How To Test Depth Perception

Depth perception is an integral part of everyday life, and it's needed when determining distance and how quickly an object is moving towards you. Whether you are crossing the street or passing another car, depth perception keeps you at a safe distance.

If you have trouble perceiving distance, a depth perception test, which can be conducted at home and in an optometrist’s office, can determine how both of your eyes work together to see in three dimensions. Testing can help your eye care professional recommend depth perception exercises or corrective eye wear so that your eyes can work together to get you safely to where you need to go.

This article covers how depth perception works, how you can test it yourself or how an eye doctor will test it, the causes of poor depth perception, and some ways you can improve it.

What Is Depth Perception?

Depth perception is the ability to see things in three dimensions, including length, height, width, and distance. Depth perception works through convergence, which generally happens when both eyes focus on the same object, stretching the extraocular muscles that control the eyeball’s movement within the socket.

When both eyes are both focusing on the same object, each eye sees it from a slightly different angle since they are located on opposite sides of the face. The brain compares and processes each eye’s information to form a unified image that you see. When the process works properly—when both eyes see clearly and the image is processed efficiently—that result is called stereopsis.  

When someone does not have binocular (two-eyed) vision, the process of seeing depth becomes more complicated. At least 12% of the population has some problem with their binocular vision.

People who see through one eye, or have monocular vision, may have some trouble with depth perception. Over time, the brain may adjust to using the limited visual information that it gets from one eye to form an image, and this usually results in acceptable depth perception.

The consequences of poor depth perception include:

• Inability to perform normal tasks, such as driving or reading
• Learning difficulties in children
• Difficulties in playing sports

How To Test Depth Perception

At-Home Test

Before making an appointment with an optometrist for a depth perception test, you can try a home test to check your depth perception. For this test, you will just need two things: a white piece of paper with a colored circle in the middle and your index finger.

Once you have both handy, perform these steps to test your depth perception:

• Post the paper with the dot on a wall
• Hold your finger in front of the circle between your eyes and the paper
• Focus your eyes on the circle. You should see the circle clearly in the middle between the two images of your finger. The finger will appear slightly blurry and a bit transparent.
• Then, focus on your finger. The two images of your finger that you saw in the previous step should merge together into one finger while the circle splits into two.

Repeat this process a few times to see if your results change or stay consistent.

Make an appointment to see your optometrist if you see any of the following during your home test:

•    One finger is easier to see than the other.
•    One finger is larger than the other.
•    Fingers appear and disappear.
•    One finger drifts directly over the circle while the other finger is far to the left or right.
•    You can only ever see one finger.

Each of these could indicate that one eye is more dominant than the other, which can cause poor depth perception.

Getting Tested By an Optometrist

A comprehensive eye exam by an optometrist will usually include a depth perception test. They may ask you to put on a pair of 3D glasses and look at a booklet of test patterns. Each pattern has four small circles, and you will be asked to determine which circle in each pattern looks closer to you than the other three circles. If you can correctly identify the closer circle in each pattern, you are probably experiencing what is considered normal depth perception.

There are two types of depth perception tests:

• Random-dot stereograms, also referred to as the Randot Stereotest, the Random-dot E Stereotest, and the Lang Stereotest, are used to eliminate monocular cues or signals. These tests use two images, each composed of black and white dots or squares. While each eye sees a different pattern in the dots, when seen together, the patterns are seen as a specific shape.
• Contour stereotests, such as the Titmus Fly Stereotest, evaluate two horizontally different stimuli. The people taking the test looks at images (like that of a fly), and are instructed to identify the one that seems to be popping out of the page.

Causes of Depth Perception Problems

Some conditions that can cause depth perception problems include:

•    Blurry vision, usually in one eye
•    Strabismus (poor muscle control that can result in crossed eyes)
•    Amblyopia (weak or lazy eye)
•    Nerve problems in one or both eyes
•    Trauma to one or both eyes (caused by a direct blow or injury)

How to Improve Depth Perception

Vision therapy can help in treating depth perception issues. Vision therapists train a person’s brain to blend the images from each eye or ignore the image from the eye that is not as cooperative.

A few depth perception exercises can help:

• Eye rolling: Helps to strengthen nerve impulses that create awareness of proper depth. When beginning this exercise, slowly roll your eyes clockwise for a few minutes, then switch and roll them counterclockwise for a few minutes.
• Shifting your gaze: While rolling your eyes, shift your gaze slowly, especially when first beginning the exercise.
• Resting the dominant eye: So that the weaker eye does not strain. Cover the dominant eye for several minutes to allow the weaker eye to take over. This is usually done with an eye patch.
• Low light: Resting your eyes from light may ease pressure on the dominant eye without causing strain in the weaker eye.

Sometimes, an optometrist will prescribe contact lenses or eyeglasses to block unclear images from the bad eye so they do not interfere with images from the good eye.

A Word From Verywell

Depth perception problems are generally not caused by serious underlying conditions and can be easily corrected. You can try an at-home test, but after that, you should also consult an eye care professional because there is a chance that your at-home vision test was not done properly. Eye health is crucial for many different daily activities, so getting your eyes checked out by an optometrist when you have problems with your vision can avoid any unwanted disruption to your routine.