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Results for “Evoked Potentials, Visual”

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At least 217 records · Page 12Linked to original sources

PubMed1991

Bee sting optic neuritis. A case report with visual evoked potentials.

Simultaneous recordings of the pattern visual evoked potential and the pattern electroretinogram were recorded in a case of unilateral optic neuritis following a bee sting on the eye. The patient presented with severe eye pain, apoplectic visual loss, acute optic disc swelling and minimal signs of ocular inflammation and eyelid edema. The vision failed to recover. The electrophysiological recordings initially showed a delay in the P100 wave of the pattern visual evoked potential. On follow-up, a normal latency and amplitude of the P50 wave of the pattern electroretinogram was recorded with the flattening of the N95 component, but the pattern visual evoked potential was absent. The data suggests that the optic nerve was demyelinated acutely, and that subsequently axonal loss and degeneration of retinal ganglion cells occurred.

Adult↗

PubMed2004

[Brain stem auditory and visual evoked potentials in children and adolescents with Guillain-Barré syndrome].

Guillain-Barré syndrome (GBS) is the most common acquired polyradiculoneuropathy in childhood. It has been conventionally regarded as a disease exclusively of the peripheral nervous system. The involvement of the central nervous system (CNS) in patients with GBS has been rarely described. The purpose of the study was to delineate the extent of subclinical neurological changes of CNS in children and adolescents with this syndrome. Thirty patients aged 8-18 years with GBS were treated in the Chair and Department of Developmental Neurology. The upper and lower limbs paresis dominated in clinical pictures of these patients. Cranial nerve involvement was noticed in 9 children. An ascending bulbar paralysis was noted in four cases. Sensory symptoms were found in all children. The nerve conduction velocities were abnormal in all examined patients with GBS. The control group for neurophysiological studies consisted of 66 healthy children and adolescents at the matched age. Evoked potentials (EP) were registered by means of Multiliner (Toennies, Germany). Brainstem evoked potentials (BAEP) and visual evoked potentials (VEP) were always performed in the same conditions with the same equipment for the children and adolescents in the GBS and control group, according to the guidelines of the International Federation of Clinical Neurophysiology (IFCN). The following BAEP parameters were considered: the latencies of waves I to V, interpeak latencies I-III, III-V and I-V. The latencies of N75, P100, N145 as well as the amplitudes of N75/P100, P100/N145 for mono- and binocular stimulations of VEP were analysed. BAEP showed abnormalities in 6 cases and VEP in 5 cases. The statistically significant prolongation of the latencies of waves III, V and interpeak I-V were found in children and adolescents with GBS. The BAEP changes may reflect impairment at the brainstem level in these patients. In VEP recording in GBS the prolongation of latencies P100 and N145 without changes in amplitudes were found. These parameters were statistically significant in comparison to the control group. VEP results suggest the involvement of visual pathway in examined children and adolescents. EP can be used as a complementary method for the evaluation of clinically silent lesion in the auditory and optical tracts in GBS.

Adolescent↗

PubMed1999

The neonatal development of the light flash visual evoked potential.

AIMS: To follow visual development longitudinally in the normal neonate using the flash visual evoked potential (VEP) and to find indications for a relationship between potential development and visual development. METHODS: Twenty healthy infants, born at term, were included in the study. Flash and patterned flash VEPs were used. The first VEP was recorded the day of birth or just postnatally, and succeeding recordings were performed the following weeks and months. RESULTS: The data revealed different types of VEP in the neonatal period suggesting great variability in visual function on the day of birth. In the early development a potential of long latency and duration preceded the development of a more compound potential of shorter latency. The two types of responses seemed to coalesce during early development; the first late response was attenuated and was eventually integrated in the more mature VEP. At approximately five weeks of age changes in the VEP were simultaneous with the development of responsive smiling and another visual behaviour of the infants. CONCLUSIONS: The results showed many similarities between the VEP development in infants and in immature animals. In developing animals geniculo-cortical and extra-geniculate visual afferent pathways evoke two types of VEPs similar to those recorded in the present study. The early responses were also similar to previous recordings from children with lesions in the geniculo-striatal pathway or primary cortex. Our interpretation of the results was that the human VEP also consists of responses evoked by afferents running both in geniculo-cortical and extra-geniculate pathways and that the two types of responses could be separated in the VEP in the neonatal period. These findings are important for our understanding of conditions with a delay in visual maturation, for example intracranial haemorrhages, hydrocephalus, pre/dys-maturity and 'idiopathic' delayed visual maturation.

Aging↗

PubMed1987

Hemispheric asymmetry of pattern reversal visual evoked potentials in healthy subjects.

Pattern reversal visual evoked potentials were recorded from temporal leads of both hemispheres in 3 right-handed and 3 left-handed subjects. The stimuli subtended 6 degrees of visual field (full field condition), or 1 degree of visual field (foveal condition), or were restricted to the peripheral portion of the visual field (annular condition). Check sizes varied from 16 to 2.8 min of arc. The stimuli were phase-reversed at 1 or 8 Hz. Remarkable hemispheric asymmetries were found, depending on the portion of the visual field and temporal frequency. In right-handed subjects the amplitude of visual evoked potentials recorded over the left hemisphere was larger for stimuli phase-reversed at 8 Hz in full-field and annular conditions, whereas the amplitude of visual evoked potentials recorded over the right hemisphere was larger for stimuli phase-reversed at 1 Hz in the foveal condition. Different patterns of hemispheric asymmetries were observed in left-handed subjects.

Arousal↗

PubMed1977

Effect of body temperature on visual evoked potential delay and visual perception in multiple sclerosis.

Seven multiple sclerosis patients were cooled and four heated, but evoked potential delay changed in only five out 11 experiments. Control limits were set by cooling eight and heating four control subjects. One patient gave anomalous results in that although heating degraded perceptual delay and visual acuity, and depressed the sine wave grating MTF, double-flash resolution was improved. An explanation is proposed in terms of the pattern of axonal demyelination. The medium frequency flicker evoked potential test seems to be a less reliable means of monitoring the progress of demyelination in multiple sclerosis patients than is double-flash campimetry or perceptual delay campimetry, although in some situations the objectivity of the evoked potential test would be advantageous.

Body Temperature↗

PubMedDate not supplied

Interdependance of the level of the steady potential of the brain and visual evoked potentials in human aging: the norm and Alzheimer's disease.

The interrelationships between the amplitude-temporal parameters of the visual evoked potential (VEP) and of the level of the steady potential (LSP) of the brain in healthy middle-aged and elderly people and in Alzheimer's disease patients. The existence of a statistically significant correlation between the LSP and the amplitude-temporal characteristics of the VEP. The interrelationship is intensified both during aging in the norm and especially in Alzheimer's disease patients. The most stable positive correlation exists between the local LSP and in the occipital region and the amplitudes of the N1 and P2 components of the VEP.

Adult↗

PubMed1982

Asymmetry and ventral course of the human geniculostriate pathway as determined by hippocampal visual evoked potentials and subsequent visual field defects after temporal lobectomy.

Twenty-two patients with psychomotor epilepsy were implanted with depth electrodes along the axis of the mesial temporal lobe to identify an operable unilateral epileptic focus. Neuronal and field potentials were recorded in response to diffuse retinal illumination and clear short-latency responses were found in parahippocampal gyrus. These visual afferents in the mesial temporal lobe are assumed to be both from subcortical and cortical visual areas. There was a clear asymmetry in the ventral trajectory of the geniculostriate pathway as evidenced by asymmetric neuronal and field potential responses to brief flashes in right vs. left hippocampal gyrus and confirmed by a corresponding partial visual field deficit following therapeutic anterior temporal lobectomy. These results demonstrate that there is a retinotopic organization of fibers in the human geniculostriate pathway and that this pathway may have considerable variability in the anterior and ventral course these fibers take through the temporal lobe. These findings adequately account for the presence of direct projections from geniculate to hippocampal cortex and for unexpected hemianopsias with standard resections of the temporal lobe when there is a deviant detour of the geniculostriate pathway.

Dominance, Cerebral↗

PubMed1987

Measurement and definition of changes in the visual evoked potential to different stimulus intensities.

Visual evoked potentials (VEPs) were recorded from the vertex to 5 intensities of light flashes. Measures were taken of peak-to-trough, prestimulus baseline-to-peak, and timeband amplitude for P1, N1, and P2 waveforms. Augmenting/reducing was defined by traditional (amplitude/intensity slope, monotonicity) and non-traditional (strength of the nervous system, combined amplitude response) criteria. In support of Connolly and Gruzelier ([1982) Psychophysiology, 19: 599-608], analyses showed that data collected by traditional methods contravened assumptions underlying VEP augmenting/reducing methodology. Specifically, 20% of total peaks occurred outside designated timebands, amplitude/intensity slopes explained only 30-46% variance, and levels of agreement between different definitions were low. Researchers ought to ensure that VEPs are admissible before using them or consider employing non-traditional criteria to avoid rejecting large numbers of inadmissible data.

Adolescent↗

PubMed1985

Visual evoked potentials in the great apes.

Visual evoked potentials (VEPs) in response to flash stimuli were recorded from occipital and central-scalp electrodes in the chimpanzee and gorilla. The most notable occipital component of the VEP was a surface-positive wave (P90), the latency of which decreased with development. Central scalp responses, apparent only in older animals, included a characteristic long-latency 'vertex wave' (N125-P225). Observed responses are similar to those reported for humans and monkeys, but appear to share more specific features of human VEPs.

Animals↗

PubMedDate not supplied

Three-dimensional human pattern visual evoked potentials. I. Normal subjects.

Pattern visual evoked potentials (PVEPs) were obtained from 30 normal adult volunteers, recording from both a conventional horizontal occipital array and three orthogonal bipolar antipodal channels approximating the three dimensions of space. Central and eccentric fixation of 60' checks and central fixation of 30' checks under binocular and monocular viewing conditions was employed. The three antipodal wave forms were displayed as a single 3-D Lissajous trajectory which contained four apices, corresponding to P40 (apex A), N70 (apex B), P100 (apex C) and N125 (apex D). The 3-D evoked potentials depicted the dynamic nature of the human PVEP in terms of changes in the 3-D voltage-voltage-voltage plots of the recordings. The orientation of the A-B, B-C and C-D curvilinear segments reflected the stimulating condition (central fixation vs. right vs. left hemi-field stimulation) for all subjects with more accuracy than did the wave forms from the conventional array. Spherical statistical methods are described for quantifying and evaluating 3-D evoked potential recordings.

Adult↗

PubMed1999

Maturation of the flash visual evoked potential in preterm infants.

Flash visual evoked potentials (VEPs) were recorded from 67 infants of < 33 weeks gestation with normal neurological outcome at 24 months corrected age. Cross sectional and longitudinal data showed the emergence of peak components of the waveform with increase in maturity. The first major negative peak, with a latency around 300 ms in the most immature subjects, was the most prominent and consistent component. This peak showed a decrease in latency with increase in post-conceptional age, maturing by a mean rate of 5.5 ms/week. The role of VEPs in predicting brain injury in preterm infants can be determined.

Brain Diseases↗

PubMed1988

Pattern visual evoked potentials in hyperthyroidism.

Pattern reversal visual evoked potentials (VEPs) have been elicited in 16 female hyperthyroid patients before and after treatment and compared with those from a similar group of age and sex matched control subjects. No effect on latency was seen, and although larger amplitude values were noted in the thyrotoxic group these too were not significant. We would conclude that hyperthyroidism per se has little effect on the pattern reversal VEP, and any observed effect on these potentials is probably due to other factors.

Adult↗

PubMed1981

Pattern-onset visual evoked potentials in suspected multiple sclerosis.

Visual evoked potentials (VEPs) were obtained by monocular stimulation using a checkerboard pattern-reversal and pattern-onset technique. In 11 normal subjects, pattern-onset VEPs were generally larger, better defined, and less ambiguous than those elicited by pattern-reversal, because of the biphasic waveform characteristically obtained with pattern-onset stimulation. In 68 of 105 patients with possible multiple sclerosis, VEPs were normal in latency by both methods, and in nine adequate comparison was not possible. The incidence of normal VEPs to pattern-reversal was similar to that found in several other studies of patients with possible multiple sclerosis. Among the remaining 28 patients in whom VEP abnormalities were found, an increased latency was detected in 75% with the pattern-reversal technique, and in 96% by pattern-onset. In these patients, VEP abnormalities were obtained by monocular stimulation of each of 46 eyes, and among these the pattern-reversal technique yielded abnormalities in 59% and the pattern-onset method in 98%. These results indicate that VEPs elicited by pattern-onset are useful in investigating patients with suspected multiple sclerosis, and the diagnostic yield may be greater than with conventional pattern-reversal techniques.

Adult↗

PubMed2001

Fish oil supplementation improves visual evoked potentials in children with phenylketonuria.

Visual evoked potentials (VEP) were measured in 36 patients with early-treated phenylketonuria (PKU; aged 1 to 11 years) and good metabolic control before and after supplementation with omega-3 long-chain polyunsaturated fatty acids (LC-PUFA) from fish oil. Patients with PKU had significantly longer P100 latencies than 22 age-matched control subjects. After 3 months of LC-PUFA supplementation, VEP latencies improved significantly in PKU patients but did not change in 12 untreated healthy children. The authors conclude that omega-3 LC-PUFA are essential substrates for nervous system function even beyond infancy.

Child↗

PubMed1982

Changes in the visual evoked potentials of hydrocephalic children.

The visual evoked potentials (VEPs) of a group of 84 hydrocephalic children, aged between 2 days and 15 years, were studied. The variables analyzed were age, ventriculomegaly, head size, and the presence or absence of a functioning shunt. In infants, an increase in the latency of the primary positive wave (P2) was confirmed, but this was present consistently only when ventriculomegaly was accompanied by increased head size. Improvement in the VEP was slow to follow shunting. No change in the latency of P2 was found during hydrocephalic episodes in older children.

Adolescent↗

PubMed1993

[Visual evoked potential from dura in rats].

Visual evoked potentials (VEPs) were recorded from 8 different points (from points A and B near the bregma to points G and H near the occipital bone) of the dura under parietal bone in rats. The study was performed with 68 adult male Slc: Wistar/ST rats weighing 259.9-298.0g. VEPs recorded from the dura had a large negative component with a peak around 45 msec (N1), a large positive component with a peak around 75 msec and a large negative component with a peak around 120 msec (N2). Points A and B were not suitable for recording of the VEPs because some rats showed no N2 peak. The amplitude of peaks N1 to P at point E, upper the left optic layer of the superior colliculus, was higher than those from other points. Point E was the best position for recording of the VEP from dura in Slc: Wistar/ST rats.

Animals↗

PubMedDate not supplied

An instrument to monitor the luminance of pattern visual evoked potential stimuli.

When recording pattern visual evoked potentials it is important that the overall luminance of the pattern and the relative luminance of the pattern elements (for example checks or bars) are maintained at a constant level. This paper describes a low-cost battery-powered instrument designed and constructed to measure the luminance of specific areas of the screen on which the pattern is projected.

Calibration↗

PubMed1992

[Magnetic stimulation motor evoked potential in multiple sclerosis. Comparison with visual evoked potentials, brain stem auditory evoked potentials and somatosensory evoked potentials].

This study consists of 45 patients with clinically definite MS, laboratory supported definite MS and clinically probable MS. We compared MEP results with other multimodal evoked potentials (VEP, BAEP and SEP). The abnormal rate of MEP was 87.6%, which was the highest. Abnormal MEP showed prolonged central motor conduction time (CMCT), consistent with pathological change of the demyelination. There was a evident correlation between the abnormal MEP and VEP, which is consistent with the most common MS (Devic Syndrome) in our country.

Adolescent↗