Binocular alignment changes between sitting and supine positions in patients with dizziness

Vertical and torsional ocular misalignment can occur from mild traumatic brain injury or inner ear pathology, which may vary depending on head position. Here, we evaluate differences in a behavioral measure of binocular alignment in both upright and supine head position. Ocular perception of vertical and torsional alignment was measured using the torsional and vertical alignment nulling (TAN, VAN) task in N = 52 veterans with dizziness (N = 38 with traumatic brain injury), N = 41 civilians with vestibular schwannoma resection (UVD), and N = 33 healthy controls for both positions. The interquartile range within each group, regardless of head position, was greater for torsional compared to vertical misalignment. We use generalized estimating equations to compare average TAN (torsional) scores and VAN (vertical) scores between groups and test position. Compared to the healthy controls, TAN was significantly increased by + 0.4186 degrees in veterans (P = 0.030) and by + 0.5747 degrees in UVD (P = 0.010), but there was no difference with head position. For VAN, no difference was found between the three groups, but the misalignment did worsen by 0.0888 degrees (P = 0.0070) as the head position moved from upright to supine. Head position had negligible effects on this behavioral measure of vertical and torsional binocular misalignment, and torsional misalignments were worse than controls in both veterans with dizziness and patients with vestibular nerve resection although neither reported torsional diplopia. Our data suggests that the tolerance for roll misalignment may be abnormally large in patients with dizziness. Alternatively, perceptual roll misalignments may be a manifest cause for dizziness, and therefore a useful proxy for distinguishing differences in putative otolith function in veterans with dizziness.