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PubMed2004

Flash visual evoked potentials predict visual outcome in traumatic optic neuropathy.

PURPOSE: To determine the significance of flash visual evoked potentials (FVEP) in the evaluation of patients with traumatic optic neuropathy (TON). METHODS: Eleven head-injured patients admitted to our center were diagnosed with unilateral TON. For every patient, FVEPs were obtained in both the affected eye and the unaffected eye. The normal eye thus functioned as each subject's internal control. We determined the amplitudes of FVEP waveforms for each eye and calculated an amplitude ratio of the affected/normal side for all individuals. The best-corrected visual acuity was obtained for each eye 2 weeks after acute hospitalization. We then determined the relation between best-corrected visual acuity in TON and the FVEP amplitude ratio. RESULTS: In 4 patients in whom the amplitude ratio was at least 0.5, visual acuity in the affected eye was 20/30 or better. In 7 patients, the amplitude ratio was less than 0.5, and visual acuity in the eye with TON did not exceed 20/300 (Pearson r = -0.93, p = 0.0001). CONCLUSIONS: Flash visual evoked potentials are highly predictive of the degree of visual function in unilateral TON. Finding FVEP amplitudes that are at least 50% of the normal eye appears to be critical in anticipating good, long-term visual outcome.

Adolescent↗
PubMed2002

[Evaluation of the developing human visual system using flash-visual evoked potential].

Flash visual evoked potential (Flash-VEP) is easily recorded in preterm infants. However, its clinical application has not been established due to its great variability in response. Our longitudinal studies on the two components of the N1 wave facilitated peak definition and established normal ranges that are clinically valuable. The N1a (early component of the N1) peak latency decreases at about 4.6 msec/week between 30 and 40 weeks postmenstrual age. A flash-VEP study in the preterm period enables us to observe the neuronal development in the human visual system that normally proceeds in utero. Flash-VEP analyses on preterm infants demonstrated that the decrease in the N1a peak latency reflects the progress of myelination in the visual pathway according to the developmental program irrespective of preterm birth. The developmental changes of the N1 wave configuration reflect the maturation of the neuronal networks in the visual cortex, which is accelerated by extrauterine visual experience. Using improved methodology and peak denomination that we proposed, flash-VEP can be applied to preterm infants safely, and should provide us with neuro-developmental information of the human cerebrum.

Cerebral Hemorrhage↗
PubMed1980

Clinical uses of the visually evoked potential.

The visually evoked potential is defined and described. The development of this test as a valuable clinical aid is traced. Its assistance in the diagnosis of Lesions of the Optic Nerve and Visual Pathways is shown, together with its use and assessment of visual acuity and visual fields both in infancy and adults. Future developments of this test are reviewed.

Aged↗
PubMed1977

Clinical aspects of the visually evoked potential.

The visually evoked potential (VEP) was studied in normal and abnormal human subjects, and in Rhesus monkeys with central, paracentral, and peripheral photocoagulation lesions. A relatively simple protocol for clinical VEP testing is described. The monkeys showed similar VEP responses but these were smaller in amplitude than those obtained from human subjects. Central, but not paracentral or peripheral retinal lesions were associated with VEP abnormalities. For both monkey and human subjects, some variability of responses between normal and subjects was noted. Generally, there are differences in VEP responses obtained from the affected eye of abnormal subjects who had one eye which could serve as a control, as compared to responses from the normal eye. In these subjects as well as in subjects with two abnormal eyes, computer analysis of digitized VEP data from 10 Hz stimulus responses was performed. Fourier transformation analyses showed abnormalities which could be detected easily by evaluating the pattern of the amplitudes of the fundamental and first three harmonics. With this technique, it was possible to group correctly normal VEP's with eyes with normal visual acuity (greater than or equal to 20/30 or 0.67), and abnormal VEP's with eyes with poor visual acuity (less than 20/30 or 0.67) in 72% of cases. Analysis of the data obtained with 1 Hz and 10 Hz stimulation suggests that the components of the VEP related to visual acuity occur within the first 60-100 msec of the response, corresponding to the primary evoked response of Chiganek. The second, smaller wave of the response complex to 10 Hz flash stimuli corresponds to the primary evoked response, and is closely related to visual acuity. This was further supported in another series in which the digitized data was filtered around the stimulating frequency. It was possible to recognize visually this VEP waveform and subjectively interpret the record correctly in 85% of eyes with regard to visual acuity. Therefore, the clinician can "read" the VEP record in response to nonpatterned flash stimuli. This test was further validated in a series of patients with opacities of the ocular media, such as cataract, corneal scarring, and vitreous hemorrhage. VEP promises to become a procedure of diagnostic and prognostic value in ophthalmology.

Adolescent↗
PubMed1978

The effects of chiasmal compression on the pattern visual evoked potential.

The visual evoked potentials (VEPs) to pattern reversal stimulation (26' individual check subtense, 11 degrees total field) have been examined in 10 patients with proven chiasmal compression. Bipolar occipital-sylvian and occipital-parietal recordings were taken with electrodes placed according to the Modified Maudsley system. In all patients abnormalities, taking the form of latency delays or amplitude reductions, were found in response to monocular stimulation which, without exception, were maximal in the traces corresponding to the hemisphere contralateral to the field defect. In seven patients responses to a 13' pattern were also examined. In six of these the lateralisation of abnormality was enhanced. The discrepancy between these and previous findings is discussed, the importance of stimulus and recording parameters being stressed.

Adult↗
PubMed1982

Spectral analysis of visual potentials evoked by sine wave modulated light in migraine.

Visual evoked potentials to unstructured sine wave-modulated light were measured in 30 common migraine patients and 23 controls. The fundamental and the second harmonic components of the response were analysed separately in the frequency domain by power spectrum estimation. The absolute and relative powers of the fundamental component were significantly larger in the patients at 16-22 Hz stimulation both initially, in the onset phase, and later, in the steady-state phase, whereas those of the 2nd harmonic component were smaller in the later stages of stimulation. Significant difference occurred in the dynamics of the 2nd harmonic response between patients and controls. No significant difference was observed at 10 Hz stimulation.

Adult↗
PubMed2005

Multifocal visual evoked potential in nonorganic visual field loss.

OBJECTIVE: To evaluate the use of multifocal visual evoked potentials in the diagnosis of nonorganic visual field loss. METHODS: Five patients with unexplained visual field loss underwent full neuro-ophthalmic examination, Humphrey visual field testing, and multifocal visual evoked potential testing using the Accumap objective perimeter (ObjectiVision Pty Ltd, Sydney, Australia). RESULTS: In all 5 cases, the results of the ophthalmic examination did not correlate with the degree of visual field loss seen on Humphrey visual field testing. Multifocal visual evoked potentials testing showed essentially normal tracings. CONCLUSIONS: Multifocal visual evoked potentials may be useful in cases of difficult to prove functional visual field loss or in cases in which objective documentation of normal function is needed.

Adolescent↗
PubMed1997

Study of brain stem auditory-evoked potentials (BAEPs) and visual-evoked potentials (VEPs) in leprosy.

A study of brain stem auditory-evoked potentials (BAEPs) and visual-evoked potentials (VEPs) was done on 25 newly diagnosed patients with leprosy whose diagnosis was confirmed by skin biopsy. The results were compared with 25 age- and sex-matched healthy controls. In BAEPs the important observations were the prolonged latency of wave V in 13 (52%), delayed interpeak latency (IPL) of wave I-III in 5 (20%) cases, of wave III-V in 12/25 (40%), suggesting a conduction abnormality of the VIII cranial nerve in its peripheral part, in its nucleus and in its connection in the brain stem. In VEPs, a delayed peak latency of major positive potential (P100) was seen in 20 cases (80%; 11/13, 84.6% TT; 7/10, 70% LL; 2/2, 100% BL), suggestive of subclinical optic nerve involvement. The BAEPs and VEPs were both abnormal in 10 cases (40%; 3/13, 23% TT; 5/10, 50% LL; 2/2, 100% BL). Conduction abnormalities of the central nervous system (CNS) were observed more frequently in lepromatous leprosy, as in other forms of peripheral neuropathy such as hereditary motor sensory neuropathy type I (HMSN I). There is a fair possibility of similar multiple demyelinating lesions in the CNS also, as is seen in leprous peripheral neuropathy. This hypothesis requires further strengthening by an extensive study of multimodality evoked potentials with magnetic resonance imaging in the patients. Histopathological and immunofluorescent studies of autopsy material of the brain can also contribute significantly to solve the dilemma.

Adolescent↗
PubMed1985

Effect of gamma-vinyl GABA on human pattern evoked visual potentials.

We studied the effects on human visual evoked potentials of gamma-vinyl GABA, an anticonvulsant drug that increases cerebral levels of gamma-aminobutyric acid. The subjects were 15 epileptic patients undergoing a clinical trial of this drug. Serial recordings were made from each patient periodically for 1 year. The stimulus was a reversing checkerboard pattern with a check size of 50 minutes. Plasma levels of other antiepileptic medications remained constant throughout the study. No changes, other than a normal variation of +/- 5 msec, were observed in peak latency throughout the study. These results indicate that there are no GABA-ergic effects on the P100 component evoked by large checkerboard pattern-reversal.

Adult↗
PubMed2001

Spectral analysis of visual potentials evoked by pattern-reversal checkerboard in juvenile patients with headache.

Changes in visual evoked potentials, mainly affecting the amplitude of the major positive wave, are referred to by many authors and are related to the pathophysiological basis of primary headache. We performed both transient pattern-reversal visual evoked potentials and spectral analysis by means of fast Fourier transform of 8-Hz steady-state pattern-reversal visual evoked potentials in 34 children affected with migraine (14 with aura, 20 without aura), and compared them with 14 patients with tension-type headache and 10 healthy subjects. The amplitude of the response to the transient stimulation (P100) was higher and the latency shorter in the patients with headache compared with the controls, but the difference was not statistically significant. The absolute power of the first harmonic (1F) obtained by the spectral analysis of the steady-state stimulation was increased in all the patients with headache compared with the controls, and the increase was significant in patients with migraine. These data seem to confirm the hypothesis of abnormal processing of visual input in migraineurs and could be interpreted as neurophysiological support for the theory that different headache types are related conditions. Furthermore, the spectral analysis of steady-state pattern-reversal visual evoked potentials could be proposed as a test to diagnose migraine.

Child↗
PubMed1993

Visual evoked potentials and visual processing in stimulant drug-exposed infants.

Prenatal exposure to cocaine and amphetamines has been associated with many adverse effects in infants, including neurological abnormalities. Recent evidence shows that the visual system may be useful in infancy to evaluate neurological functioning. Visual evoked potentials (VEPs) and visual recognition memory testing were carried out on eight infants with prenatal drug-exposure and eight controls, matched for ethnicity and socio-economic status. The drug-exposed infants performed significantly worse on the visual recognition test. However, there were no differences between groups on VEP testing and no correlations between tests. The results suggest that the difficulties found in visual recognition memory of drug-exposed infants are not related to neurological maturity, as measured by VEPs.

Amphetamines↗
PubMed1982

Visual evoked potentials and positron emission tomographic mapping of regional cerebral blood flow and cerebral metabolism: can the neuronal potential generators be visualized?

Visual evoked potentials (VEPs) and visual evoked spectrum array (VESA) to flashes and pattern-reversal were correlated with regional cerebral blood flow (rCBF) or local cerebral glucose metabolism in 4 hemianopsic patients and one subject with cortical blindness. Normal VEPs, topographical distribution and occipital rCBF were noted in hemianopsic patients with macular sparing. A dissociation of topographical distribution of VEPs to flashes and pattern-reversal was demonstrated in one patient with hemianopsia and macular splitting. In this case, rCBF showed unilateral activation of visual areas 17, 18 and 19 of the cortex. The distribution of surface-recorded potentials reflected the complex interaction of electrical field potentials within at least 3 cortical areas rather than volume transmission of striate dipoles alone. VEPs were preserved in a cortically blind patient. rCBF and local cerebral glucose metabolism revealed a functioning island of occipital cortex that most likely represented the generator of the VEP. The combination of VEP and PET permits the correlation of electrophysiological events with the visualization of cortical areas presumably activated by the same visual stimulus.

Blindness↗
PubMed1995

[New methods of stimulation of evoked visual potentials].

We report new approach to stimulation of visual evoked potentials generating graphical shemes on display of personal computer. System is based on original research of authors. It permits a stimulation of individual types of retinal cells using either pattern reversal modus or movements, or their mutual combination. System is suitable for introduction into common clinical praxis due to availability and simplicity. It allow standard routine examination of not only usual pattern reversal stimulation but also of movement stimulation. Until now, standardly managed devises do not permit examine later way of stimulation.

Computer Graphics↗
PubMedDate not supplied

Postnatal development of brainstem auditory-evoked potentials, electroretinograms, and visual-evoked potentials in the calf.

Brainstem auditory-evoked potentials (BAEP), electroretinograms (ERG), and visual-evoked potentials (VEP) were recorded for eight calves from birth to 56 days and the values compared with previously determined adult responses. The BAEPs, ERGs, and VEPs recorded within the first 24 hours after birth contained all of the peaks seen in adult recordings. Varying degrees of maturation of the responses were documented as changes in latency and amplitude with age. The BAEPs were adult-like at birth, with latencies falling within the mean, plus or minus one standard deviation, for adult cows. A small but significant decrease in latency with age was seen for the first, second, and fourth peaks of the response. The ERG amplitudes were also within the adult range for the entire period of the study. Latencies to the a- and b-waves declined during the first 14 days and then stabilized at adult values. The VEP latencies decreased with age, with late peaks changing more than early peaks. Latencies of all but the first peak decreased to values less than the adult range. Two VEP amplitudes increased significantly with age. Developmental appears in the calf and other precocious species are compared to those in altricious (nonprecocious) species.

Animals↗
PubMedDate not supplied

[Visual potentials evoked by a pattern reversal checkerboard in 50 depressed patients].

The pertinency of the visual evoked potentials (VEP) was studied as an index of depression in a group of 50 depressed patients (according to DSM III criteria). The VEP recordings were realized before an antidepressive treatment (D0) and 4 weeks after the beginning of the treatment (D28). Identical recordings were realized with 15 healthy and voluntary reference subjects. Stimulations were reversal checkerboard. The analysis of the results indicate at D0 a reduction of P1 and N1 latencies in the depressed people compared to the reference subjects, and an increase of the P1-N1 amplitude. These differences disappear at D28 (after the antidepressive treatment), as we don't notice any significative difference between D0 and D28 with the reference subjects. The interpretation of these results leads to the hypothesis of a neurophysiological modification of the attentional processes during the depression state. The antidepressive treatment seems merely to produce a normalization of the evoked responses in the depressed patients.

Adult↗
PubMed1999

[Effect of levodopa therapy on visual evoked potentials and visual acuity in amblyopia].

Amblyopia represents the most common form of visual impairment in children, affecting approximately 2% of the population. To determine the efficacy of the dopamine agonist levodopa for childhood amblyopia, a double-masked, placebo-controlled randomised study was performed on 32 amblyopic children with central fixation between 4 and 17 years. Subjects received 2 mg/kg levodopa benzeraside or placebo 3 times per day over a 1 week period. Estimates of visual acuity for each eye (Snellen visual acuity) were obtained, and pattern-shift visually evoked potentials (VEP) were examined by an opthalmologist and a neurologist. At the end of dosing regimens, the levodopa group was significantly improved in visual acuity by 1.4 lines and pattern VEP amplitudes. No changes could be detected after placebo administration. One week after the termination of the treatment, Snellen line acuity and pattern VEP amplitude were decreased to pretreatment levels. The transient effect of levodopa points to a long-term treatment with the substance. Our results should therefore encourage further long-term clinical trials investigating the therapeutic potential of levodopa in amblyopia.

Adolescent↗
PubMed1994

Focal visual evoked potentials generated by scanning laser ophthalmoscope in patients with age-related macular degeneration treated by perifoveal photocoagulation.

Perifoveal laser photocoagulation has been proposed for the treatment of subfoveal neovascular membranes in age-related macular degeneration. We evaluated residual function in seven eyes of six treated patients by means of transient focal visual potentials evoked with a scanning laser ophthalmoscope. The site of the preferred retinal locus was determined. The modulation of the helium-neon laser beam generated three tests (a homogeneous 6 x 6 degrees square--offset and onset--and two alternating pattern checkerboards 6 x 6 degrees and 2.5 x 2.5 degrees 60', 2 Hz) projected onto the preferred retinal locus. The focal visual evoked potentials were recorded. One eye had an unstable fixation with no discernible focal visual evoked potentials. The other six eyes had a stable fixation located in the superior retina, temporally for the right eyes and nasally for the left eyes. The homogeneous 6 x 6 degrees square evoked discernible responses in all six patients. The two checkerboards evoked discernible responses in five of six patients. These results were compared with those recorded in four controls in whom the three tests were projected onto the same retinal areas as in the patients. Evoked responses were more often recorded in the preferred retinal locus of the treated patients with age-related macular degeneration than in the corresponding retinal areas of the controls. The scanning laser ophthalmoscope allowed us to control the site of stimulation in the patients' and controls' retinas. These preliminary results suggest that there may be a functional plasticity of the visual system after therapeutic laser-induced central scotoma.

Aged↗