Abstract
Vestibular implants are devices designed to rehabilitate patients with a bilateral vestibular loss (BVL). These patients lack a properly functioning vestibulo-ocular reflex (VOR), which impairs gaze stabilization abilities and results in an abnormal loss of visual acuity (VA) in dynamic situations (i.e., severely limiting the patient's ability to read signs or recognize faces while walking). We previously demonstrated that the VOR can be artificially restored in a group of BVL patients fitted with a prototype vestibular implant. This study was designed to investigate whether these promising results could be translated to a close-to-reality task, significantly improving VA abilities while walking. Six BVL patients previously implanted with a vestibular implant prototype participated in the experiments. VA was determined using Sloan letters displayed on a computer screen, in four conditions: (1) with the patient standing still without moving (static), (2) while the patient was walking on a treadmill at constant speed with the vestibular implant prototype turned off (systemOFF), (3) while the patient was walking on a treadmill at constant speed with the vestibular implant prototype turned on providing coherent motion information (systemONmotion), and (4) a “placebo” condition where the patient was walking on a treadmill at constant speed with the vestibular implant prototype turned on providing reversed motion information (systemONsham). The analysis (one-way repeated measures analysis of variance) revealed a statistically significant effect of the test condition [F(3, 12) = 30.5, p < 0.001]. Significant decreases in VA were observed with the systemOFF condition when compared to the static condition (Tukey post-hoc p < 0.001). When the vestibular implant was turned on, delivering pertinent motion information (systemONmotion) the VA improved to close to normal values. The improvement disappeared in the placebo condition (systemONsham) and VA-values also dropped significantly in this condition (Tukey post-hoc p < 0.001). These results are a significant step forward in the field, demonstrating for the first time in humans that gaze stabilization abilities can be restored with a vestibular implant prototype. The vestibular implant shows considerable promise of being the first-ever effective therapeutic alternative for patients with a BVL in the near future.
Highlights
The vestibular implant is a device designed to artificially restore the vestibular function using motion modulated electrical stimulation of the peripheral vestibular system
Our group has recently demonstrated partial restoration of the vestibulo-ocular reflex (VOR) in a group of bilateral loss of the vestibular function (BVL) patients fitted with a prototype vestibular implant, using motion modulated electrical stimulation of the vestibular nerve (Perez Fornos et al, 2014)
Compared to the static condition, all six patients experienced a drop in visual acuity (VA) while walking on the treadmill in the systemOFF condition, ranging from 0.13 to 0.28 logMAR in absolute value
Summary
The vestibular implant is a device designed to artificially restore the vestibular function using motion modulated electrical stimulation of the peripheral vestibular system. In the past two decades, several groups have demonstrated that three key aspects of vestibular function: the vestibulo-ocular reflex (VOR; Merfeld et al, 2007; Lewis et al, 2010; Dai et al, 2011; Perez Fornos et al, 2014), specific postural responses (Phillips et al, 2013), as well as vestibular percepts (Guinand et al, 2015) can be artificially elicited and restored using a vestibular implant This confirms that it is possible to effectively transmit motion information to the central nervous with such a device. These results can be considered as a milestone in the development of a vestibular implant, confirming in humans pioneering findings obtained in animal research (Gong and Merfeld, 2002; Dai et al, 2011)
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