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Results for “Evoked Potentials, Visual”

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PubMed1989

[Inter-individual variability of mean latencies in the dynamic topography of short latency visual evoked potentials and the origin of brainstem potentials evaluated by the dipole tracing method in normal subjects].

To determine the normal pattern of the short latency visual evoked potentials (SVEP) in clinical diagnosis, in a previous report, the normal responses were classified into the following three types: uniform type, brainstem dominant type and occipital dominant type, according to the strength of the potentials. In the present report the latencies of N40 and P50, which constitute the SVEP, were investigated. In addition, the burst origin of these potentials was investigated using the dipole tracing method for P50 obtained through dynamic topography. Optic nerve potentials of N40 appeared first in the anterior region (from 37.1msec to 40.4msec following the stimulus) after the fourth retinal oscillatory potentials and soon extended to the posterior region (after about 2msec). This potential appeared in approximately about 65%, because of the low amplitude. P50 appeared 45.8-53.6msec after the stimulus about 100% and burst 2-4 times in the same place. Using the dipole tracing method, the origin of P50 was estimated to the near the deep center of the brain, probably around the brainstem. The same results were obtained using dynamic topography.

Adult↗

PubMed1987

First-order Wiener kernel visually evoked potentials obtained from multiple sclerosis patients.

Visually evoked potentials (VEP) were measured in multiple sclerosis patients with five sizes of reversing check stimuli. The VEPs were obtained using random binary sequence triggered check reversals. The random binary sequence was cross-correlated with scalp potential responses to obtain the estimates of the linear response of the system. For each evaluation a series of five VEPs, one for each of five check sizes, was done. A correlation coefficient was calculated to evaluate check size versus amplitude of the major negative wave. A tabulation was made to compare Snellen chart visual acuity with these correlation coefficients. For the eyes with a Snellen acuity of 20/20, 63% of the VEP amplitudes increased as the check size was decreased with correlation coefficients of -0.6 to -1. For the eyes with a Snellen acuity of 20/70 or less the amplitude decreased with the check size decrease, showing a correlation coefficient of +0.6 to +1 in 45% of the evaluations. The check size giving the largest amplitude was also tabulated with respect to the visual acuity, but did not appear to have as strong a relationship to visual acuity.

Evoked Potentials, Visual↗

PubMed2001

Application of visual evoked potentials for preoperative estimation of visual function in eyes with dense cataract.

PURPOSE: To determine whether the temporal frequency characteristics of the visual system as determined by visually evoked potentials (VEP) can be used for a preoperative estimation of the visual function in eyes with cataracts. METHODS: Light stimuli driven by a pseudorandom binary sequence (PRBS) of 40950 ms duration were presented and EEG recordings were made from 13 control and 20 patients with cataracts preoperatively and 1 week after cataract operation. The first kernel of the PRBS-VEP was obtained as the first-order cross-correlation function between PRBS and PRBS-VEP. The Fourier transform of this function was used as the temporal frequency characteristic (TFC). RESULTS: The mean +/- standard deviation of the latency and amplitude of the VEP in normal controls were 110.8+/-4.3 ms and 2.01+/-0.67 microV, respectively. A high correlation (r>0.7) between the pre-and postoperative VEP waveform was obtained in 13 eyes (65%), and 14 eyes (70%) in the VEP-TFC curves. The sensitivity of the examination was 73%, 27%, and 91% for the latency, amplitude and TFC of the VEP, respectively. The specificity of the examination was 67%, 100%, and 89% for the same measures. Eleven of 12 eyes with abnormal TFC preoperatively showed retinal or optic nerve lesions postoperatively. False-negative results were seen in cases with delayed corneal edema. CONCLUSION: Postoperative visual function of patients with cataracts can be predicted by preoperative measurement of the TFC obtained by PRBS-VEP.

Adult↗

PubMedDate not supplied

The sequential processing of visual motion in the human electroretinogram and visual evoked potential.

Mechanisms of motion vision in the human have been studied extensively by psychophysical methods but less frequently by electrophysiological techniques. It is the purpose of the present investigation to study electrical potentials of the eye (electroretinogram, ERG) and of the brain (visual evoked potential, VEP) in response to moving regular square-wave stripe patterns spanning a wide range of contrasts, spatial frequencies, and speeds. The results show that ERG amplitudes increase linearly with contrast while VEPs, in agreement with the literature, show an amplitude saturation at low contrast. Furthermore, retinal responses oscillate with the fundamental temporal stimulus frequency of the moving pattern while brain responses do not. In both the retina and the brain, the response amplitudes are tuned to certain speeds which is in agreement with the nonlinear correlation-type motion detector. Along the ascending slopes (which means increasing amplitudes) of the tuning functions, the ERG curves overlap at all spatial frequencies if plotted as a function of temporal stimulation frequency. The ascending slopes of the tuning functions of the VEP overlap if plotted as a function of speed. The descending slopes (which means decreasing amplitudes) of the tuning functions show little (ERG) or no (VEP) overlap and the waveforms at high speeds approach pattern-offset-onset responses. These observations suggest that in the retina motion processing along the ascending slopes of the tuning curves takes place by coding the temporal stimulation frequency which depends on the spatial frequency of the moving pattern. In the brain, however, motion processing is by speed independent of spatial frequency. Simple calculations show that the VEP information is decoded from the ERG signal into a speed signal.

Contrast Sensitivity↗

PubMed1998

[The usefulness of visual evoked potentials for the evaluation of visual pathways in children and adolescents with selected neuro-ophthalmological syndromes. (Summary of the doctor of medicine degree dissertation)].

OBJECTIVES: Much study and care have been devoted to evaluated lesions of the visual pathway in children and adolescents with different neuroophthalmological disorders. The aim of the study was to determine the usefulness of visual evoked potentials (VEP) for evaluation of visual pathway in young patients with cerebral palsy, sclerosis multiplex and subacute sclerosing panencephalitis. MATERIAL AND METHODS: During the research 63 healthy children and 78 pathological ones, between 5 and 18 years of age, were studied. First ophthalmological examination was performed and next VEPs were recorded. For poorly cooperative children, a flash on TV screen was used as a stimulus, and for normal mental children a pattern-reversal black and white checkboard was used. The comparison of VEP in normal healthy subjects and pathological ones was the last part of the investigation to evaluate visual system of patients. RESULTS: In all groups of patients, both with visual complains and without them, pathological results of VEP were found. The pathology of VEP were connected with shape, amplitudes and latencies of the peaks N75, P100, N145. CONCLUSIONS: The VEP is a good and objective method of diagnosis in neuroophthalmological patients, which supplies extra information about lesions of visual pathway. It allows to detect subclinical lesions. It is a noninvasive and painless diagnostical method and it can be repeated a few times in various periods of illness and even in poorly cooperative patients.

Adolescent↗

PubMed1982

Measurement of visual evoked potential in the asphyctic fetus and during neonatal survival.

Visual evoked potentials were measured in eight exteriorized near-term fetal lambs prior to and during 8 minutes of asphyxia and during 1 hour of newborn survival. Four of the lambs were then extubated, and measurements were continued while the lambs were observed for behavior and gross motor function. Early in the asphyctic period, marked changes in the visual evoked potential occurred in association with a fall in Po2, whereas during the postexposure period the visual evoked potential appeared to recover independently of cardiovascular or arterial blood gas values. Moreover, early wave components of the visual evoked potentials were more resistant to asphyxia than were later components and responded more quickly to resuscitative efforts. During the survival period the visual evoked potential did not correlate with gross motor function when animals were exposed to moderate acidosis. After severe acidosis abnormal visual evoked potentials were seen during periods of clinical deterioration.

Acidosis↗

PubMedDate not supplied

Dichoptic luminance beat visual evoked potentials in the assessment of binocularity in children.

Direct evidence of a distinct cortical binocular pathway has been provided by the production of nonlinear (difference) beats from dichoptic luminance stimulation in stereonormal adults and the absence or diminution of these beats in stereoblind subjects. We have investigated a clinically useful application of this technique in a pediatric population with potentially abnormal binocular vision. We recorded dichoptic luminance beat visual evoked potentials (VEPs) from 20 children (ages 7 months to 8 years) with abnormal binocular ability secondary to strabismus and/or amblyopia and compared this to a control group of 20 children with normal binocularity. Stereoblind children generated significantly lower dichoptic signal-to-noise ratios than stereonormal children (P < .001). Responses to monoptic multifrequency flicker were not significantly different between the two groups (P = .936). This dichoptic VEP can be performed quickly and easily on young children and gives a quantitative assessment of cortical binocularity that may not be determinable by standard clinical methods. This technique may also prove useful for the preoperative gradation of binocular potential and prediction of postoperative binocular fusion.

Amblyopia↗

PubMed1998

[Visual evoked potentials and static perimetry in functional visual deficits].

The author presents application of visual evoked potentials and static perimetry in hysterical amblyopia, psychical blindness, malingerers, amblyopia, cortical blindness and visual acuity assessment in infants. The author emphasizes the influence of multiple factors on the results and interpretation of the examination.

Evoked Potentials, Visual↗

PubMed1980

Evoked potentials and contingent negative variation during treatment of multiple sclerosis with spinal cord stimulation.

Cervical somatosensory evoked potentials, brainstem evoked potentials, visual evoked potentials, and the cerebral contingent negative variation were recorded in patients with definite multiple sclerosis before, during, and after spinal cord stimulation. Improvements were seen in the cervical somatosensory and brainstem evoked potentials but neither the visual evoked potential nor the contingent negative variation changed in association with spinal cord stimulation. The results indicate that spinal cord stimulation acts at spinal and brainstem levels and that the clinical improvements seen in patients are caused by an action at these levels rather than by any cerebral arousal or motivational effect. The evoked potentials were not useful in predicting which patients were likely to respond to stimulation.

Brain Stem↗

PubMed2003

Acuity, ophthalmoscopy, and visually evoked potentials in the prediction of visual outcome in infants with bilateral optic nerve hypoplasia.

PURPOSE: To determine whether Teller Acuity Cards, transient visually evoked potentials (VEPs), and optic disc size estimated from ophthalmoscopy were predictive of acuity outcome in infants and young children with bilateral optic nerve hypoplasia (ONH). METHODS: Twenty-eight infants (mean age, 7 months) with bilateral ONH underwent clinical assessment, including ophthalmoscopy. All but a few of these patients underwent neuroimaging studies, analysis of transient VEPs to multiple stimuli, and repeated acuity assessment. Acuity outcome was assessed, on average, 28 months later. RESULTS: Acuity outcome was significantly correlated with the estimated optic disc diameter, initial acuity, and VEP signal-to-noise ratios (r = 0.80, 0.71, 0.69, respectively; all P <.001). Multiple regression analysis showed that the initial acuity and estimated optic disc diameter accounted for 73% of the variation in acuity outcome. VEPs to white-black gratings segregated infants by 6 months of age, whose acuity outcome was better or worse than 5.6 cycles/degree (20/100). CONCLUSIONS: Acuity outcome was predicted in infants with bilateral ONH with a linear equation using initial acuity and estimated optic disc diameter. Additionally, analysis of VEPs may segregate infants with a good visual outcome from those with a poor visual outcome. Longer follow-up will be necessary to determine final Snellen acuity.

Child, Preschool↗

PubMed2001

Pattern visual evoked potential in the diagnosis of functional visual loss.

OBJECTIVE: To study the pattern visual evoked potential (P-VEP) in the diagnosis of functional visual loss. STUDY DESIGN: Retrospective study of observational case series. PARTICIPANTS: Seventy-two subjects whose best corrected visual acuity (VA) was 20/50 or worse, with or without visual field defect, and whose visual abnormalities could not be explained by the findings of ophthalmologic and neurologic examination were included in this study. MAIN OUTCOME MEASURES: To compare the P-VEP estimated acuity to the initial subjective VA and to the best-performed VA. RESULTS: Seventy-two subjects with functional visual loss had normal P-VEPs. The initial subjective VA was 20/50 in 9 subjects and < or =20/200 in 42 subjects. After clinical examination and reassurance, the best-performed VA was > or =20/50 in 53 subjects and < or =20/200 in 8 subjects. The discrepancy between the P-VEP estimated acuity and the best-performed VA was less than 3 lines of Snellen acuity in 63 of 72 (87.5%) subjects and more than 4 lines in 6 subjects. These six subjects were three women with loss of vision of unknown origin and three men with injury-related visual loss. CONCLUSIONS: P-VEP has the advantage of objectively predicting VA and is a useful test in the diagnosis of functional visual loss.

Adolescent↗

PubMed2004

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

We examined the effects of inter-modal attention and mental arithmetic on Humphrey visual field sensitivity and multifocal visual evoked potential (mfVEP) amplitude. Four normally sighted subjects (ages ranging from 24 to 58 years) participated in this study. Monocular visual field sensitivity was measured under two conditions: (1) standard testing condition and (2) while the subject performed a Paced Auditory Serial Addition Task (PASAT). Monocular mfVEPs were recorded in response to a 60-sector stimulus. The checkerboard pattern in each sector was contrast reversed according to a binary m-sequence. mfVEPs were recorded under two conditions: (1) standard testing conditions and (2) while the subject performed a PASAT. We found that, when compared to the no-task condition, all subjects had locations of significantly reduced Humphrey visual field sensitivities when performing the PASAT. In contrast, there were no significant decreases in mfVEP amplitude in any sector for any of the subjects while performing the PASAT. Our findings indicate that divided attention and ongoing mental processes did not affect the mfVEP. Therefore, the mfVEP provides an objective measure of visual field function that may be useful for some patients with unreliable automated static perimetry results.

Adult↗

PubMedDate not supplied

The development of auditory and visual evoked potentials in early treated phenylketonuric children.

Brain-stem auditory evoked potentials (BAEPs) and flash visual evoked potentials (F-VEPs) were gathered from 8 early treated phenylketonuric (PKU) children in a prospective longitudinal investigation during the 1st to the 12th months after birth. No consistent differences were found in the wave morphology of evoked potentials in PKU children from that of age-matched controls. Studying the latency of some components showed that in BAEPs, wave I latency was similar to control values for the whole year, but that the I-V interpeak mean latency (I-V IPL) was always significantly longer than in controls. In F-VEPs wave N1 latency was significantly longer than in controls only at 1-2 months of age, but returned to control values at 3-4 months (when all children were on dietary therapy) and remained in this range up to the 12th month. The mean latency of the P2 wave of flash VEPs was always significantly longer in PKU children than in controls. These results show that relevant alterations in evoked potentials may be found in PKU children several months after starting dietary therapy. This suggests that information processing in the brain may be impaired for a long time, due to abnormal metabolic conditions between birth and the onset of dietary therapy.

Brain↗

PubMed1999

Brainstem auditory and visual evoked potentials in children with protein-energy malnutrition.

BACKGROUND: To determine the effects of malnutrition on the developing brain with brainstem auditory evoked potentials (BAEP) and flash visual evoked potentials (fVEP). METHODS: The BAEP and fVEP of 11 kwashiorkor (8 +/- 1.56 months) and 10 marasmus (7.9 +/- 1.27 months) patients and 10 healthy control subjects (7.65 +/- 0.82 months) were recorded and the measurements were compared with each other in relation with plasma total protein and albumin levels. RESULTS: There were no differences between the mean latencies of the waves I, II, III and IV and mean interpeak latencies (IPL) of the waves I-III of the BAEP and the wave IV (N2) of the fVEP between the three groups. Mean latency of the wave V and mean IPL of the waves I-V and the waves III-V were significantly different between the three groups. The kwashiorkor group had significantly longer mean latency of the wave V than the marasmus group on the right ear and the control group on the both of the ears. The kwashiorkor group had significantly longer mean IPL of the waves I-V than the marasmus group on the right ear and than the control group on the left ear. The kwashiorkor group had also significantly longer mean IPL of the waves III-V than the control group on the left. CONCLUSIONS: The BAEP and fVEP are non-invasive electrophysiologic methods reflecting the integrity or disruption of the central neurologic pathways. The present results confirm the disruption of the central nervous system with the BAEP in children with protein-energy malnutrition, especially in kwashiorkor patients.

Analysis of Variance↗

PubMed1978

Visual evoked potential in man: early oscillatory potentials.

Short latency visual evoked oscillatory potentials to bright light stimulation were recorded from the scalp of 15 normal human adult subjects. The onset latencies of these potentials recorded over anterior frontal and posterior scalp regions were 9--17 msec and 13--24 msec, respectively. The frequency of the oscillations was about 100 c/sec. These potentials were widespread in their distribution over the scalp but were most prominent at midline and parasagittal recording locations. Like similar potentials recorded in animals, it seems that these potentials arise in both subcortical and cortical visual structures. The mechanism underlying the generation of these potentials and their possible functional significance are discussed.

Adolescent↗

PubMedDate not supplied

Left-right asymmetry of visual evoked potentials in brain-damaged patients: a mathematical model and experimental results.

The left-right asymmetry in the potential amplitude on the scalp was studied in poststroke patients by using flash visual evoked potential (VEP) and a numerical two-dimensional model of the head. The left-right asymmetry of the VEP was measured in three patients after thrombosis, in one after hemorrhage, and in one healthy subject. The numerical model used computed tomography images to define the different compartments of the head. The volume conductor equation for the potential distribution created by a dipole source in the occipital region was solved numerically with use of a finite volume method. Left-right asymmetry was calculated with several values of conductivity of the damaged region. The experimental results revealed a negative asymmetry in the three patients after thrombosis (i.e., the potential amplitude over the ischemic hemisphere was smaller than that over the intact hemisphere), whereas, in the patient after hemorrhage, a positive asymmetry was found. Nonsignificant left-right asymmetry was found in the healthy subject. The numerical model revealed that the electrical conductivity of the damaged tissue has a major effect on the left-right asymmetry. Negative asymmetry, such as that found for patients after thrombosis, was obtained when the conductivity of the damaged region was greater than that of the brain, whereas positive asymmetry (hemorrhage patient) was obtained when that conductivity was smaller than that of the brain. This finding indicates that the left-right asymmetry in the scalp VEP of patients after brain damage may be a result of changes in the conductivity of the volume conductor (the ischemic region) between the source and the electrodes.

Cerebrovascular Disorders↗

PubMed1979

Visual evoked potentials in infants with hydrocephalus.

Visual evoked potentials to flash stimuli were recorded in 15 infants with hydrocephalus. All demonstrated increased latencies for the prominent positive component (P2) of the response, compared to the mean value for age-matched controls. In nine infants studied prior to and 1 week after shunt procedure, the P2 latency decreased.

Evoked Potentials↗

PubMed2004

Effects of visual contrast on visual evoked potentials and Doppler signal.

We studied visually evoked cerebral blood flow responses (VEFR) and visual evoked potentials (VEP) to different visual contrasts and analysed the relationship between them. The records were made from 35 healthy volunteers aged 38.6 +/- 10.1 years. The stimulus was a black-and-white checkerboard with visual contrasts (VC) of 1%, 10% and 100%. The VEFR were measured in the posterior cerebral artery using transcranial Doppler, and the VEP were recorded from the occipital leads. We found the relationship between visual contrast and VEFR (r = 0.79, P < 0.01) as well as between visual contrast and VEP (r = 0.71, P < 0.01). We also found moderate association between the VEP and the VEFR (r = 0.69, P < 0.01). The analysis of the regression slopes between two different age subgroups (P < 0.01) did not show a significant difference (P = 0.020). We concluded that a simultaneous recording of VEFR and VEP to visual contrasts could allow an assessment of neurovascular coupling in humans.

Adult↗