Precautions to Minimise Monocular Clues

The Frisby Stereotest is specifically designed to assess stereopsis (depth perception) without providing any monocular cues.  All Frisby Stereotests have precautions built into them to minimise the chances of correctly responding on the basis of such cues. 

Although monocular cues are a hazard in all stereotests, the Frisby Stereotest (Near) has been judged to have the least susceptibility to monocular cues when compared with other commonly used near stereotests, such as in the study Monocular Cues in Tests of Stereoacuity*.  Misconceptions about monocular cues in the Frisby Stereotest have been caused by incorrect test administration.

For the Frisby Stereotest to work as intended, it must be presented at a slight distance from a plain, well-lit background (approximately 5–10 cm away), and not laid flat on a surface.  Equally, the test plate and the patient’s head must be held still.  Read our Test Procedure for full instructions, which also accompany each test.

When positioned correctly like this, the test effectively eliminates monocular depth cues such as shadows or reflections, ensuring that patients must rely purely on binocular disparity to perceive depth.

By laying the plate flat against a surface such as the box’s pull-down flap, monocular clues can be seen, and this feature is a method to enable the tester to confirm test understanding by the patient if required, by showing the patient the target revealed, and therefore confirming what they are looking for when the test begins.

Over 50 years’ of research and clinical validation confirm that the Frisby Stereotest is a true test of stereopsis, making it a highly reliable tool for detecting binocular vision disorders. Proper training in its use ensures accurate results and prevents the risk of false positives from incorrect test positioning.

If you would like further guidance on administering the test correctly, please contact us for additional support materials and training resources.

* Source: Holmes, J. M. & Leske, D.A. Transactions of Orthoptic Congress, Stockholm, Sweden, 1999).