PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Evoked Potentials, Visual”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 397 records · Page 22Linked to original sources
PubMed1990

Visual evoked potentials in rotogravure printers exposed to toluene.

Visual evoked potentials (VEPs) from stimulation by checkerboard pattern reversal were examined in 54 rotogravure printers exposed to toluene (all men, aged 22-64 years, duration of exposure 1-41 years). A control group consisted of 46 subjects (23 men and 23 women; aged 22-54 years). Compared with controls the exposed group showed more frequent responses with reduced reproducibility or absence of some waves, or both; the mean P1 wave latency was prolonged and mean amplitudes N1P1 and P1N2 were reduced. The VEPs were abnormal in 24% of workers. The frequency of abnormal VEPs correlated positively with the duration of exposure to toluene and also with the degree of alcohol drinking. No association was found between measurements of VEP and electroencephalogram (EEG) or electromyogram (EMG) examinations. A VEP measurement was made in 78% of the exposed workers two years after the first examination. No statistically significant difference between the two results was found. This suggests a marked stability of the observed VEP changes. These changes can be interpreted as a subclinical sign of dysfunction of the central nervous system (CNS) related to exposure to toluene and also to alcohol consumption.

Adult↗
PubMed1992

Visual evoked potentials in guinea pigs with brain lesion.

Visual evoked potentials (VEPs) were recorded in 10 adult male guinea pigs with brain lesion. Lesions were produced in 5 animals by superficial suction of the occipital lobe. The other 5 animals were orally administered with hexachlorophene (about 35 mg/kg/day) for 28 days. In the VEP following the ablation of the occipital lobe, the peaks P10, N20, P55, N75, N140 and P200 disappeared in many cases. The amplitude of the peak N40 decreased to approximately one half its control VEP. In the VEP obtained from the animals administered with hexachlorophene, the peak latencies of N20, P30, P55, N75 and P100 were slightly prolonged after the 7th day following the first administration. On the other hand, there was no change in the latency of N40 during the whole period of administration. The peak-to-peak amplitude showed some variability in different peaks. Histologically, diffuse status spongiosis were found in the white matter of the cerebrum, cerebellum, and brain stem. As described above, the ablation of the occipital lobe caused markedly depressed VEPs, however, the responses to the photic stimulation persisted after the injury. On the other hand, the VEPs of animals administered with hexachlorophene showed a high probability of peak appearance, and a decrease in amplitude was not marked.

Animals↗
PubMed1992

[Maximum entropy method and Fourier transform for wave analysis of pattern visual evoked potentials].

To estimate spectral analysis of pattern visual evoked potentials (P-VEPs) the maximum entropy method (MEM) and fast Fourier transform (FFT) were investigated. P-VEPs were recorded in 16 normal eyes using the reversal pattern of 2 c/d vertical sine wave gratings. Six temporal frequencies (2, 3, 4, 6, 8, 12 Hz) were used. MEM power spectrum with the parameter (dimension of autoregression model) which was decided final prediction error (FPE) method did not necessarily always give satisfactory results. The MEM power spectrum of transient VEP changed in manner different from that of steady state VEP as the dimension of autoregression model varied. In steady state VEP the peak of the MEM spectrum was positioned accurately at dimension 50 but in transient VEP the peak positioned accurately at a larger dimension. Both in MEM and FFT the curves of the square root of the power vs temporal frequency resembled each other and had temporal tuning with a maximum at 6 Hz. At lower temporal frequencies (2, 3 Hz) the correlation coefficient increased gradually as the harmonic component became higher (2 nd less than 4 th less than 6 h). MEM powers in the second harmonic component were highly correlated with FFT power in temporal frequency above 4Hz. These results showed that the MEM power spectrum had higher resolution than FFT and had different properties especially at lower temporal frequencies. MEM with optimum parameters should be very useful for wave analysis of P-VEPs.

Evoked Potentials, Visual↗
PubMed1990

[Development of visual evoked potentials in guinea pigs].

The development of visual evoked potential (VEP) was studied in guinea pigs as a function of age. Ten newborn guinea pigs from 3 litters were used, and experiments were carried out with the animals over an age span ranging from 1 to 90 days. Periodic recordings were obtained at 5 day intervals from the first up to the twentieth day after birth and at 30 day intervals from the thirtieth to ninetieth day after birth. The results were as follows: 1) The VEP comprised 7 peaks at the first day after birth, while after the fifth day it was composed of 9 peaks. 2) During the development of the guinea pigs, the latencies of VEP decreased. The reduction of the latencies of peak N2 amounted to about 25% from the first to the thirtieth day. 3) The amplitude of the initial negative spike increased from the first to the fifth day after birth, and decreased after the fifth day.

Age Factors↗
PubMed1985

[Visual evoked potentials: methodologic problems--variations of stimulus parameters].

The evaluation of visual potentials (VEP) evoked by pattern reversal includes the latency and amplitude of P100. An increase in the mean brightness or contrast of the checkerboard stimulus results in an increase in amplitude and a decrease in latency of P100. A square edge subtense of 20' in checkerboard pattern or a spatial frequency of 3-4 cyc/degrees in stripe pattern produce maximum responses. Transient VEPs are recorded at low repetition rates (less than 2 Hz), steady state VEPs at temporal frequencies above 8 Hz. In the latter condition the VEP takes the character of a sinusoidal train of waves which, compared to transient stimulation allows for a better measurement of VEP amplitude. The latency of P100 increases with the age of the subject. The influence of the different stimulus parameters and recording techniques must be known and have to be kept constant in order to record reliable and reproducible VEPs.

Adolescent↗
PubMed1985

Standards for the assessment of visual evoked potentials in an ethnically heterogeneous adult population.

Visual evoked potentials (VEPs) were recorded by chequerboard pattern-reversal stimulation in 276 normal adult subjects aged 15-73 years. The sample comprised comparable white, coloured and black groups of both sexes. Significantly shorter latencies of the major positive component were found in both male and female black subjects compared with those in whites. No significant differences were found between the amplitudes in the different population groups, but females in each population group showed significantly higher amplitudes of the major positive component than males. There was a close relationship between latency and amplitude for both right and left eyes. Except in coloured females, a non-linear relationship of the major positive component with age was demonstrated, the shortest latency being at about 35 years of age. It is suggested that the following criteria be used in the evaluation of VEP recordings: latency as well as the difference between latencies and amplitudes of the two sides of the major positive component (P1) as compared with standardized values for ethnic, sex and age groups.

Adolescent↗
PubMed1981

Visual evoked potential habituation in mental deficiency.

Habituation of visual evoked potentials (VEPs) may be a helpful tool in the comparative investigation of mental and neural physiologic processes. Through-train and across-train procedures of VEP averaging were performed during habituation in three groups of male children exhibiting mental retardation (idiopathic, exogenous, chromosomal) and in normal children. The children with idiopathic and exogenous mental retardation reached the same VEP habituation level as the normal children (amplitude reduction of 20-60% of early and late VEP components). The across-train averaging showed however a slower than normal development of habituation in these mentally retarded subjects. Habituation failed to occur in the low-grade mentally retarded children, who displayed a reverse tendency of increasing VEP amplitudes and of VEP variability during repetitive flash applications.

Adaptation, Ocular↗
PubMed1997

Maturation of human visual evoked potentials: 27 weeks conceptional age to 2 years.

Visual evoked potentials to pattern reversal and diffuse flash stimulation were recorded from 520 consecutive pediatric patients and 11 normal infants between the ages of 27 weeks post-conception and 24 months. The latency and peak-to-peak amplitude of the first reproducible positive peak of the binocular pattern visual evoked potential (P100) were measured for five check sizes subtending from 15' to 4 degrees of arc. Three developmental trends were noted: 1) a rapid increase in pattern resolution near term, 2) a subsequent decrease in the latency of P100, and 3) a gradual increase in the amplitude of P100. These three trends reflect the multiplicity of early maturation and are discussed in terms of changes in receptor growth and density, pathway myelination, and cortical synaptivity.

Age Factors↗
PubMed2004

Visual evoked potentials in disproportionately growth-retarded human neonates.

To study brain function in the neonatal period, disproportionately growth-retarded (n = 33) and appropriately grown (n = 21) infants were examined using Doppler flow velocities prenatally and visual evoked potentials postnatally. Visual evoked potentials recordings were made at gestation of 40 and 46 weeks. The group of growth-retarded infants had significantly prolonged latencies to both of the two major peaks (designated P and N), most pronounced for the P peak. This result was observed at both ages investigated and corresponds to a developmental delay of 3 weeks. For individuals, the increase in P latency correlated to prenatal flow indices and to neonatal anthropometric parameters indicative of growth retardation. We conclude that in utero growth retardation affects brain development as assessed by visual evoked potentials in the neonatal period. This developmental delay may be produced by intracerebral factors during the process of growth retardation, and these alterations may have a prognostic value.

Anthropometry↗
PubMed1982

Steady-state and transient visual evoked potentials in clinical practice.

The electrophysiological analysis of visual evoked responses is a powerful tool for the study of visual function. The combined application of pattern-reversal transient visual evoked potentials, critical frequency of photic driving, and visual evoked spectrum array has enhanced the reliability and the yield of these tests for the diagnosis of visual dysfunctions. Prechiasmatic and retrochiasmatic lesions are characterized by different abnormalities. Prechiasmatic lesions often can be further differentiated into retinal and optic nerve lesions by the simultaneous recording of retinal and cortical potentials.

Adult↗
PubMedDate not supplied

Pattern visual evoked potentials and brainstem auditory evoked responses in uremic patients.

With the improvement of dialysis therapy and subsequent increase in the average lifespan of uremic patients more interest has been directed towards neurological complications induced by chronic renal failure. Twelve uremic patients were selected on the basis of negative neurological and psychiatric examinations. Electroencephalogram, pattern visual evoked potentials (VEPs) and brainstem auditory evoked responses (BAERs) were recorded in all patients. Pathological latency increases of VEPs in six patients and of BAERs in three patients had been observed. These findings have been related by the authors to the action of toxic substances or to the presence of minimal demyelinating lesions of CNS. Since these pathological findings were observed in patients who were normal at the clinical examination, it has been suggested that the evoked potentials recording might be a sensitive index of initial early lesions of the CNS in uremic patients (Acta neurol. belg., 1982, 82, 72-79).

Adult↗
PubMed2004

[The visual evoked potentials in open angle glaucoma].

PURPOSE: The study purpose to analyse the variations of Visual Evoked Potentials on a group of patients with Open Angle Glaucoma. MATERIAL AND METHOD: It was performed the Visual Evoked Potential recordings on a number of patients with Open Angle Glaucoma in different stages of evolutions. Some of the patients were monitored by the Visual Evoked Potentials recordings in a dynamic way, before and after the law pressure treatment. The type of Visual Evoked Potentials recording was pattern reversal with vertical bars. RESULTS: In incipient stage of Open Angle Glaucoma the alteration of the tract was minimal with inconstant presence of the N75 and N135 waves and just a few variation of the delay of P100. In advanced stages of Open Angle Glaucoma the alterations of the tract were important: the delay of P100 wave. In absolute stage the tract was null. CONCLUSIONS: The alterations of Visual Evoked Potentials tract was influenced by the different stages of evolution of Open Angle Glaucoma. The gradual alteration of the Visual Evoked Potential tract represents a prognosis of the disease.

Adult↗
PubMed1984

[Effect of sleep deprivation on visual evoked potentials and brain stem auditory evoked potentials in epileptics].

The article reports on the first study of the evoked activity of the brain in epileptic patients (n = 20) following sleep deprivation. An analysis of the data obtained has revealed a tendency to the shortening of the peak latent intervals of visual evoked potentials in the range of 100-200 mu sec and the V component and the interpeak interval III-V of evoked auditory trunk potentials in patients with temporal epilepsy. The phenomenon may indicate the elimination of stabilizing control involving the specific conductive pathways and, possibly, an accelerated conduction of a specific sensor signal.

Adolescent↗
PubMed1985

Visual evoked potentials and brainstem auditory evoked potentials in migraine and transient ischemic attacks.

A study of brainstem auditory evoked potentials (BAEPs) and pattern reversal visual evoked potentials (VEPs), recorded in intercritical phase, was carried out in 20 subjects (10 suffering from common migraine and 10 suffering from vertebrobasilar TIA) in order to obtain a comparative evaluation of cortical-subcortical functions. The data we obtained demonstrate the presence of BAEPs alterations in patients with previous vertebrobasilar TIA: no abnormalities were found in the migraine group. VEPs parameters are normal in both groups. Our data show that the study of the so-called "stimulus-related" potentials, such as BAEPs and pattern reversal VEPs, is useful in evaluating the damage produced by any noxa, while it cannot clearly emphasize individual factors predisposing to a specific pathology, as the absence of specific alterations in migraine patients demonstrates.

Adult↗
PubMedDate not supplied

Effects of fluoxetine on habituation of pattern reversal visually evoked potentials in migraine prophylaxis.

OBJECTIVE: To investigate the effects of fluoxetine in migraine prophylaxis on habituation of visually evoked potentials. BACKGROUND: Habituation of pattern reversal visually evoked potentials was found to be abnormal in migraine between attack, and this abnormality was most likely due to serotonergic pathway dysfunction in the brain stem. METHODS: One hundred nineteen subjects were included in the study: 40 healthy volunteers and 79 migraineurs not taking any prophylactic migraine medication (44 without aura and 35 with aura). Visually evoked potentials in migraineurs were recorded in the headache-free interval. Amplitude change of the visually evoked potentials (N1-P1) was measured between the first and fifth block of 50 sequential averagings during continuous stimulation at 3.1 Hz. All migraineurs were placed on fluoxetine 20 mg/day for prophylaxis of migraine. One month later, visually evoked potentials were recorded again. RESULTS: Mean amplitude changes in the fifth block expressed as percentages of the first block were -13.4% +/- 19.2% in healthy volunteers, 9.8% +/- 23.3% in migraine without aura, and 4.4% +/- 8.7% in migraine with aura during the baseline period. The difference was significant between migraineurs and healthy volunteers (both P= 0.0001), but not between migraineur groups. After treatment, amplitude changes were -9.3% +/- 14.5% in migraine without aura and -10.1% +/- 11.5% in migraine with aura. Habituation pattern tended to normalize with prophylactic treatment, and mean amplitude changes were not significant between migraineurs and healthy volunteers (both P = 0.4). CONCLUSIONS: We concluded that the fluoxetine prophylaxis corrects the interictal deficit of habituation in migraineurs.

Adult↗
PubMed2004

Clinical application of the multifocal visual evoked potential.

BACKGROUND: Measures of visual function thresholds such as visual acuity and visual fields are generally dependent on subjective responses and assume maintenance of fixation, attention and motivation. In the young, elderly, cognitively impaired or malingering populations, such measures may be inaccurate or difficult to obtain. The Visual Evoked Response Imaging System (VERIS) has been claimed to give more objective topographic recordings of retinal and cortical function. This paper aims to explore the adequacy of this technique in four unusual, unrelated, clinically difficult cases. METHODS: Multifocal visual evoked potentials (mfVEPs) recorded on the VERIS System 3.01 are used to assess visual function in four cases with contradictory clinical findings or unreliable subjective responses. RESULTS: Patient 1 had sustained a head injury and had normal ocular and pupil examination but light perception in the right eye and 6/5 acuity in the left. Multifocal VEPs showed a marked depression of the right visual field with little macular response. Patient 2 had sustained a head injury, had a left field hemianopia, possible macular sparing and loss of much of the right field, reduced but variable visual acuities, good near vision and normal ocular fundi. Multifocal VEPs showed a severe depression in both visual fields (L more than R) with little macular response. Patient 3 had a left optic nerve meningioma and experienced great difficulty with visual field assessment. mfVEPs showed a bilateral depression in the superior field particularly the left field, with a larger deficit in the left eye. Patient 4 had unexplained visual acuity and peripheral field deficits. mfVEP results were inconclusive in this case. DISCUSSION: Where there is difficulty performing traditional techniques or conflicting clinical findings, mfVEPs may provide additional objective information to aid in the assessment of patients.

Adult↗
PubMed1991

Flash visual-evoked potentials and flash electroretinography in the preoperative visual prognosis of eyes with cataracts.

This study evaluated the reliability of flash visual-evoked potentials and flash electroretinography in the prognosis of postoperative visual acuity after cataract extraction. We tested 94 patients with cataract in whom the preoperative visual acuity ranged from light perception to 3/10. On the basis of the electrophysiologic tests, we formulated three types of preoperative visual prognosis: high, intermediate, and poor. To assess the postoperative visual acuity, all subjects were followed for at least three months after cataract extraction. Visual acuity was subdivided in three arbitrary classes: less than or equal to 1/10, between 2/10 and 5/10, and between 6/10 and 10/10. Finally, we evaluated the reliability of our preoperative prognosis. Statistical analysis of our results (using the chi-square test) showed our predictions were highly significant for the total sample, revealing a strict correlation between our prognosis and the final visual acuity.

Adult↗