Vision Screening Online Training Program - Stereo Acuity Test Stereo Butterfly

Vision Screening Online Training Program

Module 7 (continued): Stereo Acuity Test - Stereo Butterfly
(C&TC: Usually performed by a nurse or medical assistant)

Testing for stereo acuity is checking the child’s ability to see the depth or distance of an object. In order to have depth perception, both eyes must work together. When both eyes are properly functioning, the brain fuses the two images gained from each eye to form one image. If one eye is not functioning properly, as in the case of strabismus or amblyopia, the child’s brain will be unable or have a difficult time fusing images, affecting their ability to see depth properly. In these cases, the child will not be able to see the image portrayed on the stereo acuity test.

Stereopsis measurement should be performed before the eyes are dissociated by tests such as the cover test.

Ages: Age 3 years through 8 years (C&TC) or 3rd grade (Early Childhood and school screenings).
Purpose: To check for problems with stereo acuity or depth perception which tend to be an occurrence for children with strabismus.
Description: By noting if the child is able to see the raised “butterfly” while wearing special glasses, the observer is able to check for stereo acuity problems.

Stereo butterfly card, and polarized glasses.

Image of a Stereo Butterfly Card and polarized glasses.
Stereo Butterfly. Stereo Optical Company, Inc. Chicago, IL.

Facilities: A well-lit, glare free location
  1. Place the polarized glasses on the child. Do not remove prescription glasses if the child wears them.
    • (Hint: If the child hesitates, tell him or her that you are putting on glasses that look like sunglasses or that they are magic glasses so they can see magic pictures.)
    • If the polarized glasses are too large for the child, put a short piece of masking tape on the top of the glasses and use the other end of the tape to hold the glasses on the child’s forehead.
    • When showing the child the test targets, be sure he/she keeps his/her head straight up, as tilting to one side or allowing the glasses to tilt on his nose, will interfere with the test.
  2. At 20 inches away from the child, hold the stereo butterfly card upright. Ask the child what the figure is that they see. If the child cannot name it or has difficulty, point at the butterfly figure on the card and say “that’s a butterfly. Show the card to the child 5 times.
    • (Note: Slightly rotate (don’t tilt!) the card from side to side or up and down to pick up light in order to have optimal viewing of the stereo image)

    Screener at 20 inches away from child.

  3. Move back to 40 inches from the child and repeat the test.

Screener at 40 inches away from child.

Pass: Child is able to point to the butterfly at least 4 times at 20 inches and 40 inches.
The child cannot distinguish the butterfly figure in the stereo butterfly card, or can only see it when the card is approximately 20 inches or closer.


Screening for stereo acuity is testing a child's ability to see images 3-dimensionally or to check depth perception.

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