Displacement of the egocentric visual midline in altitudinal postchiasmatic scotomata

Vertical and horizontal bar bisection was assessed in six patients with homonymous altitudinal scotomata, four of whom had additional hemianopic scotomas. Analysis of performance showed a small but significant deviation of the bisection midline ("egocentric midline") to the upper field in four patients with blindness of the upper hemifield and a more pronounced deviation to the inferior hemifield in two patients with lower altitudinal field defects. In addition, horizontal bar bisection showed a shift of the egocentric midline towards the scotoma in all four patients with left- or right-sided homonymous hemianopia. Hence, location of the scotoma predicted direction of the shift of the egocentric midline but not degree of shift.