The multifocal visual evoked potential: An objective measure of visual fields?

Visual Evoked Potentials as a Biomarker in Multiple Sclerosis and Associated Optic Neuritis

: ABSTRACT:: Multiple sclerosis (MS) is an inflammatory, degenerative disease of the central nervous system (CNS) characterized by progressive neurological decline over time. The need for better "biomarkers" to more precisely capture and track the effects of demyelination, remyelination, and associated neuroaxonal injury is a well-recognized challenge in the field of MS. To this end, visual evoked potentials (VEPs) have a role in assessing the extent of demyelination along the optic nerve, as a functionally eloquent CNS region. Moreover, VEPs testing can be used to predict the extent of recovery after optic neuritis (ON) and capture disabling effects of clinical and subclinical demyelination events in the afferent visual pathway. In this review, the evolving role of VEPs in the diagnosis of patients with ON and MS and the utility of VEPs testing in determining therapeutic benefits of emerging MS treatments is discussed.

Investigating the effects of glaucomatous damage on the multifocal visual evoked potential parameters

PURPOSE

To investigate the effects of glaucomatous damage on the mfVEP parameters of patients suffering from primary open-angle glaucoma (POAG).

METHODS

Fifteen healthy subjects and 15 patients with unilateral POAG participated in this study. In addition, routine ophthalmological examinations including visual acuity, anterior segment examination, posterior segment examination, intraocular pressure, mfVEP with electrophysiological system, RETI-port/Scan 21, and visual field test with automated Humphrey ZEISS HFA II 750i Perimeter were also performed.

RESULTS

The results show that there was a strong correlation between the ∆MDs and the number of abnormal points with the ∆amplitudes more than 256 nV, in patients (n = 15, r = 0.802, p < 0.05), but no correlations were found between the mean sensitivity differences (ΔPSDs) and mfVEP parameters.

CONCLUSIONS

Comparing the monocular mfVEP responses from both eyes is an appropriate method to detect unilateral damage. Achievement of more development and making the mfVEP test more functional can be a solution for early diagnosis in most of the eye diseases.

Robust sensory gating in the cortical visual evoked potential using two spatially separated stimuli

OBJECTIVE

Sensory gating has been reported to be either absent or weak in the cortical visual evoked potential (VEP) response to diffuse or spatially overlapping stimuli. In this study, the authors evaluated sensory gating to two spatially separated visual stimuli.

METHODS

Spatially separated stimuli were presented either singly or in combination at the same or different onset times and the VEP recorded at either Oz, or O1 and O2, referenced to Cz.

RESULTS

When one visual stimulus is flashed on, the VEP response to another non-overlapping stimulus is almost completely suppressed.

CONCLUSIONS

The VEP does not reflect the bulk activation of retinotopically organized visual cortex, but rather it primarily reflects a distributed mode of visual cortical activity that only indicates that at least one visual stimulus was presented, and not how many or in what order.

SIGNIFICANCE

Other studies performing intracortical recordings of the local field potential (LFP) in visual cortex have identified a slow-distributed component that exhibits the same nonlinearity found here in the VEP, suggesting that these two phenomena are related.

Discordance between subjective perimetric visual fields and objective multifocal visual evoked potential-determined visual fields in patients with hemianopsia

PURPOSE

To investigate the concordance between subjectively and objectively acquired visual fields in patients with subjectively determined hemianopsia.

DESIGN

Retrospective observational study.

METHODS

Ten patients, six men and four women, ranging in age from 28 to 68 years, were studied. Goldmann or Humphrey perimeters were used to obtain the subjectively determined visual fields for up to 25 degrees of eccentricity, and the VERIS Scientific System (Electro-Diagnostic Imaging, San Francisco, California, USA) was used to record multifocal visual evoked potential [VEPs] (mfVEPs) to obtain the objective visual fields. Each of the 60 black-and-white segments of the checkerboard stimulus was alternated according to a binary m sequence. The first slices of the second-order kernels were extracted and analyzed.

RESULTS

In five cases, the visual field loci where the mfVEPs were within normal limits corresponded to the scotomatous areas obtained by conventional perimetry. In these discordant cases, the lesions (e.g., arteriovenous malformation) were located in the occipital lobe. Two of these cases had a complete recovery of the subjective visual field. The lesions of the concordant cases were located outside the occipital lobe (e.g., pituitary adenoma). In these cases, no visual field improvement was seen. The temporal crescent syndrome was ruled out in patients with posterior lesions by computed tomography (CT) or magnetic resonance imaging (MRI) findings.

CONCLUSIONS

In some patients with occipital lesions, the subjective and objective visual field results are discordant, and some of them will show a recovery of the visual field deficits.