Subjective Visual Vertical during Caloric Stimulation in Healthy Subjects: Implications to Research and Neurorehabilitation

Evaluation of subjective visual vertical and horizontal in patients with acoustic neuroma based on virtual reality

Objective

To investigate potential differences in absolute deviation values of subjective visual vertical and horizontal between unilateral acoustic neuroma patients and healthy young adults under varying degrees of static head tilt, as well as the impact of proprioception on these values, with the aim of determining the effect of acoustic neuroma on gravity sensory pathway function in patients.

Methods

We recruited 22 patients diagnosed with unilateral acoustic neuroma and 25 healthy young adults and employed virtual reality technology to assess the absolute deviation values of subjective visual vertical (SVV) and subjective visual horizontal (SVH) under eight different static tilted head positions (Head centered (0° tilt), PdP, Head tilt 15°, 30°, 45° to the left and right), then compare and analyze intergroup differences.

Results

In the Head-centered position, both SVV and SVH absolute deviated values were significantly higher in the AN group compared to healthy young adults. The AN group exhibited significantly higher absolute deviation values of SVV compared to the healthy group when tilting their head 30° left and right. Additionally, when tilting their heads to the right at 15° and 45° the AN group showed significant increases in SVH absolute deviated values compared to healthy adults. The SVV and SVH absolute deviation values of LAN and SAN groups did not reach statistical significance. The results of the SVV test for PDP position did not show any significant differences among all groups. However, the SVH test revealed that the absolute deviation values of the LAN group was significantly higher than that of healthy individuals.

Conclusion

Our study shows that the gravity sensing function of patients with unilateral acoustic neuroma is affected to different degrees, however, the degree of gravity sensing function damage of patients has little relationship with tumor size. When acoustic neuroma is larger than 2 cm, the effect of proprioception on patients' SVH outcome is noteworthy. So, we should pay attention to the postoperative follow-up of patients with acoustic neuroma and the evaluation of vestibular rehabilitation effect. Meanwhile, for patients opting for conservative treatment, it is imperative to monitor the dynamic changes in vestibular function and seize timely opportunities for intervention.

Stimulation from Cochlear Implant Electrodes Assists with Recovery from Asymmetric Perceptual Tilt: Evidence from the Subjective Visual Vertical Test

Vestibular end organ impairment is highly prevalent in children who have sensorineural hearing loss (SNHL) rehabilitated with cochlear implants (CIs). As a result, spatial perception is likely to be impacted in this population. Of particular interest is the perception of visual vertical because it reflects a perceptual tilt in the roll axis and is sensitive to an imbalance in otolith function. The objectives of the present study were thus to identify abnormalities in perception of the vertical plane in children with SNHL and determine whether such abnormalities could be resolved with stimulation from the CI. Participants included 53 children (15.2 ± 4.0 years of age) with SNHL and vestibular loss, confirmed with vestibular evoked myogenic potential (VEMP) testing. Testing protocol was validated in a sample of nine young adults with normal hearing (28.8 ± 7.7 years). Perception of visual vertical was assessed using the static Subjective Visual Vertical (SVV) test performed with and without stimulation in the participants with cochleovestibular loss. Trains of electrical pulses were delivered by an electrode in the left and/or right ear. Asymmetric spatial orientation deficits were found in nearly half of the participants with CIs (24/53 [45%]). The abnormal perception in this cohort was exacerbated by visual tilts in the direction of their deficit. Electric pulse trains delivered using the CI shifted this abnormal perception towards center (i.e., normal; p = 0.007). Importantly, this benefit was realized regardless of which ear was stimulated. These results suggest a role for CI stimulation beyond the auditory system, in particular, for improving vestibular/balance function.