![]() Finally, we analyzed and quantified test–retest reliability to determine the variability of the ASTEROID, Randot Circles, and Randot Preschool stereotests. Then, we compared the ASTEROID stereotest to the current clinical standards, Randot Circles and Randot Preschool. We approached this in the following ways: first, we compared the ASTEROID stereotest (taken on a 3D tablet) to our research standard test: a psychophysical stereotest presented on a state-of-the-art 3D projector. The aim of this study was, primarily, to test the validity of the ASTEROID stereotest as a viable clinical test of depth perception. 20 This colorful, interactive test uses an adaptive Bayesian staircase starting at 1000 arcsec to determine each patient's stereo threshold at a fine sampling resolution. To solve the known limitations of Randot Circles and Randot Preschool stereotests (Stereo Optical Company, Inc., Chicago, IL) and to create a more entertaining and adaptive test, a group of researchers at Newcastle University, UK, has developed a new stereotest, ASTEROID (short for Accurate STEReotest On a mobIle Device), in the form of a game on a glasses-free 3D tablet. These tests have their own drawbacks, 14 as they can contain artifacts 15 such as monocular cues, 16 only classify stereo threshold into a set number of discrete values, and have poor test–retest reliability. These shorter clinical tests (e.g., Randot Circles, Randot Preschool) are presented as books, which are certainly less expensive and not nearly as bulky as a large projector system. 13 Shorter tests that are easier to administer are more useful for clinical practice, as they can be used as quick screening tests for binocular vision problems. Such a test would require specialized equipment (such as a large, bulky 3D projector) to isolate the binocular vision system, a dedicated laboratory set-up, trained personnel, and a long and intensive test procedure to ensure the best measurement. 7, 10, 11 Random-dot stereograms have an advantage over other tests of stereo threshold that are used in clinical or research settings, as they provide no monocular cues to depth 8, 12 and therefore probe global stereopsis.Ī psychophysical, research standard stereoacuity test would be the most effective way to measure stereo threshold. In an RDS, the image structure is defined solely by the correlation between left and right eye images the random dot textures of the stereograms contain no object or contour structures when viewed monocularly. 9 It is generally considered best to measure stereopsis using stimuli in which binocular disparity is the only cue to depth, such as random-dot stereograms (RDSs). This is the smallest depth interval between two stimuli that a subject can detect using only stereoscopic cues. The standard quantitative measure of stereopsis is the stereo threshold, or stereoacuity. 8 Global stereopsis, on the other hand, must be probed with more complex targets that lack monocular cues. The contour targets in such stereograms contain some monocular cues, allowing them to be solved by patients with abnormal binocular vision. 7 Local stereopsis can be probed with simple targets containing contour elements. 6 Stereopsis can be separated into two distinct forms: global and local. 5 The term “stereopsis” refers to the impression of depth arising from binocular disparity and represents one of the truly binocular cues to depth. The brain measures this horizontal disparity between the images of the two eyes and processes these images to produce a sensation of depth. Because a human's two eyes are placed in different horizontal positions on the head, each eye perceives the same three-dimensional (3D) scene from a slightly different angle. 1 – 4 The primary advantage of binocular vision lies in the neural combination of the visual overlap between the two eyes and the resulting perception of depth. Binocular vision has been shown to be superior to monocular vision when performing complex visual tasks.
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