Subjective visual vertical and visual dependency in patients with multiple sclerosis

Spatial orientation is an inherent ability governed by the complex integration of visual, vestibular and proprioceptive inputs. The degree to which an individual relies upon visual cues, as opposed to the vestibular or proprioceptive cues, is termed visual dependence. Although abnormal visual dependence has been documented in other neurological disorders, it is not known whether MS leads to visual dependence, and if so whether this is related to disease progression, clinical disability, or neuro-inflammatory burden in the central nervous system.

To evaluate SVV and visual dependence using a novel mobile virtual reality-based system for subjective visual vertical assessment (VIRVEST) and evaluate its relationship with the Expanded Disability Scale Score (EDSS), MS course and clinical findings.

The study included 59 patients with MS and 59 controls. Four tests were integrated in VIRVEST system and performed by each patient: a static SVV, dynamic SVV with clockwise and counter-clockwise background stimulus rotation, and SVV in a virtual reality background - a boat floating in the wavy water - to be adjusted vertically. Visual dependence was evaluated as a function of dynamic SVV.

Patients with MS manifest larger biases in both static and dynamic SVV than healthy controls (p<0.001), in addition to higher visual dependence scores (p<0.05). MS patients with an EDSS score >4.5 had larger values of dynamic SVV and when compared to MS patients with lower EDSS scores (p<0.01), and visual dependence was related to disease severity. Patients with progressive MS disease course demonstrated statistically significantly larger dynamic SVV and visual dependence scores when compared to MS patients with relapsing-remitting disease (p<0.01). The mean System Usability Scores for the VIRVEST system corresponded to a patient perceived adjective rating of ``excellent''.

We have evaluated the application of a novel virtual reality-based SVV test in patients with MS. We identified greater dynamic SVV errors suggestive of visual dependence in patients with MS versus controls and show that dynamic SVV abnormalities are related to disability measures. We suggest that this paradigm is effective at identifying visual dependence in neurological patients, and may have application in clinical settings, given high system usability scores.