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PubMed1994

[Binocular competitive mechanisms in the visual cortex in early developing kittens of monocular deprivation and reverse suture revealed by pattern visual evoked potential].

Using contrast reversing square- wave gratings as stimuli the pattern visual evoked potentials (P-VEP) and pattern electroretinograms (P-ERG) were simultaneously recorded to determine the spatial frequency tuning curves for kittens of monocular deprivation (from 8th to 12th postnatal week) and reverse suture (from 12th to 15th postnatal week), as compared with those of normal kittens of the same age and adult cats. The results showed that in the range from spatial frequency 0.12 to 1.5 c/d the amplitudes of P-VEP responses driven respectively by the left and the right eyes in normal kittens were similar but clearly smaller than those driven binocularly. For kittens with one eye deprived, the P-VEP amplitudes driven by the deprived eye decreased markedly. In contrast, the P-VEP amplitudes driven by the undeprived eye increased significantly, while the P-VEP amplitudes driven by simultaneous stimulation of both eyes were intermediate between the two monocular responses. For the reversely sutured kittens, the P-VEP amplitudes driven by the formally deprived eye recovered to some extent, while the P-VEP amplitudes driven by the reversely sutured eye decreased, and their amplitudes tended to be quite close. The P-VEP amplitude driven by both eyes was the biggest. Neither such shift of spatial frequency tuning curves of the P-VEP in adult cats, nor such functional competition between the two eye in P-ERG responses during early development of kittens of monocular deprivation and reverse suture was found.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

[Visual evoked potentials in infants in health and hypoplasia of the optic nerve].

Visual evoked potentials (VEP) in response to chess field reversion were studied in 29 infants aged from 6 weeks to 1.5 years with optic nerve hypoplasia and in healthy age-matched controls. Analysis of VEP in healthy children showed that the interval between weeks 6-9 and 16-20 of life was the period of their most rapid maturation, this making this period in the development of the optic system of man particularly significant. Three types of VEP disorders were detected in patients with optic nerve hypoplasia; these types correlate with the size of the optic disk and behavioral reactions of a child. Together with the clinical data, VEP may be used for assessing the function of the optic system of children with optic nerve hypoplasia and for early diagnosis of this disease.

Age Factors↗
PubMed1997

Visual evoked potential and electroencephalogram of healthy females during the menstrual cycle.

Flash visual evoked potential (VEP) and electroencephalogram (EEG) changes during the menstrual cycle were studied using healthy females having regular menstruation, with 21 at the follicular phase (FP) and 23 at the luteal phase (LP). The following results were obtained. (1) The waveforms of Group Mean VEPs of both groups had approximately similar triphasic contours, consisting of 16 components of P 1-N 8 up to 500 msec of latency. (2) Latencies tended to be longer in LP. (3) Interpeak amplitudes tended to be larger in LP, and one VEP interpeak amplitude (P 5-N 7) of long latency component was significantly larger at LP after eliminating the effect of body height by ANCOVA for 2 CH. (4) Quantitative analysis of EEGs between FP and LP resulted in a tendency for increased alpha, and decreased beta power % at LP. Since estrogen increases the VEP amplitude, and decreases the VEP latency and the alpha activity of EEGs, the large VEP amplitude, the tendency for prolonged VEP latency, and the tendency for increased alpha power % at LP observed in this study indicate that the VEP amplitude at LP reflects the effect of estrogen, and that the VEP latency and EEGs at LP reflect the effect of progesterone.

Adult↗
PubMed2001

Pattern visual evoked potentials in malingering.

OBJECTIVES: We previously developed a new method for estimating objective visual acuity by means of pattern visual evoked potentials (PVEP). In this study, this method was applied to the diagnosis of malingering. MATERIALS AND METHODS: Six patients ranging in age from 40 to 54 years (mean 47 years) with suspected malingering were evaluated by means of the visual evoked potential test, optokinetic nystagmus (OKN) inhibition test, and the visual field test. In the PVEP study, the stimulus consisted of black and white checkerboards (39', 26', 15', and 9') with a visual angle of 8 degrees, contrast level of 15%, and a frequency of 0.7 Hz. One hundred PVEP responses were averaged per session. RESULTS: Routine ophthalmic examinations were normal in all patients. Five patients had a tubularly constricted visual field, and the remaining patient had a normal visual field. The objective visual acuities of the six patients estimated from PVEP were better than their subjective visual acuities estimated with Landolt rings. CONCLUSIONS: Among a variety of psychophysical and electrophysiologic ancillary tests, we consider our PVEP method a useful method for objectively determining visual acuity in a patient with signs of ocular malingering.

Adult↗
PubMed2003

The pattern--reversal visual evoked potentials in children with migraine with aura and without aura.

PURPOSE: Studies of the visual evoked potentials (VEP) in migraine have yielded contradictory results. Several investigators suggested that VEP may be helpful test in diagnosis of a child with headache. The aim of our study was to compare interictal pattern-reversal visual evoked potentials (PR-VEP) in children and adolescents with migraine and tension-type headaches and to evaluate VEP parameters in migraine with and without aura. MATERIAL AND METHODS: The study was carried out in 93 children and adolescents aged 7-18 years with attack headaches. RESULTS: 51 children had diagnosed migraine. In this group 30 children (59%) had migraine without aura (MO), 12 children (23.5%) migraine with aura (MA) and 9 (17.5%) patients other variants of migraine (MV): hemiplegic, ophthalmoplegic, basilar. In control group 42 children were classified as tension-type headaches. All children had PR-VEP performed in headache-free period, without prophylactic treatment. The P100 mean latency was significantly longer in migraine than in tension-type headache. Amplitudes N1-P100 and P100-N2 were significantly larger in migraneurs compared with tension-type headache. The mean amplitudes of N1-P100 and P100-N2 were significantly lower in MA compared with group MO. There were no statistically significant differences of other PR-VEP parameters between MA, MO, MV. If we compare individual results of each patient with migraine with mean value +/- 2 standard deviations (SD) of tension-type headaches group, only 25% have VEP abnormalities of latency or amplitude above 2SD value in tension-type headache group. CONCLUSIONS: The diagnosis of migraine in children actually remains predominantly based on medical history, due to low sensitivity and specificity of electrodiagnostic tests in headaches. However PR-VEP may support the diagnosis of migraine in some cases. VEP could be also helpful method in studying the pathogenesis of different forms of migraine. VEP abnormalities in migraine can be related to a cortical spreading depression and a central neurotransmitter alterations.

Adolescent↗
PubMed1985

Dynamic topography of visual evoked potential in children: a study of the development of the visual system.

To study the development of the visual system, the dynamic topography of the visual evoked potential (VDT) was investigated in 30 normal children aged from two weeks to four years. Twenty-three of the 30 children (77%) showed reliable VDT. The results showed three steps in the development of the visual system in these young children. The first step was seen during the first 4 months after birth, and it was represented by a shortening of duration and an increasing of amplitude in N70 in the occipital region. The second step was seen between 9 months and 2 years of age, and it was represented by a shortening of duration and an increasing of amplitude in P100 and P150 over a widespread area in the occipito-parieto-temporal region. The third step was not clearly seen until 3 years of age, and was represented by the appearance of P200, the so called "vertex potential", around the occipitoparietal region. These three steps in the development of the visual system seemed to be closely related to the time-course of the development in the myelination and maturation of the neuron synapses in the visual pathway and visual cortex. With the aid of VDT, it was possible to clarify that the visual system in children develops step by step from a low level to a high level of the visual function.

Aging↗
PubMed1988

Multi-channel visual evoked potentials in early compressive lesions of the chiasm.

The sensitivity of transient, pattern-reversal visual evoked potentials in the detection of early compressive lesions of the chiasm is controversial in the literature. There have been claims that the technique is capable of detecting an abnormality in the absence of any demonstrable visual field loss, and conversely that VEPs are not reliable for the detection of chiasmal lesions even when a bitemporal hemianopsia is clearly recordable. Using nine patients with pituitary adenoma we attempted to quantify the extent of visual field loss and correlate the diagnostic capabilities of topographically recorded potentials following full- and half-field stimulus presentations of various field and check sizes. Differential light thresholds were measured and quantified according to one investigator's graticule for the neural representation of visual space. Results show a strong correlation between the degree of information loss and the diagnostic value of the visual evoked potential. The technique was, however, capable of detecting abnormality in the absence of recordable field loss when large field and check sizes were used.

Adenoma↗
PubMed1984

[Contribution of visual evoked potentials (VEP) to neurology].

It is widely admitted that visual evoked potentials (VEPs) are clinically useful for diagnostic purposes in multiple sclerosis (MS). Delayed P100 component to pattern shift stimulation indicates a dissemination of the demyelinating process when routine ophthalmological investigations are normal. The delay of P100 may be observed early in the course of the disease following an attack of optic neuritis (ON); in the absence of previous ON the P100 latency may appear later after the onset. The P100 latency exceptionally returns to normal values. Compared with somatosensory or brain-stem auditory evoked potentials VEPs are the most efficient for the detection of silent lesions in MS. Longitudinal studies demonstrate that the percentage of MS patients with abnormal VEPs increases with time during the course of the disease. Delayed P100 component may also be recorded in patients with heredodegenerative or toxic optic neuropathies, but the clinical context is very different. The detection of bitemporal visual field defects with VEPs is more uncertain. In patients with cortical blindness VEPs may persist. When compared with usual campimetric investigations, VEPs do not represent a simple and reliable means of investigating lateral homonymous hemianopsia.

Epilepsy↗
PubMed1994

Directional asymmetries in interhemispheric transmission time: evidence from visual evoked potentials.

The hypothesis was tested that interhemispheric transfer time (IHTT), as measured in the latency of bilaterally recorded visual evoked potentials, is directionally asymmetric, i.e. that an IHTT is faster for transmission from right-to-left hemisphere, than from left-to-right. A meta-analysis of 18 experiments within the published literature reporting visual evoked potential IHTTs indicates a significant experiment-wise predominance of faster right-to-left IHTTs. A new experiment is also reported in which significantly faster right-to-left IHTT was found in visual evoked potentials recorded from parietal electrodes to lateral visual field presentations while subjects performed a task requiring complex stimulus recognition and analysis, and a choice response.

Choice Behavior↗
PubMed2003

The clinical features of albinism and their correlation with visual evoked potentials.

AIM: To investigate the relation between the clinical and electrophysiological abnormalities of patients undergoing visual evoked potential investigation for albinism. METHODS: 40 subjects with a probable or possible clinical diagnosis of albinism underwent pattern appearance and/or flash visual evoked potential (VEP) examination. The VEP findings are correlated with the clinical features of albinism determined by clinical examination and orthoptic assessment. RESULTS: The majority of patients with clinical evidence of albinism showed a contralateral predominance in the VEPs. There was close correlation between the clinical signs of albinism and the degree of contralateral VEP predominance. This manifested as an interhemispheric latency asymmetry to monocular pattern appearance stimulation but amplitude asymmetry to flash stimulation. The strongest correlation for pattern appearance interhemispheric latency difference was with foveal hypoplasia (rho = 0.58; p = 0.0003) followed by nystagmus (rho = 0.48; p = 0.0027) and iris transillumination (rho = 0.33; p = 0.039). The VEP abnormalities were of greater magnitude in those patients with most features of albinism. Several patients with apparently mild disorders of ocular pigmentation had small but significantly abnormal VEP latency asymmetries. CONCLUSION: There is a strong association between the magnitude of the interhemispheric latency asymmetry of the pattern appearance VEP, and of amplitude asymmetry of the flash VEP, with the clinical signs of albinism. The data are consistent with a spectrum of abnormalities in albinism involving both clinical expression and electrophysiological misrouting, which is wider than previously recognised.

Adolescent↗
PubMed1991

Visual evoked potentials in optic nerve injury. Does it merit a mention?

The value of Visual Evoked Potentials (VEP) in the management of indirect optic nerve injury was prospectively studied in 128 patients. In fifty patients who were either unconscious, uncooperative or had massive black eye, preventing the assessment of vision, a light Emitting Diode (LED) was used to record visual evoked potentials. The initial VEPs were normal in 17, abnormal in 49 and absent in 62. All 17 patients with normal VEP showed visual recovery. Amongst the 49 patients with abnormal VEP, 43 (88%) showed improvement. In 62 patients, initial VEPs showed no response but, in 12 subsequent VEP recordings wave formation was demonstrated. Thus in 50 patients repeated VEP recordings failed to demonstrate wave formation, and none of them improved. This study, thus brings out the high predictive value of both positive and negative VEPs, and specially the role of LED.

Evoked Potentials, Visual↗
PubMed1992

Flash and pattern-reversal visual evoked potential abnormalities in infants and children with cerebral blindness.

Visual evoked potentials (VEPs) were recorded of 60 infants and children with cerebral blindness, aged between six weeks and 10 years, and compared with age-matched normative data. Every patient had abnormal VEPs. 18 had absent flash and pattern VEPs and 13 had atypical or atypical and asymmetrical flash and pattern VEPs. Of the remaining 29, most had greater abnormality of pattern than of flash VEPs and greater abnormalities over parietal and temporal than occipital areas. Eight patients had normal occipital responses to flash and five others had delayed responses with normal morphology. One had normal occipital responses to pattern stimuli. All of these had abnormal late occipital responses or abnormal responses over the parietal and temporal areas. It is recommended that visual assessments using VEPs employ both flash and pattern stimuli, that pre-occipital as well as occipital recordings be made and that tracings be compared with age-specific normative data.

Blindness↗
PubMed1987

Color-specific effects of intense laser exposure on visual evoked potentials in rhesus monkeys.

Color-specific visual impairments following exposure to intense laser flashes were investigated using visual evoked potentials (VEPs) recorded from four anesthetized rhesus monkeys. Steady-state VEPs were recorded from the primary visual cortex in response to counterphasing high-contrast sine-wave gratings composed of either luminance contrast (red-black, green-black, and blue-black) or chromatic contrast (red-green). The effects of laser flashes in the red (647 nm), green (514 nm), and blue (476 nm) regions of the visible spectrum were assessed. Only slight wavelength-specific effects were demonstrated, primarily for the red-black grating relative to the other two luminance gratings. Recovery functions for VEPs to the red-green chromatic grating were similar to those of the three luminance gratings. The results are discussed in terms of nonopponent (luminance) and opponent (chromatic) processing.

Animals↗
PubMed1997

[Use of neural networks for analysis of visual evoked potentials developing a type of "pattern"--preliminary report].

PURPOSE: The authors present the "pattern" visual evoked potentials (VEP) analysis with use of the artificial neural networks (ANN). MATERIALS AND METHODS: The study involved 11 patients with compressive chiasmal optic neuropathy, 20 patients with optic neuritis, 12 patients with anterior ischaemic optic neuropathy, 20 patients with optic nerve atrophy from neuritis, 8 patients with demyelinative neuropathy, 5 patients with oedema optic nerve, 20 healthy persons. The tests of visual evoked potentials were performed with the use of computer system UTAS-E1000. Classification of potentials was made by correlation of outputs of ANN with results of confirmed neuro-ophthalmology conditions. RESULTS: ANN of different architecture were classified correctly in 80-100% of VEP record samples. CONCLUSIONS: The obtained correctness of classification confirms usefulness of VEP analysis as the objective diagnostic method in some neuro-ophthalmological diseases and indicates application of ANN in multifactor analysis.

Adolescent↗
PubMed1980

The incidence and nature of visual pathway involvement in Friedreich's ataxia. A clinical and visual evoked potential study of 22 patients.

Pattern-reversal visual evoked potentials (VEP) were recorded from 22 patients (mean age 33.7 years) with Friedreich's ataxia, 15 of whom also had a detailed neuro-ophthalmological assessment prior to the VEP examination. None had noted symptomatic visual impairment. Eleven of the 15 (73 per cent) examined clinically had one or more neuro-ophthalmic abnormality and 14/22 (64 per cent) had an abnormal VEP study which was always binocular and comprised absent responses, or most commonly, increased P100 component latencies. The maximum P100 latency was 143 ms and the group mean was 118 ms. The P100 amplitude was also generally reduced particularly in those patients with latencies less than 115 ms (upper limit of normal), while in those with latencies above the normal range there was a significant inverse correlation between the P100 amplitude and latency. The waveform, temporal dispersion and interocular differences were normal in almost all patients with identifiable responses, including those with prolonged VEP latencies. Electroretinograms recorded from three selected patients were either normal or minimally abnormal and suggested secondary rather than primary retinal involvement. The only VEP parameter to correlate with either the duration of the generalized disease or the visual acuity was the P100 amplitude. A good correlation was found between the VEP and the clinical neuro-ophthalmic findings. Temporal pallor of the optic disc was most often associated with an abnormal VEP result and impaired visual acuity or colour vision were uncommon in the absence of VEP abnormalities. The VEP changes and those obtained from 24 age- and acuity-matched cases of demyelinating optic neuritis are contrasted and the probable pathophysiology is discussed. Two main conclusions emerge from this study. First, there is a high incidence of asymptomatic visual pathway involvement in Friedreich's ataxia which can be demonstrated by both clinical and VEP examination. Secondly, the VEP changes in Friedreich's ataxia differ from those found in typical demyelinating optic neuropathy and are consistent with progressive nerve fibre loss and associated slowing of conduction, indicating that the visual pathway is affected by the same widespread process of axonal degeneration found throughout the nervous system.

Adult↗
PubMedDate not supplied

Assessment of hepatic encephalopathy with visual evoked potentials compared with conventional methods.

Thirty-six patients with advanced chronic liver disease of predominantly alcoholic etiology and with a documented history or current physical evidence of hepatic encephalopathy were studied and compared to 30 healthy controls. Assessment was made of their mental state, number connection test, venous blood ammonia, electroencephalography and visual evoked potentials with both pattern reversal and flash stimuli. Because of considerable inter- and intraindividual variation in waveform, visual evoked potentials from flash stimuli were considered unreliable. In pattern reversal visual evoked potentials, the latency of the N1 and P1 waves was significantly longer (p less than 0.05) in patients than in controls; however, the wave latencies did not correlate with the mental state score. The mental state score correlated with the number connection test (r = 0.69, p less than 0.001), asterixis (r = 0.36, p less than 0.05), electroencephalography mean dominant frequency (r = 0.44, p less than 0.01) and blood ammonia (r = 0.60, p less than 0.01). In 14 patients studied sequentially, change in the mental state score correlated with change in the number connection test (r = 0.80, p less than 0.01) and asterixis (r = 0.75, p less than 0.01) but not with change in the electroencephalography, blood ammonia or visual evoked potential wave latencies. Although visual evoked potentials are abnormal in patients with alcoholic cirrhosis and encephalopathy, they are less accurate in assessing the level of consciousness than simple bedside evaluation with a number connection test.

Adult↗
PubMedDate not supplied

Visual evoked potentials and magnocellular and parvocellular segregation.

We have measured visual evoked potentials (VEPs) to luminance-modulated, square-wave alternating, 3-deg homogeneous disks for stimulus frequencies ranging from 1 Hz to 16.7 Hz. The aim of the study was to determine the range of frequencies at which we could reproduce the two-branched contrast-response (C-R) curves we had seen at 1 Hz (Valberg & Rudvin, 1997) and which we interpreted as magnocellular (MC) and parvocellular (PC) segregation. Low-contrast stimuli elicited relatively simple responses to luminance increments resulting in waveforms that may be the signatures of inputs from magnocellular channels to the visual cortex. At all frequencies, the C-R curves of the main waveforms were characterized by a steep slope at low contrasts and a leveling off at 10%-20% Michelson contrast. This was typically followed by an abrupt increase in slope at higher contrasts, giving a distinctive two-branched C-R curve. On the assumption that the low-contrast, high-gain branch reflects the responsivity of magnocellular-pathway inputs to the cortex, the high-contrast branch may be attributed to additional parvocellular activation. While a two-branched curve was maintained for frequencies up to 8 Hz, the high-contrast response was significantly compromised at 16.7 Hz, revealing a differential low-pass filtering. A model decomposing the measured VEP response into two separate C-R curves yielded a difference in sensitivity of the putative MC- and PC-mediated response that, when plotted as a function of frequency, followed a trend similar to that found for single cells. Due to temporal overlap of responses, the MC and PC contributions to the waveforms were hard to distinguish in the transient VEP. However, curves of time-to-peak (delay) as a function of contrast often went through a minimum before the high-contrast gain increase of the corresponding C-R curve, supporting the notion of a recruitment of new cell ensembles in the transition from low to high contrasts.

Adult↗