Lang Stereo Test
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The Lang Stereotest was created to simplify stereopsis screening in children. It is based on two principles: random dots and cylindrical gratings. Random dots of Jules are currently used in stereograms. When seen monocularly, they do not provide form cues, whereas in binocular vision stereoscopic forms are recognized. The disadvantage of most random dots is that they require red/green or polarized glasses.
Cylindrical screens were invented by the Swiss Ophthalmologist and physiologist WR Hess (Nobel Prize 1949) in 1912. The images of the two eyes are separated by a system of fine parallel cylindrical strips. Beneath each cylinder there are two fine strips of pictures, one seen by the right, the other seen by the left eye. These two methods were combined for the first time in the Lang Stereotest. This technique has two advantages: no glasses are required and the eye movements of children can be easily observed.
The Lang Stereotest I measures disparities: Star 600, Cat 1200 Car 550 seconds of arc