LANG-STEREOTEST

Development and characteristics:

The LANG-STEREOTEST was developed by the Swiss ophthalmologist Joseph Lang in the beginning of the eighties. The easy-to-use test is applied for the early detection of problems in stereoscopic vision in children and infants, but also in adults. Since many years, the test has been very much estimated by ophthalmologists, paediatricians and doctors working in the primary health care or in prevention. Two versions are available (LANG-STEREOTEST I and II) which only differ in the type of stereoscopic objects to be recognized. The LANG-STEREOTEST II additionally contains a picture that can be recognized with only one eye (a star). The test-plates are solid and can easily be carried around due to their handy postcard-size. These are distributed together with a fitting case, a brief instruction as well as a detailed test-description in several languages.

 

The Importance of stereopsis:

Stereopsis or depth perception can be characterized as the highest degree of binocular vision. It therefore represents one of the most important partial functions of the human visual sense. In a limited extent, stereoscopic vision is actually possible with only one eye, for example due to perspective and shadow effects or parallel displacement, as well as with certain forms of strabismus (with the so-called anomalous retinal correspondence which occurs when non-corresponding retinal points have the same sense of visual direction). However, a completely missing or limited stereopsis can lead to severe handicaps in many life-domains and professions. This is a reason why this function should already be regularly examined in children and later within the education of jobs requiring an accurate stereoscopic vision.

 

Functional principle of the LANG-STEREOTEST

The LANG-STEREOTEST for the first time combines two functional principles of stereograms: The random dots of Julesz and 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 (Nobel Prize in 1949) in 1912. 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.

Particularities in comparison to other stereo-test methods:

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.

Other common, so-called haploscopic test-procedures, such as the Titmus-test are based on polarization and therefore require special glasses. The TNO-test uses the red-green-dissociation and hence needs corresponding red-green-glasses as well. With the LANG-STEREOTEST however, the dissociation in haploscopic pictures is ensured by the cylinder gratings on the surface of the test-plate.

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 – in the LANG-STEREOTEST I a cat, a star and a car, in the LANG-STEREOTEST II an elephant, a car and a moon – differ in disparity and perceived distance, the cat respectively the elephant being the closest.