Eye movement studies with a vestibular prosthesis/

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2010.Cataloged from PDF version of thesis.Includes bibliographical references.Vestibular loss, which can manifest as dizziness, imbalance, or spatial disorientation, is widespread and often caused by inner ear hair cell malfunction. To address these problems, we are developing a vestibular implant analogous to cochlear implants for the deaf. This vestibular prosthesis provides pulsatile electrical stimulation to the vestibular nerve. Prosthesis effectiveness is assessed using the vestibulo-ocular reflex (VOR), since the VOR helps stabilize gaze in healthy individuals by evoking eye movements that compensate for head movements. In this thesis, the prosthesis was used to probe the high frequency VOR in squirrel monkeys and guinea pigs. In two studies, modulated stimulation was applied acutely to characterize the VOR between 1.5 and 701 Hz. A third study characterized the VOR response to chronic stimulation with a constant rate of 250 Hz. The VOR has previously been characterized up to 50 Hz in monkeys and 2 Hz in guinea pigs by physically rotating subjects. This range was extended in these studies, by using electrical stimulation from the prosthesis. Eye movement spectral peaks were used to characterize the VOR frequency response. The VOR was measurable up to 267 Hz in squirrel monkeys and 151 Hz in guinea pigs. The magnitude response was similar in both species - it increased gradually with frequency, peaked (at 140 Hz in squirrel monkeys and 50 Hz in guinea pigs), and then rolled off.(cont.) The high frequency fall-off was consistent with the low-pass nature of the oculomotor plant. The phase responses had a linear lag with frequency, consistent with a fixed 4 ms delay of the VOR three-neuronarc. Since the VOR responds at high frequencies, this raises the question whether the prosthesis causes eye movements at the prosthesis pulse rate, since electrical stimulation elicits neural responses that are phase-locked with the stimulation. Such responses might cause visual blurring for a patient using the device. This thesis shows that such eye movements are measurable, and have substantial velocity magnitude of 8.1 deg/s initially, but within 30 minutes the magnitude reduces by 80% and probably does not yield perceptible visual blurring.by Michael A. Saginaw.Ph.D

The Vestibular Implant: Quo Vadis?

Objective: To assess the progress of the development of the vestibular implant (VI) and its feasibility short-term. Data sources: A search was performed in Pubmed, Medline, and Embase. Key words used were “vestibular prosth*” and “VI.” The only search limit was language: English or Dutch. Additional sources were medical books, conference lectures and our personal experience with per-operative vestibular stimulation in patients selected for cochlear implantation. Study selection: All studies about the VI and related topics were included and evaluated by two reviewers. No study was excluded since every study investigated different aspects of the VI. Data extraction and synthesis: Data was extracted by the first author from selected reports, supplemented by additional information, medical books conference lectures. Since each study had its own point of interest with its own outcomes, it was not possible to compare data of different studies. Conclusion: To use a basic VI in humans seems feasible in the very near future. Investigations show that electric stimulation of the canal nerves induces a nystagmus which corresponds to the plane of the canal which is innervated by the stimulated nerve branch. The brain is able to adapt to a higher baseline stimulation, while still reacting on a dynamic component. The best response will be achieved by a combination of the optimal stimulus (stimulus profile, stimulus location, precompensation), complemented by central vestibular adaptation. The degree of response will probably vary between individuals, depending on pathology and their ability to adapt

Implante vestibular : ele realmente funciona? : uma revisão sistemática

Introdução: Pessoas com perda vestibular apresentam um déficit no sistema vestibular, o qual é o principal responsável pelo controle postural, pela estabilização do olhar e orientação espacial enquanto a cabeça se movimenta. Não há tratamento efetivo para uma perda vestibular bilateral. Recentemente, foi desenvolvido um implante vestibular para pessoas com perda vestibular bilateral para melhorar essa função e, consequentemente, a qualidade de vida desses pacientes. Objetivo: Identificar na literatura científica evidências de que o implante vestibular melhora a função vestibular de pessoas com déficit vestibular. Método: Cento e quarenta e seis artigos foram encontrados em cinco bases de dados e 323 artigos da literatura cinzenta, mencionando a relação entre implante vestibular e função vestibular em humanos. A estratégia PICOS (População, Intervenção, Comparação e Desfechos) foi utilizada para definir os critérios de elegibilidade. Os estudos que preencheram os critérios de inclusão para esta segunda etapa foram incluídos em uma síntese qualitativa, e cada tipo de estudo foi analisado de acordo com a avaliação de risco de viés do Joanna Briggs Institute através da critical appraisal checklist for quasi-experimental studies e da critical appraisa lchecklist for case reports. Resultados: Dos 21 artigos incluídos cujos textos completos foram lidos, 10 foram selecionados para a análise qualitativa na presente revisão sistemática. Todos os dez artigos analisados através da critical appraisal checklist mostraram um baixo risco de viés. O número total de amostras nos artigos avaliados foi de 18 pacientes com implantes vestibulares. Conclusões: Em conjunto, esses achados apoiam a viabilidade do implante vestibular para a restauração do reflexo vestíbulo-ocular em uma ampla faixa de frequências e ilustram novos desafios para o desenvolvimento desta tecnologia.Introduction: People with vestibular loss present a deficit in the vestibular system, which is primarily responsible for promoting postural control, gaze stabilization, and spatial orientation while the head moves. There is no effective treatment for a bilateral loss of vestibular function. Recently, a vestibular implant was developed for people with bilateral loss of vestibular function to improve this function and, consequently, the quality of life of these patients. Objective: To identify in the scientific literature evidence that vestibular implants in people with vestibular deficit improves vestibular function. Methods: One hundred and forty six articles were found from five databases and 323 articles from the gray literature mentioning the relationship between vestibular implant and vestibular function in humans. The PICOS strategy (Population, Intervention, Comparison and Outcome) was used to define the eligibility criteria. The studies that met the inclusion criteria for this second step were included in a qualitative synthesis, and each type of study was analyzed according to the bias risk assessment of the Joanna Briggs Institute through the critical assessment checklist Joanna Briggs institute for quasi-experimental studies and the Joanna Briggs institute critical assessment checklist for case reports. Results: Of the 21 articles included in reading the full text, 10 studies were selected for the qualitative analysis in the present systematic review. All ten articles analyzed through the critical assessment checklist Joanna Briggs institute showed a low risk of bias. The total number of samples in the evaluated articles was 18 patients with vestibular implants. Conclusions: Taken together, these findings support the feasibility of vestibular implant for restoration of the vestibulo-ocular reflex in a broad frequency range and illustrate new challenges for the development of this technology

Towards Integrating Vestibular Implant Stimulation of the Semicircular Canals and the Otolith End Organs to Drive Posture, Gait, and Eye-Stabilizing Reflexes

Individuals who suffer from bilateral vestibular hypofunction see an increased risk of falling and a decreased quality of life due to symptoms like imbalance, difficulty keeping their eyes on target during head movement, and difficulty walking. The current standard of care to address these symptoms involves rehabilitation exercises to train the central nervous system to rely on visual and proprioceptive signals to compensate for a loss in vestibular signal. However, no sensory substitution can compensate for the extremely fast ocular and spinal reflexes driven by the vestibular nerves. Decades of research led to the development of multichannel vestibular prostheses designed to electrically stimulate the vestibular nerve endings to provide head movement information from a three-axis motion processing unit. The Johns Hopkins Multichannel Vestibular Implant Early Feasibility Study implanted nine study participants with a unilateral vestibular implant targeting the three semicircular canals. The Johns Hopkins Multichannel Vestibular Implant for clinical use does not incorporate circuitry or hardware to stimulate the remaining two sensory organs of the vestibular system, the otolith end organs, responsible for encoding gravitoinertial accelerations that contribute to ocular and spinal reflexes. Stimulation to these end organs were not the priority because they typically elicit much smaller ocular reflexes and encode slower, low-frequency information that can more easily be compensated by the visual and proprioceptive systems. Additionally, their sensory epithelia encode a wider range of information, so mapping a three-axis accelerometer’s signal to stimulation parameters is not straightforward. The research described in this dissertation first assesses the need for otolith-targeted stimulation by measuring otolith-related vestibulo-spinal reflexes via clinical tests of posture and gait in the Multichannel Vestibular Implant Early Feasibility Study with individuals receiving only semicircular canal-targeted stimulation. In the following chapters, the research expands on previous work done in normally functioning chinchillas to explore otolith-targeted stimulation in a rodent model of bilateral vestibular hypofunction and to understand and optimize the stimulation parameters that will be physiologically relevant and useful to restore otolith-specific information to the vestibular nerve endings. The work described in this dissertation is a step toward a more complete vestibular prosthesis to help restore the otolith-driven reflexes to individuals with profound vestibular loss

Development of a Biomimetic Semicircular Canal with MEMS Sensors to Restore Balance

© 2001-2012 IEEE. A third of adults over the age of 50 suffer from chronic impairment of balance, posture, and/or gaze stability due to partial or complete impairment of the sensory cells in the inner ear responsible for these functions. The consequences of impaired balance organ can be dizziness, social withdrawal, and acceleration of the further functional decline. Despite the significant progress in biomedical sensing technologies, current artificial vestibular systems fail to function in practical situations and in very low frequencies. Herein, we introduced a novel biomechanical device that closely mimics the human vestibular system. A microelectromechanical systems (MEMS) flow sensor was first developed to mimic the vestibular haircell sensors. The sensor was then embedded into a three-dimensional (3D) printed semicircular canal and tested at various angular accelerations in the frequency range from 0.5Hz to 1.5Hz. The miniaturized device embedded into a 3D printed model will respond to mechanical deflections and essentially restore the sense of balance in patients with vestibular dysfunctions. The experimental and simulation studies of semicircular canal presented in this work will pave the way for the development of balance sensory system, which could lead to the design of a low-cost and commercially viable medical device with significant health benefits and economic potential

Continuous Restoration of the Human Vestibulo-Ocular Reflex Using a Multichannel Vestibular Implant

Bilateral loss of vestibular sensation causes blurry vision during head movement, postural instability, chronic unsteadiness, and an increased fall risk. Individuals who fail to compensate despite rehabilitation therapy and cessation of exacerbating medications have no adequate treatment options. Inspired by the success of cochlear implants in restoring hearing, prosthetic stimulation of vestibular afferent neurons to encode head motion has been investigated as a potential treatment. Until now, no human had been continuously stimulated for more than a day, and human responses had not been assessed using 3-dimensional (3D) binocular oculography, without which one cannot determine whether an implant independently stimulates each of the implanted ear’s three semicircular canals. We report 3D binocular vestibulo-ocular reflex (VOR) responses in four human subjects with bilateral vestibular loss who were each implanted with a system designed to provide long-term motion-modulated prosthetic stimulation via electrodes in the semicircular canals of one ear. Initiation of prosthetic stimulation evoked nystagmus that decayed within 30 minutes. Stimulation targeting one canal produced 3D VOR responses aligned with that canal’s anatomic axis, while targeting canal pairs reliably yielded responses aligned with a vector sum of individual responses. Over 8 weeks of continuous use, modulated electrical stimulation produced robust and stable VOR responses that grew predictably with stimulus intensity and aligned approximately with any specified 3D head rotation axis. Combining mechanical and electrical stimulation enhanced low frequency responses. These results demonstrate that a vestibular implant can partially restore 3D inner ear sensation to individuals disabled by vestibular loss. Lastly, we show that temporal discretization inherent to cochlear implant signal processing has minimal effects on evoked responses, motivating a future combined device

Alignment of angular velocity sensors for a vestibular prosthesis

Vestibular prosthetics transmit angular velocities to the nervous system via electrical stimulation. Head-fixed gyroscopes measure angular motion, but the gyroscope coordinate system will not be coincident with the sensory organs the prosthetic replaces. Here we show a simple calibration method to align gyroscope measurements with the anatomical coordinate system. We benchmarked the method with simulated movements and obtain proof-of-concept with one healthy subject. The method was robust to misalignment, required little data, and minimal processing

O implante vestibular melhora a função vestibular de pacientes com déficit labiríntico ? uma revisão sistemática

Dissertação (mestrado)—Universidade de Brasília, Faculdade de Ciências da Saúde, Programa de Pós-Graduação em Ciências da Saúde, 2019.Introdução: Pessoas com lesões labirínticas apresentam déficit no sistema vestibular, principal responsável pelo controle postural, estabilização do olhar e orientação espacial durante as movimentações cefálicas. Recentemente, desenvolveu-se o implante vestibular para pessoas com perda vestibular bilateral, com a finalidade de restaurar a função labiríntica e, consequentemente, a qualidade de vida desses pacientes. Objetivo: Identificar, na literatura científica, evidências se o implante vestibular melhora a função vestibular de pacientes com déficit labiríntico. Método: Revisão sistemática na qual 146 artigos foram encontrados em cinco bases de dados e 323 artigos da literatura cinzenta, mencionando a relação entre implante vestibular e função vestibular em humanos. A estratégia PICOS (população, intervenção, comparação, resultados e tipos de estudos) foi utilizada para definir os critérios de elegibilidade. Os estudos que preencheram os critérios de inclusão nessa primeira etapa foram incluídos em uma segunda etapa para síntese qualitativa, e cada tipo de estudo foi analisado de acordo com a avaliação de risco de viés do Joanna Briggs Institute por meio da lista de verificação de avaliação crítica para estudos quase-experimentais (estudos experimentais não randomizados) e da lista de verificação de avaliação crítica para relatos de caso. Resultados: Dos 21 artigos incluídos, 10 foram selecionados para a análise qualitativa na presente revisão sistemática. Todos os 10 artigos foram analisados por meio da lista de verificação de avaliação crítica do Joanna Briggs Institute e 9 estudos mostraram um baixo risco de viés e um estudo apresentou risco de viés moderado. O número total de amostras nos artigos avaliados foi de 18 pacientes com implante vestibular. Conclusões: Em conjunto, estes achados apoiam a viabilidade do implante vestibular para a restauração do reflexo vestíbulo-ocular em uma ampla faixa de frequências e ilustram novos desafios para o desenvolvimento desta tecnologia.Introduction: People with vestibular loss present a deficit in the vestibular system, which is primarily responsible for promoting postural control, gaze stabilization, and spatial orientation while the head moves. Recently, a vestibular implant was developed for people with bilateral loss of vestibular function to improve this function and, consequently, the quality of life of these patients. Objective: To identify, in the scientific literature, evidence if the vestibular implant in people with vestibular deficit improves vestibular function. Methods: One hundred forty-six articles were found from five databases and 323 articles from the gray literature mentioning the relationship between vestibular implant and vestibular function in humans. The PICOS strategy (population, intervention, comparison, outcome and study type) was used to define the eligibility criteria. The studies that met the inclusion criteria in this first step were included in a second step for qualitative synthesis, and each type of study was analyzed according to the bias risk assessment of the Joanna Briggs Institute through the critical assessment checklist Joanna Briggs Institute for quasi-experimental studies and the critical assessment checklist for case reports. Results: Of the 21 articles, 10 studies were selected for the qualitative analysis in the present systematic review. All ten articles were analyzed through the critical assessment checklist Joanna Briggs Institute and nine studies showed a low risk of bias and one study showed moderate risk of bias. The total number of samples in the evaluated articles was 18 patients with vestibular implants. Conclusion: Taken together, these findings support the feasibility of vestibular implant for restoration of the vestibulo-ocular reflex in a broad frequency range and illustrate new challenges for the development of this technology

Restoring Sensation of Gravitoinertial Acceleration through Prosthetic Stimulation of the Utricle and Saccule

Individuals with bilateral vestibular hypofunction suffer reduced quality of life due to loss of postural and ocular reflexes essential to maintaining balance and visual acuity during head movements. Vestibular stimulation has demonstrated success in restoring sensation of angular head rotations using electrical stimulation of the semi-circular canals (SCCs). Efforts toward utricle and saccule stimulation to restore sensation of gravitoinertial acceleration have been limited due to the complexity of the otolith end organs and otolith-ocular reflexes (OORs). Four key pieces of technology were developed to extend prosthetic stimulation to the utricle and saccule: a low-noise scleral coil system to record binocular 3D eye movements; a motion platform control system for automated presentation of rotational and translational stimuli; custom electrode arrays with fifty contacts targeting the SCCs, utricle and saccule; and a general-purpose neuroelectronic stimulator for vestibular and other neuromodulation applications. Using these new technologies, OORs were first characterized in six chinchillas to establish OOR norms during translations and static tilts. Results led to creation of a model that infers the axis of head tilt from measured binocular eye movements and thereby provides a context and means to assess the selectivity of prosthetic utricle and saccule stimulation. The model confirms the expectation that excitation of the left utricle and saccule primarily encodes tilts that bring the left ear down. Three of the chinchillas were implanted with electrode arrays in the left ear. Step changes in pulse rate were delivered to utricle and saccule electrodes near the maculae while measuring 3D binocular eye movements with the animal stationary in darkness. These stimuli elicited sustained ocular counter-roll responses that increased in magnitude as pulse rate or amplitude increased. Bipolar stimulation via neighboring electrodes elicited slow-rising or delayed onset of ocular counter-rolls (consistent with normal translational OOR low-pass filter behavior). Two chinchillas showed different direction of electrically-evoked ocular counter-roll between utricle versus saccule stimulation. Only near-neighbor bipolar electrode combinations elicited eye responses compensatory for tilts other than the ‘usual’ left ear down, suggesting the need for distributing multiple bipolar electrode pairs across the maculae to achieve selective stimulation and restore 3D sensation of gravitoinertial acceleration