What is Stereoscopic Vision?

To understand how stereoscopic vision works, do this small experiment:

1. Cover the right eye with your palm and focus on an object at a distance using the left eye.
2. Switch and cover the left eye and observe the object with the right eye.
3. Look at the object with both eyes.

You’ll notice that you can see the object with one eye, but you’ll need both to perceive the object’s size and distance (binocular depth perception). Stereoscopic vision is the brain’s ability to create cohesive 3D images using visual information from both eyes.

In this post, we’ll look at stereoscopic vision in depth, including:

• Types of stereoscopic vision 
• Stereoscopic binocular vision vs. other vision types
• Importance and applications of stereoscopic vision
• Common questions about stereoscopic vision

What is Stereoscopic Vision?

Stereoscopic vision is the brain’s ability to interpret visual information from both eyes to create a clear three-dimensional (3D) image.¹ It’s also called binocular stereopsis.

If your eyes worked independently, your vision would be distorted since each eye focuses from a slightly different angle.

A good example of stereoscopic vision is the lines on railroad tracks. When you observe the lines further away, they may appear to be getting closer together. This is interpreted as the lines being farther away.  

Stereoscopic Deficiency

Any condition that affects the eyes’ ability to see correctly can affect your stereoscopic vision and impact your ability to judge the distance of objects. A common cause of stereoscopic deficiency is strabismus (crossed eyes).²

Someone with strabismus has dysfunctional eye muscles causing one eye to look at one object while the other eye turns in a different direction. 

Other causes include:

• Amblyopia (lazy eye)
• Blindness in one eye
• Brain trauma
• Eye injury
• Cataract (clouding of the eye lens)

How Does Stereoscopic Vision Work?

In stereoscopic vision, the brain combines visual information from both eyes to perceive an object. It allows you to see a three-dimensional object by taking in various factors.

These factors include:

• Distance
• Size
• Depth
• Shape
• Contrast
• Color
• Movement

How Does Binocular Disparity Contribute to Stereoscopic Vision?

Binocular disparities refer to the differences in each eye’s perspective. These disparities occur because each eye is in different positions on the head, viewing an object from slightly different angles.

Each image from both eyes is two-dimensional (2D). The brain must analyze them to make a three-dimensional image.⁶

The optic nerve transmits binocular disparities to the brain’s visual cortex to create a three-dimensional image, resulting in stereoscopic vision. Generally, a greater binocular disparity between the two images indicates that the object is closer to you and vice versa.

Importance and Applications of Stereoscopic Vision

Below are the applications and importance of stereoscopic vision:

• In daily life: Humans use stereoscopic vision to understand an object’s depth and appearance in visual space. It also helps in performing fine-motor tasks such as threading a needle. 
• Manufacturing. 3D vision technology in manufacturing checks and directs how products are assembled (checking the size and ensuring accuracy).
• Art/entertainment. Stereo vision is now used to reproduce visual reality for artistic purposes. It’s currently used in 3D movies, virtual-reality headsets, and multi-parallax displays.
• Medicine. Stereoscopic vision has relevance in ophthalmology. For example, clinical stereo-acuity tests are used to manage conditions like strabismus and amblyopia.  

What is Stereoscopic Depth Perception and How Does it Function?

Stereoscopic depth perception is the ability of the eyes to observe an image and interpret it in 3D. It gives you the visual capacity to deduce an object in length, width, size, appearance, and distance.

Stereoscopic depth perception is how you judge an image against other visible options in your visual field. It is classified into two cues.

Monocular Cues

A monocular depth cue happens when your brain can interpret an image using stimuli from one eye, such as in a person with one blind eye.

Monocular depth cues include:

• Image size disparity. Distant images appear to be smaller.
• Overlap or interposition. One image blocks the ability to view another image.
• Motion parallax.⁴ Images further away appear to move slower than those close by. 
• Linear perspective. Angles of two adjacent objects and the distance between them appear smaller and smaller.
• Aerial perspective. It makes distant objects appear blurrier, lighter in color, and less detailed than those close to you.
• Lights and shade. Tells your eyes the position of an object in relation to the light and nearby objects.

Binocular Cues

Binocular cues are more complex and coordinated. Both eyes should be fixated on a similar object, and the images must fuse before optical impulses reach the visual cortex for interpretation.

Examples of binocular depth cues are:

• Binocular fusion. Your brain combines the images from each eye to make a single image.
• Retinal disparity. Each eye produces a slightly different image allowing you to see images in 3D.

How Does Stereoscopic Binocular Vision Differ from Other Types of Vision?

The outstanding characteristic of stereoscopic binocular vision is that both eyes cooperate and observe the same item simultaneously. The brain interprets the visualized object as a single image in 3D. Below are other types of vision distinct from stereoscopic binocular vision. 

Monocular Vision

Unlike stereoscopic binocular vision, monocular vision utilizes visual stimuli from one eye. Someone may be forced to use one eye if the other is impaired. When only one eye is used for vision, depth perception is reduced.

Diplopia (Double Vision)

Diplopia is when someone sees two images of the same object.⁵ It results from ocular misalignment or an optical problem.

Diplopia due to ocular misalignment can be corrected by monocular viewing (using one eye to see). However, monocular viewing cannot correct diplopia caused by optical problems.

Diplopia also reduces depth perception, which affects activities such as driving, reading, and walking.

Different Types of Stereoscopic Vision

There are two types of stereopsis:

Coarse Stereopsis

Also referred to as gross stereopsis, coarse stereopsis determines the depth of objects in the peripheral field of view. It’s important for space orientation while you’re in motion (e.g. when walking down a staircase).

Fine Stereopsis (Quantitative Solidification)

Also referred to as quantitative stereopsis, this type of vision determines the depth of the objects in the central visual area. It’s tested during an eye exam and is based on static differences.

It’s important for performing fine-motor tasks such as threading a needle. Fine stereopsis requires good visual acuity in both eyes to detect small spatial differences. However, it’s easily disrupted by early visual deprivation.⁷

Summary

• Stereoscopic vision is the process in which the brain merges the distinct images captured by each eye to produce a 3D image.
• The mechanisms of eye movement and horizontal offset make it possible for both eyes to perceive depth (the ability to see objects in 3D). 
• Any condition that affects the eyes’ ability to see correctly can affect your stereoscopic vision and impact your ability to judge the distance of objects. 
• A common cause of stereoscopic deficiency is strabismus (crossed eyes). Others include cataracts, amblyopia (lazy eye), brain trauma, eye injury, etc.,
• Stereoscopic vision is used in daily life, medicine, manufacturing, and art.