Correct Frisby Stereotest Presentation: Eliminating Monocular Cues

The Frisby Stereotest measures real physical depth — the target disc is embedded within the plate and sits at a genuinely different depth plane from the background when the plate is held correctly in front of it. This is the mechanism that eliminates monocular cues and makes the Frisby unique among clinical stereotests.

A small number of studies published in the 1980s and 1990s reported the presence of monocular cues in the Frisby Stereotest. These findings have since been attributed to incorrect test presentation — specifically, holding the plate flat against or close to a background surface, which collapses the real depth difference the test relies upon and can introduce shadow or edge artefacts visible monocularly. This is not a design limitation; it is a presentation error that invalidates the test entirely, in the same way that any clinical instrument produces invalid results when used outside its specified conditions.

Correct Presentation 

Incorrect Presentation

When presented correctly — plate held several inches in front of a plain background — the Frisby Stereotest eliminates monocular cues by design. All published studies citing monocular cues should be interpreted in the context of whether correct presentation protocol was followed.

For full test instructions, see the Test Instructions page.