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PubMedDate not supplied

Effect of check size on the pattern reversal visual evoked potential.

Modifications of the components of pattern-reversal visual evoked potentials (PR-VEP) with changes in check size of the stimulating pattern were studied in 11 healthy subjects. We made use of 8 different check sizes ranging between 10 and 90 min of arc. Changes in the check size modified in different manners the latencies and amplitudes of N75, P100 and N145. Two-step statistical analyses using the polynomial regression analysis method revealed significant modifications of latencies of the 3 components, but non-significant modifications of the amplitudes, except for N75. The latency and amplitude of N75 showed a significant inverse linear relationship with the logarithm of the check size, while the P100 and N145 latencies showed significant curvilinear relationships, with minimal latencies at check sizes around 35 min. These findings suggest different physiological properties of N75 from those of P100 and N145, and hence, the necessity to establish normal values for each check size of stimulation, for application in clinical studies.

Adult↗

PubMed1989

Visual evoked potential--a tool in the diagnosis of hepatic encephalopathy?

Visual evoked potentials (VEP) have been suggested to be of value in the diagnosis of subclinical and mild hepatic encephalopathy. In the present study, a comparison between VEP and four psychometric tests (number connection test A and B, digit symbol and word memory test) was performed in 42 cirrhotic patients, 17 of whom had clinical signs of encephalopathy. The results were compared to sex- and age-matched healthy controls. The VEP latencies for P2 (the second positive wave) and N3 (the third negative wave) were 11% and 26% longer (P less than 0.01-0.001) in the patients than in the controls. Moreover, the latencies for N2 (the second negative wave) and P2 were longer in the encephalopathic as compared to the non-encephalopathic patients (P less than 0.05). There was a significant correlation between the latencies for N2 and number connection tests A and B and digit symbol test. However, of the patients with clinical encephalopathy, less than half had VEP latencies longer than the mean +/- 2 S.D. above those for the controls. In contrast, none of the encephalopathic patients had normal results on the psychometric tests. This study demonstrates that although statistically significant differences exist between groups of cirrhotic patients and controls, VEP is not a reliable tool for the diagnosis of encephalopathy in the individual patient.

Adult↗

PubMed1999

Visual evoked potential interhemispheric transfer time in different frequency bands.

OBJECTIVE: Visual evoked potentials (VEP) have been used to estimate interhemispheric transfer time (IHTT). However, the complex wave of VEP is most probably formed by different generators of neural populations that act through different frequency channels. If the main peaks of VEP are established by different types of generators, which can also be connected to each other by a different type of callosal fibres, we would be able to estimate a wide range of various IHTT by measuring the latency between time-locked peaks of narrow band-pass filtered VEP. This research aimed to test this hypothesis. METHODS: Nine right-handed men were presented with a reversal of a checkerboard pattern as stimuli at RVF or LVF, and EEG was recorded at O1, O2, P3, P4. The grand-averaged VEPs were transformed to the frequency domain by means of the fast Fourier transform to obtain the amplitude frequency characteristics. Band-pass filters were chosen adequately, according to tuning frequencies indicated by clear peaks in the amplitude frequency characteristics. The chosen band pass filters (4-8 Hz, 8-15 Hz, 15-20 Hz, 20-32 Hz) were applied to the VEP of the subjects, and 4 different components of VEPs for each VEP were obtained. The latency of P100 and N160 of unfiltered VEP was measured. In the band-pass digital filter applied VEPs, positive and negative peaks, which are consistent with P100 and N160, were measured for each subject. Latency differences between hemispheres for digitally unfiltered and filtered VEPs were computed to estimate IHTT. RESULTS: In the different frequency bands, different IHTTs were estimated, ranging from 3 ms to 30 ms. Approximately 16 ms for theta band, 11 ms for alpha band, 6 ms for 15-20 Hz and 3 ms for 20-32 Hz bands were found. CONCLUSIONS: Our findings support the hypothesis which states that unfiltered VEPs provide us with only a rough estimation of IHTT. Also, they are consistent with anatomical findings that describe callosal fibres of varying dimensions, predicting various velocities between hemispheres.

Adult↗

PubMed1991

[Specificity of visual evoked potential alterations in Alzheimer's disease].

We have studied visual evoked potentials (VEP) in four groups: healthy young and aged subjects and aged patients suffering from depression or Alzheimer's disease (AD). In the flash modality, peak IV delay in AD patients as compared to aged controls corresponded to lengthened III-IV interlatency (IL). When AD and depressed patients were compared, peak IV delay in the former did not reach significance. Normal aging resulted in delayed peaks II and III, without IL modification. In the pattern reversal modality, no difference was observed between AD patients and aged, healthy or depressed controls. Aging delayed peaks P50 to P180. The abnormality exhibited by AD patients was specific to this group. However, the lack of significant difference between AD and depressed groups argues against the ability of VEP to differentiate those conditions.

Adult↗

PubMed2001

Aging of the chromatic onset visual evoked potential.

PURPOSE: To examine changes in the chromatic onset visual evoked potential (VEP) as a function of aging. METHODS: VEP's were measured in response to chromatic sinusoidal gratings (1.0 and 0.5 cpd), selectively chosen to modulate the L-M channel and S - (L+M) channel and presented in onset-offset mode. Responses to achromatic gratings presented in a reversal mode were also measured. Twenty subjects were tested, ranging in age from 21 to 93 years. RESULTS: Unlike changes observed earlier in life, the general shape of the chromatic onset wave-form changed little with age; however, latencies increased significantly as a function of age. Amplitude changes revealed a decreasing trend that was not statistically significant. There was little change in the achromatic responses with age. CONCLUSIONS: Our results demonstrate a systematic slowing of the chromatic onset VEP with age. The gradual nature of the latency changes and the lack of dramatic and complex wave-form shape changes may allow development of age-based normative data for use in clinical settings.

Adult↗

PubMed1997

Visual evoked potentials: a diagnostic test for migraine headache in children.

Visual evoked potentials (VEPs) were performed in a blind fashion in 114 children aged 3 to 17 years with different types of headaches, in order to investigate whether this could be helpful in the diagnosis of migraine versus other types of headaches in children. The study showed that the amplitude between P100 and N2 was significantly larger in children with migraine headaches (mean 19.8 microvol, SD 7.75) compared with other types of headaches (mean 13.1 microvol, SD 7.45). These results suggest that the sensitivity of VEP P100 amplitude to distinguish migraine headaches in children is 67%, the specificity of VEP is 83%, and the predictive positive value is 83%. VEP study might be helpful in work-up of a child with headache, particularly a young child, when signs and symptoms may not be characteristic.

Adolescent↗

PubMed1997

Visual evoked potentials for prediction of neurodevelopmental outcome in preterm infants.

Visual evoked potentials (VEPs) have proved to be accurate predictors of outcome in term infants with hypoxic-ischemic encephalopathy. Parallels between term asphyxia and hypoxic-ischemic injury in the preterm brain suggested the hypothesis that VEPs may predict the development of periventricular leukomalacia (PVL) and later cerebral palsy. 123 infants less than 32 weeks' gestational age were enrolled in the study. VEPs were done in the first 3 weeks of life (usually first week). VEPs did show a statistically significant association with PVL (p < 0.04) although false-positive recordings were twice as frequent as true-positive recordings. VEPs were not associated with grade III-IV intraventricular hemorrhage (p = 1.0). Unlike asphyxiated term infants, VEPs were not predictive of abnormal neurodevelopmental outcome in the preterm population.

Aging↗

PubMed1995

Visual alterations in de novo Parkinson's disease: pattern electroretinogram latencies are more delayed and more reversible by levodopa than are visual evoked potentials.

There are increased latencies of pattern-reversal visual evoked potentials (VEPs) and electroretinograms (PERGs) in Parkinson's disease (PD) patients who have not received therapy. This study aimed to evaluate whether these delays are present in the early stage of PD and whether they are dopamine-sensitive. The results show that both PERG P50 and VEP P100 latencies are increased (p < 0.0001) in a group of patients with de novo PD (13 subjects; 13.3 +/- 5.6 months' mean disease duration) before therapy in comparison with an age-matched control group (eight subjects). A larger latency increase (9.9% at the 47% contrast level and 7.8% at the 96% contrast level) was present in PERG recordings than in VEPs (6.2% at the 47% contrast level and 3.9% at the 96% contrast level). Levodopa therapy produced recovery of both PERG and VEP latency increases at both contrast levels, but only the PERG recovery at 47% of contrast was statistically significant. Before therapy, five eyes from PD patients showed no reproducible PERG at the 47% contrast level although the simultaneously recorded VEP was present. Both potentials were recordable in the same eyes at the 96% contrast level. During therapy, four of those five eyes showed a clear PERG even at the 47% contrast level. We conclude that, using an adequate midspatial frequency, both VEPs and PERGs are delayed even in the early stage of PD, and that PERGs are more sensitive if low contrast (47%) is used. The larger alterations, as well as the larger recovery during levodopa therapy, seem to correlate the PERG response more than the VEP response to dopaminergic transmission.

Aged↗

PubMed1997

Visual evoked potential guidance for posteroventral pallidotomy in Parkinson's disease.

Visual evoked potentials (VEPs) to photic stimulation of the eyes were used to identify the optic tract and thus determine the location of the globus pallidus internus (GPi) in eight patients with Parkinson's disease who then underwent posteroventral pallidotomy. Distinct waves appeared at 1 or 2 mm below the target (4 to 5 mm below the intercommissural line) and the amplitude significantly increased at 5 or 6 mm below, strongly suggesting that the electrode was in contact with the optic tract. In the medio-lateral direction, potentials were successively recorded in an area of 4 to 8 mm length, indicating the width of the optic tract. The trajectory at the mid point showed the most significant potentials which suggested the center of the optic tract. The site of the first lesion was placed 0 to 2 mm lateral to this trajectory and 5 mm above the point at which the amplitudes of responses increased. The actual lesion site significantly differed from the tentative target in a medio-lateral direction by 1 to 5 mm (mean 3.0 +/- 1.5 mm, n = 6). The Unified Parkinson's Disease Rating Scale score significantly improved and magnetic resonance imaging taken 2 or 3 weeks after the operation showed a lesion within the GPi in each patient. Recording of VEPs greatly facilitates accurate determination of the GPi.

Aged↗

PubMedDate not supplied

[Visual evoked potentials in children with congenital glaucoma].

Phasic and established visual evoked potentials (VEP) to homogeneous light field and chess patterns were studied in 25 patients (48 eyes) aged 1.5 months to 9 years with different stages of congenital glaucoma and in 114 age-matched healthy children. Patients with almost absolute and far progressed stages of the disease presented with gross changes of VEP to both large- and small-cell chess patterns. In patients with the initial stages of decompensated congenital glaucoma VEP to mostly large-cell chess patterns were altered. These data evidence the usefulness of examining the VEP to stimuli with low spatial frequency for the early detection of congenital glaucoma.

Age Factors↗

PubMed1991

Changes in the latency of the maximum positive peak of visual evoked potential during anesthesia.

The relationship between the latency of visual evoked potential (VEP) and the anesthetic concentration was investigated in surgical patients in order to examine the applicability of VEP in monitoring of the depth of anesthesia. The VEP was recorded with a standard EEG electrode from the midline parietal region in reference to both earlobes linked to the ground. An array of light-emitting-diodes mounted in opaque goggles was used to stimulate both eyes simultaneously and photic stimuli were delivered at random inter-pulse intervals with uniform distribution ranging from 2 to 5 seconds. Fifty trials of data were averaged to estimate that Pmax latency, i.e., the latent period from the photic stimulus to the maximum positive peak arising after 170 msec. Increases in the Pmax latency following the administration of anesthetics and restorations to preanesthetic values after recovery from anesthesia were found. A significant correlation was demonstrated between the Pmax latency and the inspiratory concentration of enflurane. The latency of the Pmax showed a drastic and a sensitive prolongation from about 200 msec in the awake state up to about 600 msec at the stage where the EEG exhibits large-voltage slow waves. Thus the measurement of the Pmax latency of VEPs was found to be useful for monitoring the depth of anesthesia.

Anesthesia↗

PubMed1988

The visually evoked potential in response to vernier offsets in infants.

The visually evoked potential (VEP) was recorded from infants (1 month 25 days to 13 months 3 days) in response to vernier offsets, motion displacements, and a stationary stimulus which served as a noise control. The records were analyzed by five masked adult observers familiar with VEP recordings using a signal detection method. The results suggest that a VEP can be recorded from infants in response to a vernier offset and the response resembles that obtained from adults tested with the same procedure. However, unlike adults, infants also showed a response to a motion displacement of the same magnitude suggesting that infants may not show the same specificity for the break in colinearity characteristic of the adult VEP.

Evoked Potentials, Visual↗

PubMed1986

Involvment of the visual evoked potentials in type I insulin-dependent diabetes.

The visual evoked potentials (VEPs) elicited by pattern stimulation were studied in a group of 62 type I insulin-dependent diabetics. The patients did not have retinopathy. An attempt was made to correlate the duration of the diabetes, insulin requirement, blood glucose and glycosylated hemoglobin with the VEPs. Our study showed that the VEPs of the diabetics have frequently delayed latencies. The VEPs elicited by small checks were more often involved. These stimuli excite the smaller nerve fibers and thus it appears that these fibers are the first to be compromised in diabetes. A positive correlation was found between the VEPs latency and the duration of the diabetes. No correlation was found with the other parameters considered.

Adolescent↗

PubMed1992

The pattern visual evoked potential and pattern electroretinogram in drusen-associated optic neuropathy.

Sixteen patients (29 eyes) with optic disc drusen were studied prospectively for clinical and electrophysiologic evidence of impaired optic nerve conduction. Abnormalities were detected in the following areas: visual acuity, eight (28%) of 29 eyes; kinetic visual field, 22 (76%) of 29 eyes; results of Farnsworth-Munsell 100-Hue test, 12 (41%) of 29 eyes; and flash visual evoked potential, 13 (54%) of 24 eyes. Simultaneous pattern visual evoked potentials and results of pattern electroretinograms were recorded. The P100 latency of the pattern visual evoked potential was prolonged in 41% of eyes. The P50 and N95 components of the pattern electroretinogram were also analyzed. The P50 amplitude was reduced in only four (17%) of 24 eyes. The most common abnormality was a reduction in amplitude or the absence of the N95 component in 19 (79%) of 24 eyes, reflecting ganglion cell dysfunction. The data support mounting evidence that the P50 and N95 components of the pattern electroretinogram have different retinal origins.

Adolescent↗

PubMed1997

Relative value of the inion and mid-parietal locations as additional recording sites in pattern reversal visual evoked potentials.

Although the P100 response of pattern reversal visual evoked potentials (PRVEPs) is most commonly recorded from the midline occipital site (MO), the response at this location can occasionally be absent or poorly defined due to anatomical variability of the visual cortex. In these cases, the American Electroencephalographic Society Evoked Potential Guidelines recommends recording from the mid-parietal (MP) and Inion electrode sites. In this study, we compared the amplitude of the P100 component recorded simultaneously from MO, MP and the Inion. PRVEPs obtained following stimulation with 30' check sizes from 155 consecutive patients (310 eyes) over a 2 year period were analyzed. At each of the 3 recording sites, the peak amplitude of P100 was calculated as N75-P100, P100-N145, and the sum of N75-P100 and P100-N145. There was a statistically significant difference between the electrode sites for all 3 methods of amplitude measurement (one-way ANOVA; P < 0.0001). For each method of measurement, there was no significant difference between P100 amplitude at MO or the Inon, but a significantly reduced amplitude at MP compared to both the MO and Inion electrode sites (post hoc Scheffe, P < 0.05). The P100 amplitude was highest at the Inion in 18% of responses, including cases where the amplitude at that site was at least twice that at MO. In no case was the amplitude highest at MP. Our results indicate that the Inion is a better recording site compared to MP when acquiring PRVEPs, is often complementary to MO, and should be the first additional site to be used when extra channels are available.

Adolescent↗

PubMed1981

Visual evoked potentials in occipital lobe lesions.

Recording of visual evoked potentials (VEPs) to pattern reversal is considered to be a reliable diagnostic procedure for examining patients with anterior visual pathway lesions (optic nerves and chiasm). Less consistent results have been reported in studies of more posterior lesions. The VEPs were recorded in 20 patients with occipital lobe lesions. A maximal VEP response (P94) was recorded at the scalp electrodes situated over the involved occipital lobes and contralateral to the hemianoptic visual field defect, indicating a positive correlation of unilateral occipital lobe lesions, homonymous visual field loss, and the VEP abnormality.

Adult↗

PubMed1997

Pattern reversal visual evoked potentials in classic and common migraine.

Pattern reversal visual evoked potentials (PVEPs) to transient checkerboard were recorded in 19 patients with migraine with visual aura (i.e., classic migraine), 14 patients with migraine without aura (i.e., common migraine) in the interictal period and 43 normal subjects. Latencies and amplitudes of PVEPs in each group were analyzed. In classic migraine patients, P100 amplitude was significantly higher than in normal subjects (p < 0.01), whereas latencies of PVEPs did not significantly differ. There were no significant differences between the common migraine and normal subjects, nor within the classic and common migraine groups in latencies and amplitudes of PVEP. Four patients with classic migraine underwent PVEPs during or 1-2 h immediately after their migraine attacks. Two of these patients who underwent PVEPs 1.5-2 h after their attacks showed abnormally increased PVEP amplitudes. These results suggest that there are different pathophysiologies in the visual pathway between classic and common migraine and furthermore, classic migraine patients in interictal periods may have hyperexcitability in the visual pathway and that the increased amplitude of PVEPs after attacks may be due to cortical spreading depression.

Adolescent↗

PubMed2002

Abnormal visual projection in a human albino studied with functional magnetic resonance imaging and visual evoked potentials.

The albino visual pathway is abnormal in that many fibres from the temporal retina project to the contralateral visual cortex. The visual projections in a human albino and a control have been investigated with fMRI and VEP during independent visual stimulation of both hemifields. Activity in the occipital cortex in the normal was contralateral to the stimulated visual field, whereas it was contralateral to the stimulated eye in the albino, independent of the stimulated visual field. Thus, the albino visual cortex is activated not only by stimulation in the contralateral visual field, but also by abnormal input representing the ipsilateral visual field. These novel findings help elucidate the nature of albino misrouting.

Albinism, Oculocutaneous↗