Vision and Vision-Related Measures in Progressive Multiple Sclerosis

Assessing disease progression and treatment response in progressive multiple sclerosis

Progressive multiple sclerosis poses a considerable challenge in the evaluation of disease progression and treatment response owing to its multifaceted pathophysiology. Traditional clinical measures such as the Expanded Disability Status Scale are limited in capturing the full scope of disease and treatment effects. Advanced imaging techniques, including MRI and PET scans, have emerged as valuable tools for the assessment of neurodegenerative processes, including the respective role of adaptive and innate immunity, detailed insights into brain and spinal cord atrophy, lesion dynamics and grey matter damage. The potential of cerebrospinal fluid and blood biomarkers is increasingly recognized, with neurofilament light chain levels being a notable indicator of neuro-axonal damage. Moreover, patient-reported outcomes are crucial for reflecting the subjective experience of disease progression and treatment efficacy, covering aspects such as fatigue, cognitive function and overall quality of life. The future incorporation of digital technologies and wearable devices in research and clinical practice promises to enhance our understanding of functional impairments and disease progression. This Review offers a comprehensive examination of these diverse evaluation tools, highlighting their combined use in accurately assessing disease progression and treatment efficacy in progressive multiple sclerosis, thereby guiding more effective therapeutic strategies.

Visual evoked potentials in multiple sclerosis: P100 latency and visual pathway damage including the lateral geniculate nucleus

OBJECTIVE

To explore associations of the main component (P100) of visual evoked potentials (VEP) to pre- and postchiasmatic damage in multiple sclerosis (MS).

METHODS

31 patients (median EDSS: 2.5), 13 with previous optic neuritis (ON), and 31 healthy controls had VEP, optical coherence tomography and magnetic resonance imaging. We tested associations of P100-latency to the peripapillary retinal nerve fiber layer (pRNFL), ganglion cell/inner plexiform layers (GCIPL), lateral geniculate nucleus volume (LGN), white matter lesions of the optic radiations (OR-WML), fractional anisotropy of non-lesional optic radiations (NAOR-FA), and to the mean thickness of primary visual cortex (V1). Effect sizes are given as marginal R2 (mR2).

RESULTS

P100-latency, pRNFL, GCIPL and LGN in patients differed from controls. Within patients, P100-latency was significantly associated with GCIPL (mR2 = 0.26), and less strongly with OR-WML (mR2 = 0.17), NAOR-FA (mR2 = 0.13) and pRNFL (mR2 = 0.08). In multivariate analysis, GCIPL and NAOR-FA remained significantly associated with P100-latency (mR2 = 0.41). In ON-patients, P100-latency was significantly associated with LGN volume (mR2 = -0.56).

CONCLUSIONS

P100-latency is affected by anterior and posterior visual pathway damage. In ON-patients, damage at the synapse-level (LGN) may additionally contribute to latency delay.

SIGNIFICANCE

Our findings corroborate post-chiasmatic contributions to the VEP-signal, which may relate to distinct pathophysiological mechanisms in MS.

A Comparative Review of Typical and Atypical Optic Neuritis: Advancements in Treatments, Diagnostics, and Prognosis

Optic neuritis (ON) is a debilitating condition that through various mechanisms, including inflammation or demyelination of the optic nerve, can result in partial or total permanent vision loss if left untreated. Accurate diagnosis and promptly initiated treatment are imperative related to the potential of permanent loss of vision if left untreated, which can lead to a significant reduction in the quality of life in affected patients. ON is subtyped as "typical" or "atypical" based on underlying causative etiology. The etiology of ON can be differentiated when appropriate diagnostic testing is performed. Using history taking, neuroimaging, and visual testing to localize the underlying pathology of ON in a time-sensitive manner is critical in mitigating these unsatisfactory outcomes. Herein, we examine the differences in presentation, pathophysiology, and treatments of typical ON causes, like multiple sclerosis (MS), and atypical causes such as neuromyelitis optica spectrum disorder (NMOSD) and myelin oligodendrocyte glycoprotein (MOG)-immunoglobulin G (IgG) ON. The present investigation places focus on both neuroimaging and visual imaging in the differentiation of ON. Additionally, this review presents physicians with a better understanding of different presentations, treatments, and prognoses of ON.

Peering further into the mind's eye: combining visual evoked potential and optical coherence tomography measures enhances insight into the variance in cognitive functioning in multiple sclerosis

BACKGROUND

Spectral Optical Coherence Tomography (OCT) and Visual Evoked Potentials (VEPs) have both emerged as potentially useful biomarkers of cognitive decline in people with multiple sclerosis (PwMS). Their combined use may provide additional predictive value for identifying disease impact, progression, and remyelination capacity above-and-beyond what is captured using either approach alone.

OBJECTIVE

We examined the relationship between OCT/VEP measures and cognitive functioning in 205 PwMS. OCT measures included Retinal Nerve Fiber Layer Volume (RNFLV), Papillo-Macular Bundle Volume (PBMV), and Macular Volume (MV). VEP measures included latency of the P100, and inter-ocular latency. Cognitive performance was evaluated across seven separate domains of performance, and for overall cognition, using the NeuroTrax computerized testing battery.

RESULTS

Both OCT and VEP measures were significantly correlated with cognitive performance across several domains. Linear regression models that controlled for the influence of visual acuity revealed (1) that reduced MV was significantly predictive of poorer visual-spatial functioning, and (2) that delayed VEP latency was significantly predictive of performance in global cognitive functioning and visual-spatial functioning, after controlling for multiple comparisons. Among PwMS with normal visual acuity, PwMS with a combination of both relatively low MV and delayed VEP latency tended to have poorer performance in the domains of global, executive, and visual-spatial functioning compared to PwMS with both high MV and normal VEP latency.

CONCLUSION

Approaches that combine the use of OCT and VEP measures can enhance insight into underlying factors that contribute to variance in cognitive functioning in PwMS.

Utility of the visual system to monitor neurodegeneration in multiple sclerosis

Neurodegeneration occurs early in the multiple sclerosis (MS) disease course and is an important driver of permanent disability. Current immunomodulatory therapies do not directly target neuronal health; thus, there is a critical need to develop neuroprotective strategies in MS. Outcome measures in clinical trials primarily evaluate disease activity and clinical disability scores rather than measures of neurodegeneration. The visual system provides a noninvasive correlate of brain atrophy and neuronal function through structural and functional exams. Furthermore, optic nerve axons and their respective neuronal cell bodies in the retina, in addition to their synaptic input to the thalamus, provide a distinct anatomy to investigate neurodegenerative processes. This review discusses the utility of the visual system as an early output measure of neurodegeneration in MS as well as an important platform to evaluate neuroprotective strategies in preclinical models.

Individual differences in visual evoked potential latency are associated with variance in brain tissue volume in people with multiple sclerosis: An analysis of brain function-structure correlates

Visual evoked potentials (VEP) index visual pathway functioning, and are often used for clinical assessment and as outcome measures in people with multiple sclerosis (PwMS). VEPs may also reflect broader neural disturbances that extend beyond the visual system, but this possibility requires further investigation. In the present study, we examined the hypothesis that delayed latency of the P100 component of the VEP would be associated with broader structural changes in the brain in PwMS. We obtained VEP latency for a standard pattern-reversal checkerboard stimulus paradigm, in addition to Magnetic Resonance Imaging (MRI) measures of whole brain volume (WBV), gray matter volume (GMV), white matter volume (WMV), and T2-weighted fluid attenuated inversion recovery (FLAIR) white matter lesion volume (FLV). Correlation analyses indicated that prolonged VEP latency was significantly associated with lower WBV, GMV, and WMV, and greater FLV. VEP latency remained significantly associated with WBV, GMV, and WMV even after controlling for the variance associated with inter-ocular latency, age, time between VEP and MRI assessments, and other MRI variables. VEP latency delays were most pronounced in PwMS that exhibited low volume in both white and gray matter simultaneously. Furthermore, PwMS that had delayed VEP latency based on a clinically relevant cutoff (VEP latency ≥ 113 ms) in both eyes had lower WBV, GMV, and WMV and greater FLV in comparison to PwMS that had normal VEP latency in one or both eyes. The findings suggest that PwMS that have delayed latency in both eyes may be particularly at risk for exhibiting greater brain atrophy and lesion volume. These analyses also indicate that VEP latency may index combined gray matter and white matter disturbances, and therefore broader network connectivity and efficiency. VEP latency may therefore provide a surrogate marker of broader structural disturbances in the brain in MS.

Working Memory Phenotypes in Early Multiple Sclerosis: Appraisal of Phenotype Frequency, Progression and Test Sensitivity

Working memory (WM) impairments are common and debilitating symptoms of multiple sclerosis (MS), often emerging early in the disease. Predominantly, WM impairments are considered in a binary manner, with patients considered either impaired or not based on a single test. However, WM is comprised of different activated subcomponents depending upon the type of information (auditory, visual) and integration requirements. As such, unique WM impairment phenotypes occur. We aimed to determine the most frequent WM phenotypes in early MS, how they progress and which WM test(s) provide the best measure of WM impairment. A total of 88 participants (63 early relapsing–remitting MS: RRMS, 25 healthy controls) completed five WM tests (visual–spatial, auditory, episodic, executive) as well as the symbol digit modalities test as a measure of processing speed. RRMS patients were followed-up for two years. Factors affecting WM (age/gender/intelligence/mood) and MS factors (disease duration/disability) were also evaluated. Some 61.9% of RRMS patients were impaired on at least one WM subcomponent. The most subcomponents impaired were visual,–spatial and auditory WM. The most common WM phenotypes were; (1) visual–spatial sketchpad + episodic buffer + phonological loop + central executive, (2) visual–spatial sketchpad + central executive. The test of visual–spatial WM provided the best diagnostic accuracy for detecting WM impairment and progression. The SDMT did not achieve diagnostic accuracy greater than chance. Although this may be unsurprising, given that the SDMT is a measure of cognitive processing speed in MS, this does highlight the limitation of the SDMT as a general screening tool for cognitive impairment in early MS.

Anatomical and functional visual network patterns in progressive multiple sclerosis

The gradual accrual of disability over time in progressive multiple sclerosis is believed to be driven by widespread degeneration. Yet another facet of the problem may reside in the loss of the brain's ability to adapt to the damage incurred as the disease progresses. In this study, we attempted to examine whether changes associated with optic neuritis in the structural and functional visual networks can still be discerned in progressive patients even years after the acute insult. Forty-eight progressive multiple sclerosis patients, 21 with and 27 without prior optic neuritis, underwent structural and functional MRI, including DTI and resting state fMRI. Anatomical and functional visual networks were analyzed using graph theory-based methods. While no functional metrics were significantly different between the two groups, anatomical global efficiency and density were significantly lower in the optic neuritis group, despite no significant difference in lesion load between the groups. We conclude that long-standing distal damage to the optic nerve causes trans-synaptic effects and the early ability of the cortex to adapt may be altered, or possibly nullified. We suggest that this limited ability of the brain to compensate should be considered when attempting to explain the accumulation of disability in progressive multiple sclerosis patients.

Optical Coherence Tomography and Visual Evoked Potentials as Prognostic and Monitoring Tools in Progressive Multiple Sclerosis

Understanding the mechanisms underlying progression and developing new treatments for progressive multiple sclerosis (PMS) are among the major challenges in the field of central nervous system (CNS) demyelinating diseases. Over the last 10 years, also because of some technological advances, the visual pathways have emerged as a useful platform to study the processes of demyelination/remyelination and their relationship with axonal degeneration/protection. The wider availability and technological advances in optical coherence tomography (OCT) have allowed to add information on structural neuroretinal changes, in addition to functional information provided by visual evoked potentials (VEPs). The present review will address the role of the visual pathway as a platform to assess functional and structural damage in MS, focusing in particular on the role of VEPs and OCT, alone or in combination, in the prognosis and monitoring of PMS.

Impaired motion perception is associated with functional and structural visual pathway damage in multiple sclerosis and neuromyelitis optica spectrum disorders

Background:

Decreased motion perception has been suggested as a marker for visual pathway demyelination in optic neuritis (ON) and/or multiple sclerosis (MS).

Objectives:

To examine the influence of neuro-axonal damage on motion perception in MS and neuromyelitis optica spectrum disorders (NMOSD).

Methods:

We analysed motion perception with numbers-from-motion (NFM), visual acuity, (multifocal (mf)) VEP, optical coherence tomography in patients with MS (n = 38, confirmatory cohort n = 43), NMOSD (n = 13) and healthy controls (n = 33).

Results:

NFM was lower compared with controls in MS (B = −12.37, p < 0.001) and NMOSD (B = −34.5, p < 0.001). NFM was lower in ON than in non-ON eyes (B = −30.95, p = 0.041) in NMOSD, but not MS. In MS and NMOSD, lower NFM was associated with worse visual acuity (B = −139.4, p < 0.001/B = −77.2, p < 0.001) and low contrast letter acuity (B = 0.99, p = 0.002/B = 1.6, p < 0.001), thinner peripapillary retinal nerve fibre layer (B = 1.0, p < 0.001/ B = 0.92, p = 0.016) and ganglion cell/inner plexiform layer (B = 64.8, p < 0.001/B = 79.5, p = 0.006), but not with VEP P100 latencies. In the confirmatory MS cohort, lower NFM was associated with thinner retinal nerve fibre layer (B = 1.351, p < 0.001) and increased mfVEP P100 latencies (B = −1.159, p < 0.001).

Conclusions:

Structural neuro-axonal visual pathway damage is an important driver of motion perception impairment in MS and NMOSD.

Retinal and Brain Microglia in Multiple Sclerosis and Neurodegeneration

Microglia are the resident immune cells of the central nervous system (CNS), including the retina. Similar to brain microglia, retinal microglia are responsible for retinal surveillance, rapidly responding to changes in the environment by altering morphotype and function. Microglia become activated in inflammatory responses in neurodegenerative diseases, including multiple sclerosis (MS). When activated by stress stimuli, retinal microglia change their morphology and activity, with either beneficial or harmful consequences. In this review, we describe characteristics of CNS microglia, including those in the retina, with a focus on their morphology, activation states and function in health, ageing, MS and other neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, glaucoma and retinitis pigmentosa, to highlight their activity in disease. We also discuss contradictory findings in the literature and the potential ways of reducing inconsistencies in future by using standardised methodology, e.g., automated algorithms, to enable a more comprehensive understanding of this exciting area of research.

Visual evoked potential latency predicts cognitive function in people with multiple sclerosis

Prior studies have reported an association between visual evoked potentials (VEPs) and cognitive performance in people with multiple sclerosis (PwMS), but the specific mechanisms that account for this relationship remain unclear. We examined the relationship between VEP latency and cognitive performance in a large sample of PwMS, hypothesizing that VEP latency indexes not only visual system functioning but also general neural efficiency. Standardized performance index scores were obtained for the domains of memory, executive function, visual-spatial processing, verbal function, attention, information processing speed, and motor skills, as well as global cognitive performance (NeuroTrax battery). VEP P100 component latency was obtained using a standard checkerboard pattern-reversal paradigm. Prolonged VEP latency was significantly associated with poorer performance in multiple cognitive domains, and with the number of cognitive domains in which performance was ≥ 1 SD below the normative mean. Relationships between VEP latency and cognitive performance were significant for information processing speed, executive function, attention, motor skills, and global cognitive performance after controlling for disease duration, visual acuity, and inter-ocular latency differences. This study provides evidence that VEP latency delays index general neural inefficiency that is associated with cognitive disturbances in PwMS.

Conduction delays in the visual pathways of progressive multiple sclerosis patients covary with brain structure

In developed countries, multiple sclerosis (MS) is the leading cause of non-traumatic neurological disability in young adults. MS is a chronic demyelinating disease of the central nervous system, in which myelin is attacked, changing white matter structure and leaving lesions. The demyelination has a direct effect on white matter conductivity. This effect can be examined in the visual system, where damage is highly prevalent in MS, leading to substantial delays in conduction, commonly measured with visual evoked potentials (VEPs). The structural damage to the visual system in MS is often estimated with MRI measurements in the white matter. Recent developments in quantitative MRI (qMRI) provide improved sensitivity to myelin content and new structural methods allow better modeling of the axonal structure, leading researchers to link white matter microstructure to conduction properties of action potentials along fiber tracts. This study attempts to explain the variance in conduction latencies down the visual pathway using structural measurements of both the retina and the optic radiation (OR). Forty-eight progressive MS patients, participants in a longitudinal stem-cell therapy clinical trial, were included in this study, three and six months post final treatment. Twenty-seven patients had no history of optic neuritis, and were the main focus of this study. All participants underwent conventional MRI scans, as well as diffusion MRI and qMRI sequences to account for white matter microstructure. Optical coherence tomography scans were also obtained, and peripapillary retinal nerve fiber layer (pRNFL) thickness and macular volume measurements were extracted. Finally, latencies of recorded VEPs were estimated. Our results show that in non-optic neuritis progressive MS patients there is a relationship between the VEP latency and both retinal damage and OR lesion load. In addition, we find that qMRI values, sampled along the OR, are also correlated with VEP latency. Finally, we show that combining these parameters using PCA we can explain more than 40% of the inter-subject variance in VEP latency. In conclusion, this study contributes to understanding the relationship between the structural properties and conduction in the visual system in disease. We focus on the visual system, where the conduction latencies can be estimated, but the conclusions could be generalized to other brain systems where the white matter structure can be measured. It also highlights the importance of having multiple parameters when assessing the clinical stages of MS patients, which could have major implications for future studies of other white matter diseases.

Visualizing the Central Nervous System: Imaging Tools for Multiple Sclerosis and Neuromyelitis Optica Spectrum Disorders

Multiple sclerosis (MS) and neuromyelitis optica spectrum disorders (NMOSD) are autoimmune central nervous system conditions with increasing incidence and prevalence. While MS is the most frequent inflammatory CNS disorder in young adults, NMOSD is a rare disease, that is pathogenetically distinct from MS, and accounts for approximately 1% of demyelinating disorders, with the relative proportion within the demyelinating CNS diseases varying widely among different races and regions. Most immunomodulatory drugs used in MS are inefficacious or even harmful in NMOSD, emphasizing the need for a timely and accurate diagnosis and distinction from MS. Despite distinct immunopathology and differences in disease course and severity there might be considerable overlap in clinical and imaging findings, posing a diagnostic challenge for managing neurologists. Differential diagnosis is facilitated by positive serology for AQP4-antibodies (AQP4-ab) in NMOSD, but might be difficult in seronegative cases. Imaging of the brain, optic nerve, retina and spinal cord is of paramount importance when managing patients with autoimmune CNS conditions. Once a diagnosis has been established, imaging techniques are often deployed at regular intervals over the disease course as surrogate measures for disease activity and progression and to surveil treatment effects. While the application of some imaging modalities for monitoring of disease course was established decades ago in MS, the situation is unclear in NMOSD where work on longitudinal imaging findings and their association with clinical disability is scant. Moreover, as long-term disability is mostly attack-related in NMOSD and does not stem from insidious progression as in MS, regular follow-up imaging might not be useful in the absence of clinical events. However, with accumulating evidence for covert tissue alteration in NMOSD and with the advent of approved immunotherapies the role of imaging in the management of NMOSD may be reconsidered. By contrast, MS management still faces the challenge of implementing imaging techniques that are capable of monitoring progressive tissue loss in clinical trials and cohort studies into treatment algorithms for individual patients. This article reviews the current status of imaging research in MS and NMOSD with an emphasis on emerging modalities that have the potential to be implemented in clinical practice.

Empirical Mode Decomposition-Based Filter Applied to Multifocal Electroretinograms in Multiple Sclerosis Diagnosis

As multiple sclerosis (MS) usually affects the visual pathway, visual electrophysiological tests can be used to diagnose it. The objective of this paper is to research methods for processing multifocal electroretinogram (mfERG) recordings to improve the capacity to diagnose MS. MfERG recordings from 15 early-stage MS patients without a history of optic neuritis and from 6 control subjects were examined. A normative database was built from the control subject signals. The mfERG recordings were filtered using empirical mode decomposition (EMD). The correlation with the signals in a normative database was used as the classification feature. Using EMD-based filtering and performance correlation, the mean area under the curve (AUC) value was 0.90. The greatest discriminant capacity was obtained in ring 4 and in the inferior nasal quadrant (AUC values of 0.96 and 0.94, respectively). Our results suggest that the combination of filtering mfERG recordings using EMD and calculating the correlation with a normative database would make mfERG waveform analysis applicable to assessment of multiple sclerosis in early-stage patients.