Recently, 3D technology has made its way into the medical field, from da Vinci robotic surgery to 3D endoscopy. Humans are quite good at detecting depth on 2D images. But as you probably find when you try walking around with one eye closed, your depth perception, although enough to survive with, is not very accurate. You may find that you misjudge the height of a staircase and trip a little, or you try to catch a ball only to realise you missed it by a few centimetres.
Humans can judge depth in 2D, but they cannot judge depth accurately. And that is why 3D technology is useful in surgeries where accuracy is vital. Stereoscopic surgery seems to be preferred by many doctors, as it allows a sense of depth that cannot be felt with 2D images. This is important in surgery, as injuries may occur to the patient if instruments are not placed in precisely the right position.
In order to perceive images in 3D, display systems must mimic the way our own eyes perceive 3D. And if you close your right eye, it will appear to the right hand side of your vision. Yet when both eyes are open, our hand appears directly in the middle of your vision. Our brains receive two different images, one through each eye, and process the images into one 3D image.
In doing so, our brain is able to sense the depth of objects in front of us. We can mimic this by recording images from two cameras that are next to each other. A display device then ensures that one image is only visible to the left eye, while the other image is visible only to the right. In this way, our brains are able to give us a stereoscopic sense of depth. There are several ways of creating 3D images on monitors and TVs.
These days the most common way is to use either polarized 3D — which is commonly found in movie theatres - or active shutter 3D — which is commonly found in TVs. For surgeries, polarized 3D is the preferred technology. But why? To answer that, you need to understand how each technology works. While the other two types of 3D glasses use something called passive 3D, shutter glasses utilize active 3D.
Instead, shutter glasses work through LCD screen technology that darkens each lens, alternating the left and the right. Shutter glasses are usually battery powered, or even USB-supported, and are more expensive than traditional 3D glasses. The cost of these glasses make a huge difference to the image quality. You can get shutter glasses from Samsung, Panasonic, Sony, and more. How 3D glasses work depends solely on how the eyes work and communicate with your brain.
Human eyes have binocular vision that works best when you use both eyes simultaneously. Binocular vision gives you depth perception and allows you to tell which objects in your line of sight are closer or farther away. Binocular vision relies on the distance between your eyes to present you with two different perspectives on the same thing. The distance between your eyes is generally about two inches apart, so the images each eye presents help to build a complete picture.
All types of 3D glasses work by making each eye see two different things. Still, the brain figures it out. When looking at something very far away, the lines of sight from our eyes are parallel. To simulate looking out to infinity, you need to recreate that on screen. But, say you portray a distant object by setting the lines of sight seven centimeters apart on screen for someone whose eyes are seven centimeters apart.
Since everyone has a different distance between their eyes and sees the screen from a different place, the image is somewhat wrong for everybody. As scientists, we trick your vision. That tells us about the algorithms the brain uses to process visual input.
My lab studies praying mantises. We give them 3-D glasses to fool their vision. Mantises strike at things they think are in range. Mantises may compute this vision differently than humans. This might help mantises find camouflaged prey. Levi, D. Stereopsis and amblyopia: A mini-review. Vision Research, , 17— Nityananda, V. Current Biology, 28 4 , Every month, we choose one reader question and get an answer from a top neuroscientist.
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