Long stereo test
The Lang stereo test , named after its developer, the Swiss ophthalmologist Joseph Lang, is a test method for examining and assessing spatial vision ( stereopsis ), especially in children and toddlers. On an area the size of a postcard, it shows three test images (cat, star and car), which are presented in different disparities of 1200, 600 and 550 arc seconds at a distance of approx. 40 cm. Compared to other methods, the method has the advantage that no further glasses have to be put on to separate the visual impressions (e.g. red-green glasses or polarization glasses). This makes examining young children much easier and also allows eye movements to be assessed . Another advantage is the quality of the examination results. While other test methods are used for existing anomalies, e.g. B. microstrabismus , can allow positive results, the result of the long stereo test will usually be negative in these cases.
It is nevertheless possible that patients with amblyopia caused by high anisometropia ( refraction amblyopia or amblyopia ex anisometropia ) achieve a positive result. The test is therefore unsuitable as a substitute for a visual acuity test .
In practice, this test is also suitable as a quick screening method, for example when it comes to distinguishing pseudostrabism (e.g. in epicanthus ) from real strabismus . In the positive case it suggests an intact stereopsis. For this reason, it is also suitable for use in pediatric practices or by opticians .
Working principle
The functionality of the long stereo test is based on a combination of the principles of random dots (according to Julesz) and the cylinder raster method (according to Hess). While the random dots are used as stochastically arranged points in various stereograms in connection with polarization or red-green glasses, the cylinder raster method uses a system of finest, parallel arranged half-cylinders to separate the visual impressions of both eyes. It is therefore not necessary to wear additional glasses. However, it is not possible to display and thus carry out the test by means of projection or on a screen.
Long stereo test II
A further development of the long stereo test is the long stereo test II . The principle is the same, and it is also used to examine the stereopsis, but has somewhat finer images with a disparity of 600 (elephant), 400 (car) and 200 arc seconds (crescent moon). There is also another image, a star that can also be recognized monocularly. It is intended to improve alertness in young children.
See also
literature
- Herbert Kaufmann (Ed.): Strabismus. With the collaboration of Wilfried de Decker et al. Enke, Stuttgart 1986, ISBN 3-432-95391-7 .
- Joseph Lang: microstrabismus. The importance of microtropy for amblyopia, for the pathogenesis of the large squint angle and for the heredity of strabismus (= library of the ophthalmologist. Issue 62). 2nd, revised and expanded edition. Enke, Stuttgart 1982, ISBN 3-432-83502-7 .
