Scleral Search Coil Research Articles

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°, peak-velocity 150°/s and peak-acceleration 3,000°/s(2). 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.

Binocular Eye Movement Control and Motion Perception: What Is Being Tracked?

We investigated under what conditions humans can make independent slow phase eye movements. The ability to make independent movements of the two eyes generally is attributed to few specialized lateral eyed animal species, for example chameleons. In our study, we showed that humans also can move the eyes in different directions. To maintain binocular retinal correspondence independent slow phase movements of each eye are produced. We used the scleral search coil method to measure binocular eye movements in response to dichoptically viewed visual stimuli oscillating in orthogonal direction. Correlated stimuli led to orthogonal slow eye movements, while the binocularly perceived motion was the vector sum of the motion presented to each eye. The importance of binocular fusion on independency of the movements of the two eyes was investigated with anti-correlated stimuli. The perceived global motion pattern of anti-correlated dichoptic stimuli was perceived as an oblique oscillatory motion, as well as resulted in a conjugate oblique motion of the eyes. We propose that the ability to make independent slow phase eye movements in humans is used to maintain binocular retinal correspondence. Eye-of-origin and binocular information are used during the processing of binocular visual information, and it is decided at an early stage whether binocular or monocular motion information and independent slow phase eye movements of each eye are produced during binocular tracking.

Video Head Impulse Test Diagnoses Vestibulotoxicity

ObjectiveVideo oculography is a simple, accurate alternative to the scleral search coil method measuring individual semicircular canal function in Head Impulse Testing (HIT). Here we compare the video HIT with the caloric test for the diagnosis of unilateral or bilateral vestibulotoxicity due to systemic gentamicin therapy.MethodUsing the video HIT (ICS Impulse – GN Otometrics, Taastrup, Denmark) we studied 23/126 patients with gentamicin vestibulotoxicity; 5 unilateral, 18 bilateral. All 126 had caloric testing (30°C, 44°C); 82 also had 0°C testing. The video HIT took about 15 minutes and gave immediate results.ResultsAll 126 patients had severe unilateral or bilateral impairment of lateral semicircular canal function on caloric testing. Slow phase velocity was under 5°/s for each 30 or 44°C irrigation and under 7°/s for each 0°C irrigation. The video HIT correctly detected this loss in all 23 patients tested. During the video HIT the gain of the vestibulo‐ocular reflex from each lateral semicircular canal varied from 0.3 to 0.9 (N > 0.95). While a gain of 0.9 is near normal, the data in each patient showed covert or overt catch‐up saccades, confirming the vestibulo‐ocular reflex deficit.ConclusionThe video HIT is a simple, accurate way of immediately diagnosing unilateral or bilateral gentamicin vestibulotoxicity avoiding the need for caloric testing. It might be applicable for monitoring of patients receiving potentially vestibulotoxic drugs and might in time replace the caloric test for the diagnosis of peripheral vestibulopathies.

Differential representation of auditory categories between cell classes in primate auditory cortex

A comprehensive understanding of the neural mechanisms of cognitive function requires an understanding of how neural representations are transformed across different scales of neural organization: from within local microcircuits to across different brain areas. However, the neural transformations within the local microcircuits are poorly understood. Particularly, the role that two main cell classes of neurons in cortical microcircuits (i.e. pyramidal neurons and interneurons) have in auditory behaviour and cognition remains unknown. In this study, we tested the hypothesis that pyramidal cells and interneurons in the auditory cortex play a differential role in auditory categorization. To test this hypothesis, we recorded single-unit activity from the auditory cortex of rhesus monkeys while they categorized speech sounds. Based on the spike-waveform shape, a neuron was classified as either a narrow-spiking putative interneuron or a broad-spiking putative pyramidal neuron. We found that putative interneurons and pyramidal neurons in the auditory cortex differentially coded category information: interneurons were more selective for auditory categories than pyramidal neurons. These differences between cell classes may be an essential property of the neural computations underlying auditory categorization within the microcircuitry of the auditory cortex.

The Under-compensatory Roll aVOR Does Not Affect Dynamic Visual Acuity

Rotations of the head evoke compensatory reflexive eye rotations in the orbit to stabilize images onto the fovea. In normal humans, the angular vestibulo-ocular reflex (aVOR) gain (eye/head velocity) changes depending on the head rotation plane. For pitch and yaw head rotations, the gain is near unity, but during roll head rotations, the aVOR gain is ∼ 0.7. The purpose of this study was to determine whether this physiological discrepancy affects dynamic visual acuity (DVA)--a functional measure of the aVOR that requires subjects to identify letters of varying acuities during head rotation. We used the scleral search coil technique to measure eye and head velocity during passive DVA testing in yaw, roll, and pitch head impulses in healthy controls and patients with unilateral vestibular hypofunction (UVH). For control subjects, the mean aVOR gain during roll impulses was significantly lower than the mean aVOR gain during yaw and pitch impulses; however, there was no difference in DVA between yaw, roll, or pitch. For subjects with UVH, only aVOR gain during head rotations toward the affected side (yaw) were asymmetric (ipsilesional, 0.32 ± 0.17, vs. contralesional, 0.95 ± 0.05), with no asymmetry during roll or pitch. Similarly, there was a large asymmetry for DVA only during yaw head rotations, with no asymmetry in roll or pitch. Interestingly, DVA during roll toward the affected ear was better than DVA during yaw toward the affected ear--even though the ipsilesional roll aVOR gain was 60 % lower. During roll, the axis of eye rotation remains nearly perpendicular to the fovea, resulting in minimal displacement between the fovea and fixation target image projected onto the back of the eye. For subjects with UVH, the DVA score during passive horizontal impulses is a better indicator of poor gaze stability than during passive roll or pitch.

Could Different Smooth Pursuit and Saccadic Abnormalities in Spinocerebellar Ataxia Type 3 (SCA3) Be Explained by a Single Deficient Mechanism? (P02.259)

Objective: To evaluate smooth pursuit and saccade characteristics in SCA3 while trying to reveal if different abnormalities could be explained by a single mechanism. Background Different types of eye movement abnormalities are frequently found in the clinical examination of patients with SCA3. However, an objective documentation of those abnormalities using precise measures of eye movements is relatively scarce. Design/Methods: Smooth pursuit and saccadic eye movements were recorded in nine SCA3 patients and two controls using a scleral search coil system. Results: All SCA3 patients have jerky pursuit gain and abnormal saccades. Abnormal saccades were of two types: three patients have a low peak velocity, while the other six patients have normal peak velocity but have a significant occurrence of pathological dynamic overshoot, that is a small saccade that follows the main saccade, in the opposite direction, with no delay. This dynamic overshoot was not clinically detectable and different from hypermetric (position) overshoot saccades in which a corrective saccade that follows a main saccade is initiated after the eye comes to a complete rest. Conclusions: Saccadic dynamic overshoot is frequent in SCA3. Using models from engineering control systems, we hypothesize that a lack of velocity feedback in SCA3 patients can explain the measured abnormalities in smooth pursuit as well as the slow saccades and frequent dynamic overshoots. These results could be of significance in the search of new clinical neurophysiological biomarkers. Disclosure: Dr. Gordon has nothing to disclose. Dr. Zivotofsky has nothing to disclose. Dr. Caspi has nothing to disclose.

Head Impulse Test

ABSTRACTIn 1988, Michael Halmagyi and Ian Curthuoys described a simple yet reliable indicator of unilateral peripheral vestibular deficits at the bedside. This ‘head impulse test’ (HIT) as is has been known since, has stood the test of being a reliable indicator of vestibular deficit, especially for the horizontal semicircular canal.The test has been described using various techniques, such as the scleral search coil, the video HIT, etc. but even a simple bedside clinical evaluation with a little amount of experience usually sufficed to detect overt vestibular deficits.Numerous studies have compared the efficacy of the HIT as compared with other tests of vestibular deficit, the caloric test (CT) being the most commonly compared one. A look at the physiology behind the two tests reveals the differing pathways tested by the two tests in mention, and hence it would be wise to say that the two are complimentary, rather than exclusive of the other.The HIT today forms a vital part of the armamentarium of the otologist to arrive at rapid understanding of the nature of the vestibular deficit, the laterality of the lesion, and the probable prognostic significance.How to cite this articleKhattar VS, Hathiram BT. Head Impulse Test. Otorhinolaryngol Clin Int J 2012;4(2):106-111.

Tracking the eye non-invasively: simultaneous comparison of the scleral search coil and optical tracking techniques in the macaque monkey

From human perception to primate neurophysiology, monitoring eye position is critical to the study of vision, attention, oculomotor control, and behavior. Two principal techniques for the precise measurement of eye position—the long-standing sclera-embedded search coil and more recent optical tracking techniques—are in use in various laboratories, but no published study compares the performance of the two methods simultaneously in the same primates. Here we compare two popular systems—a sclera-embedded search coil from C-N-C Engineering and the EyeLink 1000 optical system from SR Research—by recording simultaneously from the same eye in the macaque monkey while the animal performed a simple oculomotor task. We found broad agreement between the two systems, particularly in positional accuracy during fixation, measurement of saccade amplitude, detection of fixational saccades, and sensitivity to subtle changes in eye position from trial to trial. Nonetheless, certain discrepancies persist, particularly elevated saccade peak velocities, post-saccadic ringing, influence of luminance change on reported position, and greater sample-to-sample variation in the optical system. Our study shows that optical performance now rivals that of the search coil, rendering optical systems appropriate for many if not most applications. This finding is consequential, especially for animal subjects, because the optical systems do not require invasive surgery for implantation and repair of search coils around the eye. Our data also allow laboratories using the optical system in human subjects to assess the strengths and limitations of the technique for their own applications.

False-Positive Head-Impulse Test in Cerebellar Ataxia

The objective of this study was to compare the findings of the bedside head-impulse test (HIT), passive head rotation gain, and caloric irrigation in patients with cerebellar ataxia (CA). In 16 patients with CA and bilaterally pathological bedside HIT, vestibuloocular reflex (VOR) gains were measured during HIT and passive head rotation by scleral search coil technique. Eight of the patients had pathologically reduced caloric responsiveness, while the other eight had normal caloric responses. Those with normal calorics showed a slightly reduced HIT gain (mean ± SD: 0.73 ± 0.15). In those with pathological calorics, gains 80 and 100 ms after the HIT as well as the passive rotation VOR gains were significantly lower. The corrective saccade after head turn occurred earlier in patients with pathological calorics (111 ± 62 ms after onset of the HIT) than in those with normal calorics (191 ± 17 ms, p = 0.0064). We identified two groups of patients with CA: those with an isolated moderate HIT deficit only, probably due to floccular dysfunction, and those with combined HIT, passive rotation, and caloric deficit, probably due to a peripheral vestibular deficit. From a clinical point of view, these results show that the bedside HIT alone can be false-positive for establishing a diagnosis of a bilateral peripheral vestibular deficit in patients with CA.

The 2D modified head impulse test: A 2D technique for measuring function in all six semi-circular canals

The head impulse test can be used to measure peripheral vestibular function of all six semicircular canals. Traditionally, vertical canal function is measured by rotating the head from a starting neutral position (forward facing) about a diagonal plane that bisects the sagittal and coronal planes. These types of head rotations elicit eye movements with large vertical and torsional (about the line of sight) angular velocity components. Three-dimensional (3D: horizontal, vertical and torsional) eye measurement techniques are needed to measure these velocity components. We wanted to determine whether 2D measurements coupled to a modified head impulse test are sufficient to measure function of all six canals. In this study we measured individual canal function in patients (n=5) with peripheral unilateral hypofunction and control subjects (n=4) using the traditional head impulse test and the 'gold standard' 3D (dual-coil) scleral search coil technique. We compared these results with those from our 2D modified head impulse test using the 2D coil technique (single-coil). We show that both techniques detect similar levels of asymmetrical function in patients and are equally accurate in isolating canals with hypofunction. We conclude that 2D eye measurement techniques, such as video pupil-tracking, can be used to test all six canals.

Changes of saccadic eye movements in thyroid-associated ophthalmopathy

To establish whether or not the dynamics of saccadic eye movements are significantly changed in patients with different stages of thyroid-associated ophthalmopathy (TAO) and, subsequently, if analysis of saccades could serve as an additional diagnostic tool for early detection of inflammatory activity in TAO. Thirty-seven patients with TAO and 10 age- and gender-matched control subjects were investigated. The patients were divided into four groups according to the stage of the disease: (i) early mild disease (n = 10), (ii) early severe disease (n = 11), (iii) long-standing restrictive disease (n = 10) and (iv) proven auto-immune hyperthyroidism without any signs of TAO (n = 6). Horizontal and vertical saccades with amplitudes of 10°, 20°, 30° and 40° were recorded binocularly using the induction scleral search coil technique. The two main sequence constants V(max) and C were calculated for each eye. Repeated measurement analysis of variance was carried out to test for differences between different gaze directions, eyes and groups. In horizontal saccades, significant differences were found between groups but not between abduction and adduction. In vertical saccades, differences between groups and the interaction between groups and up- and down-gaze saccades were significant. Compared with the control group, analysis of the main sequence curves revealed larger differences in patients of group 3 and 4 than in those of group 1 and 2. Whereas in the control group down-gaze saccades were faster than up-gaze saccades, the opposite behaviour was found in all patient groups. The largest differences were detected among those patients who had no signs of TAO (group 4). In this study, significant saccade differences were detected in all patients with TAO. In contrast to our earlier studies where evaluation of multiple individual saccade parameters did not reveal significant differences, analysis of the main sequence constants and mathematical reconstruction of the main sequence curves turned out to be a sensitive technique for reliable detection of subtle ocular motility changes. Significant differences were detected even in patients with auto-immune thyroiditis where no clinical signs of TAO were apparent.

Tonic and phasic components of eye movements during REM sleep in the rat

Phasic oculomotor activity is one of the features identifying rapid eye movement (REM) sleep. Recently, it has been shown in cats that, despite bursts of complex two-component rapid eye movements, the eyes tend to maintain a nasal and downward rotation during REM sleep. Although the function of eye movements during sleep remains elusive, it is important to know whether the characteristics of eye movements during sleep are species-specific in mammals. In this work, quantitative characteristics of eye movements, recorded by the scleral search coil technique, were studied during wakefulness and sleep in rats. During wakefulness, rats performed conjugated saccades at a very low rate and some eye movements associated to blinking and gnawing. Throughout non-REM sleep, eye movements were slow, mostly unconjugated and the eyes maintained a divergence in the horizontal plane. The beginning of REM sleep was characterized by a convergence and downward rotation of the eyes, which tended to persist until the end of REM sleep. Rapid eye movements, isolated and monocular at the beginning, became complex and organized in high-frequency bursts. These results demonstrate that, despite the difference in extraocular anatomy and visuomotor strategies between frontal- and lateral-eyed species, eye movements during REM sleep in rats are very similar to those described in cats. This suggests that the mechanisms generating eye movements during REM sleep are largely conserved in mammals.

Relationship of slow-phase velocity to visual acuity in infantile nystagmus associated with albinism

To investigate the relationship between slow-phase velocity of nystagmus and visual acuity in children with albinism. Twelve children with infantile nystagmus associated with albinism had eye movements recorded by binocular video-oculography (10 patients) or by scleral search coil (2 patients). In children younger than 3 years of age visual acuities was assessed by means of Teller acuity cards and corrected for age. Histograms of horizontal eye velocities were fit by a gamma distribution in all patients (r2>0.85). The velocity at the peak of the gamma distribution was compared with the limiting velocity predicted by the dynamic visual acuity (DVA) model. All histograms of slow-phase eye velocity were skewed toward lower velocities, with the peak distribution ranging from 5 to 20 degrees/second. The velocity at the peak of the gamma distribution for each subject was uniformly equal to or below the limiting velocity predicted by the DVA model. The average of the gamma distribution across all subjects corresponded to an upper limit to eye velocity of 17 degrees/second. At this velocity the DVA model predicted visual acuity of 20/50, which is lower than the average visual acuity reported in albinism. The distributions of eye velocity were lower than the limiting eye velocity predicted on the basis of DVA almost 50% of the time. Visual acuity in albinism is limited by macular hypoplasia rather than by slow-phase eye velocity of nystagmus.

Characterization of the Electrically Evoked Compound Action Potential of the Vestibular Nerve

We recorded intraoperative and postoperative electrically evoked compound action potentials (ECAPs) in rhesus monkeys implanted with a vestibular neurostimulator. The objectives were to correlate the generation of slow-phase nystagmus or eye twitches induced by electrical stimulation of the implanted semicircular canal with the presence or absence of the vestibular ECAP responses and to assess the effectiveness of ECAP monitoring during surgery to guide surgical insertion of electrode arrays into the canals. Four rhesus monkeys (a total of 7 canals) were implanted with a vestibular neurostimulator modified from the Nucleus Freedom cochlear implant. ECAP recordings were obtained during surgery or at various intervals after surgery using the Neural Response Telemetry feature of the clinical Custom Sound EP software. Eye movements during electrical stimulation of individual canals were recorded with a scleral search coil system in the same animals. Measurable vestibular ECAPs were observed intraoperatively or postoperatively in 3 implanted animals. Robust and sustained ECAPs were obtained in 3 monkeys at the test intervals of 0, 7, or greater than 100 days after implantation surgery. In all 3 animals, stimulation with electrical pulse trains produced measurable eye movements in a direction consistent with the vestibulo-ocular reflex from the implanted semicircular canal. In contrast, electrically evoked eye movements could not be measured in 3 of the 7 implanted canals, none of which produced distinct vestibular ECAPs. In 2 animals, ECAP waveforms were systematically monitored during surgery, and the procedure proved crucial to the success of vestibular implantation. Vestibular ECAPs exhibit similar morphology and growth characteristics to cochlear ECAPs from human cochlear implant patients. The ECAP measure is well correlated with the functional activation of eye movements by electrical stimulation after implantation surgery. The intraoperative ECAP recording technique is an efficient tool to guide the placement of electrode array into the semicircular canals.

Characterizing high-velocity angular vestibulo-ocular reflex function in service members post-blast exposure

Blasts (explosions) are the most common mechanism of injury in modern warfare. Traumatic brain injury (TBI) and dizziness are common sequelae associated with blasts, and many service members (SMs) report symptoms worsen with activity. The purpose of this study was to measure angular vestibulo-ocular reflex gain (aVOR) of blast-exposed SMs with TBI during head impulse testing. We also assessed their symptoms during exertion. Twenty-four SMs recovering from TBI were prospectively assigned to one of two groups based on the presence or absence of dizziness. Wireless monocular scleral search coil and rate sensor were used to characterize active and passive yaw and pitch head and eye rotations. Visual analog scale (VAS) was used to monitor symptoms during fast walking/running. For active yaw head impulses, aVOR gains were significantly lower in the symptomatic group (0.79±0.15) versus asymptomatic (0.87±0.18), but not for passive head rotation. For pitch head rotation, the symptomatic group had both active (0.915±0.24) and passive (0.878±0.22) aVOR gains lower than the asymptomatic group (active 1.03±0.27, passive 0.97±0.23). Some SMs had elevated aVOR gain. VAS scores for all symptoms were highest during exertion. Our data suggest symptomatic SMs with TBI as a result of blast have varied aVOR gain during high-velocity head impulses and provide compelling evidence of pathology affecting the vestibular system. Potential loci of injury in this population include the following: disruption of pathways relaying vestibular efference signals, differential destruction of type I vestibular hair cells, or selective damage to irregular afferent pathways-any of which may explain the common discrepancy between reports of vestibular-like symptoms and laboratory testing results. Significantly reduced pitch aVOR in symptomatic SMs and peak symptom severity during exertional testing support earlier findings in the chronic blast-exposed active duty SMs.

Applying double-magnetic induction to measure head-unrestrained gaze shifts: calibration and validation in monkey

The double magnetic induction (DMI) method has successfully been used to record head-unrestrained gaze shifts in human subjects (Bremen etal., J Neurosci Methods 160:75-84, 2007a, J Neurophysiol, 98:3759-3769, 2007b). This method employs a small golden ring placed on the eye that, when positioned within oscillating magnetic fields, induces orientation-dependent voltages in a pickup coil in front of the eye. Here we develop and test a streamlined calibration routine for use with experimental animals, in particular, with monkeys. The calibration routine requires the animal solely to accurately follow visual targets presented at random locations in the visual field. Animals can readily learn this task. In addition, we use the fact that the pickup coil can be fixed rigidly and reproducibly on implants on the animal's skull. Therefore, accumulation of calibration data leads to increasing accuracy. As a first step, we simulated gaze shifts and the resulting DMI signals. Our simulations showed that the complex DMI signals can be effectively calibrated with the use of random target sequences, which elicit substantial decoupling of eye- and head orientations in a natural way. Subsequently, we tested our paradigm on three macaque monkeys. Our results show that the data for a successful calibration can be collected in a single recording session, in which the monkey makes about 1,500-2,000 goal-directed saccades. We obtained a resolution of 30 arc minutes (measurement range [-60,+60]°). This resolution compares to the fixation resolution of the monkey's oculomotor system, and to the standard scleral search-coil method.

Eye Movements and Abducens Motoneuron Behavior after Cholinergic Activation of the Nucleus Reticularis Pontis Caudalis

the aim of this work was to characterize eye movements and abducens (ABD) motoneuron behavior after cholinergic activation of the nucleus reticularis pontis caudalis (NRPC). six female adult cats were prepared for chronic recording of eye movements (using the scleral search-coil technique), electroencephalography, electromyography, ponto-geniculo-occipital (PGO) waves in the lateral geniculate nucleus, and ABD motoneuron activities after microinjections of the cholinergic agonist carbachol into the NRPC. unilateral microinjections of carbachol in the NRPC induced tonic and phasic phenomena in the oculomotor system. Tonic effects consisted of ipsiversive rotation to the injected side, convergence, and downward rotation of the eyes. Phasic effects consisted of bursts of rhythmic rapid eye movements directed contralaterally to the injected side along with PGO-like waves in the lateral geniculate and ABD nuclei. Although tonic effects were dependent on the level of drowsiness, phasic effects were always present and appeared along with normal saccades when the animal was vigilant. ABD motoneurons showed phasic activities associated with ABD PGO-like waves during bursts of rapid eye movements, and tonic and phasic activities related to eye position and velocity during alertness. the cholinergic activation of the NRPC induces oculomotor phenomena that are somewhat similar to those described during REM sleep. A precise comparison of the dynamics and timing of the eye movements further suggests that a temporal organization of both NRPCs is needed to reproduce the complexity of the oculomotor behavior during REM sleep.

A preformed scleral search coil for measuring mouse eye movements

Mice are excellent subjects for use of genetic-manipulation techniques to study the basis of pathological and normal physiology and behavior; however behavioral analyses of associated phenotypes is often limited. To improve the accuracy and specificity of repeated measurements of vestibular function, we developed a miniaturized, contact-lens scleral search coil to measure mouse eye movements. We describe the physical attributes and document its functionality by measuring vestibuloocular responses in normal mice. This coil should greatly improve the sensitivity and documentation of vestibular dysfunction in mouse models of pathology and dysfunction while allowing screening of significant numbers of subjects.

From Cawthorne-Cooksey to Biotechnology: Where We Have Been and Where We Are Headed in Vestibular Rehabilitation?

Vestibular rehabilitation has come a long way from Cawthorne and Cooksey exercises. Although revolutionary in their foresight and still in use today, the available options for rehabilitation of vestibular disorders has dramatically in recent years. Currently in our armamentarium are specific exercises to address gaze instability, postural instability (static and dynamic), motion sensitivity, and vertigo—all symptoms relative to pathology within the peripheral and central vestibular pathways. Cochrane studies have established that vestibular rehabilitation is effective for treating unilateral peripheral vestibular hypofunction. Recent treatment guidelines and systematic reviews suggest that repositioning maneuvers are the superior treatment for benign paroxysmal positional vertigo. Our knowledge of testing and treatment of pathologies affecting the peripheral vestibular labyrinth and/or the pathways mediating vestibular afference is exploding. Just as optimal intervention for individuals with vestibular disorders commonly involves multiple disciplines, so are multiple disciplines conducting excellent research that demands vigilance in the practicing clinician. As clinicians who treat people with vestibular disorders, our interventions would be enhanced by examining data from other disciplines: emerging evidence suggests that new tests may isolate utricular from saccular function, migraines can be triggered by vestibular stimulation, and technical advances in oculomotor equipment now enable video monitoring and recording of rapid head and eye rotations. Today there are many tests that can be used by clinicians, which provide clinically meaningful information. In addition, as members of the vestibular team, physical therapists need to become more involved in other professional meetings to inform other clinicians about what we have to offer. Important opportunities for collaborating might involve the American Academy of Head and Neck Surgery, the Association for Research in Otolaryngology, and the biannual Barany Society meeting. We are pleased to report that this Special Issue of the JNPT has and outstanding cadre of international authors and coauthors from the United States, the United Kingdom, Greece, Saudi Arabia, Jordan, and Australia. The topics covered are diverse and so is the authors' expertise. The authors include physical therapists, engineers, and physicians who work to enhance the care of persons with vestibular disorders. The authors were asked to contribute to this issue based on their novel work, and we hope that their recent findings help to improve care for your patients. Most of the articles in this Special Issue include advanced technology as part of their methods. The use of the vibrotactors (Wall), scleral search coils (Scherer and Schubert), uniquely applied measures of attention (Mohammad et al), and optokinetic stimulation (Pavlou et al) all involve some degree of innovative technology to assess treatment effectiveness, measurement of vestibular function, or reveal behavior in people with vestibular dysfunction. Other articles in this issue attempt to describe treatment effectiveness in interesting patient groups including mild traumatic brain injury related to blunt (Alsalaheen et al) and blast (Gottshall) trauma, patients with report of dizziness but normal caloric findings (Hall et al), patients with canal-only versus canal and otolith dysfunction (Murray et al), and differences between treatment paradigms (Clendaniel). The future for vestibular rehabilitation is exciting and will involve interaction with multiple disciplines. In a recent survey of biomechanics laboratories, physical therapists who responded to an informal survey participated in projects in >75% of the laboratories. Physical therapists were the largest group represented at the 2010 International Gait and Mental Function meeting. In the future, we expect the merging of vestibular physical therapy with technical innovations to include virtual reality feedback/training, a vestibular prosthesis, even stem cell research to resolve pathophysiology within the labyrinth. These new technologies will need the skills and knowledge of physical therapists to help investigators determine whether the interventions are effective and/or to establish the behavioral implications of stem cell physiology to restore function. Most certainly, other clinicians/researchers will look to physical therapists for better understanding of movement problems of people with vestibular and other neuromotor disorders, and for optimal rehabilitation approaches to maximize the value of technology. We encourage all readers to examine the foundational science and evidence for using new and innovative technologies before adopting the newest device for use with their patients. Material in this Special Issue was chosen to highlight some of the investigators around the world who are making a difference in the care of people with vestibular disorders. Many basic clinical questions remain, and we still struggle with issues such as optimal dose, optimal type of exercise, and the value of continuing a home exercise program after discharge. We hope that this Special Issue will help clinicians explore some new innovations and discoveries in physical therapist examination and treatment of persons with vestibular disorders.

Overestimation of saccadic peak velocity recorded by electro-oculography compared to video-oculography and scleral search coil

Overestimation of saccadic peak velocity recorded by electro-oculography compared to video-oculography and scleral search coil