What is Stereovision - Depth Perception, or 3D Vision?

Stereovision - also known as stereopsis - is our ability to see in three dimensions and judge depth accurately. It is what allows us to understand how far away (or close) objects are, how they relate to each other in space, and how to move confidently through the world.

How does stereovision work?

Each eye sees a slightly different image of the world. The brain combines these two images into a single, three-dimensional view - creating depth perception. This process happens automatically and continuously, allowing us to interact smoothly with our environment.

Why is stereovision important?

Stereovision plays a key role in everyday activities, including:

Catching and throwing objects
Reading and focusing comfortably
Judging distances when walking, stepping or driving
Coordinating hand and eye movements

In children, it is especially important for development, learning, and confidence.

Signs a Child May Have Reduced Stereovision (Depth Perception)

Depth perception problems in children are not always obvious. Many children with reduced stereovision can still see clearly on a standard eye chart, but may struggle with activities that require accurate judgement of distance, movement, and spatial awareness.

Some children adapt well and may not realise their vision is different from others. Early testing can help identify binocular vision problems that might otherwise go unnoticed.

Common Signs of Reduced Stereovision

Children with reduced stereovision or depth perception difficulties may:

Struggle to catch or throw balls accurately
Frequently bump into objects, doorways, or furniture
Find stairs or uneven surfaces difficult
Avoid sports or activities requiring coordination
Hold books very close when reading
Tilt or turn their head when focusing
Close one eye in bright sunlight
Have reduced confidence in physical activities
Seem clumsy compared with other children of a similar age
Experience visual fatigue during close work

These signs do not always mean a child has a stereovision problem, but they can indicate that further binocular vision assessment may be helpful.

Conditions Commonly Associated with Reduced Stereovision

Reduced stereovision can occur when the eyes are not working together effectively. This may be linked to conditions such as:

Strabismus (Squint)

A misalignment of the eyes where one eye may turn inwards, outwards, upwards, or downwards. This can affect how the brain combines information from both eyes.

Amblyopia (Lazy Eye)

Reduced vision in one eye during childhood development, often associated with weaker binocular vision and reduced stereoacuity.

Binocular Vision Disorders

Some children have difficulty coordinating eye movements even when both eyes appear straight.

Following Eye Treatment

Stereovision testing may also be used during or after treatment for binocular vision conditions to assess improvement in depth perception.

Why Early Stereovision Testing Matters

Good stereovision supports many everyday activities including learning, movement, coordination, and confidence. Identifying reduced stereo vision early may help clinicians monitor binocular vision development and support appropriate treatment where needed.

Stereovision testing is commonly carried out by:

Orthoptists
Optometrists
Ophthalmologists
Paediatric vision specialists
Some Doctors such as General Practitioners

The Frisby Stereotests are designed to assess stereopsis using real depth targets viewed naturally without special glasses.

How is Stereovision Measured?

Stereovision is measured using tests called stereotests. These tests assess how well the brain combines input from both eyes and how accurately depth can be perceived. Results are typically measured in seconds of arc, with lower values indicating finer depth perception.

Stereovision is routinely assessed by optometrists (opticians), orthoptists, and ophthalmologists as part of binocular vision testing.

How Do Stereotests Work?

Different types of stereotests exist. Some use special glasses to present separate images to each eye. Unlike many stereotests, the Frisby Stereotest uses real physical depth that can be seen naturally, without the need for glasses. This allows testing in natural viewing conditions, makes it suitable for young children, as well as supporting more reliable results.

When should stereovision be tested?

Stereovision may be assessed:

· During routine eye examinations

· If a child shows signs of coordination or visual difficulty

· When a squint (strabismus) is present

· During or after treatment for amblyopia (low vision in one eye)

Early testing can help identify issues that might otherwise go unnoticed.

Learn more

Explore the Frisby Stereotests