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Adrien Chopin, Daphne Bavelier, Dennis M Levi; The prevalence and diagnosis of “stereoblindness”: A best evidence synthesis. Journal of Vision 2019;19(10):262b. doi: https://doi.org/10.1167/19.10.262b.
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© ARVO (1962-2015); The Authors (2016-present)
Stereoscopic vision is the ability to perceive depth from the difference of the two eyes’ viewpoints. Some people are totally deprived of this ability. Surprisingly, there is no consensus on the prevalence of total stereoblindness. The value strongly depends on how it is measured, and some stereoblind participants can deceive stereotests. This study aims at determining the prevalence of stereoblindness, clarifying the concept and standardizing the measure. First, we studied the dependence between reported prevalence in young healthy adults and tested presentation times and disparity magnitudes. Second, we identified four approaches to bracket the likely stereoblindness prevalence from the literature. We can take the median of (1) all studies, (2) studies with presentation times < 200ms, (3) and, in addition, with a minimal disparity < 900″ and a maximal >900″, and (4) studies controlling for eye movements with afterimages. Finally, we propose an ecological definition of stereoblindness as the inability to detect everyday life disparities and propose a quick way to test for it by modifying a common clinical stereotest. It is well-known that stereo-impairment rates decrease with longer presentations. Surprisingly, we did not confirm this data for total stereoblindness rates. We bracketed the stereoblindness prevalence between 6.1% and 7.7%. Ninety percent of everyday disparities are smaller than 1314″. Therefore, we define ecological stereoblindness as the inability to perceive disparities < 1300″. To test for stereoblindness, we recommend modifying the Random Dot Butterfly stereotest as follows: (1) test at 62 cm (1300″), (2) randomly pick a set of glasses among two, one having the left and right filters exchanged, (3) ask whether the butterfly appears as floating or as a hole, (4) score as pass for 10 out of 11 correct responses, (5) repeat the procedure twice after two errors, and score as stereoblind if the repeat is also failed.
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