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Results for “Evoked Potentials, Visual”

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PubMed2004

Observations on intraoperative monitoring of visual pathways using steady-state visual evoked potentials.

BACKGROUND AND OBJECTIVE: Former studies revealed conflicting information on the usefulness of intraoperative monitoring of visual evoked potentials. This study was designed to evaluate the characteristics of visual evoked potential recording in surgically anaesthetized patients using the modality of steady-state visual evoked potentials. METHODS: In 30 cases with non-cranial surgery steady-state visual evoked potentials were recorded in the awake and surgically anaesthetized patient using total intravenous anaesthesia. For stimulation, goggles with red light-emitting diodes at a frequency of 8.5 Hz were used. A two-channel recording with silver cup electrodes at Oz to Fz and Oz to earlobe was used. All traces were analysed for the presence of the characteristically sinusoidal waveform and amplitudes and latencies of the main peaks were measured. RESULTS: Recordings during surgery demonstrated a minor latency prolongation of 16% and a more pronounced amplitude attenuation of 67% compared to the recordings in the awake patients. These differences were statistically significant (paired t-test, P < 0.001). In surgically anaesthetized patients steady-state visual evoked potentials showed a relatively high intra- and interindividual variability. In four of 30 patients completely stable recordings were obtained, whereas in 14 patients identifiable waves were recordable in only less than 50% of the intraoperative traces. Of the total 1360 traces recorded intraoperatively clearly identifiable steady-state visual evoked potentials patterns were present in 56% of the traces. There was no correlation between the magnitude of the evoked potential amplitude and its stability in intraoperative recordings. CONCLUSIONS: We conclude from this study, that steady-state visual evoked potential recordings in the surgically anaesthetized patient appeared to be more stable compared to our earlier findings using transient visual evoked potentials. However, further efforts are necessary to improve the stability of the recordings during surgery and thus allow for a more reliable intraoperative monitoring of visual pathways in routine clinical practice.

Adult↗

PubMed1997

Visual evoked potentials, heart rate responses and memory to emotional pictorial stimuli.

Although the effects of emotional stimuli on event-related cortical potentials, heart rate, and memory have been extensively studied, the association of these variables in a single study has been neglected. The influence of pleasant, unpleasant, and neutral photographic slides on visual evoked potentials (VEPs), heart rate responses, and free recall, was investigated in 20 normal subjects. VEPs were recorded from Cz and Pz locations, and analyses were performed on both amplitudes and latencies of identifiable endogenous peaks (P2, N2 and P3), and mean amplitude in the 100-200-ms, 400-600-ms, and 600-900-ms latency ranges. An emotional effect was present on VEPs starting from about 282 ms on, as revealed by the N2, P3, and late components. Both pleasant and unpleasant slides yielded larger cortical positivity as compared to neutral ones. Peak latencies did not show any emotional effect. Heart rate data showed a deceleratory response that was larger to unpleasant slides. Free recall of the projected slides showed a better performance for emotional slides compared to neutral ones. VEPs and memory data showed the same pattern: both pleasant and unpleasant slides induced larger positivity in the event-related potentials and were better remembered than neutral slides. Positive correlations were found between the late negative VEPs component (600-900 ms), recorded from Cz, and heart rate deceleration (r = 0.62), and between P3 (at Pz location) and the number of remembered slides (r = 0.53).

Adult↗

PubMedDate not supplied

[Evaluation of the visual evoked potentials in relation to the type of visual stimulation].

A classification of visual evoked potentials (VEP) in children and adults in response to various types of vision stimulation has been developed. Four major signs underlie this classification: (1) stimulation time frequency; (2) stimulation type; (3) mode of producing the visuals stimulus; (4) mono- or binocular presentation of the stimulus. One more sign can be added to classification: significant parameters of stimulation. Basing on this classification, the author describes the major VEP modalities and gives recommendations on the practical employment of these modalities.

Adult↗

PubMed1986

Serial visual evoked potential recordings in Alzheimer's disease.

Primary presenile dementia slows the major positive component of the visual evoked potential to flash stimulation but does not affect the visual evoked potential to patterned stimulation. The progressive effect of Alzheimer's disease was followed in a 58 year old woman over three and a half years from the development of the earliest symptoms to complete mental incapacity. The pattern reversal visual evoked potential remained normal, but the flash visual evoked potential gradually slowed from 129 ms in 1981 to 153 ms in 1984. The severity of the abnormality of the flash visual evoked potential thus reflected the severity of the dementia. Electroencephalography, computed tomography, and psychometric tests indicated generalised cortical disease, but the results were not specific to dementia. The combination of a slowed flash and normal pattern visual evoked potential seems to be specific to Alzheimer's disease and supports the use of flash and pattern visual evoked potentials in routine diagnostic testing for this condition.

Alzheimer Disease↗

PubMedDate not supplied

[Visual evoked potentials in cases of damage to visual pathways at different levels].

Visual potentials induced with a checker pattern were studied in a group of patients with damage to the visual pathways at different levels, and were compared with similar potentials in 10 adult subjects without diseases. A statistically significant prolongation of latency of the main deflections (N1, P max and N2) was observed in the group of 14 patients with optic nerve damage, while in 10 patients with lesions above the chiasma different, often normal responses were obtained. High-grade deformity of visual potentials was observed in 2 cases of visual agnosia. The study of visual evoked potentials may be in the opinion of the authors, useful in cases of damage to the optic nerve, retina and cortical visual centres.

Adult↗

PubMedDate not supplied

Effect of late surgery for acquired esotropia on visual evoked potential.

PURPOSE: To asses the effect of strabismus surgery on visual evoked potential (VEP) amplitude after age 5 years in children with acquired esotropia. METHODS: Visual evoked potentials to binocular and monocular pattern reversal stimulation were recorded in 10 children aged 5 to 6 years before and 3 months after surgical correction of their esotropia. Visual function (fusion) was tested by synoptophore after strabismus surgery. Electrophysiological and clinical data were correlated following surgical intervention. RESULTS: A significant increase in pattern VEP amplitudes was noted following strabismus surgery. Visual evoked potential changes were most prominent on binocular stimulation. Binocular fusion showed similarly significant improvement after intervention. Postoperative VEP data, however, were not consistently correlated with functional improvement. CONCLUSION: Surgical intervention in esotropia, even if performed years beyond the end of the classical critical period, can have a strong effect on binocular VEPs and a beneficial effect on the development of binocular fusion.

Child↗

PubMed1996

Monitoring of intra-operative visual evoked potentials during functional endoscopic sinus surgery (FESS) under general anaesthesia.

Functional endoscopic sinus surgery (FESS) is an effective treatment for inflammatory sinus disease. The potential for major complications during FESS is high particularly under general anaesthesia. The most serious of these is injury to the eye leading to blindness. We looked at the feasibility of monitoring flash visual evoked potentials (VEP) simultaneously from both eyes during FESS. Five patients were included in this preliminary study. A haptic contact lens connected by fibreoptic cable to a photostimulator was placed on the eyes and stimulus of comparable intensity to a conventional strobe was delivered. We found that an increase in P100 latency to be an indicator of optic nerve compression. However, for this to be useful the diastolic blood pressure should not fall below 50 mmHg, the oxygen saturation should be maintained at 98 per cent and bleeding should be minimized during surgery. The changes in the amplitude of P100 was not found to be useful. While there is no substitute for learning endoscopic surgery by cadaveric dissection and supervised training we believe that in selected cases VEP monitoring can be employed with profit.

Anesthesia, General↗

PubMed2006

Comparison of pattern visual-evoked potentials to perimetry in the detection of visual loss in children with optic pathway gliomas.

PURPOSE: We sought to compare visual evoked potentials (VEPs) with standard visual field testing in children with visual pathway gliomas. METHODS: Fifteen of 40 children with visual pathway gliomas verified on magnetic resonance imaging scan who cooperated with Goldmann visual field (GVF) and 3-channel VEPs were studied. GVFs were obtained in 25 eyes with adequate vision. VEP amplitudes, latencies, and signal-to-noise ratios (SNRs) were compared with control subjects. Four of the patients (5 eyes) also had Humphrey visual field testing. RESULTS: Twenty-two of 25 eyes had a field defect, 15 eyes showed a relative or absolute hemianopia, 7 eyes showed a central or generalized depression, and 3 eyes were normal. In hemianopic eyes, 87% showed a depression (GVF) or reduced sensitivity (Humphrey field) in the opposite hemifield. VEP amplitudes and SNRs, normally largest at the midline electrode, were significantly reduced in all eyes with visual field loss. By comparison, lateral electrodes showed significantly lower amplitudes and SNRs in patients and controls. Interhemispheric VEP asymmetry (>2:1 ratio) was seen in 67% of patients with hemianopia and 53% of controls. CONCLUSIONS: Reduction of amplitude and SNR at the midline VEP electrode was a sensitive indicator of visual field loss. Interhemispheric VEP asymmetry was not reliable in detection of a hemianopic field defect. VEPs can be a reliable and objective alternative for the detection of visual loss due to optic pathway glioma in children who are intolerant to visual field testing. We recommend the test protocol include pattern-onset and check reversal stimuli of at least one high and one low spatial frequency.

Adolescent↗

PubMed1985

Visual evoked potentials in ataxia telangiectasia.

Pattern reversal visual evoked potentials (VEPs) elicited in four patients with ataxia telangiectasia revealed normal results in two and absent responses in two. The pathogenesis of the VEP abnormalities is discussed. It is surmised that the VEP changes reflect progressive degeneration of the nerve fibres in the anterior visual pathway, as in Friedreich's ataxia.

Ataxia Telangiectasia↗

PubMed1994

Stimulus preceding slow potential shifts (SPS), EEG and visual evoked potentials (VEP) in rabbits.

In experiments of a modified "amplitude trigger" design on rabbits with chronically implanted cortical electrodes we looked for correlations between the partial activation state and EEG, DC-shifts and amplitudes of visual evoked potentials. The activation states are characterized by power spectra of EEG frequencies, actual heart and respiration rates and were in strong correlation with N1 amplitude of VEP as well as polarity and amplitude of stimulus preceding slow potential shifts. Three different activation states could be separated: low vs. "optimum" vs. high activation state. The "optimum" activation state is characterized by large amplitude VEP, positive directed stimulus preceding slow potential shifts as well as a desynchronized preflash EEG.

Animals↗

PubMed1982

Clinical applications of visual evoked potentials in neurology.

Neurological applications of visual evoked potentials (VEP) have been expanding over the last decade. Stimulation techniques and waveform interpretation are reviewed. Physiologic variables including age, sex, habituation, refraction, cooperation, and factors influencing the amount of light reaching the retina will effect the VEP. Technical variables including luminance, check size, field size and color of check will also have an effect on the VEP. When properly performed, VEP can contribute important information on the visual pathways in patients with optic neuritis, multiple sclerosis, optic nerve and chiasm compressive lesions, non-compressive lesions affecting the visual pathways and neurodegenerative diseases not primarily involving the visual pathways. VEP has been shown to be a very sensitive though non-specific diagnostic tool.

Electroencephalography↗

PubMed1993

Postnatal development of visual evoked potentials in Japanese black calves.

The visual evoked potential (VEP) was recorded in six Japanese Black calves from 1 to 10 weeks after birth. The VEP waveform recorded at the 1st week was consisted of three positive and three negative peaks. The VEP showed little postnatal changes except for the shortening of the peak latencies of P1 and N3 and the increase of the peak-to-peak amplitudes of P1-N1 and P2-N2 (significant between the 1st and 10th week of age). The visual function associated with generation of the flash VEP is suggested to have almost developed at birth in the calf. The postnatal measurement of the VEP would be useful for evaluating the neurologic disorders of the visual system in young calves.

Aging↗

PubMed1985

A new laser interferometer for the stimulation of pattern-reversal visual evoked potentials.

A laser interferometer for visual-evoked-potential (VEP) stimulation that allows a rapid pattern reversal in less than 0.5 ms and a continuous variation of the spatial frequency of the pattern is described. The interferometer is applied for the assessment of objective visual acuity. The Fourier transform of the VEP response to the rapid pattern reversal shows an extremely small bandwidth.

Evoked Potentials, Visual↗

PubMed1990

[Wilson's disease. Presentation of a case with special reference to the study of evoked visual potentials].

In the present work the Authors report one case of Wilson's disease showing peculiar characteristics diagnosed in pediatric-age patients. In this case, a deep electrophysiological visual analysis was carried out six years after diagnosis. The evoked visual potential alterations might be connected to a retina dysfunction. Further studies should be carried out in order to support such hypothesis.

Child↗

PubMed1998

Does acute exposure to the electromagnetic field emitted by a mobile phone influence visual evoked potentials? A pilot study.

To search for a potential negative influence on the central nervous system (CNS) of the electromagnetic field emitted by a mobile phone, the authors performed a pilot experimental study of the influence of a single short acute exposure to the GSM mobile phone Motorola 8700, using visual evoked potentials (VEP) examination as an electrophysiological marker of CNS dysfunction. The study group consisted of 20 healthy volunteers. The duration of exposure was 5 minutes. The output power of the device was 1.5 W when the antenna was pulled up. Five parameters of VEP were evaluated by means of multifactorial ANOVA. Confounding effects of age, sex, and of the call in itself were taken into consideration. No statistically significant influence of the above-described exposure to the electromagnetic field emitted by the mobile phone on latencies or amplitudes of VEP was observed.

Adult↗

PubMed1984

Changes in the cortical components of the visual evoked potential with age in man.

Pattern visual evoked potentials (PVEPs) were recorded from 177 normal subjects aged 11-87 years. The purpose was to determine age-dependent changes in the latency of the individual components of the waveform. The initial components of the PVEP, which are thought to reflect activity in the primary visual (striate) cortex, showed no change in latency from 11-50 years followed by an abrupt increase occurring during the sixth decade. It is probable that this delay in the PVEP is mediated largely by pathophysiological changes occurring either in the eye or visual pathways, or both. The secondary components of the PVEP, which are presumed to be generated in the visual association areas of the extrastriate cortex, showed a progressive although initially very limited increase in latency starting after adolescence. It is suggested that those delays occurring between 21 and 50 years in the secondary components are mediated largely by intracortical factors. The more pronounced delays occurring for the older age groups (over 50 years) appear to be caused by a combination of cortical, subcortical and ocular changes in visual function. The prolongation of the later components in the age group 11-20 years seems to reflect maturational changes almost entirely confined to intracortical processes. The results are discussed in terms of the many conflicting reports of the effects of age on the PVEP.

Adolescent↗

PubMed1994

Pattern reversal visual evoked potentials in retinitis pigmentosa.

Pattern reversal visual evoked potentials (PR-VEPs) of 31 patients with retinitis pigmentosa (RP) and 20 normal control subjects were recorded and compared. Recordings were taken from Oz referred to Fz, by stimulating with squares subtending 60 min, presented at a visual field of 30 degrees and 98% contrast. The mean latency of the main positive component P100 of the PR-VEP of the RP patients was 116.1 msec (SD 12.71) and 114.84 after stimulation of the left and right eye respectively. These values are significantly different (p < 0.001) from the equivalent values of the normal controls (102.5 ms (SD 5.1) and 100.6 ms (SD 4.6) for the left and right eye, respectively). Fourteen patients had a P100 latency more than 3 SDs from the normal mean value. Subsequently the patients were classified into three groups (for each eye separately) according to visual acuity (VA) and comparison for PR-VEP amplitude and latency was performed. In group A patients with VA 6/6, in B with 6/9 and in G with 6/12 or more were included. Decrease of VA was significantly associated with increased latency. The amplitude was not significantly affected except for group C. All 3 groups were not significantly different in age. The P100 in group A was consistently prolonged, compared to normals. It seems that RP can introduce significant increase in the PR-VEP latency associated with decreased VA. This may have diagnostic and prognostic implications.

Adolescent↗

PubMed2000

Visual pathway abnormalities Wilson's disease: an electrophysiological study using electroretinography and visual evoked potentials.

The pathogenesis of the pattern reversal visual evoked potential (PRVEP) abnormalities in patients with Wilson's disease (WD) has not been investigated earlier. Since electroretinography (ERG) assesses the functional integrity of the retina, it was used along with PRVEP to localize the abnormalities in PRVEP in Wilson's patients. Ten newly diagnosed Wilson's disease patients underwent PRVEP and flash ERG soon after the diagnosis was established. The PRVEP latencies were prolonged in comparison with the controls (P<0.001). Photopic and scotopic A waves and oscillatory potentials were prolonged (P<0. 02) with reduction in amplitudes of photopic A and B waves (P<0.001). Six of these patients were subjected to repeat PRVEP and flash ERG after the clinical improvement with specific therapy. Comparison of the pre and post-treatment visual electrophysiological studies revealed significant reduction in latencies of PRVEP and flash ERG A wave (P<0.05) with increase in amplitudes of P100 of PRVEP (P<0.05), A and B waves of flash ERG (P<0.01). These findings confirm the reported PRVEP changes in WD and in addition demonstrate the reversibility of the retinal dysfunction which partially contributes to the PRVEP abnormalities. To the best of our knowledge this is the first study of ERG in patients with Wilson's disease in the literature. Further, there have been no earlier reports in the literature evaluating the effect of specific treatment on the PRVEP and ERG in Wilson's disease.

Adolescent↗