Abstract
Stereoscopic vision plays a critical role in visual perception; however, it is difficult to assess. In clinical settings, stereoacuity is assessed with clinical stereotests. Observers can use monocular cues to deceive some of the most common stereotests, such as the Titmus test. The Randot test has been found free of monocular cues, and here we confirm that result by testing observers under monocular viewing. However, there is a common misconception that only monocular cues can be used to deceive stereotests. Here we demonstrate that binocular non-stereoscopic cues can also be used to pass the Randot, by testing participants with the test rotated, a condition that abolishes stereopsis, and comparing the performance to a monocular viewing condition. We also assessed the Random Dot Butterfly test and discovered considerable amounts of non-stereoscopic cues, including binocular cues in the Circles that can be used to deceive the test. Participants with amblyopia had more difficulty using non-stereoscopic cues than neurotypical observers. We gathered normal-viewing Randot stereoacuities for 110 participants (90 neurotypical and 20 with amblyopia) and compared them to psychophysical stereoacuities (our gold standard). The Randot test showed low positive normalized predictive values for detecting stereoblindness. It could perfectly detect stereo-impairment but with a low sensitivity.
Highlights
One important aspect of clinical assessment of visual function is the assessment of binocular vision[1]
The availability of these cues to pass clinical stereotests has been clearly demonstrated in the Titmus Fly and Titmus Circles (Stereo Optical Co., Chicago, IL, USA)[18,19,20,21,22], the Random Dot E (Stereo Optical Co.)[23] or the Frisby-Davis 2 (Clement Clarke International, Harlow, UK)[24]
None of the participants who had measurable stereopsis when tested right side up had measurable stereopsis in the Randot Shapes when viewed with their weaker eye patched
Summary
One important aspect of clinical assessment of visual function is the assessment of binocular vision[1]. Cooper[25] noted that the cues are probably present in random-dot stereograms: he termed them as decorrelation cues The possibility that these binocular non-stereoscopic cues might be used by patients who lack genuine stereopsis to correctly report the shapes in clinical random-dot stereograms was noted by Charman and Jennings[26]. They observed that shapes in the random-dot stereograms of the TNO could be identified when the test was rotated 90 degrees so that horizontal disparities become vertical. It will not be discussed further as it is a depth cue that unlike the ones discussed above can be classified as stereoscopic[33]
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