Occipital repetitive transcranial magnetic stimulation does not affect multifocal visual evoked potentials

BACKGROUND

To identify mechanisms of cortical plasticity of the visual cortex and to quantify their significance, sensitive parameters are warranted. In this context, multifocal visual evoked potentials (mfVEPs) can make a valuable contribution as they are not associated with cancellation artifacts and include also the peripheral visual field.

OBJECTIVE

To investigate if occipital repetitive transcranial magnetic stimulation (rTMS) can induce mfVEP changes.

METHODS

18 healthy participants were included in a single-blind crossover-study receiving sessions of excitatory, occipital 10 Hz rTMS and sham stimulation. MfVEP was performed before and after each rTMS session and changes in amplitude and latency between both sessions were compared using generalized estimation equation models.

RESULTS

There was no significant difference in amplitude or latency between verum and sham group.

CONCLUSION

We conclude that occipital 10 Hz rTMS has no effect on mfVEP measures, which is in line with previous studies using full field VEP.

The electrophysiological assessment of visual function in Multiple Sclerosis

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VEPs have largely been replaced by MRI in modern MS diagnosis and management.

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Multifocal VEPs are superior to traditional VEPs in evaluating the integrity of the visual system.

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Physiological asymmetry limits interpretation of small VEP differences.

The assessment of vision is integral to the diagnosis and monitoring of patients with multiple sclerosis (MS). Visual electrophysiology, previously a critical investigation in patients with suspected MS, has in large part been supplanted by magnetic resonance imaging in clinical routine. However, the development of multi-focal visual evoked potentials and the advent of putative re-myelinating therapies that can be monitored with these techniques has led to a resurgence of interest in the field. Here, we review the clinical applications, technical considerations and limitations of visual evoked potentials in the management of patients with MS.

Cerebral Functional Magnetic Resonance Imaging and Multifocal Visual Evoked Potentials in a Patient with Unexplained Impairment of Visual Function: A Case Report

We present a case of a young female with a slowly progressing visual impairment who was examined with multifocal visual evoked potentials and functional magnetic resonance imaging (fMRI) for underlying neuronal abnormality. The fMRI examination consisted of presenting black-and-white checkerboard stimuli, and her activation patterns were compared to the patterns from 4 normal-sighted subjects. The results showed clear differences in neuronal activation between the patient and the controls in the occipital and parietal lobes. Although we have shown neuronal correlates in a case of unexplained visual loss, it is still an open question as to whether this has an organic or functional cause, which should be the subject for future research.

Multifocal visual evoked potentials in optic neuritis and multiple sclerosis: A review

Multifocal visual evoked potential (mf-VEP) represents a new approach to the classical full field (ff-)VEP with separate responses from up to 60 sectors of the visual field. A thorough literature survey of the use of mf-VEP in optic neuritis (ON) and multiple sclerosis (MS) is presented (38 published studies were retrieved). Mf-VEP provides direct topographical information of specific lesions and facilitates investigations on structural-functional correlations thus providing new methods for exploring the interplay between demyelination, atrophy and remyelination in MS. Good correlation was shown between mf-VEP and OCT, ff-VEP, MRI (MTR, DTI), 30-2 standard automated perimetry and low-contrast-visual acuity. All but one study showed superior sensitivity and specificity compared to ff-VEP, especially with regards to small, peripheral lesions or lesions of the upper visual field. Mf-VEP has shown superior sensitivity and specificity than established methods in diagnosing optic nerve lesions and tracking functional recovery following lesions. Abnormal mf-VEP responses in the fellow, non-ON afflicted eye may predict MS risk in ON patients. No standardization currently exists and no direct comparisons in ON and MS between at least 5 different commercially available mf-VEP systems have so far been published. Despite these limitations, mf-VEP is a promising new tool of diagnostic and prognostic value of mf-VEP in ON and MS.

Acute Visual Field Defect following Vitrectomy Determined to Originate from Optic Nerve by Electrophysiological Tests

Purpose

To present our findings on the cause of an acute visual field defect (VFD) that developed in a patient on the day after vitrectomy for proliferative diabetic retinopathy.

Case

A 50-year-old man complained of a blind area in the superior visual field that developed one day after vitrectomy. The patient had undergone uncomplicated vitrectomy for a long-duration vitreous hemorrhage associated with proliferative diabetic retinopathy. Residual vitreous hemorrhage hampered a clear view of the fundus. Goldmann perimetry showed a horizontal VFD in the superior field. The area corresponding to the VFD was examined by multifocal electroretinograms (mfERGs) and multifocal visual evoked potentials (mfVEPs). The amplitudes of the mfVEPs were reduced with prolonged implicit times especially when the superior hemifield was stimulated, while the amplitudes and implicit times were within the normal range when other parts of the visual field were stimulated. In addition, the full-field photopic ERGs and photopic negative responses were attenuated in the right eye. These findings suggested that the VFD did not originate from alterations in the retinal inner and middle layer but in the ganglion cells. The visual acuity improved to 1.2 but his optic disc became pale and the VFD remained unchanged more than 12 years after the surgery.

Conclusion

We suggest that vitrectomy can cause ischemic optic neuropathy by interfering with the circulation associated with diabetes mellitus. Evaluations by mfERGs, mfVEPs, and full-field photopic ERGs were helpful in making the diagnosis.