Why Test for 3D Vision?

Dr. Russel Lazarus, July 11, 2021

3D vision tests allow eye doctors to diagnose lazy eye, eye turns and other vision problems. 

If you or your child has difficulties with 3D vision, it may affect their confidence, school performance and even enjoying sports.

3D vision is also known as stereopsis or depth perception, and is your brain’s ability to see in 3D by uniting the separate images sent to the brain from your two eyes. Reduced 3D vision could be due to lazy eye. or an eye turn.

What is stereopsis?

Stereopsis is another way of saying 3D or depth perception.

Good depth perception requires the two eyes to be working together.

For the brain to achieve stereopsis, a number of conditions must be met;

  1. The eyes must be aligned – pointing in the same direction
  2. Each eye must have adequate visual acuity
  3. The image from each eye must focus on the central part on each retina

Images falling on slightly different places on the retina of each eye give each eye a slightly different perspective. This is known as disparity, and it is how stereopsis is tested.

How is stereopsis measured?

Stereopsis is measured using specific equipment known as ‘stereo tests’. The eye doctor will ask you to wear what looks like a pair of sunglasses, then show a book with images, often of a butterfly or reindeer, cartoon characters or circles and other shapes.

These images are actually in 3D, and as you identify the 3D images ‘popping out of the page’ your 3D vision (stereopsis) is measured.

The more images seen correctly, the higher your level of stereopsis, measured in seconds of arc.

A person with a lazy eye or an eye turn will not be able to correctly pick all the 3D images.

SEE RELATED: 3D Vision Is More Important than You Think

If you have any concerns with your child’s 3D vision, contact an eye doctor near you who can conduct a stereopsis test.

Find an eye doctor near you

Common Stereopsis Tests

Random Dot Stereo Tests

Various tests include the use of random dot stereo targets that are viewed with polarized glasses. Some tests, such as the Random Dot E, use single plates for testing, while others may use animals or shapes embedded in the test. The level of disparity measured varies from test to test.

These types of tests can indicate whether a patient can see 3D effects in a 3D movie or “Magic Eye” books.

Titmus Stereo Test

The Titmus stereo test consists of a combination of contour targets. The most common targets that are used for screening are animals for children, a series of circles for older patients, and a large stereo fly.

While the animal tests from 400 down to 100 seconds of arc, the circle test is from 800 to 40 seconds of arc. From the head to the thorax, the fly has varied stereo and disparity values from about 700 to 400 seconds of arc.

TNO Stereo Test

A random dot pattern is used for the TNO stereo test. Green and red glasses are required to dissociate the patient. The test contains hidden objects with multiple plates and can measure disparity values down to 15 seconds of arc.

Lang Stereo Test

This test does not need the 3D glasses. This test is a random dot test that can test disparity values of 1200 arc seconds to 200 arc seconds.

Frisby Stereo Test

Similar to the Lang test, the Frisby test doesn’t require dissociating glasses. Instead, the test uses plates that are transparent and with different thicknesses to alter the disparity in the test. The test can be done at various distances which alters the test’s discrepancy. It measures values between 600 and 20 arc seconds.

Stereopsis and lazy eye

Since stereopsis depends on good vision in both eyes, excellent oculomotor control and the development of binocular vision, it is often regarded as the gold standard for binocular visual function.

It’s important to undergo a stereo vision test so that your eye doctor can identify diseases such as amblyopia (lazy eye) and strabismus (eye turns).

LEARN MORE: Guide to Vision Therapy for Lazy Eyes

If you think you or your have issues with depth perception, schedule an appointment with an eye doctor near you who can test your stereoscopic vision.