A new vestibulo-ocular reflex recording system designed for routine vestibular clinical use.

A new vestibulo-ocular reflex (VOR) recording system was developed, which consists of an infrared eye camera, a small velocity sensor and a frequency modulator. Using this system, the head velocity signal was frequency modulated and simultaneously recorded as a sound signal on the audio track of a Hi8 video recorder with eye images. This device enabled recording of the VOR response in routine vestibular clinical practice. The reliability and effectiveness of this system were estimated by recording and analysing the VOR response against manually controlled rotation in normal subjects (n = 22) and in patients with unilateral severe vestibular hypofunction (n = 11). VOR gain on clockwise rotation viewed from the top was defined as R gain, and counterclockwise rotation as L gain. Directional preponderance (DP%) was also calculated. VOR gain towards the diseased side was significantly lower than that towards the intact side, and also significantly lower than that of normal subjects. DP% of unilateral vestibular hypofunction cases was significantly larger than that of normal subjects. These findings indicate that this VOR recording system reliably detects severe unilateral vestibular hypofunction.     

VOR gain and phase in active head rotation tests of normal subjects and patients with peripheral labyrinthine lesions

The gain and phase of the vestibulo-ocular reflex (VOR) were studied by active head rotation tests in normal subjects and in patients with unilateral or bilateral lesions of vestibular function. The examination was performed under two conditions: alert-in-dark and with spatially-fixed target. The results were evaluated using a simplified model of vestibular response. Under alert-in-dark condition, the VOR grain and phase deficits were observed on rotation to the affected side in patients with unilateral lesions and bilaterally in patients with bilateral lesions. Under spatially-fixed-target condition, these patients showed a decrease in gain at higher frequencies but no phase lag was observed. The principally new advantage was that not only VOR gain but also VOR phase could be quantified using this active head rotation test. Therefore, for diagnosing VOR dysfunction, this active head rotation test is more useful than the active head rotation tests previously reported.     

Recovery of the otolith-ocular reflex after unilateral deafferentation of the otolith organs in squirrel monkeys

The enhancement of the vestibulo-ocular reflex (VOR) gain in the eccentric rotation is mediated by the otolith organs. Functional recovery of the otolith-ocular reflex after deafferentation of the otolith organs was examined in squirrel monkeys, using the enhancement of the eccentric VOR gain as an indicator of the reflex. After unilateral deafferentation of the otolith organs, the enhancement of the eccentric VOR gain decreased and then recovered completely within eight weeks. However, the eccentric VOR gain was not enhanced after contralateral side lesions. These findings demonstrate that functional recovery of the otolith-ocular reflex is achieved after unilateral deafferentation of the otolith organs, and that afferents from the remaining otolith organs are necessary for the functional compensation.     

Unilateral Adaptation of the Human Angular Vestibulo-Ocular Reflex

A recent study showed that the angular vestibulo-ocular reflex (VOR) can be better adaptively increased using an incremental retinal image velocity error signal compared with a conventional constant large velocity-gain demand (×2). This finding has important implications for vestibular rehabilitation that seeks to improve the VOR response after injury. However, a large portion of vestibular patients have unilateral vestibular hypofunction, and training that raises their VOR response during rotations to both the ipsilesional and contralesional side is not usually ideal. We sought to determine if the vestibular response to one side could selectively be increased without affecting the contralateral response. We tested nine subjects with normal vestibular function. Using the scleral search coil and head impulse techniques, we measured the active and passive VOR gain (eye velocity / head velocity) before and after unilateral incremental VOR adaptation training, consisting of self-generated (active) head impulses, which lasted ∼15 min. The head impulses consisted of rapid, horizontal head rotations with peak-amplitude 15 ^o, peak-velocity 150 ^o/s and peak-acceleration 3,000 ^o/s². The VOR gain towards the adapting side increased after training from 0.92 ± 0.18 to 1.11 ± 0.22 (+22.7 ± 20.2 %) during active head impulses and from 0.91 ± 0.15 to 1.01 ± 0.17 (+11.3 ± 7.5 %) during passive head impulses. During active impulses, the VOR gain towards the non-adapting side also increased by ∼8 %, though this increase was ∼70 % less than to the adapting side. A similar increase did not occur during passive impulses. This study shows that unilateral vestibular adaptation is possible in humans with a normal VOR; unilateral incremental VOR adaptation may have a role in vestibular rehabilitation. The increase in passive VOR gain after active head impulse adaptation suggests that the training effect is robust.     

Long-term modifications of vertical and horizontal vestibulo-ocular reflex dynamics in man. I. After acute unilateral peripheral vestibular paralysis

Horizontal (HOR) and vertical (VERT) vestibulo-ocular reflex (VOR) responses to whole-body triangular velocity profiles with constant accelerations of 10, 15 and 20 deg/s2 were studied in two populations: normals, and patients with acute unilateral peripheral vestibular paralysis. The effect of this type of unilateral deficit on VOR gain and long time constant were determined as well as the time course of the compensation processes for HOR and VERT VOR dynamics. In the patient population, HOR VOR gain was asymmetric post deficit, being, on average, 50% and 75% of normal for rotations toward and away from the deficit, respectively. For the VERT VOR, on average, a symmetric 66% reduction occurred. The VERT VOR time constant was marginally affected by the deficit. HOR time constants were reduced for both directions of rotation. HOR and VERT VOR gain was within normal limits 1-3 months following an acute paralysis; time constants required a longer recovery period. Our results indicate that a unilateral deficit causes a markedly different alteration for HOR VOR dynamics compared to the effect on VERT VOR.     

Characterization of the vestibulo-ocular reflex evoked by high-velocity movements

OBJECTIVES/HYPOTHESIS: The horizontal angular vestibulo-ocular reflex (VOR) plays an important role in stabilizing images on the retina throughout head rotations. Current evidence suggests that the VOR behaves linearly at low velocities and nonlinearly at high velocities. The aim of the research was to evaluate and characterize the normal behavior of the reflex evoked by high-velocity head rotations. STUDY DESIGN: Case control study. METHODS: Manually applied head-thrust movements with peak velocities in the range of 100degrees to 500degrees/s and peak accelerations up to 7,000degrees/s were performed on normal volunteers. These head thrusts were comparable with those described in detail by Halmagi and coworkers. Eye and head movements were recorded using the magnetic search coil method. RESULTS: The gain of the VOR is linear at low velocities and saturates at head velocities greater than 350degrees/s. The values for the normal gain of the reflex were approximated by means of the area between two nonlinear functions. The directional difference parameter, exploring the symmetry of the reflex, indicated that the VOR in normal subjects is symmetric. CONCLUSION: The gain of the VOR in individuals with intact vestibular function is nonlinear at high angular head velocities. We propose a quantitative means using two nonlinear functions to characterize the normal range of values for the gain of the VOR in individuals with normal vestibular function. A directional difference parameter used in conjunction with the normal range of gains can detect small differences in the symmetry of the VOR and, consequently, reveal unilateral vestibular loss.     

Characteristics of vestibulo-ocular interactions in patients with unilateral lesions of the peripheral part of the vestibular system. Sinusoidal rotation. 3

In 40 patients with unilateral injury of the peripheral compartment of the vestibular system in the stage of decompensation (Group 1) and subdecompensation (Group 2), the vestibulo-ocular reflex (VOR) was investigated during sinusoidal rotation with the eyes closed. Group 1 patients showed a significant asymmetry of the VOR coefficient and a distinct shift of the VOR displacement towards injury during sinusoidal stimulation of any intensity. Group 2 patients displayed similar but less significant changes.     

Vestibular function at the end of intratympanic gentamicin treatment of patients with Ménière's disease

The aim of this study is to analyze the effects of intratympanic gentamicin injections on vestibular function in 33 patients with unilateral Meniere's Disease (according to AAO-HNS guidelines 1995) that had been unresponsive to medical therapy for at least one year. In such patients, the results of bedside examination of vestibular function vestibular examination is compared to those from laboratory tests. Intratympanic gentamicin injections (27 mg/ml) were performed at weekly intervals until symptoms or signs of vestibular hypofunction developed in the treated ear. Vestibular function was evaluated in two different rotatory chair tests. The parameters that were specifically considered were the time constant of the vestibulo-ocular reflex (VOR) after impulse rotation with a peak chair velocity of 100 degrees s(-1), and the phase and gain of the VOR after the sinusoidal harmonic acceleration (SHA) test with a peak chair velocity of 50 degrees s(-1). After treatment, both the time constant of the VOR after rotation towards the treated side and the gain in the SHA test were significantly reduced. These reductions were in accordance with the number of additional signs observed upon bedside examination at the end of the treatment. The changes observed in the VOR correlate well with the results of bedside examination of vestibular function, which in turn reflects the damage induced by intratympanic gentamicin injection.     

Relation of video-head-impulse test and caloric irrigation: a study on the recovery in unilateral vestibular neuritis

The head-impulse test (HIT) is an important test for examining unilateral vestibular hypofunction. The new video-head-impulse test (vHIT) is more sensitive and specific than the clinical bedside-head-impulse test. Alternatively, one can test for vestibular hypofunction with the caloric irrigation test. Various studies have shown that both tests may not always identify vestibular hypofunction; instead, the results of the tests might be contradictory. To further explore the question, of whether vHIT and caloric irrigation test the same part of the angular horizontal vestibulo-ocular reflex (VOR), we examined patients with unilateral vestibular neuritis at different points in time. The tonic vestibular imbalance (e.g., subjective-visual-vertical, ocular torsion and spontaneous nystagmus) and dynamic dysfunction of VOR (vHIT and bithermal caloric irrigation) were measured and quantified. While parameters of the tonic vestibular imbalance were well described by single exponential decay functions, dynamic parameters were less well defined. Therefore, to better compare the time course of pairs of two different parameters, we used a linear regression analysis. No linear correlation was found in the group and individually for the gain asymmetry and the ipsilesional gain of the vHIT with the unilateral weakness of the bithermal caloric irrigation tests. Linear correlation was found for most parameters of tonic vestibular imbalance. These findings are further evidence that vHIT and caloric irrigation test different parts of the angular VOR.     

Comparative study of the effect of gentamicin on the vestibulo-ocular and visual vestibulo-ocular reflexes in the cat

The ototoxic effect of an aminoglycoside, gentamicin, on the vestibular system was investigated in cats given daily doses of 40 mg/kg i.m. for 14 days. Periodically, measurements were made of the vestibulo-ocular reflex (VOR) and visual vestibulo-ocular reflex (ViVOR) responses induced by rotatory stimuli at various frequencies from 0.0125 Hz to 0.8 Hz. After the cessation of drug administration, a progressively declining response to VOR stimuli continued, manifested by gain (ratio of peak response to peak stimulus amplitude) and phase relationships. The ViVOR was affected only in the gain measurements. The changes in the response amplitude (gain) were greater for the VOR than for the ViVOR responses and also for the lower (0.0125 Hz) than for the higher frequencies (0.8 Hz). There was some indication that the responses improved about one month after treatment was terminated. All of these specific response changes in cats are comparable to the known effects of aminoglycides in humans, and the same theoretical interpretation of the data in the context of a model of vestibular function can be applied in both cases.     

Patterns of vestibular function following vestibular nerve section.

Bithermal caloric irrigations, low-frequency rotational chair stimulation, and posturography were performed on 20 patients before and after vestibular nerve section. Twelve patients demonstrated acute postoperative spontaneous nystagmus and rotational vestibulo-ocular reflex (VOR) asymmetry. Eight patients demonstrated minimal acute postoperative spontaneous nystagmus and VOR asymmetry. Four patients had suppression of all vestibular function characterized by an absent contralateral caloric response, low VOR gain, and falls on posturography when required to rely solely on vestibular input to maintain posture. Four patients had a severe preoperative vestibular loss and no acute change in vestibular function following surgery. Over time, 5 patients continued to manifest elevated spontaneous nystagmus, 2 patients manifested a persistent rotational VOR asymmetry, and 5 patients exhibited a return of caloric function in the operated ear. It is suggested that multiple clinical factors contributed to the variable vestibular responses demonstrated in this study.     

Vestibulo-ocular responses during static head roll and three-dimensional head impulses after vestibular neuritis

This study aimed to investigate whether unilateral vestibular neuritis (VN) causes the same deficits of ocular counter-roll during static head roll (OCR(S)) and dynamic vestibulo-ocular reflex gains during head impulses (VOR(HI)) as unilateral vestibular deafferentation (VD). Ten patients with acute and 14 patients with chronic vestibular paralysis after VN were examined. The testing battery included fundus photography of both eyes with the head upright (binocular cyclorotation) and dual search coil recordings in a three-field magnetic frame. With one dual search coil on the right eye and the other on the forehead, the following stimuli were given: i) Halmagyi-Curthoys head impulses about the vertical, horizontal and torsional axes. ii) Static roll positions of the head up to 20 degrees right- and left-ear-down by movement of the neck. The comparison group consisted of 19 healthy subjects. Compared with the VD-patients, as reported in the literature, acute VN-patients showed the same pattern of OCR(S) gain reduction and binocular cyclorotation (CRb). The main feature that distinguished chronic VN-patients from chronic VD-patients was the normalization of the torsional VOR(HI) gain to the affected side, whereas the VOR(HI) gains in the horizontal and vertical directions did not show recovery (as in the patients with chronic VD). Chronic VN-patients differed from acute VN-patients by: i) symmetrical OCR(S) gains, ii) a less pronounced CRb toward the affected side, and iii) a normal torsional VOR(HI) gain toward the affected side. Since the ipsilesional torsional VOR(HI) gain did not recover in VD-patients, the normalization of this gain in our VN-patients can only be explained by a (partial) recovery of otolith function on the side of the lesion after the neuritis.     

Influence of age on vestibulo-ocular reflex (VOR)

In this article we discuss the influence of age on the vestibulo-ocular reflex in a comparison of data from different age groups. In order to examine the influence of age, the pendular rotation test was performed in 25 otoneurologically healthy subjects and 12 patients with unilateral peripheral vestibular disorders, from 25 to 72 years of age. The subjects were divided into three groups: 20-39, 40-64 and older than 65 years. The stimulus modes were an amplitude and a frequency of 30 degrees at 0.25 Hz and of 60 degrees at 0.1 Hz, respectively. The gain, phase lag and visual suppression in VOR of the pendular rotation test were measured, and the age-dependent changes in these scores were evaluated. The following results were obtained: 1. The gain in VOR with eyes open in a dark booth was significantly decreased in the older than 65 years group. 2. The phase lag was significantly increased in the older than 65 years group. 3. There were no significant differences of VOR-visual suppression between any of the age groups. The gain in normal subjects was significantly larger than that of the affected side in patients with unilateral peripheral vestibular disorders. The phase lag in patients with unilateral peripheral vestibular disorders was significantly larger than in normal subjects. Similar to normal subjects, this stimulation caused no significant differences in the VOR-VS between the affected side and the normal side in patients with unilateral peripheral vestibular disorders.     

Effects of unilateral loss of vestibular function on the vestibulo-ocular reflex and postural control

Long-term recovery from surgically induced unilateral loss of vestibular function was studied in 14 patients. Seven patients underwent surgical extirpation or section of the vestibular nerve, and seven patients underwent labyrinthectomy without vestibular nerve section. The vestibulo-ocular reflex (VOR) and postural control were evaluated preoperatively and monitored for up to 4 years postoperatively with use of pseudorandom rotation (combined sinusoidal frequencies from 0.009 to 1.5 Hz) and moving platform posturography. Immediately following surgery all patients showed minimal reductions in the VOR gain constant, but marked reduction in the time constant, and marked increase in slow eye velocity bias. Bias returned to normal values within about 10 days, but time constants never returned to normal values. Results of standard Romberg tests in these patients were normal throughout the preoperative and postoperative periods. However, all patients showed marked postural control abnormalities in tests of the ability to maintain balance in unusual sensory environments in the immediate postoperative period. Seventy-five percent of the patients eventually recovered normal postural control. Postural control returned to near baseline performance with a time course similar to that of the VOR bias. However, postural control also continued to improve after the recovery of VOR bias was complete.     

Expression of Human ß-defensin 1 mRNA in Human Nasal Mucosa

The vestibulo-ocular reflex (VOR) allows clear vision during head movements by generating compensatory eye movements. Its response is reduced following damage to the vestibular endorgan, but recovers over time. The VOR is mediated by both direct and indirect anatomical pathways; most direct pathways include only two central synapses, both located in the brainstem. To investigate the possibility that a direct pathway is modified during the recovery of VOR gain, we measured the oculomotor response to single current pulses delivered to the vestibular labyrinth of two alert cats after plugging the contralateral horizontal canal. The response was also measured after motor learning induced by continuously worn lenses (optically induced motor learning) in two cats. The gain of the VOR was monitored concurrently. The eye movement evoked by a current pulse increased more than 100% during recovery from a plug. The electrically evoked eye movement did not change during optically induced motor learning either before the plug or after recovery. The gain of the VOR was modified in both situations. We conclude that direct VOR pathways are modified significantly during recovery after a plug, but not during optically induced learning. Our results suggest that significant modification of direct pathways may require a change in vestibular sensory input.     

Increased transmission by direct vestibulo-ocular reflex pathways after peripheral vestibular damage: a preliminary report

The vestibulo-ocular reflex (VOR) allows clear vision during head movements by generating compensatory eye movements. Its response is reduced following damage to the vestibular endorgan, but recovers over time. The VOR is mediated by both direct and indirect anatomical pathways; most direct pathways include only two central synapses, both located in the brainstem. To investigate the possibility that a direct pathway is modified during the recovery of VOR gain, we measured the oculomotor response to single current pulses delivered to the vestibular labyrinth of two alert cats after plugging the contralateral horizontal canal. The response was also measured after motor learning induced by continuously worn lenses (optically induced motor learning) in two cats. The gain of the VOR was monitored concurrently. The eye movement evoked by a current pulse increased more than 100% during recovery from a plug. The electrically evoked eye movement did not change during optically induced motor learning either before the plug or after recovery. The gain of the VOR was modified in both situations. We conclude that direct VOR pathways are modified significantly during recovery after a plug, but not during optically induced learning. Our results suggest that significant modification of direct pathways may require a change in vestibular sensory input.     

Validity and limitation of detection of peripheral vestibular imbalance from analysis of manually rotated vestibulo-ocular reflex recorded in the routine vestibular clinic

We compared the results of analysis of vestibulo-ocular reflex (VOR) obtained by manual rotation in routine vestibular clinical practice with that of caloric testing, and examined the validity and limitations of VOR analysis as a test for the estimation of peripheral vestibular function and imbalance. VOR response was recorded in daily vestibular clinical examinations by manually rotating the standard clinical chair for approximately 30 s. VOR gain was slightly, but significantly, correlated with the peak slow phase velocity of caloric response (r = 0.50, p < 0.001). However, 8 out of 12 patients with no caloric response failed to exceed the range of two standard deviations of the mean value of age-matched normal subjects, indicating that it is clinically difficult to use VOR gain alone as a estimate of unilateral vestibular function. VOR directional preponderance (VOR DP%) correlated well with caloric canal paresis (CP) (CP%; r = 0.89, p < 0.001). VOR DP% was within the normal range in patients with caloric CP% < 40 and exceeded the normal range in most cases with caloric CP% > 80. VOR DP% varied widely when caloric CP% ranged between 40 and 80. The effect of vestibular compensation on VOR DP% was examined by plotting VOR DP% divided by caloric CP% (DP/CP) against the number of days since the onset of vertigo in patients with vestibular neuritis or sudden deafness with vertigo. DP/CP was large within 50 days of the onset of vestibular damage, especially when caloric CP% was < 80, and gradually decreased with time. These results indicate that determination of VOR DP% should contribute to the early diagnosis of fresh vestibular imbalance, especially in daily clinical practice, because this type of VOR recording can be performed in < 1 min in routine vestibular clinics. The decay time constant of DP/CP was larger when caloric CP% exceeded 80, indicating that vestibular compensation proceeds more slowly when the vestibular damage is severe.     

Validity and limitation of manual rotational test to detect impaired visual-vestibular interaction due to cerebellar disorders

The aim of this study was to investigate validity and limitation of the novel infrared system to record and analyze horizontal visual-vestibular interaction using whole-body rotation rapidly and conveniently in the routine vestibular clinic. We examined 11 patients with cerebellar dysequilibrium and 25 patients with peripheral dysequilibrium for vestibulo-ocular reflex in darkness (DVOR), visually-enhanced vestibulo-ocular reflex (VEVOR), and fixation suppression of vestibulo-ocular reflex (FSVOR), and compared the results with those of examination for head-fixed smooth pursuit and fixation suppression during caloric stimulation. The manual rotation stimuli were 0.5-0.75 Hz in frequency and 60-90 degrees /s in maximal angular velocity. Gain of vestibulo-ocular reflex in darkness was not significantly correlated with maximal slow phase velocity (MSPV) of caloric-induced nystagmus at that stimulus condition either in patients with peripheral dysequilibrium or in those with cerebellar dysequilibrium. An index for fixation suppression of vestibulo-ocular reflex during rotation stimulus was significantly lower in patients with cerebellar dysequilibrium than in normal control subjects and those with peripheral dysequilibrium. On the other hand, there was no significant difference among the two disease groups and the normal control group in gain of visually-enhanced vestibulo-ocular reflex. In about a half of patients with cerebellar dysequilibrium, measured smooth pursuit gain was lower than estimated smooth pursuit gain calculated based on a simple superposition theory of vestibulo-ocular reflex and smooth pursuit. Testing fixation suppression using the present system is an unusually convenient tool for detection of cerebellar dysequilibrium.     

Voluntary control of the human vestibulo-ocular reflex

The ability of normal subjects to increase their vestibulo-ocular reflex (VOR) gain with an imagined stationary frame of reference was dependent on their strategy and the test conditions. With large amplitude sinusoidal rotation (greater than 50 degrees) subjects could not increase their VOR gain regardless of the strategy used. With small amplitude excursions (less than 50 degrees) they could significantly increase their VOR gain if they used a 'single stripe' strategy. Accompanying this increase in VOR gain was an increase in the phase lead of VOR slow phase velocity relative to head velocity. Apparently the signal used to augment the VOR gain with an imagined stationary surround had phase characteristics similar to those of primary vestibular afferent neurons.     

The dynamics of the vestibulo-ocular reflex in patients with vestibular neuritis

The dynamics of the vestibulo-ocular reflex (VOR) were studied in 14 patients at the onset of vestibular neuritis, and at follow-up 1 year later. A velocity step stimulus of 150 degrees/s was used to investigate the VOR time constant and gain, and the results were related to the caloric response. In the acute, vertiginous phase of the disease, the VOR time constant was reduced but was almost normalized 1 year later, both among patients who regained normal caloric side-difference and among those who did not. However, the increase in VOR time constant was greater among those who regained normal caloric excitability, and regression analysis showed a correlation between the prolongation of the VOR time constant and the recovery of caloric excitability. These findings suggest that VOR dynamics are modulated during the acute phase of vestibular neuritis, and that there is recovery with vestibular compensation. Furthermore, the recovery of the VOR time constant is not solely dependent on the recovery of normal caloric excitability. This implies that central storage of velocity information may be involved in the VOR, even in cases of asymmetric vestibular input after vestibular compensation.