Compensatory saccades benefit from prediction during head impulse testing in early recovery from vestibular deafferentation
The head impulse test (HIT) can identify a deficient vestibulo-ocular reflex (VOR) by the compensatory saccade (CS) generated once the head stops moving. The inward HIT is considered safer than the outward HIT, yet might have an oculomotor advantage given that the subject would presumably know the direction of head rotation. Here, we compare CS latencies following inward (presumed predictable) and outward (more unpredictable) HITs after acute unilateral vestibular nerve deafferentation. Seven patients received inward and outward HITs delivered at six consecutive postoperative days (POD) and again at POD 30. All head impulses were recorded by portable video-oculography. CS included those occurring during (covert) or after (overt) head rotation. Inward HITs included mean CS latencies (183.48 ms ± 4.47 SE) that were consistently shorter than those generated during outward HITs in the first 6 POD (p = 0.0033). Inward HITs induced more covert saccades compared to outward HITs, acutely. However, by POD 30 there were no longer any differences in latencies or proportions of CS and direction of head rotation. Patients with acute unilateral vestibular loss likely use predictive cues of head direction to elicit early CS to keep the image centered on the fovea. In acute vestibular hypofunction, inwardly applied HITs may risk a preponderance of covert saccades, yet this difference largely disappears within 30 days. Advantages of inwardly applied HITs are discussed and must be balanced against the risk of a false-negative HIT interpretation.
KeywordsCompensatory saccades Vestibular Deafferentation Latency Prediction
- 1.Halmagyi GM, Curthoys IS (1988) A clinical sign of canal paresis. ArchNeurol 45:737–739Google Scholar
- 9.EyeSeeCam (2013) VOG System. Munich, GermanyGoogle Scholar
- 14.Newman-Toker DE, Kerber KA, Hsieh YH, Pula JH, Omron R, et al (2013) HINTS outperforms ABCD2 to identify stroke in acute vestibular syndrome Atlanta, GAGoogle Scholar
- 20.Goldberg JM, Minor LB (2012) Signal Processing in Vestibular Nuclei (VN) of Alert Animals during Natural Behaviors. The Vestibular System A Sixth Sense. Oxford University Press, OxfordGoogle Scholar
- 23.Mantokoudis G, Tehrani AS, Kattah JC, Eibenberger K, Guede CI, et al (2014) Quantifying the Vestibulo-ocular reflex with Video-Oculography: Nature and Frequency of Artifacts. Audiology & Neurolology: in pressGoogle Scholar