Depth Perception: How It Works and How to Fix It
February 8, 2023 • 10:55 AM
Depth perception allows us to see the world in three dimensions. It makes it so that real life looks like, well, real life and not like a photograph or a movie. And we mean a regular movie, not the kind where you have to wear those silly glasses. (Sorry, 3-D glasses, but you just don’t have the style we expect from our eyewear.)
In order to perceive depth, our eyes and our brains work together to process hundreds of visual cues — from shadows to color contrast to which objects are in front of each other and what their sizes are relative to one another. We process all of this information in milliseconds, proving that the human brain is truly magical.
If you can catch a baseball when someone throws it to you, step on the brakes in time to stop at a red light, or pour a glass of water from a pitcher into a cup without spilling, then you can thank your eyes for the accurate depth perception. But, some people experience depth perception problems that can make it hard to accomplish these everyday tasks.
Learn how depth perception works and find out what causes depth perception issues. We’ll share what you should do if you think you’re not perceiving depth accurately.
How Does Depth Perception Work?
Human eyes are extremely good at perceiving depth because they have a little super power known as stereopsis.
Here’s how stereopsis works: Your eyes both see the same image at slightly different angles. Then, your brain combines the two images to create a single image. When the two images are combined, the new image contains extra depth information that you can’t get from a single image alone.
Only animals with eyes on the front of their heads have stereoscopic vision (aka binocular vision because — just like a pair of binoculars — you use two lenses to create one image). Animals with eyes on the sides of their heads have monocular vision, meaning each of their eyes is seeing a different image. Monocular vision gives animals a larger visual field, but a worse sense of depth.
Animals with monocular vision get some depth cues, but animals with binocular vision (like us) get all of the visual cues that monocular animals get, plus more cues that only binocular vision can provide.
Here are the monocular cues that give you a sense of depth when you look at objects at different distances. If you close one eye, you can still see these depth cues. So, you’ll still have some depth perception — it will simply be less accurate.
Interposition: This is where one object is in relation to another object. For example, imagine you’re in a room, and there’s a painting on the wall. The back of a chair is blocking the bottom of the painting. You’ll know that the chair is closer than the painting because it’s in front.
Relative size: If your brain knows the size of an object in your field of vision, it can use this information to determine how close or how far away that object is from you and from the other objects you see. It’s the depth-perception equivalent of all those “banana for scale” memes.
Linear perspective: Imagine you’re on a road trip. A long, straight road stretches out in front of you. As that road approaches the horizon, it appears to narrow. Your brain knows that as the line narrows, it’s getting farther away from you.
Texture gradient: Our eyes can see the texture of objects that are close to us, but it’s harder to see these details on distant objects. For example, if you look at a tree that’s 30 feet away, you’ll be able to see the texture of the leaves (as long as you have 20/20 vision or are wearing your distance glasses). But if you look at a tree that’s 300 feet away, you won’t see this.
Motion parallax: If you move your head, the stationary objects in your field of vision appear to move too. You can try it now — turn your head to the left or right, and notice the apparent movement of your screen. Your screen is staying still, but the perceived motion helps your brain sense depth. Closer objects and more distant objects appear to move at different speeds.
Aerial perspective: When light hits the objects in your field of vision, it causes highlights and shadows that affect the color of the objects you see. Objects that are farther away from you appear to have lower contrast and lower color saturation — they often look hazy instead of clear, which tells your brain that they’re farther away.
Accommodation: It’s not just retinal images that tell your brain how far away things are. Your ocular muscles contract a different amount to see things at different distances. So, your brain can use the contractions in your eye muscles to figure out how far away an object is.
Monocular vision gives a lot of depth cues that help us figure out the approximate location of an object in our field of vision. But, it’s the cues we get from our binocular depth perception that allow us to pinpoint the exact distance of an object. These are the two cues:
Binocular disparity: Remember those two images that your brain turns into one? The images start out slightly different because they’re taken from slightly different angles (one from your left eye and one from your right eye). Before your brain combines them, it uses the differences to figure out how far away objects are. In the two images, there will be a much bigger difference between the positions of far-away objects while close objects will look nearly the same.
Convergence: This is another depth cue that relies on your eye muscles instead of on the image you’re looking at. When you have binocular vision, both of your eyes move to look at the same object. If your eyes move closer together (in toward your nose), they’re looking at an object that’s closer to you. If they move farther apart, they’re looking at an object that’s farther away.
What Causes Poor Depth Perception?
All of the processes that lead to good depth perception require hard work from your eyes. So, typically when someone is experiencing poor depth perception, it’s a sign of vision problems.
These are the main vision problems that can lead to poor depth perception:
Amblyopia: Also called “lazy eye,” amblyopia is most common in kids, and it’s a frequent reason why a kid may need prescription glasses or vision therapy. With this condition, vision doesn’t develop correctly in one eye, which causes the brain to rely on the other eye for all of its visual information. Essentially, people with this condition have monocular vision instead of binocular vision.
Strabismus: One of the most common causes of lazy eye, strabismus happens when the eyes don’t point in the same direction. For example, one eye might point straight ahead while the other points up or down. It’s often the result of poor eye muscle control, and it can cause the brain to ignore the image from one eye.
Blurry vision: The American Academy of Ophthalmology lists 49 possible causes of blurry vision, including astigmatism, cataracts, and glaucoma. But regardless of what’s causing the blurriness, it can lead to poor depth perception, especially if your blurry vision is mostly in one eye.
Optic nerve damage: Trauma to one of your eyes can cause optic nerve damage that makes it difficult for your eye to communicate with your brain. In children, optic nerve hypoplasia — a condition where the nerve doesn’t develop properly — can cause the same issue. In either case, the brain will rely on the other eye, leading to monocular vision.
What to Do If You’re Worried About Your Depth Perception
Poor depth perception is almost always the result of a vision problem. So, if you’re worried about your depth perception, your first stop should be the eye doctor.
At a routine eye exam, your eye doctor will check your depth perception by having you cover your left eye and then your right eye. They’ll also check your overall eye health and look for issues like cataracts and glaucoma.
If your doctor identifies an issue that may be causing poor depth perception, they can help you find the right treatment options. You may need glasses if your vision is worse in one eye than the other.
If, on the other hand, your depth perception issues are caused by problems with your eye muscles, your doctor may recommend vision therapy or an eye patch. In rare cases, you may need surgery to fix the issue that’s causing your poor depth perception.
Your doctor can explain your options and help you find the best solution.
You’ve Got Depth
Depth perception is a human super power. Because of our binocular vision, we’re able to accurately locate the objects around us. This allows us to walk down stairs without tripping or cut vegetables without cutting our fingers.
Good depth perception is essential to your quality of life, so if you think you have depth perception problems, talk to your eye doctor. There are plenty of treatment options that can help improve your sense of depth and make everyday tasks easier.
And if you need glasses to treat your depth perception issues, we will be here to help you find frames that show off the depths of your personality. Our Base Frames start at just $60, and you can add a variety of snap-on Top Frames in fun patterns, like plaid, polka dots, or paw prints. Go deep, and explore the entire collection at Pair Eyewear.