An Inexpensive 6D Motion Tracking System for Posturography

Computerized posturography is most often performed with a force plate measuring center-of-pressure (COP). COP is related to postural control actions but does not monitor the outcome of those actions, i.e., center-of-mass (COM) stability. For a more complete analysis of postural control COM should also be measured; however, existing motion tracking technology is prohibitively expensive and overcomplicated for routine use. The objective of this work was to create and validate an inexpensive and convenient stereo vision system which measured a trunk-fixed target's 3D position and orientation relating to COM. The stereo vision system would be complementary to typical force plate methods providing precise 6D position measurements under laboratory conditions. The developed system's measurement accuracy was worst in the inferior-superior axis (depth) and pitch coordinates with accuracy measures 1.1 mm and 0.8°, respectively. The system's precision was worst in the depth and roll coordinates with values 0.1 mm and 0.15°, respectively. Computer modeling successfully predicted this precision with 11.3% mean error. Correlation between in vivo target position (TP) and COP was above 0.73 with COP generally demonstrating larger excursions oscillating around TP. Power spectral analysis of TP revealed 99% of the signal was bound below 1.1 Hz matching expectations for COM. The new complementary measurement method enables identification of postural control strategies and as a result more complete analysis. Stereo vision is a useful complement to typical force plate equipment. The system presented here is inexpensive and convenient demonstrating potential for routine use in clinic and research. In order to use this system in clinic, future work is required in interpretation of this system's data and normal reference values must be established across gender and age in a healthy population followed by values from patients with different pathologies

Caracterización de la dehiscencia bilateral del conducto semicircular superior

In the superior canal dehiscence syndrome, patients can have sound- or pressure-induced vertigo and oscillopsia. They may also present conductive hearing loss or higher than normal bone conduction thresholds. Clinical manifestations are due to the effect of a third mobile window in the inner ear created by the dehiscence. Diagnosis is based on clinical manifestations, vertical and rotatory nystagmus induced by sound and pressure reflecting SSC stimulation, reduced threshold and increased amplitude of vestibular evoked myogenic potentials (VEMP) and temporal bone CT scan images showing the SSC dehiscence. Characteristic eye movements can be recorded with the scleral search coil technique

Vestibulo-Oculomotor Reflex Recording Using the Scleral Search Coil Technique. Review of Peripheral Vestibular Disorders

Our goal is to review vestibulo-oculomotor reflex (VOR) studies on several peripheral vestibular disorders (Ménière’s disease, vestibular neuritis, benign paroxysmal positional vertigo, superior canal dehiscence syndrome, and vestibular neuroma), using the scleral search coil (SSC) technique. Head movements are detected by vestibular receptors and the elicited VOR is responsible for compensatory 3 dimensional eye movements. Therefore, to study the VOR it is necessary to assess the direction and velocity of 3 dimensional head, and eye movements. This can be achieved using the SSC technique. Interaction between a scleral search coil and an alternating magnetic field generates an electrical signal that is proportional to eye position. Ideally, eye rotation axis is aligned with head rotation axis and VOR gain (eye velocity/head velocity) for horizontal and vertical head rotations is almost 1. The VOR gain, however, for torsional head rotations is smaller and about 0.

Vergence-Mediated Changes in Listing's Plane Do Not Occur in an Eye with Superior Oblique Palsy

PURPOSE. As a normal subject looks from far to near, Listing's plane rotates temporally in each eye. Since Listing's plane relates to the control of torsional eye position, mostly by the oblique eye muscles, the current study was conducted to test the hypothesis that a patient with isolated superior oblique palsy would have a problem controlling Listing's plane. METHOD. Using the three-dimensional scleral search coil technique, binocular Listing's plane was measured in four patients with congenital and in four patients with acquired unilateral superior oblique palsy during far-(94 cm) and near-(15 cm) viewing. The results were compared to previously published Listing's plane data collected under exactly the same conditions from 10 normal subjects. RESULTS. In patients with unilateral superior oblique palsy, either congenital or acquired, Listing's plane in the normal eye rotated temporally on near-viewing, as in normal subjects, while in the paretic eye it failed to do so. In patients with acquired superior oblique palsy, Listing's plane was already rotated temporally during far-viewing and failed to rotate any farther on near-viewing, whereas in patients with congenital superior oblique palsy Listing's plane in the paretic eye was oriented normally during far-viewing and failed to rotate any farther on near-viewing. CONCLUSIONS. These results suggest that the superior oblique muscle, at least in part, is responsible for the temporal rotation of Listing's plane that occurs in normal subjects on convergence. (Invest Ophthalmol Vis Sci. 2004;45:3043-3047) DOI:10.1167/iovs.04-0014 A lthough the eye can rotate with three degrees of freedom, during visual fixation, smooth pursuit, and saccades, it exercises only two: horizontal and vertical. Furthermore, when the head is not moving and there is no vestibular input, horizontal and vertical eye-in-head position (gaze position) determines how much the eye has rotated about its line of sight (i.e., the amount of torsion). This relationship between torsional eye position and gaze position is described by Listing's law. During visual fixation, smooth pursuit, 1 and saccades, 2 Listing's law correctly predicts that the tips of the rotation vectors used to describe eye positions all lie in a plane called the displacement plane. 3 The displacement plane is determined by Listing's plane (LP), which is head fixed and changes orientation under few conditions. For example, LP changes orientation during prolonged fusion of an imposed vertical disparity 4 and during prismatically induced horizontal and vertical vergence. 6 -9 LP rotates in each eye around a point that is not at the origin of the coordinate system describing eye position. Consequently, it is only during downward gaze that torsional eye position changes significantly on near-viewing. Temporal rotation of LP on near-viewing approximately aligns the three-dimensional eye rotation axes during saccades and, as a consequence, eye eccentricity is minimized. 11 However, another line of evidence suggests that the vergence-mediated change in LP may be due to relaxation of one extraocular muscle, the superior oblique. Eye torsion is produced mainly by the oblique eye muscles. There could be some structural differences between congenital and acquired SOPs. One study reported imaging of abnormalities of the superior oblique tendon in congenital SOP in contrast to atrophy of the superior oblique muscle in acquired SOP, 15 but this result was not replicated

Glycine receptor deficiency and its effect on the horizontal vestibulo-ocular reflex: a study on the SPD1J mouse

Inhibition is critical in the pathways controlling the vestibulo-ocular reflex (VOR) and plays a central role in the precision, accuracy and speed of this important vestibular-mediated compensatory eye movement. While γ-aminobutyric acid is the common fast inhibitory neurotransmitter in most of the VOR microcircuits, glycine is also found in key elements. For example, the omnidirectional pause neurons (OPNs) and inhibitory burst neurons in the horizontal VOR both use glycine as their preferred inhibitory neurotransmitter. Determining the precise contribution of glycine to the VOR pathway has been difficult due to the lack of selective tools; however, we used spasmodic mice that have a naturally occurring defect in the glycine receptor (GlyR) that reduces glycinergic transmission. Using this animal model, we compared the horizontal VOR in affected animals with unaffected controls. Our data showed that initial latency and initial peak velocity as well as slow-phase eye movements were unaffected by reduced glycinergic transmission. Importantly however, there were significant effects on quick-phase activity, substantially reducing their number (30–70 %), amplitude (~55 %) and peak velocity (~38 %). We suggest that the OPNs were primarily responsible for the reduced quick-phase properties, since they are part of an unmodifiable, or more ‘hard-wired’, microcircuit. In contrast, the effects of reduced glycinergic transmission on slow-phases were likely ameliorated by the intrinsically modifiable nature of this pathway. Our results also suggested there is a ‘threshold’ in GlyR-affected animals, below which the effects of reduced glycinergic transmission were undetected

Vestibulo-Oculomotor Reflex Recording Using the Scleral Search Coil Technique. Review of Peripheral Vestibular Disorders

Our goal is to review vestibulo-oculomotor reflex (VOR) studies on several peripheral vestibular disorders (Ménière’s disease, vestibular neuritis, benign paroxysmal positional vertigo, superior canal dehiscence syndrome, and vestibular neuroma), using the scleral search coil (SSC) technique. Head movements are detected by vestibular receptors and the elicited VOR is responsible for compensatory 3 dimensional eye movements. Therefore, to study the VOR it is necessary to assess the direction and velocity of 3 dimensional head, and eye movements. This can be achieved using the SSC technique. Interaction between a scleral search coil and an alternating magnetic field generates an electrical signal that is proportional to eye position. Ideally, eye rotation axis is aligned with head rotation axis and VOR gain (eye velocity/head velocity) for horizontal and vertical head rotations is almost 1. The VOR gain, however, for torsional head rotations is smaller and about 0.