Clinical Assessment of the Nystagmus Fixation Suppression Test: An Experimental Study

Abstract

Background: Assessment of nystagmus fixation suppression can be used as an additional diagnostic tool for patients with an acute vestibular syndrome to distinguish between a central or peripheral cause. We investigated the ability of physicians to detect fixation suppression using a nystagmus simulation model.

Methods: We used a nystagmus simulator to measure the accuracy of the nystagmus fixation suppression test. Fixation suppression was assessed randomly in 6170 trials by 20 otorhinolaryngologists and neurologists, segregated into 2 groups based on their neurootological experience, a beginner and an experienced group. The simulator presented random nystagmus slow velocity (SPV) reductions and presented 3 conditions with either changed nystagmus frequency, amplitude, or both.

Results: The cutoff for the discernment of fixation suppression ranged from 1.2 to 14°/s nystagmus velocity difference. The more intense the baseline nystagmus was, the more difficult was the detection of fixation suppression. There was not significant difference (P >.05) in the cutoff values in the experts group compared to the novices for all 3 different conditions. Both, novices and experts, detected frequency changes easier than differences of the nystagmus amplitude. Test sensitivity was very low (19%-65%) for discernment of small nystagmus velocity differences of <2°/s by experts.

Conclusion: In our study, there was no difference between experts and novices in detection of nystagmus suppression by visual fixation. The examiners could only detect large suppression effects at low-intensity baseline nystagmus. Overall, the sensitivity and accuracy of a clinical fixation suppression test is low and the assistance with a video-oculography device is highly recommended.

Figure 1.

In the program, users can define horizontal, vertical, and torsional movements of nystagmus. The slow phase velocity is calculated by the entered parameters amplitude and frequency. Our test program, on the other hand, calculates the amplitude, frequency, or both depending on the mode, with a defined SPV as baseline and the reduction in SPV for the second nystagmus is randomized.

Figure 2.

The cutoff for the discernment of fixation suppression increased proportionally with the baseline spontaneous nystagmus. Both novices (gray lines) and experts (black lines) detected frequency changes (FRQ) easier than differences in the nystagmus amplitude (AMP). The dotted line illustrates the cutoff for stroke detection (2°/s delta SPV).