Multifocal visual evoked potentials in demyelinating diseases of the visual pathway

Multifocal visual evoked potentials (mfVEP) provide an objective functional measure of the integrity of the visual pathway. This thesis constitutes a comprehensive assessment of mfVEP changes in demyelinating diseases of the visual pathway. The efficacy of the mfVEP technique was compared to full-field pattern-reversal visual evoked potential and the results illustrate a superiority of the mfVEP in detecting focal visual field defects in patients with different visual pathway disorders. The evolution of mfVEP parameters’ changes following acute optic neuritis (ON) was assessed in a longitudinal study of affected and fellow eyes in a large cohort of patients during the first 12 months after attack. The results indicated that mfVEP amplitude can be used as an early predictor of post-ON axonal loss. Additionally, the apparently more severe involvement of ON eyes in the MS subgroup may be due to subclinical inflammation along the visual pathway. The analysis of latency delay in fellow eyes in ON patients indicated that the observed changes are most likely due to subclinical demyelination in the visual pathway and a reflection of the burden of disease in MS patients rather than a result of adaptive cortical plasticity to compensate for delayed transmission of visual information. The last study evaluated the relationship between mfVEP latency and posterior visual pathway lesions in MS patients which demonstrated a significant evidence linking the mfVEP changes with retro-geniculate inflammatory demyelinating lesions

Diagnostic ability of multifocal electroretinogram in early multiple sclerosis using a new signal analysis method

Purpose To determine if a novel analysis method will increase the diagnostic value of the multifocal electroretinogram (mfERG) in diagnosing early-stage multiple sclerosis (MS). Methods We studied the mfERG signals of OD (Oculus Dexter) eyes of fifteen patients diagnosed with early-stage MS (in all cases < 12 months) and without a history of optic neuritis (ON) (F: M = 11:4), and those of six controls (F:M = 3:3). We obtained values of amplitude and latency of N1 and P1 waves, and a method to assess normalized root-mean-square error (FNRMSE) between model signals and mfERG recordings was used. Responses of each eye were analysed at a global level, and by rings, quadrants and hemispheres. AUC (area under the ROC curve) is used as discriminant factor. Results The standard method of analysis obtains further discrimination between controls and MS in ring R3 (AUC = 0.82), analysing N1 waves amplitudes. In all of the retina analysis regions, FNRMSE value shows a greater discriminating power than the standard method. The highest AUC value (AUC = 0.91) was in the superior temporal quadrant. Conclusion By analysing mfERG recordings and contrasting them with those of healthy controls it is possible to detect early-stage MS in patients without a previous history of ON

A computer-aided diagnosis of multiple sclerosis based on mfVEP recordings.

Introduction: The aim of this study is to develop a computer-aided diagnosis system to identify subjects at differing stages of development of multiple sclerosis (MS) using multifocal visual-evoked potentials (mfVEPs). Using an automatic classifier, diagnosis is performed first on the eyes and then on the subjects. Patients: MfVEP signals were obtained from patients with Radiologically Isolated Syndrome (RIS) (n = 30 eyes), patients with Clinically Isolated Syndrome (CIS) (n = 62 eyes), patients with definite MS (n = 56 eyes) and 22 control subjects (n = 44 eyes). The CIS and MS groups were divided into two subgroups: those with eyes affected by optic neuritis (ON) and those without (non-ON). Methods: For individual eye diagnosis, a feature vector was formed with information about the intensity, latency and singular values of the mfVEP signals. A flat multiclass classifier (FMC) and a hierarchical classifier (HC) were tested and both were implemented using the k-Nearest Neighbour (k-NN) algorithm. The output of the best eye classifier was used to classify the subjects. In the event of divergence, the eye with the best mfVEP recording was selected. Results: In the eye classifier, the HC performed better than the FMC (accuracy = 0.74 and extended Matthew Correlation Coefficient (MCC) = 0.68). In the subject classification, accuracy = 0.95 and MCC = 0.93, confirming that it may be a promising tool for MS diagnosis. Chirped-pulse φOTDR provides distributed strain measurement via a time-delay estimation process. We propose a lower bound for performance, after reducing sampling error and compensating phase-noise. We attempt to reach the limit, attaining unprecedented pε/√Hz sensitivities. Conclusion: In addition to amplitude (axonal loss) and latency (demyelination), it has shown that the singular values of the mfVEP signals provide discriminatory information that may be used to identify subjects with differing degrees of the disease.Secretaría de Estado de Investigación, Desarrollo e InnovaciónInstituto de Salud Carlos II

Diagnosis of multiple sclerosis using multifocal ERG data feature fusion

The purpose of this paper is to implement a computer-aided diagnosis (CAD) system for multiple sclerosis (MS) based on analysing the outer retina as assessed by multifocal electroretinograms (mfERGs). MfERG recordings taken with the RETI?port/scan 21 (Roland Consult) device from 15 eyes of patients diagnosed with incipient relapsing-remitting MS and without prior optic neuritis, and from 6 eyes of control subjects, are selected. The mfERG recordings are grouped (whole macular visual field, five rings, and four quadrants). For each group, the correlation with a normative database of adaptively filtered signals, based on empirical model decomposition (EMD) and three features from the continuous wavelet transform (CWT) domain, are obtained. Of the initial 40 features, the 4 most relevant are selected in two stages: a) using a filter method and b) using a wrapper-feature selection method. The Support Vector Machine (SVM) is used as a classifier. With the optimal CAD configuration, a Matthews correlation coefficient value of 0.89 (accuracy = 0.95, specificity = 1.0 and sensitivity = 0.93) is obtained. This study identified an outer retina dysfunction in patients with recent MS by analysing the outer retina responses in the mfERG and employing an SVM as a classifier. In conclusion, a promising new electrophysiological-biomarker method based on feature fusion for MS diagnosis was identified.Agencia Estatal de InvestigaciónInstituto de Salud Carlos II

Promoting and measuring remyelination and neuroprotection in clinical trials of people with multiple sclerosis

The most tractable strategy to delay or prevent the progressive phase of MS is to promote endogenous remyelination; doing so restores nerve conduction and prevents demyelinated axons from degenerating. The rate-limiting stage in this process is differentiation of oligodendrocyte progenitor cells (OPCs) into mature, myelinating, oligodendrocytes. In animals, agonism of the retinoid X receptor (RXR)-γ enhances remyelination in this way. Metformin also promotes remyelination, this time by overcoming an age-associated block to the responsiveness of OPCs to pro-differentiation factors. In this PhD I show that bexarotene, a non-selective agonist of the RXR receptor, promotes remyelination in people with relapsing remitting multiple sclerosis. Converging evidence from electrophysiology and neuroimaging in a phase II clinical trial (CCMR One) demonstrate that this occurs in demyelinated lesions and is greatest in lesions located in grey matter regions of the brain. I additionally conducted analyses which suggest an age-dependency of bexarotene’s remyelinating effect and led a follow-up sub study of the trial participants which showed the treatment effect afforded by bexarotene is sustained, years after treatment. Unfortunately, bexarotene was poorly tolerated, and so the legacy of this trial will likely be one of shaping the framework for future assessments of remyelinating therapies. As such, I designed, obtained funding and secured approvals for a clinical trial to test the remyelinating effect of the combination of metformin with clemastine (CCMR Two), implementing lessons from CCMR One in the trial design; this is due to commence participant recruitment in 2021. In exploring treatments for progressive forms of MS, not limited to the process of remyelination, I worked with the MS Society to develop and implement a rigorous, expert-led, evidence-based approach to the selection of licensed drugs for repurposing and testing in clinical trials of people with progressive MS. I reviewed the preclinical and clinical literature for a list of compounds and condensed these into a database of summary documents. These were presented to a panel of experts and people affected by MS, ultimately leading to four treatments being recommended for immediate testing in progressive MS trials: R-α-lipoic acid, metformin, the combination treatment of R-α-lipoic acid and metformin, and niacin. Regrettably, much of my research has been halted by the COVID-19 pandemic. In this PhD I had additionally sought to evaluate electrophysiological techniques for quantifying remyelination and neuroprotection – multifocal VEP and saccadometry – in cohorts of people with MS and in the setting of the CCMR Two trial. Instead, when these studies were delayed, I embraced an opportunity to help the Cambridge COVID-19 research effort, working on the RECOVERY trial in the first wave, and leading my own project to analyse enrolment to treatment trials, ultimately describing the barriers to, and implications of, low recruitment rates in advance of the subsequent waves. Consequently, further exploratory research with electrophysiology and the CCMR Two trial will be the subject of post-doctoral research.Multiple Sclerosis Society of the United Kingdo

A multilayered approach to the automatic analysis of the multifocal electroretinogram

The multifocal electroretinogram (mfERG) provides spatial and temporal information on the retina’s function in an objective manner, making it a valuable tool for monitoring a wide range of retinal abnormalities. Analysis of this clinical test can however be both difficult and subjective, particularly if recordings are contaminated with noise, for example muscle movement or blinking. This can sometimes result in inconsistencies in the interpretation process. An automated and objective method for analysing the mfERG would be beneficial, for example in multi-centre clinical trials when large volumes of data require quick and consistent interpretation. The aim of this thesis was therefore to develop a system capable of standardising mfERG analysis. A series of methods aimed at achieving this are presented. These include a technique for grading the quality of a recording, both during and after a test, and several approaches for stating if a waveform contains a physiological response or no significant retinal function. Different techniques are also utilised to report if a response is within normal latency and amplitude values. The integrity of a recording was assessed by viewing the raw, uncorrelated data in the frequency domain; clear differences between acceptable and unacceptable recordings were revealed. A scale ranging from excellent to unreportable was defined for the recording quality, first in terms of noise resulting from blinking and loss of fixation, and secondly, for muscle noise. 50 mfERG tests of varying recording quality were graded using this method with particular emphasis on the distinction between a test which should or should not be reported. Three experts also assessed the mfERG recordings independently; the grading provided by the experts was compared with that of the system. Three approaches were investigated to classify a mfERG waveform as ‘response’ or ‘no response’ (i.e. whether or not it contained a physiological response): artificial neural networks (ANN); analysis of the frequency domain profile; and the signal to noise ratio. These techniques were then combined using an ANN to provide a final classification for ‘response’ or ‘no response’. Two methods were studied to differentiate responses which were delayed from those within normal timing limits: ANN; and spline fitting. Again the output of each was combined to provide a latency classification for the mfERG waveform. Finally spline fitting was utilised to classify responses as ‘decreased in amplitude’ or ‘not decreased’. 1000 mfERG waveforms were subsequently analysed by an expert; these represented a wide variety of retinal function and quality. Classifications stated by the system were compared with those of the expert to assess its performance. An agreement of 94% was achieved between the experts and the system when making the distinction between tests which should or should not be reported. The final system classified 95% of the 1000 mfERG waveforms correctly as ‘response’ or ‘no response’. Of those said to represent an area of functioning retina it concurred with the expert for 93% of the responses when categorising them as normal or abnormal in terms of their P1 amplitude and latency. The majority of misclassifications were made when analysing waveforms with a P1 amplitude or latency close to the boundary between normal and abnormal. It was evident that the multilayered system has the potential to provide an objective and automated assessment of the mfERG test; this would not replace the expert but can provide an initial analysis for the expert to review

Electroretinographic Mapping of Retinal Function: Evaluation and Clinical Application

The conventional electroretinogram (ERG) is an electrophysiological examination that is used to assess the extent of retinal function within the eye. The test exploits the retina's ability to convert photons of light into electrical impulses. A flash stimulus is employed to evoke an electrical potential within the retinal cells (cones, rods and bipolar cells). These potentials, generated in the retina, are then recorded at the corneal surface of the eye using a contact lens or scleral electrode. The electrical potential generated possesses several distinct components that can be used to locate dysfunction from discrete layers of the retina. Although the ERG is used routinely in the diagnosis and monitoring of a wide range of retinal disorders its application is restricted because the diffuse stimulation of the retina evokes a global response thereby preventing the detection of localised abnormalities. A new technique has recently been developed, the Visual Evoked Response Imaging System (VERIS), which overcomes some of the shortfalls of the conventional electroretinogram. This new method allows functional mapping of the retina by the ERG. The technique enables simultaneous recording from a large number of retinal areas. Each area is independently stimulated in a sequence employing Pseudo Random Binary Sequences (PRBS). The sequences of stimulation are uncorrelated (achieved by temporal modulation of the sequence for each area) therefore the individual responses from different areas of the retina can be extracted. This thesis describes the evaluation of this system with regards to its potential within routine clinical practice. A number of investigations were performed to fulfil this evaluation. Possible factors that may influence the integrity of data obtained from the new technique were investigated and, where possible, minimised. These factors included quantifying the effects of filtering bandwidth, refractive errors, electrode type, response measurement method, luminance, contrast, dilation and the artefacts associated with poor patient shielding (from extraneous electromagnetic interference). The findings from these investigations were used to optimise the recovery of local ERG responses and established a protocol for future investigations. A custom software program was developed for analysis and interpretation of data. A study was undertaken to quantify the repeatability and reproducibility of the technique and to provide normative values. Finally these results were used to assess the techniques ability to objectively detect and quantify several retinal disorders. The investigations indicated that the system was of particular benefit in the assessment of local retinal pathology. However the system suffered a higher exclusion criteria than conventional electrophysiology and was unable, in the clinical setting, to identify retinal pathologies selectively affecting the ganglion cell layer. These factors limited the systems application within clinical practice. Current developments are aimed at improving the technique and establishing a routine clinical test with improved sensitivity and specificity that can be successfully applied to a wider population group

Phenotypic Characterization with Software Development for Analysis of the Visual System in Animal Models of Neurodevelopmental Diseases

A neurofibromatose tipo 1 (NF1) é uma perturbação do desenvolvimento neurológico com implicações cognitivas adultas. Provoca anomalias do sistema nervoso central e afeta 1 em 3000 indivíduos em todo o mundo. Contudo, pouco se sabe sobre os efeitos no sistema visual e como estes podem estar associados a défices cognitivos e preveem a sua progressão. Neste trabalho, avalia-se as potenciais alterações na fisiologia da retina num modelo genético de murgalho de NF1, utilizando uma técnica neurofisiológica não invasiva, o eletroretinograma (ERG), para determinar o seu potencial diagnóstico. Como um indicador fiável da função da retina em resposta à luz, o ERG tem a capacidade de ajudar a nossa interpretação da fisiopatologia das perturbações do neurodesenvolvimento e neurodegenerativas. Os principais objetivos desta tese são a caracterização fenotípica do sistema visual num modelo animal de NF1 e o desenvolvimento de ferramentas informáticas (MATLAB e Phyton) para processamento de sinais, análise de forma de onda, extração de características, e classificação. Verificou-se que os parâmetros ERG relacionados principalmente com a atividade oscilatória inibitória revelam alterações subtis dependentes do sexo. Para vários potenciais oscilatórios, machos e fêmeas exibem alterações opostas associadas ao genótipo mutante. Além disso, as características do ERG foram utilizadas para formar um classificador de aprendizagem de máquina baseado nos aglomerados significativos encontrados para algumas interações entre indivíduos, um classificador que se destina a ser capaz de receber um sinal e devolver o provável diagnóstico.Neurofibromatosis type 1 (NF1) is a neurodevelopmental disorder with adult cognitive implications. It causes central nervous system anomalies and affects 1 in 3000 individuals worldwide. However, little is known about the effects on the visual system circuitry and how these may be associated with cognitive deficits and predicts its progression. In this work, it was evaluated the potential alterations in retinal physiology in a genetic mouse model of NF1, using a non-invasive neurophysiological technique, the electroretinogram (ERG), to ascertain its diagnostic potential. As a reliable indicator of retinal function in response to light, the ERG has the ability to aid our interpretation of the pathophysiology of neurodevelopmental and neurodegenerative disorders. The main objectives of this thesis are the phenotypic characterization of the visual system in an animal model of NF1 and the development of computer tools (MATLAB and Phyton) for signal processing, waveform analysis, feature extraction, and classification. This work found that ERG parameters mainly related to inhibitory oscillatory activity reveal subtle sex-dependent alterations. For various oscillatory potentials males and females exhibit opposite changes associated with the transgenic background. Furthermore, the ERG features were used to form a machine learning classifier based on the significant clusters found for some interactions between individuals, a classifier that is meant to be able to receive a signal and return the likely diagnosis

The Effect of nutritional supplementation on subjective and objective measures of visual and retinal function:a random controlled trial

In industrialised countries age-related macular disease (ARMD) is the leading cause of visual loss in older people. Because oxidative stress is purported to be associated with an increased risk of disease development the role of antioxidant supplementation is of interest. Lutein is a carotenoid antioxidant that accumulates within the retina and is thought to filter blue light. Increased levels of lutein have been associated with reduced risk of developing ARMD and improvements in visual and retinal function in eyes with ARMD. The aim of this randomised controlled trial (RCT) was to investigate the effect of a lutein-based nutritional supplement on subjective and objective measures of visual function in healthy eyes and in eyes with age-related maculopathy (ARM) – an early form of ARMD. Supplement withdrawal effects were also investigated. A sample size of 66 healthy older (HO), healthy younger (HY), and ARM eyes were randomly allocated to receive a lutein-based supplement or no treatment for 40 weeks. The supplemented group then stopped supplementation to look at the effects of withdrawal over a further 20 weeks. The primary outcome measure was multifocal electroretinogram (mfERG) N1P1 amplitude. Secondary outcome measures were mfERG N1, P1 and N2 latency, contrast sensitivity (CS), Visual acuity (VA) and macular pigment optical density (MPOD). Sample sizes were sufficient for the RCT to have an 80% power to detect a significant clinical effect at the 5% significance level for all outcome measures when the healthy eye groups were combined, and CS, VA and mfERG in the ARM group. This RCT demonstrates significant improvements in MPOD in HY and HO supplemented eyes. When HY and HO supplemented groups were combined, MPOD improvements were maintained, and mfERG ring 2 P1 latency became shorter. On withdrawal of the supplement mfERG ring 1 N1P1 amplitude reduced in HO eyes. When HO and HY groups were combined, mfERG ring 1 and ring 2 N1P1 amplitudes were reduced. In ARM eyes, ring 3 N2 latency and ring 4 P1 latency became longer. These statistically significant changes may not be clinically significant. The finding that a lutein-based supplement increases MPOD in healthy eyes, but does not increase mfERG amplitudes contrasts with the CARMIS study and contributes to the debate on the use of nutritional supplementation in ARM