Changes In Vestibulo-ocular Reflex Research Articles

Trunk Instability in the Pitch, Yaw, and Roll Planes during Clinical Balance Tests: Axis Differences and Correlations to vHIT Asymmetries Following Acute Unilateral Vestibular Loss

BACKGROUND: Clinical dynamic posturography concentrates on the pitch and roll but not on the yaw plane instability measures. This emphasis may not represent the axis instability observed in clinical stance and gait tasks for patients with balance deficits in comparison to healthy control (HC) subjects, nor the expected instability based on correlations with vestibulo-ocular reflex (VOR) deficits. To examine the axis stability changes with vestibular loss, we measured trunk sway in all three directions (pitch, roll, and yaw) during the stance and gait tasks of patients with acute unilateral vestibular neuritis (aUVN) and compared the results with those of HC. Concurrent changes in VORs were also examined and correlated with trunk balance deficits. METHODS: The results of 11 patients (mean age of 61 years) recorded within 6 days of aUVN onset were compared within those of 8 age-matched healthy controls (HCs). All subjects performed a two-legged stance task—standing with eyes closed on foam (s2ecf), a semi-gait task—walking eight tandem steps (tan8), and four gait tasks—walking 3 m with head rotating laterally, pitching, or eyes closed (w3hr, w3hp, w3ec), and walking over four barriers 24 cm high, spaced 1 m apart (barr). The tasks’ peak-to-peak yaw, pitch and roll angles, and angular velocities were measured with a gyroscope system (SwayStarTM) mounted at L1-3 and combined into three, axis-specific, balance control indexes (BCI), using angles (a) for the tandem gait and barriers task, and angular velocities (v) for all other tasks, as follows: axis BCI = (2 × 2ecf)v + 1.5 × (w3hr + w3hp + w3ec)v + (tan8 + 12 × barr)a. RESULTS: Yaw and pitch BCIs were significantly (p ≤ 0.004) greater (88 and 30%, respectively) than roll BCIs for aUVN patients. For HCs, only yaw but not pitch BCIs were greater (p = 0.002) than those of roll (72%). The order of BCI aUVN vs. HC differences was pitch, yaw, and roll at 55, 44, and 31%, respectively (p ≤ 0.002). This difference with respect to roll corresponded to the known greater yaw plane than roll plane asymmetry (40 vs. 22%) following aUVN based on VOR responses. However, the lower pitch plane asymmetry (3.5%) in VOR responses did not correspond with the pitch plane instability observed in the balance control tests. The increases in pitch plane instability in UVL subjects were, however, highly correlated with those of roll and yaw. CONCLUSIONS: These results indicate that greater yaw than pitch and roll trunk motion during clinical balance tasks is common for aUVN patients and HCs. However, aUVN leads to a larger increase in pitch than yaw plane instability and a smaller increase in roll plane instability. This difference with respect to roll corresponds to the known greater yaw plane than roll plane asymmetry (40 vs. 22%) following aUVN observed in VOR responses. However, the lower pitch plane asymmetry (3.5%) in VOR responses does not correspond with the enhanced movements in the pitch plane, observed in balance control tasks. Whether asymmetries in vestibular-evoked myogenic potentials (Vemps) are better correlated with the deficits in pitch plane balance control remains to be investigated. The current results provide a strong rationale for the clinical testing of directional specific balance responses, especially yaw and pitch, and the linking of balance results for yaw and roll to VOR asymmetries.

Vestibulo-Ocular Reflex in the Aging Population.

The aim of this study was to evaluate vestibulo-ocular reflex (VOR) of individuals over 60 years of age who have not been diagnosed with a specific vestibular pathology. Bilateral six-semicircular canal video head impulse test (vHIT), Dizziness Handicap Inventory and European Evaluation of Vertigo scales were applied to participants. In total, 103 participants were included in the study (75 male, 28 female), and the mean age was 69.35 ± 7.41 years. The mean age of 7th decade group was 64.32±3.12 (59 participants; 38 male, 21 female), and the mean age of 8th decade and older group was 76.11±5.93 (44 participants; 37 male, 7 female). No significant differences were found between the VOR gains of the lateral or vertical semicircular canals between the 7th decade and 8th decade and older groups (p>0.05). In the 8th decade and older group, the presence of right lateral semicircular canal corrective saccade and left posterior semicircular canal corrective saccade showed a positively moderate correlation with VOR gains of the same semicircular canals (r=0.455, p=0.002, and r=0.518, p=0.001, respectively). No significant correlation was found between age and VOR gain in the 7th decade group, however, there was a negatively weak correlation between age and left lateral semicircular canal VOR gain (r=-0.366, p=0.017) in the 8th decade and older group. While assessing the age-related changes in VOR using vHIT, it must be considered that the changes related to aging of the vestibular system begin to emerge in the population over 70 years of age, and corrective saccade findings may be more informative than VOR gains in revealing these changes.

Effects of Visual Input Changes on Canal and Otolith- Dependent Vestibulo-Ocular Reflexes: A Review Study

Background and Aim: There is an integration between visual and vestibular systems. Changes in visual inputs can result in different changes in the Vestibulo-Ocular Reflex (VOR). This review study investigate the changes in VOR due to changes in visual inputs. In this regard, the effects of different conditions such as visual deprivation, changes in visual acuity, visual-vestibular conflict, and binocular vision dysfunction on VOR were assessed.
 Recent Findings: Changes in visual inputs and visual-vestibular conflicts can lead to different changes in VOR.
 Conclusion: The changes in VOR effects vary from slight to severe transformation dependent on the time course, severity and duration of changes in visual inputs.
 Keywords: Vestibulo-ocular reflex; visual inputs; refractive errors; head impulse test

Visual suppression of vestibulo-ocular reflex in patients treated with carotid artery revascularization: A potential biomarker for cerebral perfusion

BackgroundCarotid endarterectomy (CEA) and carotid artery stenting (CAS) are common treatments for ischemic stroke prevention in patients with carotid artery stenosis. However, the beneficial effects of CEA/CAS for cerebral hypoperfusion due to carotid artery stenosis have yet to be fully established. As dizziness is a common symptom in patients with carotid artery stenosis, we aimed to evaluate the effects of CEA/CAS on cerebral function in patients with carotid artery stenosis, using equilibrium function tests. MethodsThis prospective observational cohort study included 50 patients who had carotid artery stenosis and were scheduled to undergo CEA or CAS. Before CEA/CAS, we quantitatively evaluated the vestibulo-ocular reflex (VOR) and vestibular evoked myogenic potential (VEMP), as indicators of brainstem/inner ear functions related to balance, and visual suppression of VOR, as an indicator of cerebral control over the brainstem reflex related to balance. These were then compared with supratentorial cerebral blood flow (CBF). Changes in VOR, VEMP, visual suppression of VOR, CBF, and dizziness after CEA/CAS were also evaluated. ResultsThe visual suppression rates of VOR correlated with supratentorial CBFs before CEA/CAS (correlation coefficient = 0.47, p = 0.003). The visual suppression rates of VOR (p < 0.001) and supratentorial CBFs (p = 0.003) were improved by CEA/CAS, while VOR and VEMP did not change. Symptoms of dizziness improved after CEA/CAS. ConclusionsOur results suggest that visual suppression of the VOR may be a novel and practical marker for the beneficial effects of CEA/CAS on supratentorial cerebral function.

Acute Alcohol Intake Impairs the Velocity Storage Mechanism and Affects Both High-Frequency Vestibular-Ocular Reflex and Postural Control

Background: Acute alcohol intake is known to cause gait instability, dizziness, and lack of psychomotor coordination. Previous studies demonstrated the positive effects of alcohol on the oculomotor system and the low-frequency vestibulo-ocular reflex (VOR). However, the low-frequency VORs is a rather un-physiologic stimulation, and the reported explanations regarding the relations between the alcohol-induced VOR changes and posture control are inconsistent. OBJECTIVE: The present study evaluates how acute alcohol intake affects more physiologic mid- to high-frequency VORs, postural control, and elucidates the connection between the VOR and posture control after alcohol intake. Methods: A total of 31 healthy volunteers participated. Each participant received calculated amounts of alcohol drinks according to their body weight and genders with the targeted blood alcohol content (BAC) level of 0.05% using the Widmark formula. A vestibular test battery composed of posturography, video head impulse test, rotatory chair test (slow harmonic acceleration (SHA) and step velocity), and subjective visual vertical/horizontal tests (SVV/SVH) were conducted twice in alcohol-free condition (no alcohol intake within 24 h) and acute alcohol condition. Results: Acute alcohol intake decreased stability scores in all NS/EO (normal stability-eyes open), NS/EC (normal stability- eyes closed), PS/EO (perturbed stability-eyes open), and PS/EC (perturbed stability-eyes closed) conditions. High-frequency VOR gains decreased, but mid-frequency VOR gains were not significantly affected by alcohol intake. In addition, time constants were reduced significantly after alcohol ingestion in both clockwise and counter-clockwise rotation. Phase lead in SHA test and SVV/SVH was not affected by alcohol intake. Conclusion: Acute alcohol intake affected postural stability, high-acceleration head impulses, and the velocity storage mechanism.

Changes in Vestibulo-Ocular Reflex Gain After Surgical Plugging of Superior Semicircular Canal Dehiscence.

Superior semicircular canal dehiscence (SCD), which is characterized by a “third mobile window” in the inner ear, causes various vestibular and auditory symptoms and signs. Surgical plugging of the superior semicircular canal (SC) can eliminate the symptoms associated with increased perilymph mobility due to the presence of the third window. However, the natural course of vestibular function after surgical plugging remains unknown. Therefore, we explored longitudinal vestibular function after surgery in 11 subjects with SCD who underwent SC plugging using the middle cranial fossa approach. Changes in vestibulo-ocular reflex (VOR) gain in all planes were measured over 1 year with the video head impulse test. We also evaluated surgical outcomes, including changes in symptoms, audiometric results, and electrophysiological tests, to assess whether plugging eliminated third mobile window effects. The mean VOR gain for the plugged SC decreased from 0.81 ± 0.05 before surgery to 0.65 ± 0.08 on examinations performed within 1 week after surgery but normalized thereafter. Four of seven subjects who were able to perform both VOR tests before surgery and immediately after surgery had pathologic values (SC VOR gain < 0.70). Conversely, the mean VOR gain in the other canals remained unchanged over 1 year. The majority of symptoms and signs were absent or markedly decreased at the last follow-up evaluation, and no complications associated with the surgery were reported. Surgical plugging significantly attenuated the air-bone gap, in particular at low frequencies, because of increased bone conduction thresholds and deceased air conduction thresholds. Moreover, surgical plugging significantly increased vestibular-evoked myogenic potential thresholds and decreased the ratio of summating potential to action potential in plugged ears. Postoperative heavily T2-weighted images were available for two subjects and showed complete obliteration of the T2-bright signal intensity in the patent SC lumen in preoperative imaging based on filling defect at the site of plugging. Our results suggest that successful plugging of dehiscent SCs is closely associated with a transient, rather than persistent, disturbance of labyrinthine activity exclusively involved in plugged SCs, which may have clinical implications for timely and individualized vestibular rehabilitation.

The Early Postoperative Effects of Cochlear Implantation on Horizontal Semicircular Canal Function.

To use video head impulse testing to examine the effect of cochlear implantation (CI) on horizontal SCC vestibulo-ocular reflex (VOR) gain early after surgery, and to relate outcomes to subjective imbalance. Prospective cohort study. Academic tertiary referral center. Thirty-seven (23F:14M) adult cochlear implant recipients (mean age, 55; age range, 20-80). Cochlear implantation. The VOR of the horizontal semicircular canal of both the operated and non-operated ears was examined using video head impulse testing before surgery and at days 1, 7, and 28 following surgery. VOR gain, VOR gain asymmetry, and the change in VOR gain from preoperative baseline where the primary outcome measures. Subjective imbalance was assessed using a structured questionnaire. VOR gain value for the operated ear was 0.88 ± 0.21. Mean VOR gain on day 1 postoperatively was 0.86 ± 0.19; on day 7, 0.87 ± 0.17, and on day 30, 0.91 ± 0.21. Before surgery median asymmery was -5.50%, on day 1 it was -5.30%, at day 7, -6.44%, and at day 30 it was -2.61%. There was no significant difference between these measures for the cohort across the four time points. Thirteen of 37 (35%) of patients experienced imbalance in the follow-up period, but this was not correlated to changes in VOR gain. Horizontal semicircular canal function is preserved in the immediate and early postoperative period. This suggests that horizontal semicircular canal impairment is not likely to be responsible for postoperative imbalance.

Integrating postural and vestibular dimensions to depict impairment in moderate-to-severe obstructive sleep apnea syndrome patients.

Vestibular dysfunction was linked to moderate-to-severe obstructive sleep apnea syndrome (OSAS) patients in literature. However, due to a lack of knowledge among valid and recent implementations conceived to study postural control on static posturography (SP) and vestibulo-ocular reflex (VOR) gain under physiological conditions (video Head Impulse Test; vHIT), the aim of this work was to integrate (i) VOR changes via vHIT implementation, (ii) postural arrangement by studying both classical parameters and frequency spectra (PS) and (iii) correlation between these findings, polygraphic (PG) and subjective scores along Dizziness Handicap Inventory (DHI) and Epworth Sleepiness Scale (ESS). Thus, 32 moderate-to-severe OSAS patients and 32 healthy subjects - studied by using PG, DHI and ESS - underwent vHIT and SP posturographic assessment. Analysis of variance was performed to disclose between-group effects and correlation analysis was implemented between otoneurological, PG, DHI and ESS values. OSAS group demonstrated a significant decay of VOR gain and an increase in both frequency spectra PS values, especially within the low-frequency interval, and in classical posturographic SP parameters. Further, positive and negative correlations between mean SaO2 and gain and low frequency interval spectra PS were found, respectively. Strengthening previous hypothesis related to brainstem chronic hypoxemia phenomena affecting vestibular network, implementation of these data could generate future attentions (i) for screening under physiological conditions postural and vestibular detriments in OSAS subjects, especially exposed at risk settings, and (ii) among PG parameters, such as mean SaO2 , to propose further reliable tools in monitoring postural and vestibular decay in these patients demonstrating PG parameters detriments.

Intra-Attack Vestibuloocular Reflex Changes in Ménière's Disease.

Ménière's attack has been shown to temporarily alter the vestibuloocular reflex (VOR). A patient with unilateral Ménière's disease was serially evaluated with the video Head Impulse Test during single, untreated episodes of acute vertigo. Spontaneous nystagmus activity was concurrently recorded in order to establish the three typical phases of Ménière's attack (irritative, paralytic, and recovery) and correlate them with VOR performance. The onset of attack was associated with a quick change in VOR gain on the side of the affected ear. While a rapidly progressive reduction of the VOR was evident at the paralytic nystagmus phase, in the recovery phase the VOR gain returned to normal and the direction of the previous nystagmus reversed. The membrane rupture potassium intoxication theory provides a good foundation with which to explain these dynamic VOR changes and the observed triphasic direction behavior of the spontaneous nystagmus. We additionally postulated that endolymphatic fluid displacement could have a synergic effect during the earliest phase of attack.

Video head impulse test in peripheral vestibular diseases

The function of the semicircular canal receptors and the pathway of the vestibulo-ocular reflex (VOR) can be diagnosed with the clinical head impulse test. The aim of the study was to investigate the horizontal VOR by means of video head impulse test in peripheral vestibular disorders. Using the vHIT, we examined horizontal semicircular canal VOR in a group of 55 patients and a control group of 20 healthy subjects. The group of patients included 10 cases of vestibular neuritis (VN), 6 cases of vestibular schwannoma (VS), 12 cases of Meniere's disease (MD), and 15 cases of bilateral vestibulopathy (BV), as well as 13 cases of idiopathic sudden hearing loss with vertigo (ISHL). Instantaneous gains of 40 ms, 60 ms and 80 ms of horizontal VOR were 0.88 ± 0.17, 0.94 ± 0.13 and 0.96 ± 0.13, respectively. Regression gain at 60 ms was 0.99 ± 0.11, and asymmetry was 5.6 ± 3.5. Normal range of 60 ms instantaneous gain was > 0.73, normal range of regression gain was > 0.80. Abnormal vHIT was found in VS (100%), VN (90.9%), BV (86.7%), MD (40.0%) and ISHL (38.5%). Three conditions of refixation saccades occurred in cases with abnormal VOR: isolated covert saccades (12.5%), isolated overt saccades (45.0%) and the combination of overt and covert saccades (42.5%). The vHIT detects abnormal VOR changes in the combination of gain assessment and refixation saccades. Since isolated covert saccades in VOR changes can only be seen with vHIT, peripheral vestibular disorders are likely to be misdiagnosed with the HIT.

Epidemiology of vestibulo-ocular reflex function: data from the Baltimore Longitudinal Study of Aging.

To determine age-related changes in vestibulo-ocular reflex (VOR) function in community-dwelling adults, and evaluate these for associations with demographic characteristics and cardiovascular risk factors. Cross-sectional analysis within the Baltimore Longitudinal Study of Aging (BLSA), a longitudinal prospective cohort study. Vestibular testing laboratory within an acute care teaching hospital. Community-dwelling adults enrolled in the BLSA. Horizontal VOR gain measurement using video head-impulse testing and visual acuity testing. VOR gain was calculated as the ratio of eye velocity to head velocity. Demographic and cardiovascular risk factor data were collected through study questionnaires. One hundred nine subjects were analyzed with mean age (SD) 69.9 years (14.2), with a range from 26 to 92 years. VOR gain remained stable from age 26 to 79 after which it significantly declined at a rate of 0.012/year (p = 0.033) in adjusted analyses. Individuals aged 80 years or older had a nearly 8-fold increased odds of VOR gain less than 0.80 relative to those aged less than 80 years in multivariate models (prevalence of 13.2% vs. 2.8%; OR 7.79, 95% CI: 1.04-58.38). Otherwise, VOR gain did not differ significantly across demographic or cardiovascular risk groups. We report age-related decline in VOR function in individuals aged 80 years and older. Further analyses are in progress to establish the significance of these VOR abnormalities to functional and mobility outcomes in older individuals.

Caloric Test and Video‐Head‐Impulse (v‐HIT): Usefulness as Screening Tool of Vestibular Pathology

Objectives: Investigate the horizontal vestibulo-ocular reflex (VOR) by means of vHIT in peripheral vestibular disorders. Methods: Prospective clinical trial at a university hospital. Using 2 vHIT equipments (Otometrics(R) and Ullmer(R)), and the caloric response as gold standard, we examined the VOR in a group of 73 patients, and a control group of 18 healthy subjects. The group of patients included BPPV (n = 26), vestibular neuritis (VN) (n = 12), Ménière’s disease (MD) (n = 10), and idiopatic vestibulopathy (IV) (n = 25). Results: An abnormal VOR gain (less than 0.60) was found in 70.4% of all cases, whereas healthy subjects showed a normal gain in 94.44% of cases. An abnormal vHIT was found more commonly in VN (91.66%) and MD (80%), P &lt; .05. Isolated covert saccades and/or isolated overt saccades were present in all cases showing poor VOR gain. Caloric responses were paretic in 75% of cases showing poor VOR gain in vHIT, showing good correlation. Conclusions: The vHIT detects abnormal VOR changes in the combination of gain assessment and refixation saccades. vHIT might be a good screening tool to assess vestibular disorders, avoiding caloric stimulation in certain patients.

Clinical interest of postural and vestibulo-ocular reflex changes induced by cervical muscles and skull vibration in compensated unilateral vestibular lesion patients

Skull vibration induces nystagmus in unilateral vestibular lesion (UVL) patients. Vibration of skull, posterior cervical muscles or inferior limb muscles alters posture in recent UVL patients. This study aimed to investigate the postural effect of vibration in chronic compensated UVL patients. Vibration was applied successively to vertex, each mastoid, each side of posterior cervical muscles and of triceps surae in 12 UVL patients and 9 healthy subjects. Eye movements were recorded with videonystagmography. Postural control was evaluated in eyes open (EO) and eyes closed (EC) conditions. Sway area, sway path, anteroposterior and medio-lateral sways were recorded.A vibration induced nystagmus (VIN) beating toward the healthy side was obtained for each UVL patient during mastoid vibration. In EO, only sway path was higher in UVL group during vibration of mastoids and posterior cervical muscles.The EO postural impairments of UVL patients could be related to the eye movements or VIN, leading to visual perturbations, or to a proprioceptive error signal, providing an erroneous representation of head position. The vibration-induced sway was too small to be clinically useful. Vestibulo-ocular reflex observed with videonystagmography during mastoid vibration seems more relevant to reveal chronic UVL than vestibulo-spinal reflex observed with posturography.

Rotational Tests of Vestibular Function

Rotational tests are aimed at producing a more natural, precise, repeatable, and broadband evaluation of the vestibular function. Currently, two types of rotation tests are in clinical use: passive whole-body rotation where the stimulus is produced by a motorized chair, and active rotation where the stimulus is produced by voluntary head movements. In both methods, the frequency response of the vestibulo-ocular reflex (VOR) is determined by measuring the eye movements and comparing the head velocity with the slow-phase eye velocity. Rotation tests offer several advantages over other vestibular function tests in patients with bilateral caloric weakness, in young children, or in patients for whom VOR changes have to be assessed over time. In most other patients, rotation tests do not offer a significant advantage because of their low sensitivity to common vestibular abnormalities.

Interaction between Ocular Stabilization Reflexes in Patients with Whiplash Injury

In the past few decades, the automobile has become an increasingly more popular means of transport, which has led to an increasing number of rear-end collisions and consequently has resulted in more patients with whiplash-associated disorders (WADs). Recently, it was found that the gain of one of the ocular stabilization reflexes-the cervico-ocular reflex (COR)-is elevated in patients with whiplash injury. The COR responds to proprioceptive signals from the neck and acts in conjunction with the vestibulo-ocular reflex (VOR) and the optokinetic reflex (OKR) to preserve stable vision on the retina during head motion. Therefore, an investigation was conducted to determine whether the reported elevation of the COR in WADs is accompanied by changes in VOR or OKR. Eye movements of 13 patients and 18 age-matched healthy controls were recorded with an infrared eye-tracking device. Analysis confirmed a significant increase in COR gain in whiplash patients. Meanwhile the VOR and OKR gains remained the same. No correlation was found between the gains of the reflexes in individual patients. This is in contrast to earlier observations in elderly subjects and subjects with labyrinthine defects, who showed increases in COR gain and decreases in VOR gain. Impaired neck motion, altered proprioception of the neck, or disorganization in the process of VOR plasticity could explain the lack of change in VOR gain.

Vergence-dependent adaptation of the vestibulo-ocular reflex.

The gain of the vestibulo-ocular reflex (VOR) normally depends on the distance between the subject and the visual target, but it remains uncertain whether vergence angle can be linked to changes in VOR gain through a process of context-dependent adaptation. In this study, we examined this question with an adaptation paradigm that modified the normal relationship between vergence angle and retinal image motion. Subjects were rotated sinusoidally while they viewed an optokinetic (OKN) stimulus through either diverging or converging prisms. In three subjects the diverging prisms were worn while the OKN stimulus moved out of phase with the head, and the converging prisms were worn when the OKN stimulus moved in-phase with the head. The relationship between the vergence angle and OKN stimulus was reversed in the fourth subject. After 2 h of training, the VOR gain at the two vergence angles changed significantly in all of the subjects, evidenced by the two different VOR gains that could be immediately accessed by switching between the diverged and converged conditions. The results demonstrate that subjects can learn to use vergence angle as the contextual cue that retrieves adaptive changes in the angular VOR.

Vestibulo-ocular, optokinetic and postural function in diabetes mellitus.

We compared vestibulo-ocular reflex, optokinetic reflex and postural function in subjects with insulin-dependent diabetes mellitus (IDDM) and non-insulin-dependent diabetes mellitus (NIDDM), as well as non-diabetic controls. Both IDDM and NIDDM subjects exhibited significant deficits in gaze-holding in darkness (p < 0.05), small changes in vestibulo-ocular reflex (VOR) phase re velocity (p < 0.005) without a change in VOR gain, and a decrease in optokinetic reflex (OKR) slow phase velocity (p < 0.001). In addition, a smaller decrease was found in OKR quick phase amplitude (p < 0.02); postural sway was increased in both diabetic groups (p < 0.05), although this was not specific to the conditions of the Clinical Test of Sensory Interaction and Balance (CTSIB) that test vestibular contributions to postural stability. No differences were found in optokinetic afternystagmus or latency to circularvection. These results suggest that both IDDM and NIDDM are associated with deficits in gaze-holding, VOR and OKR function.

Age-related changes in vestibular function: a longitudinal study.

The objective of this study was to identify age-related changes in the vestibulo-ocular reflex (VOR) in normal older subjects and patients complaining of disequilibrium followed serially over time. Cross-sectional studies have found decreases in vestibular function in older subjects compared to younger subjects, but no prior longitudinal studies have been made following the same older subjects over time. We measured VOR responses using step and sinusoidal stimuli in 110 normal subjects and 51 patients with disequilibrium of unknown cause. This report focuses on 57 normal subjects who were able to return for five yearly examinations and 7 patients who were found to have severe bilateral vestibulopathy on the initial examination. In the normal subjects, there was a significant shortening of the VOR time constant to step changes in angular velocity and an amplitude-dependent decrease in gain and increase in phase lead of low-frequency sinusoidal responses over the five examinations. There was also a decrease in the gain of visual-vestibular responses at low frequencies of sinusoidal stimulation over the five examinations. The patients with bilateral vestibulopathy showed relatively little change in vestibular function over the five years of follow-up. This is the first longitudinal study to show age-related decreases in vestibular responses in normal older subjects. The VOR changes identified were not associated with symptoms or signs of disequilibrium. A small subgroup of patients with disequilibrium of unknown cause had profound bilateral vestibulopathy that remained stable during follow-up. These patients likely had an underlying disease even though in most cases the disease process could not be identified.

Recovery from vestibular ototoxicity.

Determine whether subjects with documented vestibular ototoxicity recover vestibular function and, if so, investigate the recovery dynamics. Prospective and retrospective reviews and repeated measures. Clinical research and technology center. Twenty-eight subjects who received vestibulotoxic medications were followed for at least 12 months after initial treatment. Our subject sample was compared with a published database of normal individuals. All 28 subjects received systemically administered medications known to be ototoxic. The subjects' treating physicians controlled medication, dosage, and administration schedules. Tests of horizontal canal vestibulo-ocular function were performed. Subjects' auditory and vestibular symptoms were recorded. Eleven subjects (39%) showed changes in horizontal canal vestibulo-ocular gain constant (GC) and/or time constant (TC) consistent with vestibular ototoxicity. When tested 1 year after ototoxic drug administration, eight of the nine subjects who experienced ototoxic decrease in GC showed a recovery of GC to normal limits. Only one of the eight subjects who experienced ototoxic decrease in TC showed recovery of TC to within normal limits. Ototoxicity onset and recovery were independent of baseline vestibular function, and ototoxicity onset did not correlate with cumulative dose of ototoxic medication. There was no relationship between subjective symptoms and ototoxicity onset. Recovery of GC after vestibular ototoxicity is more commonly observed than recovery of TC. Because ototoxic changes developed and continued in an unpredictable time and manner in relation to ototoxic drug administration, we propose that once ototoxic changes in vestibulo-ocular reflex are detected, ototoxic medications should be discontinued as soon as possible.

Long-term Vestibulo-ocular Reflex Changes in Patients with Vestibular Ablation

Long-term changes in the parameters of the vestibulo-ocular reflex (VOR) were evaluated using recently developed multilevel statistical modelling techniques in a group of patients who had undergone ablative inner ear procedures. Data from 84 patients were available for study. The most dramatic recovery in the VOR occurred during the first 60 postoperative days, however, slow changes continued, levelling off at about 120 days. While frequency was a highly significant predictor of outcomes in all parameters, age showed significant predictive value only to phase measures (p=0.006) and gender had no effect. Sum gain at the lowest frequency tested remained below the 5th percentile and at the higher frequencies remained below the 50th percentile for normal subjects. Phase decreased exponentially, but remained above the 95th percentile for normal subjects, except at the highest frequency where it remained above the 50th percentile. DC bias decreased exponentially, dropping to the 50th percentile by day 146. Asymmetry stayed between the 50th and 95th percentile, except at the highest frequency, where it was at the 50th percentile by day 125.