Investigation of Retinal Position with Converging Lines of Sight
Meissner (23) was the first to investigate the cyclorotary position of the retinas with different and especially with symmetrical convergence positions. He began with the observation that if one fixates a point behind or in front of the plane, a line in the median plane and vertical to the fixation surface appears in parallel double images only at a quite specific tilt of the fixation plane to the head. If the fixation plane is relatively higher, the double images diverge upward, and if they are crossed, the fixation plane lies relatively lower and the crossed double images converge upward. One can make the double images parallel by tilting the observation line with its upper end away from the head in the first case or toward the head in the latter case. From the acute angle which the observation line makes with the fixation plane, and from the convergence angle of the lines of sight, Meissner then sought to calculate the angle between the vertical dividing line and the fixation plane. This method is useful in principle, but the way in which Meissner used it contains several sources of error which I have specified earlier (17).
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