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Results for “Evoked Potentials, Visual”

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PubMed1995

Effects of bilirubin on visual evoked potentials in term infants.

UNLABELLED: To determine bilirubin-induced neurotoxicity, serial visual evoked potentials (VEPs) of 72 infants with neonatal hyperbilirubinaemia and 22 controls were evaluated and compared in four sessions for 8 weeks after birth. The levels of maximal serum bilirubin were found positively related to the wave latencies of first VEP. Within 8 weeks after birth, the wave latencies were significantly prolonged in infants in the severe and moderate groups than in the controls. The amplitudes of VEPs were apparently lower in severe and moderate groups than in the control group only in the 1st week after birth. At 1 year, 4 of the 18 infants in the severe group had poor motor skills and one had general hypotonia. CONCLUSION: These results suggest that bilirubin may affect the visual pathways, and that VEP is a useful adjunct to the neurological assessment of neonatal hyperbilirubinaemia.

Bilirubin↗

PubMed1985

Monoamine oxidase inhibition cannot account for changes in visual evoked potentials produced by chlordimeform.

Chlordimeform (CDM), a formamidine insecticide and monoamine oxidase (MAO) inhibitor, has recently been shown to produce large changes in visual evoked potentials of hooded rats (Boyes and Dyer, 1984a). Two experiments were performed to determine if the changes in evoked potentials were a result of the inhibition of MAO. In the first, the degree of inhibition of MAO in the brains of rats treated with chlordimeform (1.0-100 mg/kg, i.p.) was compared with that produced by pargyline (0.3-30 mg/kg, i.p.). Both compounds preferentially inhibited MAO-B, although MAO-A was substantially inhibited at larger doses. Pargyline was a relatively more potent inhibitor of MAO than chlordimeform, but not more efficacious. In the second experiment, pattern reversal evoked potentials (PREPs) and flash-evoked potentials (FEPs) were recorded from groups of rats after treatment with either saline, 0.4 mg/kg pargyline, 20 mg/kg pargyline or 40 mg/kg chlordimeform. The latter two groups were selected so as to have similar levels of inhibition of MAO, about 90% inhibition of MAO-B and 60% inhibition of MAO-A. The results showed a doubling of the amplitude of pattern reversal evoked potentials and increased latencies of the pattern reversal evoked potential and the flash-evoked-potentials in the chlordimeform-treated group, but no significant changes from saline control values in the pargyline-treated groups. These results confirm that chlordimeform is a MAO inhibitor at doses which produce behavioral and electrophysiological changes, but demonstrate further that the changes in visual evoked potentials produced by chlordimeform are not a direct result of the inhibition of MAO.

Amidines↗

PubMed2001

Electroencephalogram-based scaling of multifocal visual evoked potentials: effect on intersubject amplitude variability.

PURPOSE: The interindividual variability of the visual evoked potential (VEP) has been recognized as a problem for interpretation of clinical results. This study examines whether VEP variability can be reduced by scaling responses according to underlying electroencephalogram (EEG) activity. METHODS: A multifocal objective perimeter provided different random check patterns to each of 58 points extending out to 32 degrees nasally. A multichannel VEP was recorded (bipolar occipital cross electrodes, 7 min/eye). One hundred normal subjects (age 58.9 +/- 10.7 years) were tested. The amplitude and inter-eye asymmetry coefficient for each point of the field was calculated. VEP signals were then normalized according to underlying EEG activity recorded using Fourier transform to quantify EEG levels. High alpha-rhythm and electrocardiogram contamination were removed before scaling. RESULTS: High intersubject variability was present in the multifocal VEP, with amplitude in women on average 33% larger than in men. The variability for all left eyes was 42.2% +/- 3.9%, for right eyes 41.7% +/- 4.4% (coefficient of variability [CV]). There was a strong correlation between EEG activity and the amplitude of the VEP (left eye, r = 0.83; P < 0.001; right eye, r = 0.82; P < 0.001). When this was used to normalize VEP results, the CVs dropped to 24.6% +/- 3.1% (P < 0.0001) and 24.0% +/- 3.2% (P < 0.0001), respectively. The gender difference was effectively removed. CONCLUSIONS: Using underlying EEG amplitudes to normalize an individual's VEP substantially reduces intersubject variability, including differences between men and women. This renders the use of a normal database more reliable when applying the multifocal VEP in the clinical detection of visual field changes.

Adult↗

PubMed2000

A study of EEG, electroretinogram, visual evoked potential, and eye movements in classical lissencephaly.

EEG, flash electroretinogram (ERG), and visual evoked potential (VEP) findings are described in eight children with classical lissencephaly (six girls, two boys), with a mean age of 17.6 months (range 2 to 60 months). The EEG shows typically high-voltage activity. Eye movements were formally recorded in two patients, and both showed features associated with oculomotor apraxia. The ERG and VEP to flash stimulation were normal in all cases. Two subjects had pattern reversal stimulation, and their pattern VEPs were within normal limits. Some patients with lissencephaly may appear to have delayed visual maturation on first presentation, and EEG and eye movement studies are valuable in indicating neurological deficiency at an early stage in these subjects.

Apraxias↗

PubMed1992

Apparent accommodation in pseudophakic eyes as measured with visually evoked potentials.

We measured apparent accommodation with pattern reversal visually evoked cortical potentials in 27 pseudophakic eyes after the implantation of posterior chamber intraocular lenses. The patients ranged in age from 47-83 years. The amplitude of accommodation was not significantly different between pseudophakic eyes and normal phakic eyes. Apparent accommodation was inversely proportional to the pupillary diameter and was significantly correlated with corneal astigmatism. No significant relationship was noted between apparent accommodation and age of patients, corrected visual acuity, or refractive error.

Accommodation, Ocular↗

PubMed1989

[Pattern electroretinography and pattern visual evoked potentials in maculopathy: a comparison with sensory tests].

The retinal and cortical potentials for pattern reversal were recorded in 58 eyes of 30 patients afflicted with macular disease. The highest incidence of abnormality (79%) was found for the amplitudes P-ERG and P-VECP. Total field EOG and L-ERG were affected less frequently (41% and 25%). The P-ERG amplitude correlated significantly with the sensitivity of the central 10 degrees visual field (static perimetry). The P-VECP threshold check size showed a close correlation with visual acuity. Thus, the recording of pattern-evoked retinal and cortical potentials serves as a supplementary means of assessing types of maculopathy.

Adolescent↗

PubMed1994

[The comparative study of pattern visual evoked potential in the normal infants and adults].

This paper presents the pattern visual evoked potential (PVEP) results and comparative study between the two groups of 65 normal infants at the age of 3, 6, 9, 12 months and 18 normal adults. The different pattern spatial frequency stimulations (74', 25', 6') were given to the infants and adults. In the infant group, the latencies of P1 components of PVEP delayed significantly and amplitudes of PVEP decreased significantly between 74' and 6' spatial frequency with the spatial frequency of stimulation increasing. In the same spatial frequency stimulation, when 3 months infant group was compared with the 6, 9, 12 months infant and adult groups, the latencies of N1 and P1 waves showed significant difference, but no difference was found in the amplitudes of P1 wave. Our results might indicate that the visual function expressed by low, medium, and high spatial frequency in infants from 6 to 12 months could reach the level in adults, and in 3 months infants, not maturely develop.

Adult↗

PubMed1998

Steady-state visual evoked potentials to computer monitor flicker.

In the present study, steady-state visual evoked potentials (S-VEP) in response to amplitude-modulated light from a computer monitor (colour sVGA, 15-inch tube) have been examined. S-VEPs to computer monitors with different refresh rates (60 Hz or 72 Hz) and screen brightness (65 cd/m2 or 6 cd/m2) were recorded in 13 subjects with normal or corrected-to-normal vision. EEG samples were amplified, averaged and stored using Cadwell Excel EMG-EP recorder and a regression model was applied for the amplitude analysis. The mean values of S-VEP amplitude at 60 Hz were found to be significantly higher at 60 Hz refresh rate vs. 72 Hz (F1,12 = 14.1; P = 0.003). Effect of screen brightness (F2,24 = 6.5; e = 0.62; P = 0.00075) as well as the interaction effect of refresh rate and screen brightness (F2,24 = 11.6; P = 0.0003) were also found to be significant. Data obtained show that the characteristics of amplitude-modulated light from a computer monitor (frequency, brightness, waveform) are sufficient to elicit S-VEP, and the influence is not only restricted to the peripheral divisions of the visual system as it was shown earlier, but also extends to the central brain structures.

Adult↗

PubMed1998

Stimulus duration, neural adaptation, and sweep visual evoked potential acuity estimates.

PURPOSE: Results in several studies have suggested that the visual evoked potential (VEP) amplitude can vary with stimulus duration. The purpose of this study was to determine whether acuity estimates obtained by extrapolation of the sweep VEP are altered by this adaptation effect. METHODS: Sweep VEP data were obtained from 16 healthy observers under binocular viewing conditions. Data were acquired with a commercially available VEP unit using standard electrode recording techniques. Three sweeps (high spatial frequencies, medium spatial frequencies, and low spatial frequencies) were run. The subjects' visual acuity at the monitor distance was 6/6 for the high spatial frequency sweep. For the medium and low spatial frequency sweeps, the subjects were dioptrically blurred to 6/15 (medium spatial frequencies) or 6/30 (low spatial frequencies) at the monitor distance. Each sweep consisted of six spatial frequencies (contrast 80%; temporal frequency (TF) = 7.5 Hz; screen luminance = 100 candela [cd]/m2). For each spatial frequency, the stimulus duration was 8 seconds, partitioned into 1-second bins. A minimum of eight sweeps were obtained per subject. An acuity estimate was obtained for each second's data by fitting a line to the high spatial frequencies (excluding noise) and extrapolating this line to the x-axis. With this technique, estimates could not be obtained for 29 of 384 possible acuities. RESULTS: The sweep VEP acuities for the 16 subjects did not change significantly over the 8 seconds of data collection for the high, medium, or low spatial frequency sweep (repeated measures analysis of variance [ANOVA]: high, P = 0.25; medium, P = 0.50; low, P = 0.23). In any given subject, there was a 1- to 2-octave range in acuity estimates over the 8 seconds of stimulus presentation (high, 1.23+/-0.417 octaves; medium, 1.41+/-0.593 octaves; low, 1.52+/-0.475 octaves; mean +/- SD). CONCLUSIONS: These results suggest that there is not a significant change in sweep VEP acuity estimates over an 8-second stimulus presentation. Thus, neural adaptation does not significantly affect the clinical use of the sweep VEP.

Adaptation, Physiological↗

PubMed2000

[Monitor visual function with flash visual evoked potential during orbital surgery].

OBJECTIVE: To evaluate the feasibility and reliability of monitoring visual function with flash visual evoked potential (FVEP) during orbital surgery. METHOD: The visual function of 82 cases was monitored during orbital surgery with FVEP. Of these cases, the intraoperative and postoperative visual functions (IOVF and POVF) were compared. RESULTS: Sixty-nine cases were successfully monitored. Sixty-seven cases obtained the accordance of IOVF and POVF, and there were false positive in 1 case and false negative in 1 case. CONCLUSION: Intraoperative monitoring of visual function with FVEP can show the surgical injury of the optic nerve and unsuitable procedures, and decrease the surgical blind rate.

Adolescent↗

PubMed1993

Cerebral function analyzing monitor and visual evoked potentials as a noninvasive method of detecting cerebral dysfunction in patients with acute hepatic and renal failure treated with intermittent machine hemofiltration.

We monitored the effect of 7 intermittent machine hemofiltration treatments in 4 patients with fulminant hepatic failure who had progressed to grade IV coma and developed acute oliguric renal failure. Prior to treatment the processed EEG showed excess slow wave activity, and the latency of the later visual evoked potentials (N2 and P2) was delayed. Following treatment there was a further increase in both EEG slow wave activity and latency of the N1, N2, and P2 potentials. Intracranial pressure increased from a median of 8 mm Hg (2-12, range) to 14 (8-28) following treatment, p < 0.05. There was a correlation between intracranial pressure and all of the later visual evoked potentials, for N3 r = 0.71, for P1 r = 0.39, and P2 r = 0.74, all p < 0.05. Although there appeared to be a good correlation between intracranial pressure and the noninvasive electrophysiological recordings, there were major changes in intracranial pressure, cerebral perfusion pressure, and cerebrospinal fluid pH during the first hour of treatment, during which time there were no discernable changes in EEG or evoked potentials. In this study, non-invasive neurophysiological methods were not found to be reliable as invasive methods in assessing acute, minute-by-minute changes in cerebral metabolism but these methods may have a role in the longer term in assessing patient prognosis.

Acute Kidney Injury↗

PubMed1977

Binocular interactions in the human visual evoked potential after short-term occlusion and anisometropia.

The human visual evoked potential was recorded during 9 hr. of monocular occlusion or deprivation of fine detail by anisometropia. Some decrement in the response from the occluded eye was evident, but the major result was a sustained increase in the response from the nonoccluded eye. The anisometropic condition produced no decrement for stimulation of the deprived eye, but again there was an increase in the response from the nondeprived eye. Under some conditions the changes became apparent after only 6 hr. of deprivation. The data may be interpreted in terms of binocular competition or reciprocal inhibition at the level of the visual cortex or lateral geniculate nucleus.

Evoked Potentials↗

PubMed2005

Contrast response properties of magnocellular and parvocellular pathways in retinitis pigmentosa assessed by the visual evoked potential.

PURPOSE: To evaluate the contrast response of the visual system in retinitis pigmentosa (RP) under conditions designed to emphasize the parvocellular (PC) and magnocellular (MC) pathways. METHOD: Visual evoked potentials (VEPs) were measured in 10 patients with RP and in 10 age-equivalent control subjects with normal visual acuity and color vision, by using an array of isolated checks that were presented against a steady yellow background. The checks were modulated sinusoidally, either in isoluminant chromatic contrast (5.6 Hz), to favor the chromatic PC pathway, or in luminance contrast (5.6 and 11.2 Hz), to favor the MC pathway. Response amplitude and phase at the stimulus (fundamental) frequency were derived from Fourier analysis, and contrast response functions were fit with a Michaelis-Menten equation to derive R(max), the maximum response amplitude, and sigma, the contrast necessary to produce R(max)/2. RESULTS: In the control subjects, the mean amplitude function for chromatic modulation increased approximately linearly with increasing contrast, whereas the function for luminance modulation increased sharply at low contrasts and saturated at contrasts above approximately 30% for both temporal frequencies, as expected. The patients with RP showed primarily a reduction in R(max) with little change in sigma in all testing conditions. The reduction in R(max) was equivalent for chromatic modulation and luminance modulation at 5.6 Hz, but was substantially lower for luminance modulation at 11.2 Hz. CONCLUSION: Contrast processing was impaired within both the MC and PC pathways in these patients with RP, but the degree of impairment within the MC pathway depended on temporal frequency. These VEP results are in general agreement with recent psychophysical studies of contrast sensitivity losses in patients with RP, and further they characterize contrast processing deficits in these patients at suprathreshold levels.

Adult↗

PubMed1993

[The effects of ketamine, propofol and nitrous oxide on visual evoked potential during fentanyl anesthesia].

To evaluate the effects of ketamine, N2O, propofol on visual evoked potential (VEP) during fentanyl anesthesia, 14 patients undergoing transphenoid pituitary dissections were studied. Visual stimulation was done by using the goggles with red light diodes through closed eyelids and responses were recorded in one channel montage, Cz against Oz. The stimulus frequency was 1.9 flashes/sec. The VEPs were recorded from skin incision until the opening of the dura. For comparison, the preanesthesia to anesthesia values were determined. The ratio for N2 (N75) latency were 100.5 +/- 13.9% in ketamine group, 104 +/- 3.5% in N2O group, 100.5 +/- 4.2% in propofol group. The ratios for P2 (P100) latency were 97.45 +/- 5.7% in ketamine group, 101.9 +/- 3.5% in N2O group, 96.8 +/- 5.5% in propofol group. For N2P2 amplitude, the ratios were 36.3% +/- 31.4% in ketamine group, 138.5 +/- 58.0% in N2O group, 80.8 +/- 42.2% in propofol group. The percentage of inadequate recordings were 2.5 +/- 4.3% in ketamine group, 19.2 +/- 2.2% in N2O group and 20.6 +/- 16.0% in propofol group. The percentage of false positive results were 0 +/- 0% in ketamine group, 9.8 +/- 19.9% in N2O group, 12.7 +/- 13.2% in propofol group. Satisfactory anesthesia was achieved in all groups except for ketamine group which required additional medications for elevated blood pressure and intracranial pressure, and postoperative nausea and vomiting. It is concluded that there was great variability of VEP during anesthesia and surgery. Amplitude rather than latency changes were observed during anesthesia combined with fentanyl.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMedDate not supplied

Visual evoked potentials induced by illusory outlines (Kanizsa's square).

This report describes studies of visual evoked potentials (VEP) in ten subjects produced in response to Kanizsa's square and a control stimulus which did not involve a visual illusion but which had a similar spatial organization. The results showed that the amplitude-time characteristics of VEP depended on the illusory outlines. Differences in the parameters of VEP produced using the two stimuli were seen in the occipital, parietal, and temporal areas. VEP amplitude differences between the peaks of the N180 and P230 waves increased and the latent period of the N300 wave decreased on presentation of the illusory outlines as compared with the control stimulus. Interstimulus differences in amplitude were seen in the left and right occipital and left temporal areas, while differences in latency were seen in the left occipital lead. The data supported the suggestion that the visual perception system includes two areas encoding illusory outlines, which are associated with different aspects of visual analysis--encoding of individual signs and their complexes (O1 and O2) and comparing sensory codes with codes stored in memory (T5).

Adult↗

PubMed1984

Deliberate alteration of the visual evoked potential.

Seven out of 12 normal subjects could deliberately produce abnormal pattern-reversal visual evoked potentials (VEPs) which simulated disorders of the anterior visual pathways without detection. In six the mechanism was near-point accommodation and in one eccentric fixation. If voluntary suppression of the VEPs is suspected various modifications to the recording technique may be of value. These include the use of a large check size and stimulus field and binocular stimulation.

Adult↗

PubMed1981

Human visual system modulation transfer function measured by evoked potentials.

Visual potentials evoked by checkerboard pattern reversal were studied using temporal frequencies between 3 and 12 Hz (i.e. 6 and 24 reversal per sec, with sinusoidal or square wave modulation). Sinusoidal modulation evoked lower amplitude potentials than square wave modulation, at all frequencies used. Evoked potential amplitude vs temporal stimulation frequency curves for both modulations showed a maximum at approximately 4 Hz, with a slight decrease for lower frequencies, and a steep fall-off for higher frequencies starting at 7 Hz (values beyond 12 Hz were not measurable), unlike de Lange's psychophysical data. Accordingly, different brain generators are hypothesized for evoked potentials and psychophysical functions.

Brain↗

PubMed1985

Visual evoked potential correlates of laser flashblindness in rhesus monkeys I. Argon laser flashes.

The visual evoked potential (VEP) in four rhesus monkeys was used to assess the transient loss of visual function resulting from single 100-ms argon laser flashes (476.5 and 514.5 nm) whose energy levels did not exceed the maximum permissible exposure (MPE). VEP's were elicited by high-contrast square-wave test gratings which were phase-reversed at a frequency of 6 Hz, and were recorded using bipolar electrodes implanted in the foveal projection region of area 17. The parameters which were investigated included (1) flash size (focused vs. expanded), (2) position of the electrode's receptive field relative to the position of the flash (0, 1.5, 3.0, and 4.5-deg separation), (3) flash exposure level (50, 5.0, and 0.5% of the MPE), (4) peak wavelength of the test grating (454, 540, and 630 nm), and (5) spatial frequency of the test grating (1.0, 4.0, 6.0, and 12.0 c/deg). The results of the flash-size experiment revealed that the expanded flash, whose retinal diameter was approximately 750 microns, eliminated or severely attenuated the VEP for a longer duration than did the focused flash and also resulted in a more gradual recovery function. The combined results of the flash position and energy level experiments indicated that the effective energy of the focused flash declined rapidly beyond 1.5 deg, but still approximated 4% of its maximum value as far as 4.5 deg from its center. Few, if any, wavelength-specific effects were observed after exposure to either the 476.5- or 514.5-nm flashes, even when the energy of the flashes was reduced to a small fraction of the MPE. Finally, the flash effect was considerably longer in duration for the 12.0 c/deg grating relative to the low and intermediate frequency gratings. In general, the findings suggest that the focused and expanded argon laser flashes produce a VEP suppression whose time course and other characteristics correlate well with those associated with behaviorally observed flashblindness in humans after exposure to intense noncoherent flashes.

Animals↗