Eye movements in vestibular disorders

Altered Oculomotor and Vestibulo-ocular Function in Children and Adolescents Postconcussion

OBJECTIVE

To document (1) oculomotor (OM) and vestibulo-ocular (VO) function in children with concussion who were symptomatic at the time of assessment and to compare it with that in children with concussion who were clinically recovered (asymptomatic) and in children with no concussive injury, and (2) the extent to which OM and VO function relates to postconcussion symptom severity in injured children.

SETTING

Participants were recruited from a concussion clinic or the community.

PARTICIPANTS

A total of 108 youth with concussion (72 symptomatic; 36 recovered) and 79 healthy youth (aged 9-18 years). Youth with concussion were included if aged 9 to 18 years, had no previous concussion within the last 12 months, less than 90 days since injury, and no known existing visual disorders or learning disabilities.

STUDY DESIGN

A prospective cross-sectional study.

MAIN MEASURES

All participants were tested for OM and VO function with a commercial virtual reality (VR) eye-tracking system (Neuroflex®, Montreal,Québec, Canada). Participants in the concussion group who completed the postconcussion symptoms were scored with the Post-Concussion Symptom Inventory.

RESULTS

There was a significant group effect for vergence during smooth pursuit (F2,176 = 10.90; P < .05), mean latency during saccades (F2,171 = 5.99; P = .003), and mean response delay during antisaccades (F2,177 = 9.07; P < .05), where children with symptomatic concussion showed poorer performance than clinically recovered and healthy children. Similar results were found in VO for average vestibular ocular reflex gain in the horizontal leftward (F2,168 = 7; P = .001) and rightward directions (F2,163 = 13.08; P < .05) and vertical upward (F2,147 = 7.60; P = .001) and downward directions (F2,144 = 13.70; P < .05). Mean saccade error was positively correlated to total Post-Concussion Symptom Inventory scores in younger clinically recovered children.

CONCLUSION

VR eye tracking may be an effective tool for identifying OM and VO deficits in the subacute phase (<90 days) postconcussion.

How a Subclinical Unilateral Vestibular Signal Improves Binocular Vision

The present study aimed to determine if an infra-liminal asymmetric vestibular signal could account for some of the visual complaints commonly encountered in chronic vestibular patients. We used infra-liminal galvanic vestibular stimulation (GVS) to investigate its potential effects on visuo-oculomotor behavior. A total of 78 healthy volunteers, 34 aged from 20 to 25 years old and 44 aged from 40 to 60 years old, were included in a crossover study to assess the impact of infra-liminal stimulation on convergence, divergence, proximal convergence point, and stereopsis. Under GVS stimulation, a repeated measures ANOVA showed a significant variation in near convergence (p < 0.001), far convergence (p < 0.001), and far divergence (p = 0.052). We also observed an unexpected effect of instantaneous blocking of the retest effect on the far divergence measurement. Further investigations are necessary to establish causal relationships, but GVS could be considered a behavioral modulator in non-pharmacological vestibular therapies.

Multiple system atrophy with oculomotor abnormalities as a prominent manifestation: A case series

RATIONALE

Multiple system atrophy (MSA) is a group of adult-onset sporadic neurodegenerative diseases, mainly classified as MSA-C and MSA-P types. Due to the diversity of clinical symptoms, diagnosis faces a significant challenge. In the present case, we report a patient with isolated vertigo as the first presentation and abnormalities of the oculomotor system as the characteristic manifestations.

CASE CONCERN

A 64-year-old male had dizziness for 1 year, aggravated for 4 months, with accompanying symptoms of unsteady walking. Physical examination revealed spontaneous nystagmus, abnormal ataxic movements, and a broad basal gait. Video nystagmography revealed saccade intrusions and macrosaccadic oscillations, and opsoclonus. Magnetic resonance imaging (MRI) was unremarkable early, and positron emission tomography-computed tomography (PET-CT) announced a reduction in the volume of the cerebellum and brainstem.

DIAGNOSIS

The diagnosis of the possibility of MSA type-C, peripheral neuropathy, hypertension, and lacunar cerebral infarction was performed.

CONCLUSION

Atypical early clinical presentation may lead to delays, and identifying the critical problem through the patient simple clinical status requires long-term clinical experience and various ancillary examination tools.

Evaluation of the Video Ocular Counter-Roll (vOCR) as a New Clinical Test of Otolith Function in Peripheral Vestibulopathy

Importance

Video-oculography (VOG) goggles have been integrated into the assessment of semicircular canal function in patients with vestibular disorders. However, a similar bedside VOG method for testing otolith function is lacking.

Objective

To evaluate the use of VOG-based measurement of ocular counter-roll (vOCR) as a clinical test of otolith function.

Design, Setting, and Participants

A case-control study was conducted to compare vOCR measurement among patients at various stages of unilateral loss of vestibular function with healthy controls. The receiver operating characteristic curve method was used to determine the diagnostic accuracy of the vOCR test in detecting loss of otolith function. Participants were recruited at a tertiary center including the Johns Hopkins outpatient clinic and Johns Hopkins Hospital, Baltimore, Maryland. Participants included 56 individuals with acute (≤4 weeks after surgery), subacute (4 weeks-6 months after surgery), and chronic (>6 months after surgery) unilateral vestibular loss as well as healthy controls. A simple bedside maneuver with en bloc, 30° lateral tilt of the head and trunk was used for vOCR measurement. The study was conducted from February 2, 2017, to March 10, 2019.

Intervention

In each participant vOCR was measured during static tilts of the head and trunk en bloc.

Main Outcomes and Measures

The vOCR measurements and diagnostic accuracy of vOCR in detecting patients with loss of vestibular function from healthy controls.

Results

Of the 56 participants, 28 (50.0%) were men; mean (SD) age was 53.5 (11.4) years. The mean (SD) time of acute unilateral vestibular loss was 9 (7) days (range, 2-17 days) in the acute group, 61 (39) days (range, 28-172 days) in the subacute group, and 985 (1066) days (range 185-4200 days) in the chronic group. The vOCR test showed reduction on the side of vestibular loss, and the deficit was greater in patients with acute and subacute vestibular loss than in patients with chronic loss and healthy controls (acute vs chronic: -1.81°; 95% CI, -3.45° to -0.17°; acute vs control: -3.18°; 95% CI, -4.83° to -1.54°; subacute vs chronic: -0.63°; 95% CI, -2.28° to 1.01°; subacute vs control: -2.01°; 95% CI, -3.65° to -0.36°; acute vs subacute: -1.17°; 95% CI, -2.88° to 0.52°; and chronic vs control: -1.37°; 95% CI, -2.96° to 0.21°). The asymmetry in vOCR between the side of vestibular loss and healthy side was significantly higher in patients with acute vs chronic loss (0.28; 95% CI, 0.06-0.51). Overall, the performance of the vOCR test in discriminating between patients with vestibular loss and healthy controls was 0.83 (area under the receiver operating characteristic curve). The best vOCR threshold to detect vestibular loss at the 30° tilt was 4.5°, with a sensitivity of 80% (95% CI, 0.62%-0.88%) and specificity of 82% (95% CI, 0.57%-1.00%).

Conclusions and Relevance

The findings of this case-control study suggest that the vOCR test can be performed with a simple bedside maneuver and may be used to detect or track loss of otolith function.

Tracking Eye Movements During Sleep in Mice

Eye movement is not only for adjusting the visual field and maintaining the stability of visual information on the retina, but also provides an external manifestation of the cognitive status of the brain. Recent studies showed similarity in eye movement patterns between wakefulness and rapid eye movement (REM) sleep, indicating that the brain status of REM sleep likely resembles that of awake status. REM sleep in humans could be divided into phasic REM and tonic REM sleep according to the difference in eye movement frequencies. Mice are the most commonly used animal model for studying neuronal and molecular mechanisms underlying sleep. However, there was a lack of details for eye movement patterns during REM sleep, hence it remains unknown whether REM sleep can be further divided into different stages in mice. Here we developed a device combining electroencephalogram (EEG), electromyogram (EMG) as well as eye movements recording in mice to study the eye movement patterns during sleep. We implanted a magnet beneath the conjunctiva of eye and tracked eye movements using a magnetic sensor. The magnetic signals showed strong correlation with video-oculography in head-fixed mice, indicating that the magnetic signals reflect the direction and magnitude of eye movement. We also found that the magnet implanted beneath the conjunctiva exhibited good biocompatibility. Finally, we examined eye movement in sleep–wake cycle, and discriminated tonic REM and phasic REM according to the frequency of eye movements, finding that compared to tonic REM, phasic REM exhibited higher oscillation power at 0.50 Hz, and lower oscillation power at 1.50–7.25 Hz and 9.50–12.00 Hz. Our device allowed to simultaneously record EEG, EMG, and eye movements during sleep and wakefulness, providing a convenient and high temporal-spatial resolution tool for studying eye movements in sleep and other researches in mice.

An Algorithm for the Diagnosis of Vestibular, Cerebellar, and Oculomotor Disorders Using a Systematized Clinical Bedside Examination

The bedside examination associated with their clinical history remains the most critical means to accurately diagnose the cause for most of the signs and symptoms related to pathology of the cerebellum and vestibular system in patients presenting with dizziness and imbalance. This paper focuses on those critical bedside examinations, suggests when laboratory testing might be useful to confirm the clinical suspicion, and considers the shared neural circuitry within the visual and vestibular systems to offer an algorithmic approach in conducting the clinical bedside examination.

Ipsilateral Saccade Hypometria and Contralateral Saccadic Pursuit in a Focal Brainstem Lesion: a Rare Oculomotor Pattern

Eye movement examination may be used to rapidly differentiate peripheral and central vestibular syndromes in patients with acute unsteadiness. The analysis of oculomotor impairments may also support the accurate localization of cerebral lesions, particularly those in the brainstem, that are often loosely defined by cerebral MRIs. Saccades, smooth pursuit, and nystagmus were recorded with video-oculography in a patient who had developed sudden vertigo as a consequence of a focal lesion in the depth of the brachium pontis. The patient had shown a previously unreported pattern of eye movement impairments consisting of (i) ipsilesional hypometric saccades, (ii) contralesional saccadic smooth pursuit, and (iii) unilateral gaze-evoked nystagmus. These symptoms enabled the precise localization of the trajectory of pontocerebellar saccadic tracts in the depth of the brachium pontis. We propose that this rare association resulted from a disruption of cerebellar afferents of saccadic pathways and of cerebellar efferents of horizontal smooth pursuit pathways. This reported case emphasizes the crucial role of careful bedside oculomotor examination in order to discriminate between peripheral and central vestibular syndromes in the diagnosis of sudden vertigo. Moreover, it reveals an exceptional pattern of oculomotor impairments that may allow for the precise localization of the trajectory of cerebellar saccadic afferent pathways in the depth of the brachium pontis.

Shared variance of oculomotor phenotypes in a large sample of healthy young men

This study used canonical correlation analysis to investigate patterns of shared variance between parameters measured in seven different occulomotor function tasks, namely the visually guided saccade task, the antisaccade task, the closed-loop smooth-pursuit task, the open-loop smooth-pursuit task, and three active visual fixation tasks. These tasks were performed by 2130 young army recruits. Only a small percentage (1-10%) of shared variance existed between sets of parameters for all oculomotor function tasks measured. The most correlated tasks were the visually guided saccade and the antisaccade. The first common factor correlated with speed of performance between these tasks (latency), while the second and third correlated with accuracy of performance. Better performance in active visual fixation tasks correlated with better performance accuracy (lower error rate) and increased speed (lower latency) in the antisaccade and saccade tasks as well as better performance in the closed-loop smooth-pursuit task (increase in gain and decrease in the rate of unwanted saccades during pursuit). Better performance in the closed-loop smooth-pursuit task (increased gain and decreased number of unwanted saccades) also correlated with increased accuracy and increased speed of performing saccades and antisaccades. Finally, the open-loop fixation task had no correlation with all other oculomotor tasks except for a very weak negative correlation with the closed-loop pursuit task where better performance (increased gain) in one correlated with worse performance (decreased gain) in the other. The results of this analysis showed that a small percentage of variance is shared among different oculomotor function tasks. The structure of this shared variance could be used to derive common oculomotor function indices to study their relation to genetic and other sources of inter-subject variation.

Founder mutation in IKBKAP gene causes vestibular impairment in familial dysautonomia

OBJECTIVE

To assess vestibular function in patients with familial dysautonomia (FD), a hereditary sensory and autonomic neuropathy - caused by a mutation in the IKBKAP gene (c.2204 + 6 T>C) - and characterized by marked gait ataxia.

METHODS

Cervical and vestibular evoked myogenic potentials (cVEMPs and oVEMPs) were recorded from the sternocleidomastoid (SCM) and extraocular muscles in 14 homozygous patients, 2 heterozygous patients, and 15 healthy controls during percussion of the forehead.

RESULTS

cVEMP and oVEMP amplitudes were significantly lower, and peak latencies significantly delayed, in the FD patients. There were no differences in overall EMG during attempted maximal voluntary contractions of the SCM muscle, suggesting intact efferent function. The two heterozygotes with a minor haplotype missense (R696P) mutation in exon 19 of the IKBKAP gene had cVEMP responses less affected than the homozygous.

CONCLUSIONS

The founder mutation in the IKBKAP gene affects the development of vestibular afferent pathways, leading to attenuated cVEMPs.

SIGNIFICANCE

Vestibular abnormalities may contribute to the gait ataxia in FD.

Balance versus hearing after cochlear implant in an adult

The effect of vestibular rehabilitation (VR) on anxiety, dizziness and poor balance that developed after cochlear implant (CI) surgery is described. A 54-year-old woman, with profound hearing loss since the age of 2 years, underwent right CI surgery 2 years previously. On implant activation, the patient immediately felt dizziness and imbalance, which affected the ability to perform activities of daily living and increased anxiety to where the patient considered the CI removal. Prior to VR the patient was evaluated with the Dizziness Handicap Inventory and the Visual Vertigo Dizziness Questionnaire and clinically with the Zur Balance Scale and Video Head Impulse Test. The patient underwent 14 VR sessions over 4 months that included compensation, adaptation and habituation exercises. After VR the patient was able to maintain good balance while using the CI. Dizziness and anxiety improved dramatically. This report increases awareness that a CI could compromise balance, which can be overcome with personalised VR.