Oculomotor compensatory strategies in bilateral vestibulopathy: Predictive and active conditions of head movements

BackgroundImpaired vestibulo-ocular reflex (VOR) can be compensated by catch-up saccades and/or increased residual VOR. Prediction and intention seem able to potentiate both responses, but how do these effects combine, particularly in individuals with bilateral vestibulopathy (BVP), remains largely unknown.ObjectiveTo compare the impact of passive, predictive and voluntary conditions of head impulse tests (HIT) on global oculomotor compensatory responses in individual with BVP.MethodsHIT were performed in Passive(P)-Random, Passive(P)-Cued and Active head movement conditions. VOR gain and latency and gain of the 1^st catch up saccades were calculated for the 32 tested ears. Among the 1^st catch up saccade, a separate analysis of covert saccades was performed.ResultsLatency of covert saccades was shorter in the Active compared to P-Random and P-Cued. First saccades showed shorter latency and greater gain in the P-Cued condition versus P-Random. VOR gain was significantly higher in the Active condition compared to P-Random and P-Cued. Most individuals enhanced catch-up saccades and VOR gain simultaneously while others either boosted VOR gain while reducing saccade efficiency, or enhanced saccade efficiency while decreasing VOR gain.ConclusionsPrediction and intention improve gaze during HIT in individuals with BVP by optimising existent oculomotor responses. During active movements, these effects combined according to subjects' individual strategies.