Unsteadiness and drunkenness sensations as a new sub-type of BPPV.

AIM: Benign Paroxysmal Positional Vertigo (BPPV) represents at least 35% of vertigo cases and perhaps much more. The aim of this study was to review a proposed new type of BPPV which may be detected by using a mechanical assistance in BPPV diagnostic and therapeutic maneuvers. MATERIELS AND METHODS: The prospective study extracted subjects from 465 patients who presented with some positional vertigo or unsteadiness. Only 152 dizzy patients, who presented with positional nystagmus but no true vertigo, were included. The TRV armchair permits rotation of patients wearing infrared video goggles in all semi-circular planes. Treatment effectiveness was defined as absence of symptoms or findings 3 days after the therapy sessions. If not initially successful, repeat therapeutic sessions were performed or patients underwent further vestibular examination and sometime MRI. RESULTS: One hundred nine of the 152 patients demonstrated a low level canalithiasis showing nystagmus. Unusual data were collected: Ninety seven had a lateral canal and 12 had posterior canal conditions. The average of the patients was 62 and they had an average of 1.6 mechanical therapeutic maneuvres to reach the success end-point. CONCLUSION: Some patients have persistent unsteadiness or drunkenness sensations after being treated by conventional maneuvers for BPPV. Often considered a post-BPPV otolithic syndrome an alternative possibility is BPPV with a very few otoliths in the lateral canal. The therapeutic technique using the mechanical chair permits to improved diagnosis of canalithiasis, especially that involving the horizontal canals. Some mild dizziness, which may be disabling and chronic can be better investigated and treated with mechanical assistance.

Vestibular migraine may be an important cause of dizziness/vertigo in perimenopausal period.

Migraine disorders are more prevalent among women than men. The ovarian neurosteroids play an important role in this sex difference by modulating neurotransmitter systems involving migraine pathogenesis. During perimenopause, unlike the postmenopausal period, women are under unstable fluctuations of ovarian neurosteroid levels. Such fluctuations might be an important interval-specific trigger for activating migraines. Along with migraine headache, dizziness is one of the most common complaints of perimenopause. A significant portion of this dizziness may be caused by vestibular migraine that has heterogeneous clinical features with dizziness and/or migraine headache. Because of this variation in phenomenology, the symptom of dizziness and vertigo during perimenopause is frequently misclassified as being a nonspecific climacteric symptom or having psychological origin. The recognition of vestibular migraine and its heterogeneous clinical presentations are important to understand, differentiate and correctly diagnose the symptom of dizziness and vertigo during perimenopausal transition. Further, recognition of the steroid influences on migraine genesis will lead to improved treatment regimens for vertigo from migraine.

The virtual retinal display as a low-vision computer interface: a pilot study.

This pilot study examined the performance of an alternative computer visual interface, the Virtual Retinal Display (VRD), for low-vision use. The VRD scans laser light directly onto the retina, creating a virtual image. Since visually impaired individuals can have difficulty using computer displays, a matched comparison study was done between the VRD and the standard cathode ray tube (CRT) monitor. Reading speed and acuity tests were collected from 13 low-vision volunteers selected to represent the broad range of partially sighted individuals actively involved in the work force. Forty-six percent of subjects had highest visual acuity while viewing the VRD; 30% of subjects had highest acuity viewing the CRT; and 24% of subjects had equal acuity across the two displays. Although mean reading speed across all 13 subjects indicated no significant difference between displays, individual subjects with predominantly optical causes of low vision exhibited clinically important increases in reading speed versus the CRT. However, most subjects with predominantly retinal damage showed a slight disadvantage using the VRD. We give theoretical explanation to the bifurcated results and conclude that for a subset of low-vision users, the VRD technology is very promising as a basis for future low-vision aids.

Intractable benign paroxysmal positional vertigo in patients with Meniere's disease.

OBJECTIVE: To provide a detailed description of the coexistence of benign paroxysmal positional vertigo (BPPV) and Meniere's disease in individuals and to offer a possible mechanism that explains the findings in these patients. STUDY DESIGN: Retrospective. METHODS: Chart review. RESULTS: Of 162 patients diagnosed with Meniere's disease between January 1998 and January 1999, 9 were found to have both "definite" Meniere's disease and "certain" BPPV. Meniere's symptoms preceded the onset of BPPV in all of our patients. Seven of the 9 patients were female. Except for one patient who experienced BPPV bilaterally, BPPV was limited to the same ear as the Meniere's disease. All patients presented with intractable BPPV that did not respond completely to otolith repositioning procedures. A detailed description of five patients is presented. CONCLUSION: Our data, in conjunction with that of others, suggest that Meniere's disease may predispose patients to intractable BPPV. Hydropically induced damage to the maculae of the utricle and saccule or partial obstruction of the membranous labyrinth may be possible mechanisms that explain the coexistence of Meniere's disease and BPPV.

Adaptation of the VOR in patients with low VOR gains.

Six subjects with histories of vertigo and with vestibulo-ocular reflex (VOR) gains less than 0.5 were tested in an adaptation protocol. After initial VOR testing in the dark, the subjects had a computer-driven visual display system placed on their heads. The system had the capability for variation of visual image magnification. The magnification was set to be 5% greater than the subject's average VOR gain. Subjects then performed active head movements as they carried out a visual searching task looking for objects in a panoramic scene. After 6 minutes with each image, the magnification was increased by 3 to 5%. The process was repeated for a total of 5 images, for a total increase in magnification of approximately 20% over 30 minutes. The VOR gain was measured again. In 17 of 18 conditions tested, the VOR gain increased. The average increase was 16%. Significant increases in VOR gain occurred at 0.32 and 0.64 Hz. The VOR gain increase in these patients occurred in a visual environment that lowered VOR gain in normal subjects. These results suggest that the VOR has an adaptation mechanism tuned to correct for small changes in required gain. Further research is necessary to determine if this method can result in persistent VOR gain improvements and reduction in symptoms and disability in patients with vestibular disorders.

The virtual retinal display: a new technology for virtual reality and augmented vision in medicine.

INTRODUCTION: The Virtual Retinal Display (VRD) is a new technology for creating visual images. It was developed at the Human Interface Technology Laboratory (HIT Lab) by Dr. Thomas A. Furness III. The VRD creates images by scanning low power laser light directly onto the retina. This special method results in images that are bright, high contrast and high resolution. In this paper, we describe how the VRD functions, the special consequences of its mechanism of action and potential medical applications of the VRD, including surgical displays and displays for people with low vision. A description of its safety analysis will also be included. In one set of tests we had a number of patients with partial loss of vision view images with the VRD. There were two groups of subjects: patients with macular degeneration, a degenerative disease of the retina and patients with keratoconus. Typical VRD images are on the order of 300 nanowatts. VRD images are also readily viewed superimposed on ambient room light. In our low vision test subjects, 5 out of 8 subjects with macular degeneration felt the VRD images were better and brighter than the CRT or paper images and they were able to reach the same or better level of resolution. All patients with Keratoconus were able to resolve lines of test several lines smaller with the VRD than with their own correction. Further, they all felt that the VRD images were sharper and easier to view. The VRD is a safe new display technology. The power levels recorded from the system are several orders below the power levels prescribed by the American National Standard. The VRD readily creates images that can be easily seen in ambient roomlight and it can create images that can be seen in ambient daylight. The combination of high brightness and contrast and high resolution make the VRD an ideal candidate for use in a surgical display. Further, tests show strong potential for the VRD to be a display technology for patients with low vision.

Assessing a VR-based learning environment for anatomy education.

The purpose of the research proposed herein is to develop an empirical, methodological tool for the assessment of visual depth perception in virtual environments (VEs). Our goal is to develop and employ a behaviorally-based method for assessing the impact of VE design features on the perception of visual depth as indexed by the performance of fundamental perceptual-motor activities. Specifically, in this experiment we will assess the affect of two dimensions of VE system design--(1) viewing condition or "level of immersion", and (2) layout/design of the VE--on the performance of an engaging, game-like task. The characteristics of the task to be employed are as follows--(1) it places no demands on cognition in the form of problem solving, retrieval of previously learned information, or other analytic activity in order to assure that (2) variations in task performance can be exclusively attributed to the extent to which the experimental factors influence visual depth perception. Subjects' performance will be assessed in terms of the speed and accuracy of task performance, as well as underlying dimensions of performance such as workload, fatigue, and physiological well being (i.e., cybersickness). The results of this experiment will provide important information on the effect of VE immersion and other VE design issues on human perception and performance. Further development, refinement, and validation of this behaviorally-based methodology will be pursued to provide user-centered design criteria for the design and use of VE systems.

Laser safety analysis of a retinal scanning display system.

The Virtual Retinal Display (VRD) is a visual display that scans modulated laser light on to the retina of the viewer's eye to create an image. Maximum permissible exposures (MPE) have been calculated for the VRD in both normal viewing and possible failure modes. The MPE power levels are compared to the measured power that enters the eye while viewing images with the VRD. The power levels indicate that the VRD is safe in both normal operating mode and in failure modes.

A magnetic resonance imaging study of double elevator palsy.

OBJECTIVE: The pathophysiology of double elevator palsy is poorly understood. We assessed two patients with this condition using magnetic resonance imaging (MRI) to evaluate the appearance of the extraocular muscles. DESIGN: Cross-sectional study. SETTING: Radiology department of a university-affiliated hospital in London, Ont. PATIENTS: Two patients from a private ophthalmology practice who had undergone complete transpositions of the horizontal rectus muscles to treat hypotropia associated with double elevator palsy. INTERVENTION: MRI. A volume scanning technique was used to obtain maximum information about the muscles. OUTCOME MEASURE: Appearance of the extraocular muscles. RESULTS: In both patients MRI showed decreased volume of the superior rectus muscle on the affected side. The other rectus muscles were normal. This suggested either congenital hypoplasia or paresis of the involved superior rectus muscle. In addition, the full tendon transpositions of the medial and lateral recti did not appreciably change the middle and deep orbital pathways of the transposed horizontal rectus muscles. CONCLUSIONS: MRI may be a useful adjunct to saccadic velocity assessments in differentiating between primary inferior rectus restriction, primary superior rectus paresis and congenital supranuclear elevator deficiency.

The human horizontal vestibulo-ocular reflex during combined linear and angular acceleration.

We employed binocular magnetic search coils to study the vestibulo-ocular reflex (VOR) and visually enhanced vestibulo-ocular reflex (VVOR) of 15 human subjects undergoing passive, whole-body rotations about a vertical (yaw) axis delivered as a series of pseudorandom transients and sinusoidal oscillations at frequencies from 0.8 to 2.0 Hz. Rotations were about a series of five axes ranging from 20 cm posterior to the eyes to 10 cm anterior to the eyes. Subjects were asked to regard visible or remembered targets 10 cm, 25 cm, and 600 cm distant from the right eye. During sinusoidal rotations, the gain and phase of the VOR and VVOR were found to be highly dependent on target distance and eccentricity of the rotational axis. For axes midway between or anterior to the eyes, sinusoidal gain decreased progressively with increasing target proximity, while, for axes posterior to the otolith organs, gain increased progressively with target proximity. These effects were large and highly significant. When targets were remote, rotational axis eccentricity nevertheless had a small but significant effect on sinusoidal gain. For sinusoidal rotational axes midway between or anterior to the eyes, a phase lead was present that increased with rotational frequency, while for axes posterior to the otolith organs phase lag increased with rotational frequency. Transient trials were analyzed during the first 25 ms and from 25 to 80 ms after the onset of the head rotation. During the initial 25 ms of transient head rotations, VOR and VVOR gains were not significantly influenced by rotational eccentricity or target distance. Later in the transient responses, 25-80 ms from movement onset, both target distance and eccentricity significantly influenced gain in a manner similar to the behavior during sinusoidal rotation. Vergence angle generally remained near the theoretically ideal value during illuminated test conditions (VVOR), while in darkness vergence often varied modestly from the ideal value. Regression analysis of instantaneous VOR gain as a function of vergence demonstrated only a weak correlation, indicating that instantaneous gain is not likely to be directly dependent on vergence. A model was proposed in which linear acceleration as sensed by the otoliths is scaled by target distance and summed with angular acceleration as sensed by the semicircular canals to control eye movements. The model was fit to the sinusoidal VOR data collected in darkness and was found to describe the major trends observed in the data. The results of the model suggest that a linear interaction exists between the canal and otolithic inputs to the VOR.

Remote medical consultation for vestibular disorders: technological solutions and case report.

Complaints of vertigo and imbalance are common presentations to primary care physicians, yet there are few specialists who diagnose and treat these problems as a significant part of their practices. We demonstrated the feasibility of remote consultation for a patient presenting with vertigo using a two-way digital video and audio network. It was possible to take an appropriate history, examine the patient, and provide a diagnosis and treatment. The patient had a common problem that causes dizziness: benign positional vertigo (BPV). An essential component of the examination was the use of a head-mounted display with embedded cameras. The cameras allowed viewing of the patient's eye movements, which were diagnostic.

The human vertical vestibulo-ocular reflex during combined linear and angular acceleration with near-target fixation.

The purpose of this study was to examine the effect of fixation target distance on the human vestibuloocular reflex (VOR) during eccentric rotation in pitch. Such rotation induces both angular and linear acceleration. Eight normal subjects viewed earth-fixed targets that were either remote or near to the eyes during whole-body rotation about an earth-horizontal axis that was either oculocentric or 15 cm posterior (eccentric) to the eyes. Eye and head movements were recorded using magnetic search coils. Using a servomotor-driven chair, passive whole-body rotations were delivered as trains of single-frequency sinusoids at frequencies from 0.8 to 2.0 Hz and as pseudorandom impulses of acceleration. In the light, the visually enhanced VOR (VVOR) was recorded while subjects were asked to fixate targets at one of several distances. In darkness, subjects were asked to remember targets that had been viewed immediately prior to the rotation. In order to eliminate slip of the retinal image of a near target when the axis of rotation of the head is posterior to the eyes, the ideal gain (compensatory eye velocity divided by head velocity) of the VVOR and VOR must exceed 1.0. Both the VOR and VVOR were found to have significantly enhanced gains during sinusoidal and pseudorandom impulses of rotation (P < 0.05). Enhancement of VVOR gain was greatest at low frequencies of head rotation and decreased with increasing frequency. However, enhanced VOR gain only slightly exceeded 1.0, and VVOR gain enhancement was significantly lower than the expected ideal values for the stimulus conditions employed (P < 0.05). During oculocentric rotations with near targets, both the VOR and VVOR tended to exhibit small phase leads that increased with rotational frequency. In contrast, during eccentric rotations with near targets, there were small phase lags that increased with frequency. Visual tracking contributes during ocular compensatory responses to sustained head rotation, although the latency of visual tracking reflexes exceeds 100 ms. In order to study initial vestibular responses prior to modification by visual tracking, we presented impulses of head acceleration in pseudorandom sequence of initial positions and directions, and evaluated the ocular response in the epoch from 25 to 80 ms after movement onset. As with sinusoidal rotations, pseudorandom eccentric head rotation in the presence of a near, earth-fixed target was associated with enhancement of VVOR and VOR gains in the interval from 25 to 80 ms from movement onset. Despite the inability of visual tracking to contribute to these responses, VVOR gain significantly exceeded VOR gain for pseudorandom accelerations. This gain enhancement indicates that target distance and linear motion of the head are considered by the human ocular motor system in adjustment of performance of the early VOR, prior to a contribution by visual following reflexes. Vergence was appropriate to target distance during all VVOR rotations, but varied during VOR rotations with remembered targets. For the 3-m target distance, vergence during the VOR was stable over each entire trial but slightly exceeded the ideal value. For the 0.1-m near target, instantaneous vergence during the VOR typically declined gradually in a manner not corresponding to the time course of instantaneous VOR gain change; mean vergence over entire trials ranged from 60 to 90% of ideal, corresponding to target distances for which ideal gain would be much higher than actually observed. These findings suggest a dissociation between vergence and VOR gain during eccentric rotation with near targets in the frequency range from 0.8 to 2.0 Hz.

Visual-vestibular interaction during standing, walking, and running.

In artificial laboratory situations where subjects undergo repetitive self-generated or externally imposed head rotations, visual-vestibular interaction during the wearing of telescopic spectacles can markedly augment gain of the vestibulo-ocular reflex (VOR). The present study was conducted to determine whether the wearing of these aids for the visually impaired is associated with similar visual-vestibular interaction during more natural activities. Angular eye and head movements of unrestrained normal volunteers were measured using magnetic search coils. In some subjects, head translations and rotations were also monitored by a flux gate magnetometer array. Measurements were performed of the VOR in darkness, and of the visually enhanced VOR (VVOR) in lit conditions, during three natural activities: 1) standing quietly; 2) walking in place; 3) running in place. These data were compared with similar measurements during repetitive voluntary head oscillations at 0.8 Hz in pitch or yaw. During VVOR, subjects viewed a target placed 6 to 10 m away and remembered this target during VOR trials in darkness. To assess the effects of altering visual-vestibular interactions, VVOR testing during normal vision was augmented by wearing of binocular telescopic spectacles of 2X, 4X, and 6X powers. Dorsoventral and mediolateral head translations were consistently phase-locked with pitch and yaw head rotations, respectively, such that head translation at least partially compensated for rotational disturbances of gaze. Angular velocity of the head was greater during walking than during standing, and was greater still during running, with a greater increase in each case for pitch as compared with yaw. Eye movements were phase compensatory for head movements. VOR gain (eye velocity divided by head velocity) was near 1.0 in both pitch and yaw during standing and during actively generated head rotation. During walking and running there was a significant decrease in angular VOR gain in pitch to approximately 0.75 (P < 0.0005). During ambulatory activities, normal and magnified vision were associated with VVOR gain enhancement in pitch and yaw that was statistically significant, but substantially less than was telescope magnification and markedly lower than was the corresponding VVOR gain measured during active head rotation. Measurements of unmagnified VOR and VVOR during walking and running showed that gain was lower than the "ideal" value of 1.0. However, since translational head perturbations during these activities partially offset the visual effects of angular disturbances, lower gains may nevertheless be associated with retinal image stability at typical indoor target distances. In contrast with performance during repetitive, uniplanar motion, vision has very limited influence on VOR gain during natural activities.

Migraine as a cause of sudden hearing loss.

Sudden hearing loss is common, but unexplained in many cases. Although usually attributed to a viral infection of the inner ear in most patients, the abrupt onset of the hearing loss in many patients argues against a viral etiology. We present 13 cases of unexplained sudden hearing loss who meet the diagnostic criteria for migraine. All had the sudden onset of hearing loss and other neurologic phenomena that could be attributed to vasospasm, including vertigo, amaurosis fugax, hemiplegia, facial pain, chest pain, and visual aura. We suggest that vasospasm of the cochlear vasculature was the cause of the sudden hearing loss in these patients. A personal and family history of migraine should be sought in patients with sudden hearing loss and when found, a trial of antispasmodic agents should be considered.

Vestibular telemedicine and rehabilitation. Applications for virtual reality.

This paper will discuss the use of Virtual Reality (VR) technologies in the rehabilitation of patients with vestibular disorders and in the provision of remote medical consultations for those patients. Patients with a vestibular problem are very common (vertigo is the second most common neurological complaint after headache) and yet there are very few vestibular neurotologists: specialists in their diagnosis and treatment. New treatments for various disorders causing vertigo now exist. This means that appropriate diagnosis can significantly improve patients' well-being. Remote medical diagnosis and treatment facilities could make the few vestibular disorder specialists much more available to patients. An analysis of the technological and economic factors influencing the provision of this service is necessary. The main long term effect of many vestibular disorders is damage to the sensing apparatus of the inner ear. The damage can lead to inappropriate interaction between visually driven orientation sensing and sensing of orientation by the inner ear. The consequence for the patient is vertigo (a sensation of turning), motion sickness and imbalance. Current rehabilitation efforts are intended to drive the nervous system to adapt to the disordered vestibular input. Adaptation appears to occur slowly in many subjects, even those within rehabilitation programs. An appropriately designed VR experience could greatly increase the rate of adaptation in these patients.

Distributed medical intelligence. A systems approach for developing and integrative health care information distribution infrastructure.

Recent trends in healthcare informatics and telemedicine indicate that systems are being developed with a primary focus on technology and business, not on the process of medicine itself. Distributed Medical Intelligence promotes the development of an integrative medical communication system which addresses the process of providing expert medical knowledge to the point of need.

Ocular pursuit movement assessment by magnetic resonance imaging.

We describe a new technique for generating cinematic magnetic resonance images. This method produces more physiological imaging of extraocular muscles than our previous method. In addition, this technique provides more comfort for the study subject and results in less head movement artifact.