Covert Saccade Triggers in Bilateral Vestibular Hypofunction

Study Overview
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Brief Summary
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Patients with chronic bilateral vestibular hypofunction may suffer from a visual instability during head movement called oscillopsia. Visual consequence of vestibular deficit can lead to a severe impairment of their quality of life. However, correcting saccades during rapid head movement, called covert-saccades, have been more recently identified. These saccades, which occur during the head movement in patients with vestibular hypofunction, present a very short latency. They could compensate for the lack of vestibular-ocular reflex and greatly decrease oscillopsia and visual impairment. The triggering of these covert-saccade is still not known. They could be of visual origin but the short latency is unusual. The objective of this study is to evaluate the potential role of visual trigger in 12 patients with chronic bilateral areflexia, using different visuo-vestibular conditions. The latency of simple visually guided saccades will also be tested in the group of patients and a group of 12 healthy controls.

Official Title
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Covert Saccade Triggers in Bilateral Vestibular Hypofunction

Conditions
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Reflex, Abnormal, Bilateral Vestibulopathy, Healthy Volunteers

Intervention / Treatment
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* Other: Covert Saccades and Virtual Reality
* Other: Actives versus passives Head Impulses
* Other: Visually guided saccades


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: For all : Age from 18 to 90 Understanding of the experimental instructions Informed Consent For Patients : Bilateral vestibular hypofunction with regards to the criteria of the of the Barany Society A. Chronic vestibular syndrome with at least three of the following symptoms Postural imbalance Unsteadiness of gait Movement-induced blurred vision or oscillopsia during walking or quick head/body movements Worsening of postural imbalance or unsteadiness of gait in darkness and/or on uneven ground B. No symptoms while sitting or lying down under static conditions C. Bilaterally reduced or absent angular VOR function documented by bilaterally pathological horizontal angular VOR gain < 0.6, measured by the video-HIT5or scleral-coil technique and/or reduced caloric response (sum of bithermal max. peak SPV on each side < 6°/sec7)and/or reduced horizontal angular VOR gain < 0.1 upon sinusoidal stimulation on a rotatorychair (0.1 Hz, Vmax = 50°/sec). D. Not better accounted for by another disease * For Healthy control No ENT or neurological disorders Exclusion Criteria: Corrected Visual Acuity lower than 5/10 Other conditions leading to oscillopsia or ataxia Oculomotor palsy, ocular instability in primary position Treatment that may affect ocular motility (psychotropes) Cervical rachis pathology with instability Cochlear Implants Non-stabilized medical disease Pregnant women Patients under tutelage Patient without social security

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 90 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Allocation: Non-Randomized
Intervention Model: Parallel Assignment
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Patients<br>Patients suffering from chronic bilateral vestibular hypofunction | Other: Covert Saccades and Virtual Reality<br>* During this intervention, patients will undergo head impulse testing while wearing virtual reality Headsets. During the head impulse tests the visual information will be modified in order to create a conflict between head rotation and rotation of the visual scene. Recording of head and eye movement will be done during these head impulses in order to verify if visual information modifies compensatory eye movements during head impulses.<br>Other: Actives versus passives Head Impulses<br>* Patients will undergo classic passive head rotation as well as active head rotation in order to compare latencies of covert saccades in both conditions.<br>Other: Visually guided saccades<br>* Patients as well as healthy control subjects will undergo testing of visually guided saccades in different conditions (step, gap, overlap) in order to compare latencies of covert saccades between both groups.<br>|
| Active Comparator: healthy subject group<br> | Other: Covert Saccades and Virtual Reality<br>* During this intervention, patients will undergo head impulse testing while wearing virtual reality Headsets. During the head impulse tests the visual information will be modified in order to create a conflict between head rotation and rotation of the visual scene. Recording of head and eye movement will be done during these head impulses in order to verify if visual information modifies compensatory eye movements during head impulses.<br>Other: Actives versus passives Head Impulses<br>* Patients will undergo classic passive head rotation as well as active head rotation in order to compare latencies of covert saccades in both conditions.<br>Other: Visually guided saccades<br>* Patients as well as healthy control subjects will undergo testing of visually guided saccades in different conditions (step, gap, overlap) in order to compare latencies of covert saccades between both groups.<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Latency of covert-saccades | Latency of covert saccades correspond to the time between the beginning of head impulse and the initiation of the first covert-saccade | Day 1 | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Frequency of covert-saccades | Frequency of covert saccades corresponds to the total amount of covert-saccades divided by the total amount of head impulse tests multiplied by 100. | Day 1 | 
| Velocity of covert-saccades | Velocity of covert saccades correspond to the maximal velocity of the first covert-saccade | day 1 | 
| Amplitude of covert-saccades | Amplitude of covert saccades correspond to amplitude of the first covert-saccade | Day 1 | 
| Latency of visually-guided saccades | Latency of visually guided saccades correspond to the time between the appearance of target and the initiation of the first saccade | Day 1 | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Saccadic Eye Movements, Bilateral Vestibulopathy, Bilateral Vestibular Hypofunction