Contribution of vergence adaptation to difference in vertical deviation between distance and near viewing in patients with superior oblique palsy

Variation of Binocular-Vertical Fusion Amplitude with Convergence

“…In another study, Gräf et al 53 found that in a group of 19 patients with superior oblique palsy, the amplitude of vertical deviation decreased with viewing distance in 4 patients. The remaining patients (61 patients in Ohtsuki et al 46 and 15 in Graf et al 53 ) in both studies either showed the opposite pattern of vertical deviation with viewing distance. Vertical deviation was smaller at far than near viewing distances or showed no difference in vertical deviation between near and far.…”

“…The magnitude of vertical tropias presented under binocular viewing conditions could be smaller at near viewing distances than at far viewing distances if the fusional vertical vergence attempted to reduce the tropia. Indeed, Ohtsuki et al 46 observed that in a group of 84 patients with superior oblique palsy, 23 had smaller vertical deviations at a near viewing distance than at a far viewing distance. In another study, Gräf et al 53 found that in a group of 19 patients with superior oblique palsy, the amplitude of vertical deviation decreased with viewing distance in 4 patients.…”

“…Vertical deviation was smaller at far than near viewing distances or showed no difference in vertical deviation between near and far. Based on the results of their prism-adaptation experiment, Ohtsuki et al 46 proposed that the more typical reduction of vertical deviation at near could be explained in part by an adaptive component of vertical vergence, which could be stimulated by attempted efforts of binocular vertical motor fusion. 54 The results for the remaining patients in both these studies contradict this prediction.…”

“…The vertical vergence response persisted after one eye was occluded and is described as a vertical phoria adaptation. Similarly, based on the results of their prism adaptation experiment, Ohtsuki et al 46 proposed that the reduction in vertical deviation in patients with superior oblique palsy could be related to the adaptable component of vertical vergence. Because in both experiments I and II, the vertical vergence stimulus was incremented only after subjects reported fusion of the targets, it raises the possibility that the VFA could be extended by a short-term adaptable component of vertical vergence.…”

“…As does convergence, 44 the vertical vergence system exhibits hysteresis after sustained periods of disparity stimulation. 33,45,46 For instance, Ogle and Prangen 33 observed that vertical vergence could respond to vertical disparities as large as 6 ⌬ within 3 to 10 minutes. The vertical vergence response persisted after one eye was occluded and is described as a vertical phoria adaptation.…”