Objective: To test the quality of postural performance in quiet upright stance in healthy young adults with vertical heterophoria (VH) within the normal range and without VH (vertical orthophoria, VO).
Methods: Twenty-six subjects took part in this study. The postural stability was measured with a force platform while the subjects fixated a target at eye level in a straight ahead position, placed at either 40 or 200cm.
Results: The results indicated that the postural control was better for subjects with VO than subjects with VH. Particularly, there was an interaction between vertical phoria and distance: the subjects with VH showed greater instability than the subjects with VO at a far distance only. An additional study showed that the cancellation of VH with a prism improved postural stability.
Conclusions: The quality of postural performance in quiet upright stance was lower in the subjects with VH. We speculate that VH, even when small in size, indicates a perturbation of the somatosensory/proprioceptive loops involved in postural control.
Significance: Vertical phoria could perhaps indicate the capacity of the central nervous system to integrate optimally proprioceptive cues.