The Visual Midline Shift and its Associations in Healthy Adults

Abstract A visual midline (VM) shift may be experienced by some individuals post-stroke, but its associations with other variables are unclear. This study explored the relationships between the VM and other vision and non-vision variables in healthy adults. Normative data were calculated, and repeatability was assessed for each test. 93 participants without a history of visual or neurological impairment were recruited. Horizontal and vertical VM were measured using a VM gauge. During visit 1, the line bisection test (LBT) for spatial neglect, ocular dominance (OD), subjective straight-ahead (SSA), and visual open loop testing were also conducted. During visit 2, all assessments were repeated in Hong Kong while participants in Canada repeated VM measurements. Results showed no significant correlation between VM gauge measurements and other vision variables for either visit (P > 0.05). Age was significantly correlated with the absolute vertical VM during the first visit (Spearman’s rho = 0.47, P < 0.001), and with the absolute horizontal VM during the second visit (Spearman’s rho = 0.30, P = 0.004). LBT and OD tests had good repeatability (Limits of Agreement for Repeatability were 4 mm for LBT and 7 cm for OD). The visual open loop and SSA had poorer repeatability. This study revealed that VM is not associated with other vision variables in healthy adults. Therefore, it may be processed by independent neurological processing. This information is important for understanding the origins of VM shift, and normative data will aid clinicians in diagnosis.