Toward Standardized Assessment of Dynamic Subjective Visual Vertical: Effects of Visual Stimulus Intensity in Health and Multiple Sclerosis

<i>Background and Objectives</i>: Decreased balance function in multiple sclerosis (MS) patients is influenced by impaired gravity perception, which can be measured by the subjective visual vertical (SVV) test. The value of this test can be increased by executing it in a moving visual background (i.e., dynamic SVV). However, clinicians and researchers use varying dynamic stimulus properties due to the lack of consensus on optimal parameters for reliably distinguishing between health and disease. <i>Materials and Methods</i>: To evaluate how dynamic visual stimulus intensity affects the perception of verticality in patients with MS and healthy individuals. <i>Materials and Methods</i>: We assessed static and dynamic SVV in 31 MS patients with dizziness and 32 age- and sex-matched controls using the virtual reality application VIRVEST. We evaluated the effects of modifying two parameters in dynamic SVV testing: rotation velocity (10°/s, 30°/s, and 60°/s) and visual field coverage (small vs. large). <i>Results</i>: The median of static SVV deviations was significantly greater in the MS group (1.8° vs. 0.9°). The mildest dynamic stimulus intensity of 10°/s, with a small visual field coverage, yielded the greatest discriminatory capacity to differentiate between the groups (AUC = 0.897; <i>p</i> < 0.001). This stimulus elicited a median SVV deviation of 4.3° in the MS group and 2.1° in the control group (<i>p</i> < 0.001) while also inducing significantly lower test-induced dizziness compared with stronger stimuli. Median visual dependence values measured at 10°/s with a small visual field coverage were 4.2 in the MS group and 2.02 in the control group (<i>p</i> < 0.001), also yielding the greatest AUC values compared to stronger stimuli (AUC = 0.828; <i>p</i> < 0.001). <i>Conclusions</i>: Our results support the use of relatively mild dynamic stimulus intensity. Future studies are encouraged to evaluate different dynamic stimulus parameters and patient populations.