Bilateral vestibular disorder. At acute stage, people with BVD are significantly unsteady but gradually regain their postural stability. They mainly experience postural and gait unsteadiness in dark environments because of insufficient input from the VOR (Xxxxx and Xxxxxxxx, 1989; Xxxxxx et al., 2017). The degree of recovery depends on the cause and extent of BVD (Xxxxx et al., 1989; Xxxxxx and Xxxxxxxx, 2000). When ototoxicity is the causative factor, improvement is often greater than when the cause of BVD is due to a slowly progressive vestibular deficit such as an autoimmune disease or neurodegeneration (Calder and Xxxxxxxx, 2000; Xxxxxx et al., 2017). People with BVD have been shown to rely to a great extent on visual input for postural control (Xxxxx et al., 1989; Xxxxx and Xxxxxxxx, 1989; Bronstein, 1995). Gradually though they can utilise proprioceptive cues more effectively, so they become less unsteady in response to visual motion. Some people may be able to maintain postural stability without input from visual cues (Xxxxxxxx and Bronstein, 1994). Xxxxxxx and colleagues (2001) showed that people with chronic BVD can resolve the conflict from visual stimuli with postural sway in a similar way as healthy adults do. However, if BVD is closer to complete lesion, people never recover the ability to balance when both vision and surface information is inadequate for an orientation reference, even with substantial improvements following VRT (Hall et al., 2022). People with BVD also, experience falls to a greater extent than people with UVD and should be informed about this increased risk (Xxxxxxx et al., 2000a; Xxxxxxx et al., 2000b; Xxxxxxx et al., 2012). The unpleasant illusion of movement or blurring of images when travelling on cars, trains, or buses, walking, and running, especially in busy surroundings, or when performing head movements known as oscillopsia, is a common clinical sign in people with BVD (Baloh and Xxxxxxxx, 1989; Bronstein et al., 2005). These people often complain to their clinicians that images “bounce up and down” during these situations but become clearer when the people stop moving (Bronstein, 2004). There is a progressive improvement to oscillopsia over time which could be because of various compensatory mechanisms such as enhancement of the cervico-ocular reflex (Bronstein and Xxxx, 1987). Although, an early study did not find a direct relationship between the magnitude of this reflex and the severity of oscillopsia (Bronstein and Xxxx, 1987). Other compens...
