ABSTRACT
BACKGROUND: For prism correction of associated phoria (at 5-6 m viewing distance), Hans-Joachim Haase developed--among other tests--the prevalence test, which consists of a central fixation target and two triangles that appear stereoscopically about 1.5 m in front of or behind the fixation target; the vertex of each triangle is directed towards the centre of the fixation target. Only when both eyes contribute equally to the perception of visual directions do the triangles appear centred (equivalence), while any perceived horizontal offset between the triangles and fixation target indicates a prevalence of one eye. Provided that monocular vision is equal in both eyes, Haase interpreted ocular prevalence as being due to a small vergence error (fixation disparity with a shift of retinal correspondence). This vergence error indicates, according to Haase, a (not yet fully corrected) heterophoria. From practical experience, Haase developed rules for transferring ocular prevalence into equivalence with prisms (MKH). If equivalence has been reached, Haase assumed that the heterophoria was fully corrected. METHOD: In 19 subjects we examined whether spherical and prismatic corrections reduce ocular prevalence. The perception of the subjects was ascertained with three methods: they were asked 1. to describe their perception orally--as proposed by H.-J. Haase--, 2. to make a drawing of their perception, and 3. to align the position of the stereo images to the central fusion target with a computer-controlled device. RESULTS: Based on the group mean, the three methods did not reveal a consistent reduction of prevalence. Only in two individuals did the drawing and the computer-controlled alignment showed reductions of prevalence that were confirmed statistically on the individual level. However, it has to be noted that these two individuals not only received prisms but also a correction of their hyperopia and anisometropia. CONCLUSION: The prevalence of one eye is a common phenomenon in normal binocular vision (with the amount of prevalence often being different for triangles presented in front of or behind the fixation target). In only a few subjects can prevalence be reduced with prisms. Equivalence as reported by oral description (method 1) was often not confirmed by drawing (method 2) or by the computer-controlled alignment (method 3). As an explanation for the differences between methods 1, 2 and 3 we assume that the oral description of the test perception was influenced by imponderables such as the expectation on the side of the experimenter and/or the desire to please on the side of the subject. The present results do not support the prevalence test--as developed by H.-J. Haase--for the correction of associated phoria.
Subject(s)
Depth Perception , Eyeglasses , Strabismus/diagnosis , Strabismus/rehabilitation , Vision Disorders/diagnosis , Vision Disorders/rehabilitation , Vision Tests/methods , Adult , Female , Fixation, Ocular , Humans , Male , Middle Aged , Prosthesis Fitting/methods , Reproducibility of Results , Sensitivity and Specificity , Treatment Outcome , Vision DisparityABSTRACT
BACKGROUND: An unequal weighting of the eyes in the directional perception of stereodisparate objects, is referred to as ocular prevalence of the right or left eye, respectively. Between 1962 and 1964 H.-J. Haase developed a valence test for the prismatic correction of heterophoria. He suggested that there would be less prevalence for stereo images presented in front of or behind a reference plane, and that this asymmetry of prevalence may be related to the direction of the associated heterophoria (eso- or exophoria). According to H.-J. Haase, the asymmetry may indicate a fixation disparity with a corresponding shift in retinal correspondence. Hence, the valence test could be an indicator for the prismatic correction of heterophoria. METHODS: Prevalence was tested in 37 subjects, using three methods: The subjects were asked to describe their perception (1), to make a paper drawing of their perception (2), and to align the position of the stereo images to the central fusion target with a computer-controlled device (3). METHODS 2 and 3 were used to reduce a possible suggestive influence on part of the investigator. The associated heterophoria was determined with the cross test by H.-J. Haase. RESULTS: Depending on whether the triangular stereo images were presented behind or in front of the reference plane, more or less prevalence was measured (mean values) in the group with exophoria than in the group with esophoria. These results were confirmed with all three methods. The asymmetry of prevalence was correlated with the direction of the associated heterophoria with r = 0.5. CONCLUSION: Statistically, these results confirm Haase's hypothesis of a relation between the asymmetry of ocular prevalence and the direction (eso- or exophoria) of the associated heterophoria. Since this relation holds true only for the group mean value, but not for each individual, the valence test cannot be generally recommended as an adjunct for the prismatic correction of heterophoria.
Subject(s)
Depth Perception/physiology , Eyeglasses , Orientation/physiology , Retina/physiopathology , Strabismus/physiopathology , Vision Disorders/diagnosis , Vision Disparity/physiology , Adult , Diagnosis, Computer-Assisted , Female , Functional Laterality/physiology , Humans , Male , Middle Aged , Psychomotor Performance/physiology , Reference Values , Sensitivity and Specificity , Statistics as Topic , Strabismus/therapy , Vision Disorders/physiopathology , Vision Disorders/therapy , Vision Tests , Vision, Binocular/physiologyABSTRACT
BACKGROUND: The theory of the "Measuring and Correction Methods of H.-J. Haase" (MCH) states that a small misalignment of one eye, called fixation disparity, indicates a difficulty in overcoming a "vergence position of rest" that is different from ortho position. This difficulty, so the theory, can cause asthenopic complaints, such as headaches, and these complaints can be relieved by prisms. The theory further claims that fixation disparity can be ascertained by a series of tests which depend on the subject's perception. The tests most decisive for the diagnosis of a so-called fixation disparity type 2 consist of stereo displays. The magnitude of the prism that allows the subject to see the test configurations in symmetry is thought to be the one that corrects the "vergence position of rest". METHODS: Nine subjects with healthy eyes in whom a "fixation disparity type 2" had been diagnosed were selected for the study. Misalignment of the eyes was determined according to the principle of the unilateral cover test. Targets identical for both eyes were presented on the screen of the Polatest E. Then, the target was deleted for one eye and the ensuing position change of the other eye was measured, using the search coil technique. This test was performed both with and without the MCH prism. RESULTS: In all 9 subjects the misalignment was less than 10 minutes of arc, i.e. in the range of normal fixation instability. Averaging across the 9 subjects, the deviation of the eye (misaligned according to MCH) was 0.79 +/- 3.45 minutes of arc in the direction opposed to that predicted by the MCH, a value not significantly different from zero. The MCH prism elicited a fusional vergence movement the magnitude of which corresponded to the magnitude of the MCH prism. CONCLUSION: Ascertaining fixation disparity with the MCH is unreliable. Accordingly, it appears dubious to correct a "vergence position of rest" on the basis of the MCH.
