Biomedical subjects

Thomas Haslwanter

Publications and source records attributed to Thomas Haslwanter.

10 recordsLinked to original sources

PubMed2005

Angular vestibulo-ocular reflex gains correlate with vertigo control after intratympanic gentamicin treatment for Meniere's disease.

OBJECTIVES: The objective of our study was to determine whether angular vestibulo-ocular reflex (aVOR) gains correlated with vertigo control after intratympanic gentamicin treatment for Meniere's disease. METHODS: We conducted a prospective study of 18 subjects with unilateral Meniere's disease treated with intratympanic gentamicin injection and followed all subjects for 1 year. We measured the gain of the aVOR elicited by rapid rotary head thrusts in each of the canal planes for each subject before and after treatment with intratympanic gentamicin by using magnetic search coils to record eye movements. RESULTS: During the follow-up period, 11 subjects ("single-treatment group"; 61%) had control of their vertigo with a single gentamicin injection. The remaining 7 subjects ("multiple-treatment group"; 39%) experienced recurrent vertigo that required a second injection of gentamicin at a mean of 6 months after the first treatment. The 11 subjects in the single-treatment group had significantly greater reduction of labyrinthine function after the first treatment, as measured by change in ipsilateral horizontal canal gain, than did the 7 subjects with vertigo recurrence. Changes in caloric asymmetry did not correlate with vertigo control. CONCLUSIONS: Our results suggest that successful treatment of Meniere's disease is closely related to attenuation of semicircular canal function as measured by horizontal canal aVOR gains.

Adult↗

PubMed2004

Enhanced smooth pursuit eye movements in patients with bilateral vestibular deficits.

Patients with bilateral vestibular deficits experience unsteady gait and oscillopsia that can reduce the quality of life, though many patients adapt remarkably well and lead mostly normal lives. One source of adaptation could be the ability of sensory-motor systems to compensate for the vestibular loss by adaptive enhancement of their performance. We studied smooth-pursuit eye movements in five patients and six healthy control subjects using a step-ramp paradigm. Eye movements were measured with scleral search coils. Patients showed open- and closed-loop pursuit gains that were about 9% higher than controls. We suggest that the challenge of living with a deficient vestibular system caused an enhancement in the pursuit system, which contributes to the patient's overall compensation.

Adult↗

PubMed2004

Human 3-D aVOR with and without otolith stimulation.

We describe in detail the frequency response of the human three-dimensional angular vestibulo-ocular response (3-D aVOR) over a frequency range of 0.05-1 Hz. Gain and phase of the human aVOR were determined for passive head rotations in the dark, with the rotation axis either aligned with or perpendicular to the direction of gravity (earth-vertical or earth-horizontal). In the latter case, the oscillations dynamically stimulated both the otolith organs and the semi-circular canals. We conducted experiments in pitch and yaw, and compared the results with previously-published roll data. Regardless of the axis of rotation and the orientation of the subject, the gain in aVOR increased with frequency to about 0.3 Hz, and was approximately constant from 0.3 to 1 Hz. The aVOR gain during pitch and yaw rotations was larger than during roll rotations. Otolith and canal cues combined differently depending upon the axis of rotation: for torsional and pitch rotations, aVOR gain was higher with otolith input; for yaw rotations the aVOR was not affected by otolith stimulation. There was a phase lead in all three dimensions for frequencies below 0.3 Hz when only the canals were stimulated. For roll and pitch rotations this phase lead vanished with dynamic otolith stimulation. In contrast, the horizontal phase showed no improvement with additional otolith input during yaw rotations. The lack of a significant otolith contribution to the yaw aVOR was observed when subjects were supine, prone or lying on their sides. Our results confirm studies with less-natural stimuli (off-vertical axis rotation) that the otoliths contribute a head-rotation signal to the aVOR. However, the magnitude of the contribution depends on the axis of rotation, with the gain in otolith-canal cross-coupling being smallest for yaw axis rotations. This could be because, in humans, typical yaw head movements will stimulate the otoliths to a much lesser extent then typical pitch and roll head movements.

Gravitation↗

PubMed2004

Improving calibration of 3-D video oculography systems.

Eye movement recordings with video-based techniques have become very popular, as long as they are restricted to the horizontal and vertical movements of the eye. Reliable measurement of the torsional component of eye movements, which is especially important in the diagnosis and investigation of pathologies, has remained a coveted goal. One of the main reasons is unresolved technical difficulties in the analysis of video-based images of the eye. Based on simulations, we present solutions to two of the primary problems: a robust and reliable calibration of horizontal and vertical eye movement recordings, and the extraction of suitable iris patterns for the determination of the torsional eye position component.

Algorithms↗

PubMed2004

Ocular rotation axes during dynamic Bielschowsky head-tilt testing in unilateral trochlear nerve palsy.

PURPOSE: To explain the positive Bielschowsky head-tilt (BHT) sign in unilateral trochlear nerve palsy (uTNP) by the kinematics of three-dimensional eye rotations. METHODS: Twelve patients with uTNP monocularly fixed on targets on a Hess screen were oscillated (+/- 35 degrees, 0.3 Hz) about the roll axis on a motorized turntable (dynamic BHT). Three-dimensional eye movements were recorded with dual search coils. Normal data were collected from 11 healthy subjects. RESULTS: The rotation axis of the viewing paretic or unaffected eye was nearly parallel to the line of sight. The rotation axis of the covered fellow eye, however, was tilted inward relative to the other axis. This convergence of axes increased with gaze toward the unaffected side. Over entire cycles of head roll, the rotation axis of either eye remained relatively stable in both the viewing and covered conditions. CONCLUSIONS: In patients with uTNP, circular gaze trajectories of the covered paretic or unaffected eye during dynamic BHT are a direct consequence of the nasal deviation of the rotation axis from the line of sight. This, in turn, is a geometrical result of decreased force by the superior oblique muscle (SO) of the covered paretic eye or, according to Hering's law, increased force parallel to the paretic SO in the covered unaffected eye. The horizontal incomitance of rotation axes along horizontal eye positions can be explained by the same mechanism.

Adolescent↗

PubMed2003

Dependence of adaptation of the human vertical angular vestibulo-ocular reflex on gravity.

We determined the spatial dependence of adaptive gain changes of the vertical angular vestibulo-ocular reflex (aVOR) on gravity in five human subjects. The gain was decreased for 1 h by sinusoidal oscillation in pitch about a spatial vertical axis in a subject-stationary surround with the head oriented left-side down. Gains were tested by sinusoidal oscillation about a spatial vertical axis while subjects were tilted in 15 degrees increments from left- to right-side down positions through the upright. Changes in gain of the vertical component of the induced eye movements were expressed as a percentage of the preadapted values for the final analysis. Vertical aVOR gain changes were maximal in the position in which the gain had been adapted and declined progressively as subjects were moved from this position. Gain changes were plotted as a function of head orientation and fit with a sine function. The bias level of the fitted sines, i.e., the gravity-independent gain change, was -29+/-10% (SD). The gains varied around this bias as a function of head position by +/-18+/-6%, which were the gravity-dependent gain changes. The gravity-dependent gain changes induced by only 1 h of adaptation persisted, gradually declining over several days. We conclude that there is a component of the vertical aVOR gain change in humans that is dependent on the head orientation in which the gain was adapted, and that this dependence can persist for substantial periods.

Adaptation, Physiological↗

PubMed2003

Eye movements during multi-axis whole-body rotations.

The semi-circular canals and the otolith organs both contribute to gaze stabilization during head movement. We investigated how these sensory signals interact when they provide conflicting information about head orientation in space. Human subjects were reoriented 90 degrees in pitch or roll during long-duration, constant-velocity rotation about the earth-vertical axis while we measured three-dimensional eye movements. After the reorientation, the otoliths correctly indicated the static orientation of the subject with respect to gravity, while the semicircular canals provided a strong signal of rotation. This rotation signal from the canals could only be consistent with a static orientation with respect to gravity if the rotation-axis indicated by the canals was exactly parallel to gravity. This was not true, so a cue-conflict existed. These conflicting stimuli elicited motion sickness and a complex tumbling sensation. Strong horizontal, vertical, and/or torsional eye movements were also induced, allowing us to study the influence of the conflict between the otoliths and the canals on all three eye-movement components. We found a shortening of the horizontal and vertical time constants of the decay of nystagmus and a trend for an increase in peak velocity following reorientation. The dumping of the velocity storage occurred regardless of whether eye velocity along that axis was compensatory to the head rotation or not. We found a trend for the axis of eye velocity to reorient to make the head-velocity signal from the canals consistent with the head-orientation signal from the otoliths, but this reorientation was small and only observed when subjects were tilted to upright. Previous models of canal-otolith interaction could not fully account for our data, particularly the decreased time constant of the decay of nystagmus. We present a model with a mechanism that reduces the velocity-storage component in the presence of a strong cue-conflict. Our study, supported by other experiments, also indicates that static otolith signals exhibit considerably smaller effects on eye movements in humans than in monkeys.

Adult↗

PubMed2003

Incomitance of ocular rotation axes in trochlear nerve palsy.

Strabismus due to palsy of a single muscle in one eye is always incomitant, which is a consequence of Hering's law of equal innervation. We asked whether this law had similar consequences on the orientation of ocular rotation axes. Patients with unilateral trochlear nerve palsy were oscillated about the nasooccipital (= roll) axis (+/-35 degrees, 0.3 Hz), and monocularly fixed on targets on a head-fixed Hess screen. Both the covered and uncovered eyes were measured with dual search coils. The rotation axis of the covered eye (paretic or healthy) tilted more nasally from the line of sight when gaze was directed toward the side of the healthy eye. The rotation axis of the viewing eye (paretic or healthy), however, remained roughly aligned with the line of sight. We conclude that incomitance due to eye muscle palsy extends to ocular rotation axes during vestibular stimulation.

Adolescent↗

PubMed2002

Changes in the three-dimensional angular vestibulo-ocular reflex following intratympanic gentamicin for Ménière's disease.

The 3-dimensional angular vestibulo-ocular reflexes (AVOR) elicited by rapid rotary head thrusts were studied in 17 subjects with unilateral Ménière's disease before and 2-10 weeks after treatment with intratympanic gentamicin and in 13 subjects after surgical unilateral vestibular destruction (SUVD). Each head thrust was in the horizontal plane or in either diagonal plane of the vertical semicircular canals, so that each head thrust effectively stimulated only one pair of canals. The AVOR gains (eye velocity/head velocity during the 30 ms before peak head velocity) for the head thrusts exciting each individual canal were averaged and taken as a measure of the function of that canal. Prior to intratympanic gentamicin, gains for head thrusts that excited canals on the affected side were 0.91 +/- 0.20 (horizontal canal, HC), 0.78 +/- 0.20 (anterior canal, AC), and 0.83 +/- 0.10 (posterior canal, PC). The asymmetries between these gain values and those for head thrusts that excited the contralateral canals were <2%. In contrast, caloric asymmetries averaged 40% +/- 32%. Intratympanic gentamicin resulted in decreased gains attributable to each canal on the treated side: 0.40 +/- 0.12 (HC), 0.35 +/- 0.14 (AC), 0.31 +/- 0.14 (PC) (p <0.01). However, the gains attributable to contralateral canals dropped only slightly, resulting in marked asymmetries between gains for excitation of ipsilateral canals versus their contralateral mates: HC: 34% +/- 12%, AC: 24% +/- 25%, and PC: 42% +/- 13%. There was no difference in the AVOR gain for excitation of the ipsilateral HC after gentamicin in patients who received a single intratympanic injection (0.39 +/- 0.11, n = 12) in comparison to those who received 2-3 injections (0.42 +/- 0.15, n = 5, p = 0.7). Gain decreases attributed to the gentamicin-treated HC and AC were not as severe as those observed after SUVD. This finding suggests that intratympanic gentamicin causes a partial vestibular lesion that may involve preservation of spontaneous discharge and/or rotational sensitivity of afferents.

Adult↗

PubMed2002

Mechanics of eye movements: implications of the "orbital revolution".

Our understanding of the functional structure of extraocular muscles has undergone a profound change: while these muscles used to be represented by strings running straight from their origin in the posterior orbita to their insertion on the globe, we now know that their paths and pulling directions are dominated by fibromuscular pulley structures, keeping them close to the orbital wall for most of their path. An overview is presented of recent models that have been developed to understand the implications of muscle pulleys for the neural control of eye movements and the applications of such models to the interpretation of experimental data.

Animals↗