What Is Depth Perception?

Ask the Optician

Depth perception allows us to understand the distance between objects. Learn about the processes that make it work, how to test your own depth perception and how to improve it.
depth perception

Wondering how to define depth perception? It refers to the ability to see objects in three dimensions, i.e., length, width, depth, and to judge how far away an object is. This also includes the ability to judge the distance between two objects.

To be able to perceive depth accurately, we generally need to have a binocular stereoscopic vision (vision in both eyes). In a process known as convergence or stereopsis, the brain collates the 2 sets of information based on the different angles of sight from our two eyes to form a unified 3D image. 

Depth perception is an innate mechanism, strengthened by visual experience. Over time, the brain is able to speed up the computation of objects in our sight. Depth perception examples take place multiple times a day without even realizing it.

When both eyes see clearly and the brain is able to process a single image effectively, it is known as stereopsis. This is the concept that makes you feel like you’re able to perceive depth when watching a 3D movie.

Monocular cues provide depth information when relying on one eye to see objects. Those with monocular vision may face depth perception inaccuracy since they have to rely on other visual cues to gauge depth.

Why is depth perception important?

Depth perception is extremely important for various reasons: 

  • It helps us to move around without bumping into things
  • It helps us to identify how far away we are from an object or to identify the distance between two objects
  • It also tells you how fast an object is coming towards you and how quickly something is moving

Therefore, depth perception keeps you safe and stops you from getting hurt. For example, depth perception allows you to drive safely as it allows you to know how far away you are from other vehicles, how fast they are going, and helps you avoid them if they are coming towards you.

What are depth cues?

Depth cues are the different tools that our eyes use to interpret depth in sensed images. These depth cues can either be physiological and psychological. 

Physiological depth cues

Accommodation: This is the process by which your eyes bring objects into focus at different distances. It ensures that light entering the eye focuses on the retina. The process involves contracting and relaxing the eye muscle to change the focal length of the lens.

Convergence: This refers to the change in eye direction that occurs when watching an object that is close to us. Our eyes point slightly inward. This cue can work effectively at a distance of fewer than 10 meters.

Binocular Parallax: Since our eyes are roughly 2 inches apart, the images received from each of our eyes are slightly different. The difference between the two images is called binocular parallax which is the most crucial depth cue when we see objects at a medium distance.

Our eyes can still calculate depth using binocular parallax even when all other cues are removed. However, this method only works well when the object is close up. When objects are far away, the 2 images our eyes receive seem more similar.

Monocular Motion ParallaxWhen we close one eye, a sense of depth can still be achieved if we move our head from side to side. While closer objects move in the opposite direction of the head movement, further objects move in the same direction. 

Furthermore, the closer object moves quickly across your retina while objects that are further away don’t move as much or do not move at all.

Psychological depth cues

Retinal Image size: Our brain calculates the sensed size of objects by comparing it to their known size to then perceive the distance.

Linear Perspective: Known objects are thought to be moving further away if they become smaller and smaller.

Texture Gradient: The further away the object is, the less of its surface texture we can see and the smoother it appears. On the other hand, when we can see more detail of an object’s surface texture, it can be calculated as being closer. 

Overlapping: We can understand if an object is closer to us when it blocks other objects from our sight. This closer object will have a more continuous borderline. 

Aerial Perspective: Depth can also be interpreted based on the relative colour and contrast of objects. An object is considered as being further away when it is blurry.

Shades and Shadows: When an object casts shades and shadows on other objects, we understand that this object is closer to the light source.

Of all the above cues, only convergence and binocular parallax are binocular (require both eyes to be open) while the rest are monocular (require only one eye to be open).

What causes depth perception problems?

Depth perception problems usually result from the following common conditions:

Blurred vision: A lack of sharpness of vision which reduces the ability of our eyes to see fine details.

Strabismus: Eyes are misaligned (cross eye syndrome) so the eyes cannot see clearly or work together effectively.

Anophthalmia: A rare congenital situation where there is an absence of one or both eyes due to many reasons such as genetic mutations, infections, etc.

Amblyopia (lazy eye): A sight disorder that is typical in children. When children encounter double vision, their brain tends to suppress the input from one eye, and over time, it favors the other eye. Read our post on dominant eyes for more information.

Optic nerve hypoplasia: A condition where the optic nerve, which sends visual signals from your eyes to your brain, has incomplete development before birth. It can result in partial or complete vision loss in children.

Macular degeneration leads to a loss in the center part of one’s vision, hence leading to declining depth perception.


You can easily test your own depth perception at home and also improve it by doing some simple exercises.

Depth perception test

No depth perception refers to the inability to see objects in 3D. It is possible to suffer from issues relating to depth perception for years without knowing. Follow these steps to quickly and easily test it right now with the following image of the tennis ball.

  1.  Hold a finger half-way between your eyes and the picture of the ball (about 6inches from your eye is good enough). The ball will be in the background. 
  2. Now focus your gaze on the ball. You should be seeing two images of your finger. It might be slightly blurry or transparent but that’s normal. If you see two fingers, it’s a sign that you have strong depth perception.
  3. Now, switch your focus from the ball to your finger. You should see two slightly hazy images of the ball on either side of the finger.

If any of the following happens, it may be a sign of poor depth perception.

  • You see a finger/ball more clearly on one side than the other.
  • You see only one finger/ball where you should be seeing two.
  • One finger/ball is larger than the other.
  • A finger/ball appears and then disappears.
  • When you close one eye at a time and your finger starts in the centre of the ball but moves far to one side when you open the other eye.

How to improve depth perception?

One of the solutions to improve poor depth perception is to wear and prescription contact lenses.

Both of these will improve the image that your ‘bad’ eye sees. You can buy eyeglasses and contact lenses to improve your depth perception online at VisionDirect for free shipping with a 24-month warranty, a hassle-free 100 day returns policy, and a price match guarantee.

Other than wearing a pair of prescription glasses, you can also do a few different exercises with your eyes to treat poor depth perception such as:

Eye rolling: Slowly roll your eyes in both directions for a few minutes at a time. This exercise helps to strengthen nerve impulses and improve eye muscles.

Shifting your gaze: You should practice this exercise together with eye-rolling as you can shift your gaze slowly while rolling your eyes.

Resting the dominant eye: Covering the dominant eye with your hand or an eye patch for a few minutes can help train the weaker eye.

If you suspect that you may have depth perception issues, visit your optician and consider incorporating eye exercises and supplementing your diet with nutrients you need for healthy vision.

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