Whatever the test symbol or the test procedure, the RDSs used in the clinic are simpler than those conducted in a laboratory environment. A previous study has confirmed that increasing dot size may improve accuracy in detecting binocular disparity - slightly, but significantly. They found that psychophysical performance decreases with smaller dot size, and stated that smaller dots might decrease the local correlation variability. In Henriksen’s study, the size of half-matched RDSs (half the dots in RDSs are correlated and half are anticorrelated) was set at 0.025°, 0.05° and 0.075° respectively. Several researchers have discussed whether dot size in a RDS could affect the test result. The mechanisms underlying these differences have not been clearly established. Although the measurements are all based on detecting the minimum disparities a subject is able to distinguish, the test result evaluated with different stereotests may differ from each other : For example, the stereoacuity measured with the TNO test is worse than the acuity measured with other methods, either in a normal population or in patients with abnormal binocular vision. In the TNO test, the test shapes are disks with a missing sector and the two stereo elements printed in red and green for viewing with red/green anaglyph stereo glasses. In the random-dot E stereo test (Vision Assessment Corporation, Illinois, USA), the letter E is hidden in a random dot array, but can be perceived with the aid of polarising spectacles that divide the images seen by the two eyes. The shape is distinguished by a real difference in depth and can be perceived without the help of any other appliance. In the Frisby stereotest (Stereotest Ltd., Sheffield, UK), the subject is asked to identify a shape hidden in an array of randomly arranged triangles of varying sizes. In Gantz’s research, the density of RDSs lower than 0.39% was considered a ‘local’ stereo target otherwise, it was considered a ‘global’ stereo target. From this point of view, a test pattern consists of a small number of random dots and may also be considered ‘local’. For example, ‘Local’ stereopsis is traditionally defined by the use of a small number of dots to form a pattern, while ‘global’ stereopsis involves the use of many dots to form a pattern. In neurophysiology research, local and global stereograms may be determined by the number of dots contained within the stereogram.
However, the two mechanisms cannot be entirely separated. The neural processing of ‘local’ and ‘global’ stereopsis may be different. the Pacman hidden in TNO stereotest (Lameris Ootech BV, Ede, Netherlands), is considered as ‘global’.
the circle pattern in the Fly Stereo Acuity Test (Vision Assessment Corporation, Illinois, USA), is considered as ‘local’, while the stereopsis to detect random dot-based stereo target, e.g. In clinical practice, the stereopsis to detect contour-based stereo target, e.g.
The advantage of this technique is that it eliminates monocular clues more thoroughly than contour based stereo tests. Random-dot stereograms (RDS) are widely used in the clinical evaluation of stereopsis. The Creative Commons Public Domain Dedication waiver ( ) applies to the data made available in this article, unless otherwise stated in a credit line to the data. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material.
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