Frisby stereotest

stereotest, Frisby 

A stereoacuity test consisting of a square transparent plate on which four similar patterns (resembling a random-dot stereogram) are printed on one side. In the central part of one of the four patterns is a circular area, which is printed on the other side of the plate and can appear in depth. The plate (made of plastic or glass) comes in three thicknesses: 6, 3 and 1mm. By using the three plates and presenting them at different distances the test can produce a retinal disparity of the circular area between 600 and 7 seconds of arc. In this test the patient's head must be kept still to avoid monocular cues. The plate can be turned upside down or rotated to alter the position of the pattern with relief. Syn. Frisby test. See random-test stereogram.
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann