because that’s where the light comes from. At the same time, the eyes must converge to the distance of the stereo content, which may be in front of or behind the screen…[thus] In 3D, the natural linkage between vergence and accommodation is broken.”
Despite Banks’ research and one of many other neurologists, the conflict between vergence and accommodation in 3D displays is not completely clear. This issue will remain a hot topic in the research community due to the rise of 3D media from games to computation simulations. The people demand comfort and enjoyable 3D experiences!
So Remember, the next time you step into a 3D movie theatre, give your eyes a break every once in awhile!