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Results for “Evoked Potentials, Visual”

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PubMed2000

Progression of visual evoked potential abnormalities in multiple sclerosis and optic neuritis.

To investigate visual signal processing in patients with optic neuritis, suspected multiple sclerosis, confirmed multiple sclerosis (MS), and optic neuritis combined with MS, pattern reversal visual evoked potentials (VEPs) were recorded in patients and normal subjects. The amplitude and latency of the first positive peak, P100 were determined to assess electrical conduction in patients as compared to normal subjects. Suspected MS patients did not differ from normal subjects in peak latencies or amplitudes. The P100 amplitude was reduced in optic neuritis, confirmed MS and optic neuritis combined with confirmed MS. The P100 and N145 latencies were prolonged in optic neuritis patients and confirmed MS patients as compared to normal subjects. The main characteristic of optic neuritis was P100 amplitude reduction, and of confirmed MS was P100 latency delay. There was a progression of the P100 latency delay and of the P100 amplitude decrement in optic neuritis, confirmed MS, and optic neuritis combined with confirmed MS. These results indicate a progression of demyelination in optic neuritis, confirmed MS, and optic neuritis combined with confirmed MS.

Adolescent↗
PubMed1980

Abnormalities of the pupil and visual-evoked potential in quinine amblyopia.

Total blindness with a transient tonic pupillary response, denervation supersensitivity, and abnormal visual-evoked potentials developed in a 54-year-old man after the use of quinine sulfate for leg cramps. He later recovered normal visual acuity. A transient tonic pupillary response, denervation supersensitivity, and abnormal visual-evoked potentials in quinine toxicity, to our knowledge, have not been previously reported.

Blindness↗
PubMed1990

Transient asymmetries of steady-state visual evoked potentials in classic migraine.

Unilateral abnormalities in the regional cerebral blood flow (rCBF) and visual evoked potentials (VEPs) during the visual aura of classic migraine have been reported. On the other hand, there are only few observations suggesting unilateral abnormality of neural function during the headache-free period. An experiment is described in which the symmetries of steady state VEPs (SVEPs) are compared in healthy subjects and classic migraineurs in the headache-free interval. In the patients an increased number of strong short-lasting interhemispheric asymmetries was found. In the serial recordings performed, pathologic recordings were obtained intermittently, usually with complete normalisation in the following session. The incidence of abnormalities was relatively independent of the interval between the recording and attack, except for the next few hours. The findings may be related to instability of occipital cortical function in classic migraine.

Adult↗
PubMed1984

Steady-state visual evoked potentials during migraine prophylaxis by propranolol and femoxetine.

The amplitude of visual evoked potentials (VEPs) for flickering light has been reported to be increased in migraine. In the present study, we have examined whether the VEPs are attenuated when the clinical state of the patient improves during a double-blind experiment with propranolol and femoxetine. VEPs for sinusoidally-modulated light were measured by spectral analysis, and an index depicting the visual reaction type was calculated. The group mean VEP index closely followed the group mean attack frequency, but individual variance was considerable. The changes were most evident in VEPs elicited by stimuli of about 20 Hz. During the treatments, the VEP and headache were also significantly correlated among subjects. The results suggest a close relationship between the enlarged VEPs and the headache mechanisms.

Adult↗
PubMed2006

Objective measurement of human visual acuity by visual evoked potentials.

Electrophysiological studies were performed to measure the threshold (upper end of range) spatial frequency using visual evoked potentials and comparison with visual acuity neuron 26 healthy subjects. The aim of the present work was to create a method for objective measurement of visual acuity. This was addressed by initial measurements using a universally accepted method of visual stimulation and processing of electroencephalograms, which allows errors due to individual differences in visual system function to be minimized. These experiments yielded a strong correlation between the threshold spatial frequency of the test grid yielding an evoked potential on presentation and visual acuity, in degrees, expressed as the resolving ability of the visual system for this optotype. A logarithmic relationship was found between these values and an equation allowing automated calculation of visual acuity (resolving ability) from electrophysiological data was derived. The results were independent of the subject's responses and therefore provides a maximally objective assessment of visual acuity.

Adolescent↗
PubMed1982

Visual prognosis for corneal transplantation based on preoperative visual evoked potential and electroretinogram.

Thirty-one corneal transplant cases underwent a visual-evoked potential and electroretinogram examination prior to keratoplasty. There were 12 cases that had a good visual prognosis and 19 cases with a poor visual prognosis based on the preoperative diagnosis and clinical examination. The addition of electrophysiologic testing in the good prognosis cases did not provide additional information, but produced one false negative, whereas tests in poor prognosis cases were helpful in predicting the visual outcome after transplant. These tests were predictive of visual outcome in 71% of all cases and in 58% of the poor prognosis group.

Adolescent↗
PubMed1989

Moyamoya disease. Posterior cerebral artery occlusion and pattern-reversal visual-evoked potential.

Although vascular abnormality in moyamoya disease predominates in the anterior and middle cerebral arteries, the posterior cerebral artery (PCA) has been found to be involved in the course of the disease. To explore PCA occlusion by noninvasive means, we studied visual-evoked potentials in the patients with PCA occlusion (occlusive group), as well as in those without PCA occlusion (nonocclusive group). The results were compared with those of other examinations that also detected an occipital lobe pathologic condition. Abnormalities of those examinations were highly specific to PCA occlusion. Positron emission tomography and pattern-reversal visual-evoked potentials yielded high incidence of abnormality in the occlusive group (86% and 75%, respectively), and expressed the side of PCA occlusion if the occlusion was unilateral. Since pattern-reversal visual-evoked potentials is popular and a low-cost examination compared with positron emission tomography, we conclude that pattern-reversal visual-evoked potentials is the most practical mean to explore PCA occlusion in the course of moyamoya disease.

Arterial Occlusive Diseases↗
PubMed1985

The effects of halothane on somatosensory and flash visual evoked potentials during operations.

Intraoperative use of somatosensory evoked potentials (SEP's) to monitor intracranial aneurysm surgery and flash visual evoked potentials (F-VEP's) for parasellar surgery have been routinely employed in our clinic. We found that both EP modalities are sensitive to the changing concentration of our standard hypotensive agent, halothane. The prolongation of the N14-N20 interpeak latency to median nerve stimulation at the wrist, and prolongation of P100 latency with altered configuration of early VEP components to flash light stimulation, appear to be the results of direct pharmacological effects of the agent and not an effect of secondary hypotension. VEP is found easily abolished by halothane at a concentration of 2.0%, while the SEP is more resistant. Halothane is not ideal however when monitoring intraoperative VEP.

Adolescent↗
PubMed1981

[Clinical applications of visual evoked potentials for detection of chiasmal and postchiasmal lesions (author's transl)].

Visual evoked potentials (VEP) were recorded in 18 patients with pathologic processes confirmed by computerized tomography in the chiasmal (n = 9) and parietooccipital region (n = 9). Reactions from the right and left hemisphere could be recorded separately in spite of using a simple one-channel apparatus and electrodes only at Oz and Cz. In 17 cases changes of the VEP provided information concerning the localization and extension of the lesion. In chiasmal processes we found a prolongation of monocular latencies, and a delayed or extinguished reaction to half-field stimulation from temporal retinal areas. However, the VEP was often pathologic for half-field stimulation of the nasal hemiretina. Pathologic VEPs were not always accompanied by visual field defects. In contrary to patients with chiasmal processes no pathologic reaction could be found to full-field stimulation in parieto-occipital lesions. Only when the affected hemisphere was stimulated selectively were diminution of amplitudes, prolongation of latencies, or extinguished responses observed. The VEP changes were uniform despite the cause of the lesion (tumor, ischemia). In chiasmal and parieto-occipital processes the VEP supplements computerized tomography by detecting deficits in function. This method appears suitable for monitoring the course of disease before and after neurosurgery.

Brain Diseases↗
PubMedDate not supplied

Ethyl alcohol effect on the visual evoked potential.

The investigations were carried out in 30 clinically healthy pilots who were given 1 g/kg of body weight of ethanol orally. Visual evoked potentials were recorded 30 and 60 minutes after alcohol ingestion in the occipital leads using an ANOPS-10 computer. It was found that ethanol caused prolongation of the latency time of all components parallel with rising concentration of ethanol in the blood. The amplitude of the late components, i.e.-N2-P2-P2-N3 and N3-P3 30 minutes after alcohol ingestion was raised, and after 60 minutes it was reduced. The analysis of the individual visual evoked potentials demonstrated three types of individual reactions to ethanol. Type I--increasing depression of the amplitude of the components with rising blood alcohol concentration, type II--rising amplitude, mainly of the late components, type III--amplitude rise in the 30th minute followed by amplitude fall in the 60th minute without reaching, however, the initial level. These changes of the visual evoked potentials suggest that alcohol exerts in the first place an effect on the subcortical structures and that this effect is a phasic one.

Adult↗
PubMedDate not supplied

[Visual evoked potentials in elderly subjects (author's transl)].

Study of visual evoked potentials by contrast stimuli (VEPL) and by luminance stimuli (VEPC) in 28 subjects aged between 65 and 95 years (mean age: 81.8 years). Changes related to aging in regard to VEP involve: an increase of latencies of VEPL affecting the early components and an increase in the maximum amplitude of VEPL. The course of EP as age progresses introduces a difference in topographical organisation with a deterioration of responses in the left occipital regions and a change in potentials recorded at the vertex. Aging would appear to cause more marked inter-individual differences which could have clinical implications by making it possible to demonstrate individual differences in the biological processes of aging.

Aged↗
PubMed2002

The effect of different hypertension models on visual evoked potentials.

Even though there is an abundance of information about the complications of hypertension, studies of its influence on visual evoked potentials (VEPs) are rare. In previous studies, it was pointed out that hypertension induces changes on VEPs. However, it has not yet been clarified which models of hypertension are more effective on VEPs. The aim of this study was to investigate this subject in rats. Animals were divided equally into six groups: control group (C), sham operated (Sham), two kidney-one clip (2K-1C), one kidney-one clip (1K-1C), deoxycorticosterone-salt (DOCA), and N-omega-nitro-L-arginine-methyl ester (L-NAME) groups. Mean arterial pressure was significantly higher in four hypertensive groups compared with control and sham groups, but there were no significant differences either among hypertensive groups or between sham and control groups. At the end of the experimental period, flash visual evoked potentials were recorded. The mean latencies of P1, N1, P2, N2, and P3 components were significantly prolonged in all hypertensive groups compared with the control and sham groups. The mean latencies of all VEPs components in the L-NAME group were longer than in the other hypertensive groups. Thiobarbituric acid-reactive substances (TBARS) were determined as an indicator of lipid peroxidation. Our data showed that hypertension caused a significant increase of lipid peroxidation in brain and retinal tissues. Additionally, plasma renin activity (PRA) was highest in the 2K-1C group and lowest in the DOCA group.

Animals↗
PubMed2004

Swept contrast visual evoked potentials and their plasticity following monocular deprivation in mice.

The swept contrast visual evoked potential technique is a quasi-psychophysical method that can help bridge the gap between cell biology and visual performance in studies of ocular dominance plasticity. In mice we found that four days of monocular deprivation diminished the amplitude of evoked potentials from the deprived eye relative to the non-deprived eye. This ocular dominance plasticity was nearly as great in adult mice as in juveniles. The monocular deprivation effect was mediated, at least in part, by enhancement of responses evoked from the non-deprived eye, rather than by depression of responses from the deprived eye.

Animals↗
PubMed1997

[Objective assessment of visual acuity with visual evoked potential].

PURPOSE: To study the technique for objectively assessment of visual acuity with Pattern Visual Evoked Potential (PVEP) and Discrete Fourier Transform (DFT). METHOD: Thirty-three normal eyes were tested in this study. Reversal square-wave gratings of eight different sizes (30, 20, 18, 12, 10, 6, 4, 2 min. of arc) were used as stimuli. The reversal rate of the stimuli was 10 times/sec. The harmonic amplitudes of VEP at 10 Hz were calculated with Discrete Fourier Transform. A relation curve between the harmonic amplitude and the size of grating was plotted from the data of each tested eye. Regression line was fitted to the data points in the approximately linear section of the curve which is near the threshold of zero amplitude. The threshold of the grating size was obtained by extrapolating of the regression line to zero amplitude, and the visual acuity was assessed with the threshold. RESULT: In seventy percent of tested eyes, the visual acuities assessed with VEPs were consistent with those measured with the International Standard Test Chart. CONCLUSION: The VEP technique for visual acuity assessment is reliable.

Adolescent↗
PubMed2000

Steady-state visually evoked potential topography during the continuous performance task in normal controls and schizophrenia.

OBJECTIVES: To examine the latency topography of the steady-state visually evoked potential (SSVEP) in patients diagnosed with schizophrenia and normal controls while undertaking a visual vigilance task. METHODS: Twenty patients diagnosed with schizophrenia and 18 normal controls performed the A-X version of the continuous performance task (CPT A-X) where subjects are required to press a micro-switch on the unpredictable appearance of an 'X' that had been preceded by an 'A.' Brain electrical activity was recorded from 64 scalp sites and a 13 Hz spatially uniform visual flicker presented with the task was used to elicit a steady-state visually evoked potential (SSVEP). RESULTS: Following the appearance of the 'A' and 'X,' the control group demonstrated a transient SSVEP latency reduction at parietal and prefrontal sites. By contrast, the patients group showed no such SSVEP latency reduction. The prefrontal SSVEP latency changes in the 500 ms interval following the appearance of the 'X' were correlated with mean individual reaction time in both populations. CONCLUSIONS: We suggest that the SSVEP latency reduction may index excitatory processes and that the absence of prefrontal SSVEP latency reduction in schizophrenic patients may be a manifestation of reduced prefrontal activity or 'hypofrontality' observed with other neuroimaging modalities.

Adult↗
PubMed1986

Amplitudes of visually evoked potentials to patterned stimuli: age and sex comparisons.

Electrophysiological age and sex differences in visual pattern responsivity were investigated. Pattern reversal evoked potentials (PREPs) and visual evoked potentials (VEPs) to patterned and unpatterned flashes were recorded from 20 normal subjects in each of 4 groups: young females and males aged 25-35 years and older females and males aged 55-70 years. PREP waves N70-P100 and P100-N150 from the older women were significantly larger than those from subjects in the other groups; mean amplitudes for the young females, young males and older males were not different. A similar effect, unusually large potentials for the older women, was obtained for VEPs, but only for VEPs elicited by patterned flashes and recorded from occipital scalp, i.e., an area overlying visual cortex which is sensitive to lines and edges. Our findings suggest that the visual system of older females is unusually responsive to patterned stimuli.

Adult↗
PubMed1983

Visual-evoked potentials elicited by laser speckle patterns. Studies on the characteristics and assessment of visual function in patients with ocular media opacities.

Visual-evoked potentials (VEPs) were recorded using a laser speckle pattern. Stimulation with a speckle pattern was elicited either by pattern appearance-disappearance or by pattern shift. The VEPs obtained by this method were similar in properties to the previous pattern VEPs that were obtained either by pattern appearance-disappearance or by pattern reversal. Patients in whom dense and diffuse ocular media opacity defied measurement by the interferometric visual acuity method were studied to test if the speckle pattern generated by diffusion from lens opacity itself could act as a stimulus for obtaining VEPs. It is concluded that the present method enables one to obtain a reliable VEP and to assess the visual function of the retino-cortical system, even in patients with mature cataracts.

Adult↗