Objective: to validate a simple bedside test to objectify the fixation suppression of the vestibulo-ocular reflex (FS-VOR) in patients with cerebellar syndrome

Background: The FS-VOR is a reliable clinical feature to test for cerebellar function, and its disturbance indicative of cerebellar pathology. It serves as a valuable clinical test for identifying a subtle cerebellar syndrome, when other cerebellar symptoms such as ataxia, dysarthria, dysmetria etc. are not yet fully present. In movement disorders, it can serve as an additional feature to differentiate  idiopathic Parkinson’s disease from atypical Parkinsonian Syndromes such as multiple system atrophy. Gold standard of assessing the FS-VOR is utilizing a video-nystagmography (VNG) system and an electronic rotary chair. Not only are such devices expensive and need expertise in interpreting results, they also are time and personnel consuming. We here describe a bedside test that allows for fast, easy to interpret and reliable assessment of the FS-VOR and enables video documentation of the test.

Method: The VOR and FS-VOR were assessed in 20 healthy subjects (mean age 56±15, 14 women) and 19 patients with a cerebellar syndrome (mean age 70±11, 10 women). VNG during a defined rotation speed on a swivel chair was compared to a simple self-made bedside test using the video function on a smart phone and asking the patient to fix their gaze on the lens whilst being rotated on the swivel chair with a defined speed. Videos were assessed by blinded raters and dichotomously rated as normal or pathological FS-VOR. Results were compared to the VNG data and reliability calculated.

Results: VNG in healthy controls showed a sufficient suppression of the horizontal VOR with a reduction of nystagmus counts of 95.0% ± 7.2 (mean ± SD), whereas in patients with cerebellar syndrome, reduction of horizontal nystagmus counts was only 26.3% ± 25.1. Video analysis by blinded raters showed an excellent inter-rater reliability of 0.85 (0.76-0.93). Comparison of VNG results to the video ratings showed a very high reliability of 0.91 (0.84 – 0.96). Sensitivity of the video analysis was 0.92 (0.83-0.96), its specifity 0.99 (0.93 – 1.00).

Conclusion: The smart phone bedside test is an easily performed, reliable, highly sensitive and specific, and inexpensive alternative to video-nystagmography for assessing the fixation suppression of the vestibulo-ocular reflex.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/fixation-suppression-the-easy-way-when-nothing-else-matters/