[The Titmus Fly Test--evaluation of subjective depth perception with a simple finger pointing trial. Clinical study of 73 patients and probands].

Background: Subjects with different binocular defects were tested for their stereoscopic achievement. The determination of the subjects limiting disparity (in seconds of arc) was not used to characterize their stereoscopic acuity, but the subjective depth perception as a simple clinical method.

Methods: 52 subjects with different binocular defects and 21 normosensoric volunteers were examined for their stereoscopic achievement. In our stereoscopic measurement we ask the subjects to indicate the subjective plane of the fly's wings manually by their own finger, or by a hand-held plastic card, or with the aid of a mechanic instrument. The results of the different methods were compared with each other.

Results: There were no differences between the results within the group of normosensoric subjects. The patients with reduced abilities exhibit significantly different results in depth perception when measured manually or by machinery. The subjective depth localization correlates well with the binocular defect and is independent of the used stereoscopic method.

Conclusions: The basic finger test of the subjective level of the Fly's wings gives a quite reasonable approximation of local stereoscopic depth perception. In terms of practical investigation the finger test shows in convincing manner whether the individual stereoscopic ability is based on normal, subnormal or anomalous binocular interaction.