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Les manifestations neuro-ophtalmologiques, observées dans la sclérose en plaques sont parfaitement déterminées à l’heure actuelle. Cependant, l’aspect chronique des troubles visuels résultants n’est pas toujours précisément évalué, or de telles lacunes sont un frein à leur prise en charge. Dans une première partie, les caractéristiques des troubles visuels chroniques ont été mesurées. Il s’agissait de quantifier le pourcentage de plaintes visuelles chroniques chez des patients atteints de sclérose en plaques puis de mesurer le degré d’intensité des troubles visuels chroniques, de déterminer leurs origines physiopathologiques et de rendre compte de leur retentissement sur la qualité de vie des patients se plaignant de troubles chroniques. Les voies visuelles afférentes étaient altérées dans 68% des cas. Des troubles oculomoteurs étaient fréquemment observés (89%) dont le nystagmus pendulaire (28%), source de gêne visuelle. Dans une seconde partie, nous nous sommes donc intéressés au nystagmus pendulaire et à sa conséquence fonctionnelle, l’oscillopsie, afin de proposer une prise en charge spécifique. Néanmoins, les mécanismes de ce nystagmus ne sont pas encore bien définis. Il était donc important de développer une hypothèse explicative à partir de l’observation de deux cas particuliers de nystagmus monoculaire et de démontrer que le nystagmus pendulaire de la sclérose en plaques est à distinguer du nystagmus pendulaire du tremblement oculopalatin, souvent confondus. Enfin, nous proposons une méthode évaluant la détection du mouvement (par stimuli de contraste asservis au regard) ainsi qu’un protocole de stimulation optocinétique tentant de réduire ce symptôme / Neuro-ophthalmic manifestations observed in multiple sclerosis are well-known. However, the chronic feature of visual dysfunctions is not always precisely determinated. These imprecision impede the development of specific therapeutic approach. In a first part, the chronic characteristics of visual dysfunctions were assessed. The percentage of chronic visual complaints in multiple sclerosis patients was quantified and then the intensity of chronic visual deficits was measured, their pathophysiologic origins determined and finally their impact on quality of life was taken into account. Visual pathways were impaired in 68% of patients. Ocular motor disorders were frequently observed (89%) including pendular nystagmus (28%), accounted for visual discomfort. In a second part, we focused on pendular nystagmus and its functional consequence, oscillopsia, to propose a specific treatment. First of all, the mechanisms of this nystagmus are not yet well defined. Therefore, we developed some hypothesis from the observation of two patients with monocular nystagmus and demonstrated in a second part that the pendular nystagmus in multiple sclerosis is distinct from the pendular nystagmus of oculopalatal tremor. Finally, we proposed a method evaluating oscillopsia (motion detection by contrast stimuli moving synchronically with gaze) that was tested before and after an optokinetic stimulation protocol aimed to reduce this symptom

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Nystagmus is an eye movement pattern that consists of a drifting gaze component, known as the slow phase, followed by a corrective quick phase component. The presence of nystagmus or the lack thereof under certain conditions can be used for various diagnostic purposes including the diagnosis of physiological, pathological and neurological conditions. The angular velocity of the quick phase can make the detection of nystagmus a challenging task for the untrained eye, since the quick phases are usually comparable with saccadic eye motions. The goal is thus to develop a fully automated diagnostic tool that can identify the presents of nystagmus in a patient’s eye motions. In this thesis, an appropriate eye tracking method was selected from a number of eye tracking methods that are commonly implemented in the literature. A video-oculography goggle concept was chosen based on criteria such as invasiveness, sampling rate, accuracy and telemedicine capability, amongst other nystagmus related necessities. A binocular video-oculography concept was chosen that satisfied the technical requirements and provided a cost-effective design. An automated analysis algorithm was developed for automatic nystagmus identification from eye motion data. The algorithm was validated by testing the performance of the algorithm on an optokinetic nystagmus signal. It proved to provide a reliable automatic identification of nystagmus beats, even in signals that contained nystagmus as well as random motion components. A statistical analysis showed that the algorithm provided a sensitivity of 91.8% and a specificity of 96.5% for pure nystagmus signals, and a sensitivity and specificity of 87.8% and 91.1% respectively for mixed signals. / AFRIKAANSE OPSOMMING: Nystagmus is ’n oogbewegingspatroon wat bestaan uit ’n dwalende tuurkomponent, wat die stadige fase genoem word, gevolg deur ’n vinnige korrigereringsbeweging wat bekend staan as die vinnige fase. Die teenwoordigheid van nystagmus, of afwesigheid daarvan in sekere gevalle, kan gebruik word in ’n verskeidenheid diagnostiese toepassings, onder andere die diagnose van fisiologiese-, patalogiese- en neurologiese kwale. Die hoeksnelheid van die vinnige fase lei daartoe dat nystagmus dikwels moeilik is om te bespeur vir ongeöefende oë, aangesien dit vergelykbaar is met saccade bewegings. Die doel van hierdie navorsing is dus die ontwikkeling van ’n stelsel wat ’n volledige automatiese identifisering van nystagmus kan behartig. ’n Gepaste oogvolgtegniek was gekies vanuit ’n aantal verskillende oogvolgmetodes wat dikwels in die praktyk gebruik word. Die finale keuse was ’n skermbril, video-oogvolgmetode wat gekies was op grond van kriteria soos onder andere, invallendheid, meetfrekwensie, akkuraatheid en geskiktheid vir telemedisyne toepassings. Die ontwikkelde brilkonsep bied ’n koste-effektiewe oplossing, met die moontlikheid om albei oë te volg en bevredig al die bogenoemde tegniese spesifikasies. ’n Geoutomatiseerde nystagmus identifiseringsalgoritme is ontwikkel. Die algoritme se effektiwiteit is getoets op optokinetiese nystagmusseine. Betroubare resultate is vekry vanaf die algoritme, selfs in die geval van gemengde seine wat bestaan uit arbritrêre- en nystagmus komponente. Statistiese analiese het gewys dat die algoritme ’n sensitiwiteit van 91.8% en ’n spesifisiteit van 96.5% kon behaal vir seine met slegs nystagmus inhoud. Vir gemengde inhoud seine het die algoritme ’n sensitiwiteit van 87.8% en spesifisiteit van 91.1% behaal.

Infantile nystagmus is a condition that causes involuntary, bilateral and conjugate oscillations of the eyes, which are predominately restricted to the horizontal plane. In order to investigate the cause of nystagmus, computational models and nonlinear dynamics techniques have been used to model and analyse the oculomotor system. Computational models are important in making predictions and creating a quantitative framework for the analysis of the oculomotor system. Parameter estimation is a critical step in the construction and analysis of these models. A preliminary parameter estimation of a nonlinear dynamics model proposed by Broomhead et al. [1] has been shown to be able to simulate both normal rapid eye movements (i.e. saccades) and nystagmus oscillations. The application of nonlinear analysis to experimental jerk nystagmus recordings, has shown that the local dimensions number of the oscillation varies across the phase angle of the nystagmus cycle. It has been hypothesised that this is due to the impact of signal dependent noise (SDN) on the neural commands in the oculomotor system. The main aims of this study were: (i) to develop parameter estimation methods for the Broomhead et al. [1] model in order to explore its predictive capacity by fitting it to experimental recordings of nystagmus waveforms and saccades; (ii) to develop a stochastic oculomotor model and examine the hypothesis that noise on the neural commands could be the cause of the behavioural characteristics measured from experimental nystagmus time series using nonlinear analysis techniques. In this work, two parameter estimation methods were developed, one for fitting the model to the experimental nystagmus waveforms and one to saccades. By using the former method, we successfully fitted the model to experimental nystagmus waveforms. This fit allowed to find the specific parameter values that set the model to generate these waveforms. The types of the waveforms that we successfully fitted were asymmetric pseudo-cycloid, jerk and jerk with extended foveation. The fit of other types of nystagmus waveforms were not examined in this work. Moreover, the results showed which waveforms the model can generate almost perfectly and the waveform characteristics of a number of jerk waveforms which it cannot exactly generate. These characteristics were on a specific type of jerk nystagmus waveforms with a very extreme fast phase. The latter parameter estimation method allowed us to explore whether the model can generate horizontal saccades of different amplitudes with the same behaviour as observed experimentally. The results suggest that the model can generate the experimental saccadic velocity profiles of different saccadic amplitudes. However, the results show that best fittings of the model to the experimental data are when different model parameter values were used for different saccadic amplitude. Our parameter estimation methods are based on multi-objective genetic algorithms (MOGA), which have the advantage of optimising biological models with a multi-objective, high-dimensional and complex search space. However, the integration of these models, for a wide range of parameter combinations, is very computationally intensive for a single central processing unit (CPU). To overcome this obstacle, we accelerated the parameter estimation method by utilising the parallel capabilities of a graphics processing unit (GPU). Depending of the GPU model, this could provide a speedup of 30 compared to a midrange CPU. The stochastic model that we developed is based on the Broomhead et al. [1] model, with signal dependent noise (SDN) and constant noise (CN) added to the neural commands. We fitted the stochastic model to saccades and jerk nystagmus waveforms. It was found that SDN and CN can cause similar variability to the local dimensions number of the oscillation as found in the experimental jerk nystagmus waveforms and in the case of saccade generation the saccadic variability recorded experimentally. However, there are small differences in the simulated behaviour compared to the nystagmus experimental data. We hypothesise that these could be caused by the inability of the model to simulate exactly key jerk waveform characteristics. Moreover, the differences between the simulations and the experimental nystagmus waveforms indicate that the proposed model requires further expansion, and this could include other oculomotor subsystem(s).

Traditionally, results from caloric testing and optokinetic nystagmus (OKN) testing are analyzed separately because caloric testing is a measure of peripheral function and OKN testing is considered to be a measure of central function. However, there is a connection between the visual system and the vestibular system in the vestibular nucleus of the brainstem. The purpose of this paper was to determine whether a relationship exists between optokinetic nystagmus results and unilateral caloric weakness results. This was determined by conducting a retrospective study of forty patients who exhibited a unilateral caloric weakness greater than or equal to twenty percent and symptoms consistent with an uncompensated vestibulopathy. Patients were later divided into two groups based on involved side. A control group consisting of ten subjects with no reported hearing or vestibular problems was also recruited. When the data of all subjects with a unilateral caloric weakness was considered together, no correlation was found between caloric response (right and left ear) and optokinetic results (gain and slow phase velocity). However, a potential trend emerged at the slow stimulus velocity (15 degrees) when comparing the patients with a right caloric weakness to those with a left caloric weakness. Subjects with a right caloric weakness showed decreased OKN gain for the right eye with a right-moving stimulus compared to the subjects with a left caloric weakness. Alternatively, subjects with a left caloric weakness showed decreased OKN gain for the left eye with a left-moving stimulus compared to the subjects with a right caloric weakness. We conclude that interpretation of OKN along with caloric results may offer potential for identification and tracking of compensation after a unilateral loss of vestibular function, but further research is needed.

Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (leaves 74-84).

Introduction: The dizziness is observed among 5 and 10% of the world population, affecting both genders. It can be of two sorts: rotatory (vertigo) or non-rotatory. The dizziness crises may injure the patients life, leading to the reduction of social coexistence and difficult the daily activities. The most common rotatory dizziness is the Benign Positional Paroxysmal Vertigo. The episodes are generally quick and triggered by the head movement, Furthermore, it may be accompanied by nausea, vomiting and fall. The diagnosis of Benign Positional Paroxysmal Vertigo is achieved through the Dix-Halpike maneuver, which shall verify the presence of nystagmus and/or giddiness. There are no reports of variation in conventional tests of patients with complaint of Benign Positional Paroxysmal Vertigo. It is observed only in vectonystagmography. The treatment of this type of dizziness is performed by canalith repositioning maneuvers. Objective: To verify the results found in the evaluations carried out by patients with Benign Positional Paroxysmal Vertigo, with emphasis on the results found in vectonystagmography and its relationship with affected semicircular canal. Material and Method: The study was performed in otology ambulatory of University Hospital of Santa Maria. The sample was composed of all patients who attended the ambulatory with complaints of. The patients have performed anamnesis, Dix-Halpike maneuver, vectonystagmography and Epley maneuver. They were divided in two groups: the control group, composed by patients with negative result in Dix-Halpike maneuver, and the study group, composed by patients with positive result in this maneuver. Results: There was prevalence of females among the patients and the average age was 57 years. The semicircular canal most affected was the anterior and the theory that prevailed was the ductolitiase. The average number of maneuvers necessaries to abolish the positioning nystagmus is 1.58 and there were 4 (6.9%) cases of recurrence. When analyzed the evidence of vectonystagmography, it was observed the presence of spontaneous nystagmus and a change in rotator testing. However, these variations are not related to the affected semicircular canal. It has occurred a predominance of normorreflexia in the caloric testing. Conclusion: The Epley maneuver is effective for patients with Benign Positional Paroxysmal Vertigo, even in cases in which they occur relapses. The variations found in vectonystagmography are not related to the affected semicircular canal. In fact, these variations are arising from the spontaneous and latent nystagmus presence. Consequently, it was not possible to verify other methods for the diagnosis of Benign Positional Paroxysmal Vertigo. / Introdução: A tontura é observada entre 5 e 10% da população mundial, atingindo ambos os gêneros. Pode ser de dois tipos: rotatória (vertigem) ou não rotatória. As crises de tontura podem prejudicar a vida do paciente, levando à redução do convívio social e dificultando as atividades de vida diária. O tipo de tontura rotatória mais comum é a Vertigem Posicional Paroxística Benigna. Os episódios geralmente são rápidos e desencadeados pelo movimento de cabeça, podendo ser acompanhado de náuseas, vômitos e queda. O diagnóstico de vertigem posicional paroxística benigna é realizado através da manobra de Dix-Halpike, que verifica a presença de nistagmo e/ou tontura. Não há relatos de alteração nos testes convencionais de pacientes com queixa de Vertigem Posicional Paroxística Benigna. Isto é verificado apenas na vectoeletronistagmografia. O tratamento desse tipo de vertigem é realizado pela manobra de reposição canalítica. Objetivo: verificar os resultados encontrados nas avaliações realizadas pelos pacientes com Vertigem Posicional Paroxística Benigna, com ênfase nos resultados encontrados na vectoeletronistagmografia e sua relação com o canal semicircular afetado. Material e Método: o estudo foi realizado no ambulatório de otologia do Hospital Universitário de Santa Maria. A amostra foi composta por todos os pacientes que compareceram ao ambulatório com queixa de vertigem posicional paroxística benigna. Os pacientes realizaram anamnese, manobra de Dix-Halpike, vectoeletronistagmografia e manobra de Epley. Estes foram divididos em dois grupos: grupo controle, composto pelos pacientes com resultado negativo na manobra de Dix-Halpike, e grupo estudo, composto pelos pacientes com resultado positivo nesta manobra. Resultados: Houve prevalência do sexo feminino entre os pacientes e a média de idade foi de 57 anos. O canal semicircular mais afetado foi posterior e a teoria que prevaleceu foi a ductolitíase. O número médio de manobras necessárias para abolir o nistagmo de posicionamento é 1,58 e houve 4 (6,9%) casos de recidiva. Quando analisada as provas da vectoeletronistagmografia, foi observada presença de nistagmo espontâneo e alteração na prova rotatória pendular decrescente. Entretanto, essas alterações não estão relacionadas com o canal semicircular afetado. Na prova calórica houve predomínio da normorreflexia. Conclusão: A manobra de Epley é eficaz para pacientes com vertigem posicional paroxística benigna, mesmo nos casos em que ocorrem recidivas. As alterações encontradas na vectoeletronistagmografia não estão relacionadas com o canal semicircular afetado. De fato, essas alterações são decorrentes da presença de nistagmo espontâneo e nistagmo latente. Consequentemente, não foi possível verificar outros métodos para o diagnóstico da vertigem posicional paroxística benigna.

The purpose of this study was to examine the prevalence of nystagmus found in healthy individuals during the positional testing subtest of the standard vestibular test battery. Positional testing involves moving the patient's head, and sometimes the entire body, into a variety of positions while observing eye movement. The hypothesis of the current study was that a relatively low percentage of participants would display nystagmus during positional testing used routinely in clinical diagnostic procedures. The findings were then compared to those of an earlier study in which 82% of normal, healthy individuals were reported to exhibit nystagmus during this testing. Twenty-five participants were selected that had no known otologic disease and who reported normal hearing sensitivity. In addition, the participants affirmed they had not consumed any alcohol or taken any medications that are known to affect nystagmus. They were then observed in nine different positions. Forty-eight percent of the participants experienced nystagmus in at least one position. Although this percentage was considerably lower than that reported in the earlier study, methodological differences appear to account for the discrepancy. Specifically, the criterion for determining the presence/absence of nystagmus potentially explains the difference in full.

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