Andrew H. Clarke

Management of posttraumatic vertigo

OBJECTIVE: To evaluate patients after blunt trauma of the head, neck, and craniocervical junction (without fractures) with vertigo and to report the results of treatment after extensive diagnostics. STUDY DESIGN: Prospective study of consecutive new cases with vertigo after trauma at different periods of onset. During 2000–2002, 63 patients were examined and treated. SETTING: Regional trauma medical center for the greater Berlin Area, tertiary referral unit. RESULTS: The primary disorders included labyrinthine concussion (18), rupture of the round window membrane (6), and cervicogenic vertigo (12). The secondary disorders included otolith disorders (5), delayed endolymphatic hydrops (12), and canalolithiasis (9). The patients were free of vertigo symptoms (except cervicogenic and otolith disorder) after treatment, which consisted of habituation training, medical and surgical therapy options. The follow-up was 1 year. CONCLUSION: Posttraumatic vertigo can be treated with a high success rate once the underlying disorder has been identified. The extent of the neurotological test battery determines the precision and quality of diagnostics. Surgical measures should be an integral part of treatment modalities if conservative treatment is not effective. SIGNIFICANCE: Minor trauma of the head, neck, and craniocervical junction can have major impact on the vestibular system at different sites. Patients need to be carefully diagnosed, even if the onset of vertigo occurs a few weeks or months after the initial trauma.

Using high frame rate CMOS sensors for three-dimensional eye tracking

A novel three-dimensional eye tracker is described and its performance evaluated. In contrast to previous devices based on conventional video standards, the present eye tracker is based on programmable CMOS image sensors, interfaced directly to digital processing circuitry to permit real-time image acquisition and processing. This architecture provides a number of important advantages, including image sampling rates of up to 400/sec measurement, direct pixel addressing for preprocessing and acquisition, and hard-disk storage of relevant image data. The reconfigurable digital processing circuitry also facilitatesin-line optimization of the front-end, time-critical processes. The primary acquisition algorithm for tracking the pupil and other eye features is designed around the generalized Hough transform. The tracker permits comprehensive measurement of eye movement (three degrees of freedom) and head movement (six degrees of freedom), and thus provides the basis for many types of vestibulo-oculomotor and visual research. The device has been qualified by the German Space Agency (DLR) and NASA for deployment on the International Space Station. It is foreseen that the device will be used together with appropriate stimulus generators as a general purpose facility for visual and vestibular experiments. Initial verification studies with an artificial eye demonstrate a measurement resolution of better than 0.1° in all three components (i.e., system noise for each of the components measured as 0.006° H, 0.005° V, and 0.016° T. Over a range of ±20° eye rotation, linearity was found to be <0.5% (H), <0.5% (V), and <2.0% (T). A comparison with the scierai search coil technique yieldednear equivalent values for the systemnoise and the thickness of Listing’s plane.

The anti-motion sickness mechanism of ginger. A comparative study with placebo and dimenhydrinate.

A controlled, double-blind study was carried out to determine whether nystagmus response to optokinetic or vestibular stimuli might be altered by some agent contained in powdered ginger root (Zingiber officinale). For comparative purposes, the test subjects were examined after medication with ginger root, placebo and with dimenhydrinate. Eye movements were recorded using standard ENG equipment and evaluation was performed by automatic nystagmus analysis. It could be demonstrated that the effect of ginger root did not differ from that found at baseline, or with placebo, i.e. it had no influence on the experimentally induced nystagmus. Dimenhydrinate, on the other hand, was found to cause a reduction in the nystagmus response to caloric, rotatory and optokinetic stimuli. From the present study it can be concluded that neither the vestibular nor the oculomotor system, both of which are of decisive importance in the occurrence of motion sickness, are influenced by ginger. A CNS mechanism, which is characteristic of the conventional anti-motion sickness drugs, can thus be excluded as regards ginger root. It is more likely that any reduction of motion-sickness symptoms derives from the influence of the ginger root agents on the gastric system.

Unilateral testing of utricular function

Abstract A modified rotatory chair test is reported in which radial acceleration, generated by eccentric displacement of the subject during constant angular velocity, is exploited as a unilateral stimulation to the otolith organs. During constant angular rate rotation, the test subject is displaced laterally on the rotating turntable by 3.5 cm, so that one labyrinth becomes aligned with the rotatory axis while the second – eccentric – labyrinth is solely exposed to the altered gravito-inertial acceleration (GIA). Previously reported results showed that the direction of the response is independent of the direction of turntable rotation, ruling out any canal influence, and indicated that in a normal population the response, measured in one eye, was symmetrical for displacement of the left and right labyrinths. This mode of stimulus thus appears to elicit a unilateral otolith-ocular response (OOR). Examination of this unilateral OOR was extended in the present study; comparative testing with head-tilt to gravity, i.e. involving bilateral stimulation to the otolith organs, was carried out. Movements of both eyes were recorded (by three-dimensional video-oculography), in order to examine response conjugacy. To verify the specificity of the unilateral stimulus, tests were performed with patients who had previously undergone unilateral section of the vestibular nerve as treatment for acoustic neuroma. The eccentric displacement profile (EDP) and head-tilt stimulus each included ten cycles of left-right oscillation in order to permit signal averaging. In the normal subjects (n=12) the torsional component of the OOR proved to be both labyrinth-symmetrical and conjugate, during both bilateral and unilateral otolith stimulation. OOR gain (ocular torsion/GIA tilt) was higher for bilateral than unilateral stimulation. Bilateral OORs, obtained from three of the five unilaterally deafferented patients, proved less symmetrical and conjugate than in the normals. Unilateral OORs in all five patients were characteristically asymmetrical, with little or no response during stimulation of the diseased labyrinth.

The dynamic contributions of the otolith organs to human ocular torsion

We measured human ocular torsion (OT) monocularly (using video) and binocularly (using search coils) while sinusoidally accelerating (0.7 g) five human subjects along an earth-horizontal axis at five frequencies (0.35, 0.4, 0.5, 0.75, and 1.0 Hz). The compensatory nature of OT was investigated by changing the relative orientation of the dynamic (linear acceleration) and static (gravitational) cues. Four subject orientations were investigated: (1) Y-upright — acceleration along the interaural (y) axis while upright; (2) Y-supine — acceleration along the y-axis while supine; (3) Z-RED — acceleration along the dorsoventral (z) axis with right ear down; (4) Z-supine — acceleration along the z-axis while supine. Linear acceleration in the Y-upright, Y-supine and Z-RED orientations elicited conjugate OT. The smaller response in the Z-supine orientation appeared disconjugate. The amplitude of the response decreased and the phase lag increased with increasing frequency for each orientation. This frequency dependence does not match the frequency response of the regular or irregular afferent otolith neurons; therefore the response dynamics cannot be explained by simple peripheral mechanisms. The Y-upright responses were larger than the Y-supine responses (P<0.05). This difference indicates that OT must be more complicated than a simple low-pass filtered response to interaural shear force, since the dynamic shear force along the interaural axis was identical in these two orientations. The Y-supine responses were, in turn, larger than the Z-RED responses (P<0.01). Interestingly, the vector sum of the Y-supine responses plus Z-RED responses was not significantly different (P=0.99) from the Y-upright responses. This suggests that, in this frequency range, the conjugate OT response during Y-upright stimulation might be composed of two components: (1) a response to shear force along the y-axis (as in Y-supine stimulation), and (2) a response to roll tilt of gravitoinertial force (as in Z-RED stimulation).

Treatment of Ménière's Disease by Low-Dosage Intratympanic Gentamicin Application : Effect on Otolith Function

Objectives: The intratympanic application of a low dosage of gentamicin is increasingly favored as treatment for Ménières disease. While posttreatment observations have confirmed a long‐term success of the therapy of vertigo attacks, clear differences in the posttreatment recovery interval can be observed. In addition to differences in central‐vestibular compensation, the degree of peripheral vestibular damage, i.e., to the saccule, utricle, and semicircular canal ampullae, varies among patients. This study provides comprehensive pre‐ and posttreatment results from unilateral functional tests of the individual vestibular receptors and of the cochlea in patients with Ménières disease.

Measuring Three Dimensions of Eye Movement in Dynamic Situations by Means of Videooculography

A primary function of the vestibular system is the stabilisation of the eye during head movement. Consequently, evaluation of reflex eye movements represents an essential means to both clinical diagnosis and researching of the vestibular function. Movements in the eye can be resolved into three orthogonal components, i.e. horizontal, vertical and torsional. As an improvement on most current techniques, which provide only measurement of the horizontal and vertical components, videooculography (VOG) facilitates non-invasive measurement of all three of the defined components. To date, only the scleral coil technique, which involves the semi-invasive placement of coil rings onto the bulbi, yields a continuous measure of eye torsion. Employment of suitable solid-state devices permit the integration of a compact, high resolution video recording system. In the basic configuration, eye movements can be observed and simultaneously recorded for later analysis or documentation. The video images of the eye are obtained by means of a miniaturised CCD video sensor mounted on a light-occluding mask. Image processing of the acquired video images determines horizontal and vertical coordinates of eye position online. Ocular torsion, as reflected by the rotation of the natural iris, is measured for each video frame. The VOG algorithm has been implemented on a PC based workstation, which permits online observation, recording and evaluation of eye movements. In addition, the technique has found clinical application as a portable eye-movement observation and recording system, allowing bedside examination and recording of transient symptoms. Preliminary results from various studies, including the objective evaluation of positional nystagmus (BPPN), are presented.

Measuring unilateral otolith function via the otolith-ocular response and the subjective visual vertical.

In the present study, attention is directed to the unilateral response of the otolith system to static and dynamic tilt, as reflected by subjective estimation of the visual vertical (oculogravic perception). Measurements were performed with a variable radius rotary chair, which permits controlled modulation of the centripetal, or radial, acceleration. By limiting the radius, i.e. eccentric displacement of the head by 3.5 cm during constant-velocity rotation about the earth-vertical axis, adequate unilateral stimulation of the otolith organ - predominantly the utricle - is generated, without involving the semicircular canals. This paradigm has been employed to measure the unilateral utriculo-ocular response. In contrast to the otolith-ocular response (OOR), the subjective visual vertical (SVV) reflects the processing of otolithic information in the higher brain centres (thalamus, vestibular cortex). Exploitation of these two complementary approaches provides useful information for both experimental and clinical scientists. The findings also reveal that centripetal acceleratory stimulation during constant angular velocity with the subject centred on axis is sufficient to localize peripheral otolith dysfunction by means of SVV estimation. This represents a novel test of otolith function that can be easily integrated into routine clinical testing.In the present study, attention is directed to the unilateral response of the otolith system to static and dynamic tilt, as reflected by subjective estimation of the visual vertical (oculogravic perception). Measurements were performed with a variable radius rotary chair, which permits controlled modulation of the centripetal, or radial, acceleration. By limiting the radius, i.e. eccentric displacement of the head by 3.5 cm during constant-velocity rotation about the earth-vertical axis, adequate unilateral stimulation of the otolith organ--predominantly the utricle--is generated, without involving the semicircular canals. This paradigm has been employed to measure the unilateral utriculo-ocular response. In contrast to the otolith-ocular response (OOR), the subjective visual vertical (SVV) reflects the processing of otolithic information in the higher brain centres (thalamus, vestibular cortex). Exploitation of these two complementary approaches provides useful information for both experimental and clinical scientists. The findings also reveal that centripetal acceleratory stimulation during constant angular velocity with the subject centred on axis is sufficient to localize peripheral otolith dysfunction by means of SVV estimation. This represents a novel test of otolith function that can be easily integrated into routine clinical testing.

Ocular Counterrolling in Response to Asymmetric Radial Acceleration

The fact that the labyrinths are positioned at approx. 3.5 cm from the head-centric axis leads to the generation of systematic radial acceleratory, or centrifugal, forces during physiological head rotations. Under physiological conditions, the forces exerted on the right and left maculae are generally assumed to be equal and opposite. In the present test, however, the subject was displaced eccentrically during constant angular velocity so that one labyrinth was aligned concentrically with the rotatory axis, whilst the other was exposed to the radial acceleration component generated by the chair rotation. In comparison with previous testing based on subjective setting of the visual vertical, three-dimensional eye movements were recorded in order to obtain an objective measure of the otolith-ocular response mechanisms in the brainstem. The results obtained from normal subjects demonstrate a predominant ocular counterroll (OCR) response to this asymmetric, or unilateral application of linear acceleration. The direction of the OCR response proved to be independent of direction of rotation. The findings demonstrate a symmetrical response magnitude for stimulation of the left and right maculae. In comparison with the OCR response to head-tilt, which can be described as critically damped, the time course of the present response appeared to be underdamped.

Evidence of unilateral isolated utricular hypofunction

Abstract Conclusions: The findings demonstrate that an enduring unilateral utricular dysfunction, possibly together with canal hypofunction, can occur after labyrinthine disease or injury. They also suggest that unilateral, isolated utricular dysfunction – or utricle paresis – can occur, representing a novel entity in the differential diagnosis of peripheral vestibular function. The occurrence of subjective visual vertical (SVV) asymmetry in the presence of symmetric vestibular evoked myogenic potentials (VEMPs) also confirms that the information from the utricles, rather than the saccules, dominates SVV estimation. Objectives: To determine the incidence of unilateral utricular hypofunction. Methods: The retrospective clinical study deals with a selection of those vestibular patients who showed pathological responses to utricle testing. Peripheral vestibular function was examined in a group of 110 patients. Utricular function was evaluated by estimation of SVV during unilateral centrifugation. Bithermal caloric testing was performed to assess unilateral semicircular canal function. Saccular function was tested by measurement of VEMPs. Results: A total of 46 patients were found with asymmetric SVV findings (p < 0.001 for healthy versus lesioned ear), but symmetric caloric responses and VEMPs. Statistical testing also verified that their SVV asymmetry factors were significantly higher than those calculated for caloric responses and VEMPs (p < 0.001).