About Frisby Stereotests
Real Depth – Test objects are viewed with natural vision
All Frisby Stereotests present ‘real depth’ -because solid objects are viewed with natural vision. That is, they do not use stereograms to create depth effects. This avoids the disadvantages of stereograms for some patient groups. For example, some young children refuse to wear red/green or polaroid spectacles. Also, some orthoptists believe that such spectacles can be dissociating if the patient has fragile binocular single vision, and thus they can give a misleading result. Moreover, some practitioners are concerned about infection risks from spectacles worn by many different people.
Easy to Use
Frisby Stereotests have been designed as easy to administer. They are made of simple materials and they involve simple presentations. Most patients find it easy to understand rapidly the task required of them and the tester has little or no difficulty in learning how to present the tests.
All Frisby Stereotests permit repeated testing without the patient learning how to pass for the wrong reasons. This is particularly advantageous if a patient is re-tested over a course of treatments or investigations.
All Frisby Stereotests allow the tester to check the patient’s understanding of the task in preliminary ‘training’ or ‘demonstration’ trials. This is a further advantage that flows from the property of repeated testing being possible.
Precautions to minimise monocular clues
All Frisby Stereotests have precautions built in to them to minimise the chances of correct responding on the basis of monocular cues. Such cues are a hazard in all stereotests. In a recent study, the Frisby Stereotest (Near) was judged to have the least susceptibility to monocular cues when compared with other commonly used near stereotests (Holmes, J. M. & Leske, D.A. Monocular clues in tests of stereoeacuity. Transactions of Orthoptic Congress, Stockholm, Sweden, 1999).
Of course, it is necessary for Frisby Stereotests to be presented correctly to avoid monocular cues, as described in the Instructions Booklet supplied with each test. In particular, the tests must be viewed squarely and stationary, with head held still, once testing proper has begun (i.e. after the initial explanatory or ‘training’ phase of the test procedure, during which monocular cues can be exploited to advantage to ensure that the patient grasps what is required of them).
Also, the plates must be shown lifted above a clear background by about 5-10cm, because if a plate is laid flat on a surface the target can become visible monocularly from shading cues.