The easy-to-use test is applied for the early detection of problems in stereoscopic vision in children and infants, but also in adults. Two versions are available (LANG-STEREOTEST I and II) which only differ in the type of stereoscopic objects to be recognized.
The test-plates are solid and can easily be carried around due to their handy postcard-size.
The LANG-STEREOTEST for the first time combines two functional principles of stereograms:
• The random dots of Julesz
• The grid of cylinders of W.R. Hess
The random dots of Julesz are applied in different stereograms using polarized glasses or the red-green-glasses. Seen with only one eye (monocular vision), these stereograms do not show any shapes, while, upon binocular inspection, figures, typically in different depths, can be seen.
Grids of cylinders were invented by the Swiss ophthalmologist and physiologist W. R. Hess. The images of the two eyes are separated by a system of tiny parallel cylindrical strips. Under each cylinder, there are two tiny strips of picture: one can only be perceived by the right, the other only by the left eye.
In contrast to the more traditional methods for examination of stereopsis, the Lang-Stereotest requires no glasses and the eye movements of the patient can be much better observed by the examiner, thanks to the first-time combination of the two technologies mentioned above.
Observing the patients eye-movement during testing has been noticed to be of particular importance in small children: once the child has recognized the different stereoscopic figures that are shown on the test-plate, he subsequently will start to look repeatedly at these figures.
Furthermore, due to the application of the random dots and the lacking of picture-outlines in the LANG-STEREOTEST, as well as in similar test using this principle (e.g. a version of the Randot-test), all monocular stereoscopic stimuli are completely eliminated. It is just the disparity of the figures represented, that generates a perception of depth and hence enables a precise perception of the shapes. Since primarily children are investigated, three objects have been chosen which are already common in this stage of life.
The three objects (cat, star and car) differ in disparity and perceived distance: the cat is closer than the car.
The test combines random dots and a lenticular grid surface, and has been designed for quick screening of binocular vision in all groups of age, including very young children. While the test card is presented at reading distance, the patient is asked about what he sees and his eye movements are being observed.
