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

Optic Nerve: Developmental Anomalies and Common Tumors

The optic nerve, also known as the second cranial nerve, is composed of axons that transmit visual information from the neurosensory retina to the visual cortex. There are multiple pathologies that can affect the human optic nerve. Congenital anomalies of the optic nerve include myelinated nerve fibers, morning glory syndrome, optic nerve choristoma, optic nerve coloboma, optic nerve hypoplasia and aplasia, and others. Tumors that can affect the optic nerve (ON) may occur primarily from within the nerve itself, from the surrounding optic nerve sheath (ONS), or secondarily spreading to the nerve from a distant site. They include optic pathway glioma, medulloepithelioma, oligodendroglioma, optic nerve sheath meningioma, and others. Here in this chapter, we will review the optic nerve anatomy, embryology, and physiology in addition to assessment of optic nerve function. Moreover, the clinical features, imaging findings, pathology, and treatment options of the most common and some rare congenital anomalies and primary tumors of the ON and sheath will be reviewed

Multifocal visual evoked potential (mfVEP) and pattern-reversal visual evoked potential changes in patients with visual pathway disorders : a case series

The purpose of this study was to evaluate multifocal visual evoked potential (mfVEP) and pattern-reversal visual evoked potential (PVEP) changes in patients with pathology at various levels of the visual pathway determined by other methods. Six patients with different visual pathway disorders, including vascular ischaemic events and compressive optic neuropathy, were reviewed. All patients were tested with both mfVEP and full-field and half-field PVEPs. Results were assessed in relation to other diagnostic tests such as magnetic resonance imaging, Humphrey visual field test, and optical coherence topography. The cases in this study demonstrate a potential higher sensitivity of mfVEP compared with conventional PVEPs in detecting lesions affecting the peripheral field, horizontal hemifields, and lesions of the post-chiasmal pathway. The limitation of the PVEP in this setting is probably due to phase cancellation and overrepresentation of the macular region. mfVEP provides a more accurate assessment of visual defects when compared with conventional PVEP. The independent assessment of different areas of the visual field improves the detection and localization of lesions and provides an objective topographical map that can be used in clinical practice as an adjunct to other diagnostic tests and to assess disease progression.14 page(s

Mechanism of delayed conduction of fellow eyes in patients with optic neuritis

To test the hypothesis that latency delay in the fellow eyes of optic neuritis (ON) patients and to compensate for delayed transmission of visual information, latency change of multi-focal visual evoked potential (mfVEP) traces in fellow eyes of 15 ON patients were analyzed. Patients with low risk (LR) for developing multiple sclerosis (MS) were examined separately from MS patients to isolate effect of cortical plasticity from potential pathological changes in disseminated disease. The small increase in latency in fellow eyes of LR group was statistically not significant. In MS patients, the latency was significantly delayed (P<0.02). The magnitude of the latency change in the fellow eyes did not correlate with the severity of latency delay in the affected eyes (R2<0.02, P=0.3). The differences between ON patients with and without MS, reported here, suggest that the presence of disseminated disease plays critical role in latency delay of the fellow eye

Multifocal VEP assessment of optic neuritis evolution

Objective: To evaluate multifocal visual evoked potentials (mfVEP) changes in optic neuritis (ON) and fellow eyes during first year after the attack. Methods: Eighty-seven patients and twenty-five controls were examined. Patients were classified as multiple sclerosis (MS) group, high risk (HR) or low risk (LR) groups for conversion to MS. mfVEP recordings and retinal nerve fiber layer (RNFL) thickness were analyzed. Results: Recovery of amplitude and shortening of latency was fastest within the first 3 months. The largest amplitude reduction and longest latency delay of the ON eye were recorded in the MS group. This was accompanied by deterioration of both parameters in fellow eyes (p < 0.03). mfVEP remained stable in fellow eyes of the LR group. Inter-eye asymmetry showed similar amount of amplitude reduction and latency delay in all three groups. RNFL thickness strongly correlated with mfVEP amplitude as early as 3 months after ON (R2 = 0.6, p = 0.001). Conclusion: mfVEP amplitude is an early predictor of post-ON axonal loss. The apparent more severe involvement of ON eyes in the MS subgroup may be due to subclinical inflammation along the visual pathway. Significance: Severity of amplitude reduction and latency delay after episode of ON is not MS-related. Retro-chiasmal demyelination is a possible factor contributing to amplitude and latency differences between MS and non-MS patients.7 page(s

Latency of multifocal visual evoked potentials in nonoptic neuritis eyes of multiple sclerosis patients associated with optic radiation lesions

Purpose: The aim of the study was to test the hypothesis that latency delay of multifocal visual evoked potentials (mfVEP) in nonoptic neuritis (NON) eyes of multiple sclerosis (MS) patients is related to retrochiasmal demyelinating lesions. Methods: A total of 57 MS patients with no history of optic neuritis at least in one eye, and 25 age- and sex-matched healthy controls was enrolled. Probabilistic tractography was used to reconstruct optic radiation (OR) fibers. The MS lesion volume within and outside of OR was calculated. Diffusion tensor imaging (DTI) indices were measured along OR fibers. The relationship of the mfVEP latency with OR lesions and DTI indices was examined. Results: Average mfVEP latency in the MS cohort was significantly delayed compared to controls (P < 0.0001). Of the patients, 77% demonstrated OR lesions. Axial, radial, and mean diffusivity were significantly abnormal in MS patients (P < 0.001). Partial correlation demonstrated significant association between mfVEP latency delay and OR lesion load. There was also significant correlation between MfVEP latency and OR DTI. Subgroup analysis revealed significantly higher correlations in patients without a history of ON in either eye compared to the fellow eye of patients with previous ON. Conclusions: The findings of this study support our hypothesis that latency delay of the mfVEP in eyes of MS patients without previous ON is related to retrogenicular demyelinating lesions. Additionally, this study demonstrated that a previous episode of ON in the fellow eye may be a significant confounding factor, masking the relationship between the latency and OR lesions.7 page(s

Optic Nerve Involvement in Farber Lipogranulomatosis: Expanding the Phenotypic Spectrum

Farber lipogranulomatosis (Farber disease [FD], MIM 228000) is a rare autosomal recessive lysosomal storage disorder caused by a deficiency of acid ceramidase (AC) and is linked to ASAH1 gene mutations. ASAH1 mutations can lead to severe reduction in AC activity that causes accumulation of ceramides in various body tissues including the retina. The onset of clinical manifestations usually occurs during infancy, and the severity depends on residual ceramidase activity. Classic clinical features of FD include painful joint swelling, progressive dysphonia, and subcutaneous nodules. We report 2 unrelated patients presenting with classic FD phenotype who shared the same homozygous pathogenic mutation in the ASAH1 gene and optic neuropathy, thereby expanding the FD phenotypic spectrum