Torsional fusional vergences and assessment of cyclodeviation by synoptophore method.

Two special slides, one in front of one eye and one in front of the other eye, were placed in the housings of a synoptophore. The slides were originally designed for the diagnosis and measurement of cyclodeviation, but they were utilised in this study for the measurement of torsional fusional vergence. This was measured by rotating one of the housings of the synoptophore and noting the point of appearance of cyclodiplopia, which was taken as the end point. For measuring vertical torsional fusional vergence the subject was required to fuse the vertical line of the slide with the circle and the vertical line of the slide with the cross, and for measuring horizontal torsional fusional vergence he was required to fuse the horizontal line of the slide with the circle and the horizontal line of t-he slide with the cross. Incyclovergence was found to be greater than excyclovergence in all the 3 positions of gaze (straight, up, down) studied. The mean amplitude of torsional fusional vergence was lowest in the primary position. Torsional fusional vergence was much less with horizontal lines than with vertical lines in all positions of gaze. The use of the horizontal line of the slide with the cross would be more advantageous for the diagnosis and measurement of cyclodeviation by the synoptophore method, as the amplitude of cyclofusion is minimal in the horizontal meridian.