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PubMed1990

[Visual evoked potentials in chronic Chagas-Mazza disease].

Both modalities of visual evoked potentials (VEP), flash (F) and pattern (P), were carried out in 17 patients with chronic Chagas disease. The patients included, between 21 and 65 years old, presented an evolution period of more than 7 years and a minimum of two positive serologies. Those patients with diabetes, alcoholism, leprosy, syphilis and degenerative diseases of the central nervous system, so as intoxications of different etiologies, and visual disorders detected through ophthalmological examination were discarded. Everyone was studied by means of routine clinical and complementary analysis, electrocardiogram, ophthalmological examination and specific analyses for the disease, like Machado-Guerreiro reaction, immunofluorescence and hemoagglutination tests. The VEP results showed alterations in the morphology of the record and a decrease of the potential amplitude in 35% of these patients. The electroneurophysiological alterations would suggest a correlation with anatomopathologic findings, that show loss of neuronal groups in autopsies of chronic Chagasic patients.

Adult↗
PubMed1996

Visual evoked potentials and dietary long chain polyunsaturated fatty acids in preterm infants.

The influence of dietary long chain polyunsaturated fatty acid (LCP) supply, and especially of docosahexaenoic acid (DHA), on evoked potential maturation, was studied in 58 healthy preterm infants using flash visual evoked potentials (VEPs), flash electroretinography (ERG), and brainstem acoustic evoked potentials (BAEPs) at 52 weeks of postconceptional age. At the same time, the fatty acid composition of red blood cell membranes was examined. The infants were fed on breast milk (n = 12), a preterm formula supplemented with LCP (PF-LCP) (n = 21), or a traditional preterm formula (PF) (n = 25). In the breast milk and PF-LCP groups the morphology and latencies of the waves that reflect the visual projecting system were similar; in the PF group the morphology was quite different and the wave latencies were significantly longer. This could mean that the maturation pattern of VEPs in preterm infants who did not receive LCP was slower. Moreover, a higher level of erythrocyte LCP, especially DHA, was found in breast milk and PF-LCP groups compared with the PF group. ERG and BAEP recordings were the same in all three groups. These results suggest that a well balanced LCP supplement in preterm formulas can positively influence the maturation of visual evoked potentials in preterm infants when breast milk is not available.

Breast Feeding↗
PubMed2006

Assessment of patients with suspected non-organic visual loss using pattern appearance visual evoked potentials.

BACKGROUND: The aim of the study was to validate the use of the short duration pattern onset visual evoked potential (PappVEP) in the objective assessment of visual acuity (VA) in patients referred with presumed non-organic visual loss. METHODS: The combination of minimum check size and minimum contrast required to elicit a consistently discernible PappVEP (amplitude >or=5 microV) were measured in ten normal subjects under conditions of induced optical blur (0 to +3 dioptres) and the relationship to Snellen VA established. The data from 100 consecutive patients (167 eyes) referred for possible non-organic visual loss (NOVL) and 20 patients with confirmed visual pathway dysfunction were reviewed in relation to the results in normal subjects. RESULTS: Snellen VA, under conditions of blur, could be predicted in normal subjects from the check size and contrast required to elicit a criterion PappVEP. These data were tabulated and a quantitative guideline established for the estimation of VA in the patients referred with suspected NOVL. Most (88%) patients referred with suspected NOVL had normal electrophysiology and PappVEPs consistent with normal Snellen VA. In others, they suggested a degree of non-organic overlay. In 20 cases of organic visual loss, PappVEPs were in close agreement with subjective VA. CONCLUSIONS: The short duration pattern onset visual-evoked potential is confirmed as a clinically useful tool in the objective assessment of patients with suspected non-organic visual loss.

Adolescent↗
PubMed1991

Visual evoked potential responses in pregnant women.

Sensory functions and their electrophysiological correlates have not been adequately documented during pregnancy. The present study reports visual evoked potential responses to pattern reversal (VEP-P) in ten third trimester pregnant women and changes in latency of NPN complex when compared with these responses in the non pregnant state. Visual evoked potentials were recorded from O1-A1 and O2-A2 scalp areas, using Ag/Agcl disc electrodes to transient pattern of black and white checkerboard with 32' size and reversal rate 1Hz. Two trials of VEP-P responses to 256 transient pattern stimuli given to each eye, were analysed and averaged by the computer of visual evoked potential recorder (MEB 5200 Nihon Kohden Japan). The latencies of various positive and negative waves, along with P1 amplitude, obtained in pregnant women, were compared with those obtained in ten non-pregnant women. The latencies of initial NPN complex (N1P1 & N2) were significantly reduced in pregnant women, indicating that pregnancy facilitates conduction process in the optic pathways.

Adult↗
PubMed1995

Visual evoked potentials in NIDDM: a longitudinal study.

In order to assess the possible progression of neurological abnormalities over time and the value of visual evoked potential alterations in predicting stability and severity of diabetes-related optic pathway disease, a longitudinal study in non-insulin-dependent diabetic patients was performed. Neurological examination, visual evoked potentials with pattern reversal, motor and sensory nerve conduction velocities and metabolic control were studied in 18 non-insulin-dependent diabetic patients and in 35 normal control subjects at baseline and again after 4.6 +/- 0.8 years (range 4-6). At the first recording the peak P100 wave latencies were significantly delayed in the diabetic patients compared with the control subjects; signs of peripheral neuropathy were detected in five patients, clinical in three and in two there was only neurophysiological alteration without clinical signs. The second recording revealed no significant alterations of P100 latencies in patients compared with baseline, but the number with clinical signs and/or neurophysiological alterations with no clinical signs of peripheral neurological disease was increased to seven. In conclusion, we observed that visual evoked potential alterations were stable over time whereas peripheral neurological disease progressed and correlated positively with metabolic control.

Case-Control Studies↗
PubMed2000

The hemispherical laterality of the visual evoked potentials during simple dot stimulus in normal human subjects.

We studied scalp visual evoked potentials (VEPs) during a simple visual attention paradigm using a dot stimulus, which was presented every 1600 ms, at the center of a screen. The visual attention paradigm consisted of three tasks: task R, task L and task N. The subjects were instructed to press a button either with the right hand (task R) or with the left hand (task L) after seeing the dot. They were also instructed just to look at a dot, without pressing the button (task N). We defined N1 as a negative wave with a latency of 50-130 ms, P1 as a positive wave with a latency of 110-150 ms and N2 as a negative wave with a latency of 130-210 ms. During task R, P1-N2 amplitude at T6 was significantly greater than that at T5. The N1-P1 and N2 amplitudes at O2 were significantly greater than those at O1. During task L, the waveforms at T6 and O2 were more clearly detected than those at T5 and O1. We conclude that there is a functional dominance of the right cerebral hemisphere in our simple visual reaction tasks.

Adult↗
PubMed1981

Abnormal visual-evoked potentials from eyes with optic nerve head drusen.

We evaluated 38 eyes (29 patients) with unilateral or bilateral optic nerve head drusen by means of visual field testing (static, tangent screen, and Goldmann perimetry), nerve fiber layer characterization (using red-free fundus photography), and flash visual-evoked potential testing. We found that 27 of 36 (75%) of the eyes with drusen had abnormal visual fields, 36 of 38 (94.7%) had abnormal nerve fiber layers, and 35 of 36 (97.2%) had abnormal visual-evoked potentials. The degree of abnormality on any one test did not reliably predict the results of either of the other two tests; however, there appeared to be an association between the visual-evoked potential aberrations and the retinal nerve layer deficits.

Adolescent↗
PubMed1985

Visual evoked potentials to lateralised stimuli in two cases of callosal agenesis.

Visual evoked potentials (VEPs) to lateralised light flashes were recorded from two acallosal patients. In one patient, these recordings were made while he performed a choice-reaction time task, and in the other patient the VEPs were obtained during a simple reaction time task. In both cases the patient's VEPs from electrode sites contralateral to the visual field of stimulus delivery resembled those of controls. Their VEPs from ipsilateral sites were aberrant, however, in that while control subjects showed a smaller and slightly delayed ipsilateral N160 component, this was not discernible in the patients' data. It is concluded that the ipsilateral N160 relies for its generation on the transcallosal transfer of information processed initially by the contralateral hemisphere.

Adult↗
PubMed1999

Global brain dynamics of transient visual evoked potentials.

The independent component analysis was applied to multichannel transient visual evoked potentials elicited by a high contrast pattern-reversal and motion-onset (motion velocity of 7 and 23 deg/s). Three overlapping independent components with different topographical distribution over the scalp were described. The first component displayed similar timing in response to all three stimuli (40-200 ms) but was a different in shape and scalp projection. This activation component is considered to reflect the stimulus properties. The second component (100-227 ms), related to negativity at about 160 ms, can be referred to visual processing of motion. The last component, attributed to positivity at 230 ms dominates in the fronto-central area and might represent a cognitive process.

Brain↗
PubMed1989

Pattern-reversal visual evoked potentials in normal 7- to 15-year-old twins: a correlation analysis.

Pattern-reversal visual evoked potentials (PRVEPs) were tested in 11 sets of monozygotic (MZ) twins and 22 sets of dizygotic (DZ) twins matched on age, sex and educational level. They ranged in age from 7 to 15 years. The PRVEPs of MZ twins exhibited a significantly greater degree of similarity than those of DZ twins. The peak latencies and amplitudes of PRVEP components obtained from MZ twin pairs were significantly correlated. The correlation coefficients for the peak latencies of the P2 (or P100) component were the only ones to differ significantly between the DZ twins of the same sex and DZ twins of opposite sexes. These coefficients, obtained using PRVEPs, were much greater than those obtained with flash visual evoked potentials.

Adolescent↗
PubMed1997

Temporal aspects of contrast visual evoked potentials in the pigmented rat: effect of dark rearing.

Cortical visual evoked potentials (VEPs) in response to gratings temporally modulated in counterphase were recorded in normal and dark-reared pigmented rats. Temporal modulation was either sinusoidal (0.25-15 Hz, steady state condition) or abrupt (0.5 Hz, transient condition). In normals, the amplitude spectrum of contrast VEPs has two peaks (at about 0.5 and 4 Hz) and a high temporal frequency cut-off of the order of 11 Hz. The VEP phase lags with temporal frequency, showing two different linear slopes for separate frequency ranges (0.25-1 Hz and 1-7 Hz) centred on the peaks of the curve. The different slopes correspond to apparent latencies of 500 and 136 msec, respectively. Dark rearing reduced the cut-off frequency by about 3 Hz and increased apparent latencies by about 42 msec in the low temporal frequency range and 30 msec in the high temporal frequency range. The latency of the first peak of transient VEPs was increased by about 47 msec. Results indicate that the frequency response of rat contrast VEPs is qualitatively similar to that of other mammals (including human), albeit shifted to a lower range of temporal frequencies. Dark rearing significantly alters the VEP temporal characteristics, suggesting that visual experience is necessary for their correct development.

Animals↗
PubMed1993

Motion-onset visual-evoked potentials as a function of retinal eccentricity in man.

Visual-evoked potentials were elicited by the motion-onset of a black-and-white square-wave grating of 2.4 cycles/deg that drifted from right to left at a velocity of 3 deg/s. The center of the 2 x 2 deg stimulus field was binocularly viewed either foveally or at eccentricities of 6, 12, or 20 deg in the lower visual field along the vertical meridian. Peak-to-peak amplitudes P1-N2 and N2-P2 were found to decrease non-linearly as a function of eccentricity. The VEP-amplitudes were standardized by setting each foveal value to 100%, and a relative measure was derived for peripheral values given by the ratio of the peripheral to the foveal values. The decrease of the relative VEP-values with eccentricity was significantly smaller than that of the relative cortical magnification factor of striate cortex in man, whereas it agreed fairly well with that of the relative point-image size of the area MT in Macaque monkey. In this respect, the motion-onset VEP is distinct from the pattern-reversal VEP, the amplitude of which decreases much more rapidly with retinal eccentricity; hence, it may involve different generating structures of the brain.

Adolescent↗
PubMed1981

Abnormal electroretinograms and visual evoked potentials in chronic papilledema using time-difference analysis.

Visual function is usually considered to be normal in papilledema. We report previously undescribed abnormalities in the electroretinograms (ERG) and visual evoked potentials (VEP) of two patients with chronic papilledema. The steady-state latencies of the ERG and VEP were calculated using time-difference analysis. The ERG was abnormal under both scotopic (slow) and photopic (fast) flicker conditions, but the VEP was abnormal only to fast flicker photopic stimulation. This may indicate a relative vulnerability of a high frequency signal system under conditions of raised intracranial pressure. The abnormalities resolved rapidly once the intracranial pressure had been normalised. The cause of the VEP and particularly the ERG abnormalities remains unknown.

Adult↗
PubMed1999

Giant visually-evoked potentials without myoclonus in the Heidenhain type of Creutzfeld-Jakob disease.

In a 64-year old woman with progressive visual impairment for 4 weeks, probable Creutzfeld-Jakob disease without myoclonus was diagnosed after rapidly progressive mental deterioration had also developed, and CSF and EEG showed characteristic findings. Pattern-reversal and flash visually-evoked potentials, recorded 5, 6, 7 and 8 weeks after onset, showed a maximum P100 latency of 210 ms, 8 weeks after onset, and a maximum N75/P100 amplitude of 33.1 microV, 5 weeks after onset. While the P100 latency progressively increased, the N75/P100 amplitude continuously decreased after reaching its maximum. In the Heidenhain type of Creutzfeld-Jakob disease giant visually-evoked potentials may be recorded during the early stages of the disease, even in the absence of myoclonus. Visually-evoked potentials may prove useful in diagnosing Creutzfeld-Jakob disease with atypical initial presentation.

Creutzfeldt-Jakob Syndrome↗
PubMed1984

Visual fatigue and visual evoked potentials in multiple sclerosis, glaucoma, ocular hypertension and Parkinson's disease.

Visual evoked potential (VEP) abnormality is widely used as an objective indication of visual pathophysiology in the diagnosis of multiple sclerosis. One major limitation of this test is that VEP abnormality is not specific to multiple sclerosis. In an attempt to explore ways of making the VEP test more specific, changes were measured in VEPs caused by superimposing upon the VEP stimulus either a flicker or a moving pattern. The rationale was to test for visual fatigueability, since it is known that some demyelinated axons fatigue rapidly. Of 10 patients with multiple sclerosis, 90% showed VEP fatigue, while none fatigued in the groups of 10 patients with glaucoma and 10 with Parkinson's disease. Fatigue is, however, not completely specific for multiple sclerosis, since three of 10 patients with ocular hypertension showed VEP fatigue.

Adult↗
PubMed2005

Simulated nystagmus reduces pattern-reversal more strongly than pattern-onset multifocal visual evoked potentials.

OBJECTIVE: In patients with nystagmus conventional pattern-reversal visual evoked potentials are severely degraded, while sizeable pattern-onset VEPs can often still be obtained. We tested whether this differential effect of retinal image motion on pattern-reversal and pattern-onset responses also applies to multifocal VEPs (mfVEPs). METHODS: In eight subjects with normal oculomotor behaviour and vision we recorded pattern-reversal and pattern-onset mfVEPs from an occipital electrode pair to 60 locations of a scaled dartboard-pattern, and to 64 locations of a uniform checkerboard-pattern. Subjects viewed the stimulus monocularly via a mirror, which was placed close to the eye and driven by a scanner with a 4 Hz sawtooth waveform at an amplitude of 2 degrees to simulate horizontal jerk nystagmus and of 0 degrees for the reference condition. RESULTS: For the scaled dartboard-stimulus we observed an eccentricity-dependent effect of induced retinal image motion on mfVEP responses: in the central visual field (0-0.5 degrees), pattern-reversal and pattern-onset responses were reduced by 73 and 42%, respectively. In the periphery (10-16 degrees), only pattern-reversal responses were reduced (by 27%), while pattern-onset responses were enhanced by 39%. Pattern-onset responses to the uniform checkerboard stimulus were enhanced by 17%, while pattern-reversal responses were reduced by 27%. CONCLUSIONS: Pattern-onset mfVEPs are more efficient than pattern-reversal mfVEPs, if retinal image motion is superimposed onto the stimulus. This is in close correspondence to previous reports on conventional VEPs. SIGNIFICANCE: This study demonstrates a differential effect of retinal image motion on pattern-reversal and pattern-onset mfVEPs and thus suggests stimulus conditions to enhance the efficiency of mfVEP recordings in patients with moderate nystagmus.

Adult↗
PubMedDate not supplied

Simultaneous pattern electroretinogram and visual evoked potential recordings in dyslexic children.

To help clarify the conflicting evidence of neurophysiologic abnormalities in children with reading problems (dyslexia), we examined pattern electroretinograms and visual evoked potentials to stimulation with checks of 24', 49' and 180', each at 5%, 42% and 100% contrast, in a group of dyslexic children and a group of normal (i.e., normally reading) children. Neurophysiologic difference between the groups was restricted to the visual evoked potential, which showed a significant prolongation of the P100 wave in dyslexic children at the highest contrast (100%) and the smallest checks (24'). There was no significant difference between normal and dyslexic children in the P50 and N95 pattern electroretinogram waves. These results support the assumption of a visual deficit in dyslexic children. However, they are not consistent with the evidence of an isolated deficit of the magnocellular function, which, theoretically, would cause more prominent visual evoked potential changes to lower contrast and the largest check stimuli.

Adolescent↗