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Results for “Evoked Potentials, Visual”

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PubMed1993

Enhancement of visual evoked potentials by stimulation during low prestimulus EEG stages.

A new algorithm for averaging of visual evoked potentials (VEPs) is introduced and compared with the conventional method. The root mean square (RMS) values of the alpha and theta band EEG activities at the vertex 1-s preceding stimulus presentation were computed: stimuli were blocked during phases of high prestimulus activity. Stimulation was applied selectively during periods of low activity. Light stimuli of 1-s duration were given to twelve healthy, voluntary subjects. The main results were: (1) The averaged VEPs at the vertex showed an increase in the N1-P2 amplitude of about 35% in comparison to experiments with conventional stimulation. This increase was in the range of 25-30% when an ISI correction was taken into account. Frontal, temporal and parietal locations showed also increases of the N1-P2 amplitude in evoked potentials. (2) VEPs were also affected qualitatively depending on the frequency content of the prestimulus activity.

Adult↗

PubMed2005

[The study of the effect of the administration of mannitol on flash visual evoked potentials].

OBJECTIVE: To study the relationship between the change of N2 wave in flash visual evoked potentials (fVEP) and the intracranial pressure after the administration of mannitol. METHODS: Fifty-two patients with elevated intracranial pressure were chosen and are divided into two groups: the former (n = 32) were treated with mannitol, the latter (n = 20) were treated with mannitol and glycerol and sodium chloride injection. The latency and amplitude of N2 wave of fVEP was measured by NIP-200 noninvasive intracranial pressure apparatus before and after the 1st, 4th, 10th administration of mannitol. RESULTS: The latency of N2 wave began to reduce at 30 min after the injection of mannitol and was lowest at 2 h. At 4 h after the injection of mannitol, the latency of N2 wave increased but was still shorter than that before the injection of mannitol. The amplitude of N2 wave did not change significantly. The reduction of the latency of N2 wave after the administration of mannitol decreased with the multiple mannitol injection. The latency of N2 wave did not change significantly after the administration of mannitol when combined with glycerol and sodium chloride injection. CONCLUSION: The latency of N2 wave of fVEP changes after the administration of mannitol, which suggests that the change of the latency of N2 wave of fVEP can reflect the change of intracranial pressure.

Adult↗

PubMed1992

Visual evoked potentials after photostress in patients with primary open-angle glaucoma and ocular hypertension.

Visual evoked potentials (VEPs) were assessed in basal condition and after photostress in normal subjects, in subjects with ocular hypertension (OHT), and in subjects with primary open-angle glaucoma (POAG). The VEPs recorded in basal condition showed that in patients with OHT and POAG a latency of the P100 peak was higher than in controls. The amplitudes were reduced in POAG patients but not in OHT patients. In all eyes, the VEPs recorded 20 s after photostress showed an increase in latency and a decrease in amplitude. In the control eyes, the functional recovery was complete after 80 s. In the eyes with OHP and in the eyes with POAG, the parameters of VEP after photostress underwent greater changes than in the control eyes. VEPs were superimposable on the basal condition (recovery time) at 73.2 s in OHT patients and at 113.2 s in POAG patients. The longer VEP recovery time after photostress observed in OHT and POAG patients could be attributed to the reduced functionality of the outer layers or the inner retinal layers of the central retina, or both. This test may be useful in the clinical evaluation for early diagnosis of glaucoma.

Adult↗

PubMed1984

[Visual evoked potentials (VEP) in anesthesia and intensive care].

Methodological considerations and different stimulation techniques of visual evoked potentials (VEP) are described. VEP can provide information about neurological function during anaesthesia, surgery and in the unconscious patient after head injury. The feasibility of the method for intraoperative monitoring in neuro- and cardiac surgery and the influence of general anaesthetics and other contributing factors such as temperature, paCO2, pO2, part are discussed.

Anesthesia↗

PubMed1993

Electroretinogram and visual evoked potential in two siblings with adult form galactosialidosis.

We recorded flash electroretinograms (ERGs), flash visual evoked potentials (VEPs), pattern ERGs and pattern VEPs in two siblings with adult form galactosialidosis. The amplitude of b-wave was decreased in flash ERGs. The peak latency of flash VEPs was within normal range. The pattern ERGs and VEPs were nonrecordable. These results suggested the damage of retinal ganglion cell and inner nuclear layer in these cases.

Adult↗

PubMed1998

Pattern shift visual evoked potential screening for HBO2 in mild-to-moderate carbon monoxide poisoning.

Pattern shift visual evoked potential (PSVEP) N75 and P100 latencies were evaluated as an objective, widely available and rapid test of brain dysfunction in a group of 11 patients in the acute phase (first 6 h) of mild-to-moderate carbon monoxide (CO) poisoning. N75 and P100 latency results were compared to nearly simultaneously obtained standard CO Neuropsychological Screening Battery (CONSB). Patients were sought in whom treatment decisions concerning hyperbaric oxygen (HBO2) vs. normobaric oxygen (NBO2) might be difficult, and were excluded from the study if confounding variables existed for CONSB or PSVEP. N75 and P100 latencies were also obtained after completion of NBO2 or HBO2 therapies. Only one patient, judged clinically to have the mildest poisoning in the series, had significantly abnormal initial PSVEP latencies. This patient's simultaneous CONSB was normal and the abnormal PSVEP latencies failed to normalize post treatment with NBO2. PSVEP latencies were not found to be a sensitive screening tool for treatment decision making in a group of acutely CO poisoned patients where treatment decisions might be difficult.

Adolescent↗

PubMed1998

[Visual evoked potentials and electroretinogram in pediatrics. Concept methodology and clinical applications].

INTRODUCTION: Since the first visual evoked potentials were obtained in the early 1940s, many important technical advances have been developed helping to produce more correct responses. One of the most important has been the incorporation of computers in the 1960s. This allowed the improvement in the relation signal/noise and consequently the responses are much more reliables technically. Also the improvement in the stimulators and electrodes necessaries for this test. However, all this advances introduced the use of the physical and technical concepts and magnitudes that sometimes fall outside the strict field of the medicine. MATERIAL AND METHODS: Therefore we have divided this work into three very different parts. The first part is dedicated to remembering and defining a series of physical concepts and their usefulness in the obtention of VEPs and ERGs specially in the physical process witch the proper use are basic to attain correct responses. In the second part we will discuss VEPs and ERGs in pediatric patients under the age of two years., concentrating basically on the every day specific problems witch appear on treating young patients. Finally we will review briefly their most frequent clinical applications.

Child, Preschool↗

PubMed2000

Which ocular and neurologic conditions cause disparate results in visual acuity scores recorded with visually evoked potential and teller acuity cards?

PURPOSE: We investigated whether disparity between visually evoked potential (VEP) acuity scores and Teller Acuity Card (TAC) scores varied according to presence of ocular or neurologic conditions. METHODS: Charts from 175 children (mean age, 34.8 months; range, 3 to 158 months) referred for visual acuity testing were examined. All children had been tested with pattern-alternation VEP and TAC and had undergone a complete eye examination. VEP and TAC acuity scores were relative to age-expected acuity scores for each acuity test. The absence and degree of macular abnormality, retinal abnormality, optic nerve hypoplasia, optic nerve atrophy, cortical visual impairment, developmental delay, cerebral palsy, seizures, and nystagmus were noted. Analysis of variance models were used to determine whether differences between VEP and TAC scores varied according to the presence of specific deficits. Logistic regression analysis determined whether degree of specific deficits was associated with a greater chance of inconsistency between VEP and TAC scores (>0.3 log unit difference). RESULTS: Inconsistent scores were found in 48% of children. Developmental delay was associated with relatively poorer TAC than VEP score, and the chance of inconsistency increased with severity of developmental delay. CONCLUSIONS: Diagnosis-dependent variability exists between TAC and VEP scores. Therefore knowledge of the clinical picture is necessary in interpretation of VEP and TAC scores. It is not clear which test is more useful when a disparity exists, either from this or previous studies. When visual acuity is assessed longitudinally in a given child, then consistency in method for acuity assessment is important.

Aging↗

PubMed2000

Influence of disease duration on visual evoked potentials in migraineurs.

OBJECTIVE: To determine the possible influence of the duration of migraine on pattern-reversal visual evoked potentials. METHODS: An investigation was conducted in 49 patients with migraine without aura according to the International Headache Society criteria. Twenty-two of these patients had had migraine for 2 years or less (group 1), and the other 27 patients had had the disease for 10 years or more (group 2). The control group consisted of 17 healthy subjects. RESULTS: Comparison of the mean P100 latency and amplitude showed no significant difference among the groups. There was, however, a good negative correlation between age and latency (r = -0.59, P =.003) in group 1, but no such correlation was observed for group 2 or the control group. CONCLUSIONS: It was concluded that the duration of migraine has no influence on pattern-reversal visual evoked potentials and that the pathogenesis of early- and late-onset migraine may be different.

Adolescent↗

PubMed1992

Impaired visual evoked potential and primary axonopathy of the optic nerve in the diabetic BB/W-rat.

The spontaneously diabetic BB/W-rat has emerged as an important model system for somatic and autonomic diabetic polyneuropathy. In this study we examined visual evoked potentials and the presence of morphometric and structural changes in the optic nerve and the retinal ganglion cells and their afferent axons contained in the retinal nerve fibre layer. A six-month duration of diabetes mellitus was associated with significant increases in the latencies of the visual evoked potentials. The latency of the first positive potential showed a 44% increase, and that of the first negative potential was prolonged by 41%. No significant changes were demonstrated at any of the amplitudes. In the optic nerve mean myelinated fibre size was significantly reduced to 82% of control values, which was accounted for by a significant reduction in axonal size. Axo-glial dysjunction, a prominent structural defect of diabetic somato-sensory neuropathy in both man and diabetic rodents, was non-significantly increased in the optic nerve. In diabetic animals retinal ganglion cells displayed dystrophic changes. No such changes were observed in age- and sex-matched control animals. Proximal axons of the retinal nerve fibre layer showed an increase in dystrophic axons in diabetic BB/W-rats. Morphometric analysis of optic nerve capillaries revealed no abnormalities except for basement membrane thickening. The present data suggest that the diabetic BB/W-rat develops a central sensory neuropathy, characterized functionally by prolonged latencies of the visual evoked potentials and structurally by an axonopathy of optic nerve fibres.

Animals↗

PubMed1982

Pattern-reversal visual evoked potentials and retinal eccentricity.

The effect of stimulation of discrete areas of the retina on visual evoked potentials (VEP) was studied in 16 normal volunteers. The stimulus consisted of a constant luminance 2 degrees 18' field containing checks of 34'30' reversing at a frequency of 500 msec. The amplitude of the VEP was highest at the fixation point and inside the 2 degrees isopter. Rapid amplitude decrement was noted with stimuli located within the 2-4 degrees isopters. No identifiable response was obtained outside the 4 degrees or 6 degrees isopter with a 2 degrees 18' stimulus. VEP could, however, be elicited by increasing the size of the stimulus. The smallest size of a field required to evoke a detectable response also varied in relations to retinal eccentricity. Stimulation at 0 degree, 8 degrees and 14 degrees horizontal eccentricities with fields of a size estimated to activate an equivalent amount visual cortex produced VEPs of similar amplitude.

Electroencephalography↗

PubMed2001

Steady state visually evoked potential (SSVEP) topography in a graded working memory task.

The steady state visually evoked potential (SSVEP) elicited by a diffuse 13-Hz visual flicker was recorded from 64 scalp sites in 30 subjects performing a low and high demand version of an object working memory task. During the perceptual component of the task, the SSVEP amplitude was reduced at left and right parieto-occipital sites. During the hold or memory component of the task, the SSVEP amplitude exhibited a load-dependent increase at frontal and occipito-parietal sites, while the SSVEP latency exhibited a load-dependent reduction at central and left frontal sites. We suggest that SSVEP amplitude changes index cortical information processing modes in that perceptual processes are associated with an SSVEP amplitude reduction, while holding information in active short-term or working memory is associated with an SSVEP amplitude increase. We also discuss changes in SSVEP amplitude and latency in terms of changes in the behavior of cortico-cortico and thalamo-cortico loops that utilize cortical layer I. Such cortico-cortico and thalamo-cortical loops are also proposed to constitute a neurophysiological mechanism for holding information in working memory.

Adult↗

PubMed1980

Visual evoked potentials in normal subjects and patients with multiple sclerosis.

Visual evoked potentials (VEPs) by checkerboard pattern-reversal stimulation were recorded in 70 subjects aged 10--69 years and in 100 patients with definite, probable or possible multiple sclerosis (MS). Longer latencies and smaller amplitudes of the major positive component were found in male subjects, in old subjects and when the amplifier's band-pass was narrowed. Subjects 10--14 years old had longer latencies and higher amplitudes than mature adults. Based on findings in the normal material, the following three criteria were used in evaluating the recordings from patients: the latency, the side difference in latencies and the ratio of amplitudes between the two sides of the major positive component with various limits for the two sexes and different age groups. The incidence of abnormal recordings was 85% for all the patients, 100% in 50 patients with definite, 70% in 50 patients with probable or possible MS, 73% in patients who had a history of spinal symptoms only, 98% if they had and 74% if they had not experienced optic neuritis. The incidence of abnormal findings increased with increasing duration of symptoms. All patients with visual acuity below 0.67 had abnormal VEPs. The high incidence of abnormal recordings confirmed the value of the test in establishing the diagnosis, and suggested that the use of different normative values for sex and age may increase the diagnostic yield without increasing the number of false positive findings.

Adolescent↗

PubMed1985

Development of visual evoked potentials in neonates. A study using light emitting diode goggles.

We used a signal averager with light emitting diode goggles as the photostimulator to study the development of the visual evoked potentials in 40 normal neonates of between 23 and 42 weeks' gestation. All except two infants of less than 24 weeks' gestation had replicable visual evoked potentials. A negative peak of latency (mean (SD), 308 (21) msec) was present in all infants, but the development of the primary positive peak depended on maturity. Only infants of 37 weeks or more had a consistent positive peak of latency (mean (SD), 220 (22) msec). The practical simplicity and reliability of this technique has distinct advantages over previous conventional recording systems. Neonatal visual evoked potentials are shown to change with maturity.

Evoked Potentials, Visual↗

PubMed1993

[Visual evoked potentials and functional asymmetry in children with with different degrees of intellectual retardation].

Visual evoked potentials (VEP) to flash and patterned visual stimuli have been recorded from occipital and central brain regions in 7-8-year-old boys with normal intellect (20 cases), with mental retardation (15 cases) and with oligophrenia of a debile degree (27 cases). A significant elongation of late-component latency has been revealed in motor brain areas VEP in oligophrenia group compared to normal subjects. A negative correlation between P190 component latency of motor area VEP to patterned visual stimulus and general and non-verbal intellectual indices has been stated in full right-handed subjects with intellectual deficiency. Such a relation was absent in right-handed patients with left dominant eye.

Child↗

PubMed1991

[Visual evoked potential and relative afferent pupillary defect in patients with unilateral optic neuritis].

The relationships between relative afferent pupillary defect (RAPD) and visual evoked potential (VEP), visual acuity or visual field in 14 patients with idiopathic unilateral optic neuritis, were investigated during the period of recovery from an acute episode. Grading of RAPD into four steps mainly based upon an escape phenomenon in a swinging flashlight test, was used to determine the degree of RAPD. The degree of RAPD significantly correlated with a reduction in VEP amplitude, visual acuity and loss of central visual field, while it did not correlate with delay in VEP latency. These results suggest that RAPD is mainly related to the integrity of central vision, and that grading of RAPD, as well as a comparison of VEP amplitude between the affected and contralateral eyes, is useful for an objective evaluation of visual functions of the affected eyes in patients with unilateral optic neuritis.

Adolescent↗

PubMed1996

Visual evoked potential evidence for parallel processing of depth- and form-related information in human visual cortex.

This paper describes the first of two complementary studies designed to identify and to investigate the properties and likely functional significance of independently generated components of scalp-recorded responses evoked by stationary patterns. These experiments compared the influence of various stimulus parameters, including site of stimulation, pattern form, nature of background field and several binocular and monocular depth cues on a single subject's visual evoked potentials. The results revealed the presence, inter alia, of two topographically distinct components with the following properties. The earlier component (C2), whose polarity depends on the stimulus location in the visual field, is: contour-specific; best evoked by discrete pattern elements, but not gratings, in the central few degrees of the visual field; insensitive to any depth cues. By contrast, the later (consistently) negative potential (LNP) is not dependent on the form of the stimulus and is larger for paracentrally (beyond 1.5 degrees) than centrally located stimuli. It is also selectively enhanced by both monocular and binocular depth-cue stimuli, including the simulated forward movement of a pattern relative to a steady textured background; a stimulus which evokes no C2. The respective response properties of these scalp potentials suggest that there is parallel processing of depth- and contour-related features of stationary stimuli in anatomically separate regions of the human visual cortex.

Cues↗

PubMed1981

Inherent characteristics of visual stimulus systems and their effect on the visual evoked potential.

The inherent stimulus characteristics of three common types of visual stimulus systems, based upon a slide projector, a television and a photic stimulator, were measured. The effect of these characteristics upon pattern visual evoked potentials (VEPS) elicited by the systems was also investigated. Considerable differences in both spatial and temporal luminance characteristics were found between the systems. The differences in spatial luminance properties produced no significant changes in the VEP waveform, but the temporal luminance properties of the television system, in particular, produced maleficent effects on the VEP. Methods of dealing with these problems and of overcoming some of the traditional disadvantages of a strobe stimulus are discussed.

Brain↗