Different test procedures are used in different countries (USA, Great Britain, Germany) and in different professions (ophthalmologists, optometrists), in order to measure the vergence angle, i.e. the angle between the visual axes of the two eyes. There is no scientific agreement which vision test procedure is most appropriate to determine whether visual strain of a person is caused by a weakness in binocular coordination and which treatment is indicated. The visual screening tests used by occupational physicians need improvement since the test of heterophoria (which is frequently used for this purpose) is hardly correlated with visual strain. However, tests of fixation disparity allow to detect about 70 % of persons with visual strain, with about 25 % false positive cases (Jaschinski, 2005).
In order to increase the diagnostic power of binocular vision tests, tests of dynamic vergence might be considered. Gall and Wick (2003) showed that persons with visual strain often have a reduced velocity in vergence changes tested with prisms that force the eyes to perform frequent changes between convergent and divergent states.
It is the aim of our applied research of binocular vision to contribute to the development of test procedures, that are useful for the diagnostic of visual strain.
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