The Stereo Butterfly (OS-149) tests and evaluates random dot stereo depth perception for both gross stereopsis (2500 to 1200 seconds of arc) and fine depth perception. The figures present on the test can be identified only with polarized 3-D viewing glasses (included) and appear to pop off the page three dimensionally! This random dot test helps identify amblyopia and strabismus. The butterfly offers three different levels of gross stereopsis and offers no monocular visual clues:

The Stereo Butterfly Test also includes: Graded circle test (800 to 40 seconds of arc) Animal test for children (400 to 100 seconds of arc)