Covert Saccades in Suppression Head Impulse Paradigm: Compensation Strategy in Unilateral Vestibulopathy

Abstract

Background and Objectives In the suppression head impulse paradigm (SHIMP), an alternative protocol to the conventional head impulse paradigm (HIMP) in the video head impulse test (vHIT), covert saccades (CSs) are infrequent, unlike in HIMP. However, some patients with unilateral vestibular loss (UVL) reportedly manifest CSs in SHIMP. This study aimed to evaluate the characteristics of CSs and their role as a compensatory strategy for vestibulopathy in patients undergoing SHIMP. Subjects and Method This retrospective study included 30 patients diagnosed with UVL based on vestibuloocular reflex (VOR) testing. vHIT was conducted using two paradigms, HIMP and SHIMP. Statistical analyses were performed to compare the characteristics of CSs between the two paradigms and assess the correlation between CSs and anticompensatory saccades (ACSs) in SHIMP. Results CSs observed in SHIMP exhibited significantly reduced amplitudes and shorter latencies than those in HIMP, with a significant correlation between latency in the two paradigms. ACSs in SHIMP were more pronounced in traces exhibiting CSs, with a positive correlation between the amplitudes of CS and ACS. Conclusion Our results suggest that CSs observed using SHIMP are associated with the augmentation of ACSs in patients with UVL. This implies that CSs in SHIMP may serve as a rehabilitation strategy, supporting VOR in maintaining forward gaze in patients with UVL. Clinically, the presence of CSs should be considered when interpreting ACSs in SHIMP.