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Results for “Evoked Potentials, Visual”

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PubMed1986

Visual evoked potential changes in chronic glaucoma and ocular hypertension.

Visual Evoked Potentials have been recorded in a group of normal patients and the results compared with a group of age matched patients with either unilateral chronic glaucoma or ocular hypertension. Pattern reversal transient and steady state responses were analysed and contrast threshold estimated using an onset-offset stimulus. Electrophysiological abnormalities were detected in 82.1 per cent of the glaucoma group and 50.9 per cent of the ocular hypertensives.

Aged↗

PubMed1986

[Pigmentary retinopathy of neonates and infants. Their examination using electroretinography and visual evoked potentials].

A method of neurophysiological investigation (electroretinography and visual evoked potentials) is described as a non invasive exploration used in awake children. E.R.G. and V.E.P. normal patterns are described in relation to age. The data obtained in pigmentary retinopathies are referred to the physiopathology of these diseases. Usefulness of both neurophysiological tests is showed in the early diagnosis. Significative abnormalities are seen even before any detectable ophthalmoscopic symptom. In pigmentary retinopathies, V.E.P. are normal while E.R.G. is slightly then severely altered. E.R.G. and V.E.P. are also helpful in the differential diagnosis: in macular diseases, E.R.G. is usually normal while V.E.P. are altered. Repeated examinations have a prognostical value: when a disease is progressing, E.R.G. becomes more and more altered and V.E.P.'s abnormalities appear.

Electroretinography↗

PubMed1983

[Visual evoked potentials in patients with trigeminal neuralgia].

Data characterizing visual evoked potentials in neuralgia of the trigeminal nerve are presented. In contrast to healthy individuals, patients with this kind of neuralgia displayed a well pronounced character of early and late components of evoked potentials not only in the occipital but also in the central regions. Other features characteristic of their potentials were a hypersynchronous post-discharge and the presence of peaks. All these findings suggest the resemblance between the central mechanisms of neuralgia of the trigeminal nerve and those of epilepsy.

Electroencephalography↗

PubMed1998

Visual evoked potentials in hypothyroidism: a long-term evaluation.

Visual Evoked Potentials (VEP) were measured in 9 new-diagnosed hypothyroid female patients--mean age 46 +/- 12 ys--before treatment, during (with monthly evaluations) thyroid hormone replacement therapy and after long-term therapy, at the achievement as well as one year after having achieved and maintained euthyroidism. Three of the hypothyroids had abnormally prolonged latencies (m.v. 131.7 +/- 7.9 ms), while 7 had lower than normal amplitude (m.v. 2.3 +/- 2.8 microV). No remarkable change of amplitude was observed after the achievement of euthyroidism, after a mean time of 5.9 +/- 4.9 months (range 2-14 months). A significant shortening of latency (m 128.3 +/- 7.6 ms), even still higher than the control value (m 122.7 +/- 3.7 ms) was found. Significant correlation between P100 latency and thyroid hormone levels was found for TT4 (r = 0.3353; p = 0.005), TT3 (r = 0.2568; p = 0.032) and FT4 (r = 0.3572; p = 0.002). No further improvement in P100 latency (m 129.5 +/- 7.2 ms; p = 0.037) was found one year after the achievement of euthyroidism, while a remarkable amplitude increase (m 9.2 +/- 3.4 micro; p = 0.001) was observed. Our findings indicate that, as well as other studied parameters, VEP are reversibly alterated in hypothyroidism, probably in relation to metabolic rather than to structural alterations. Moreover, VEP can represent a useful neurophysiologic parameter for quantitation of SNC involvement in hypothyroidism.

Adult↗

PubMedDate not supplied

[Human visual evoked potentials during the recognition of facial emotional expression].

Visual evoked potentials (VEPs) were recorded in 22 right-handed healthy subjects in the occipital, parietal, central, frontal and posterotemporal cortical areas during recognition and passive viewing of positive, negative, and neutral emotional facial expression. Peak latencies of N90, P150, and N180 VEP components appeared to be significantly shorter in response to the negative emotional expression than during administration of other facial stimuli. The differences were observed both during active recognition and passive viewing. Correct recognition was characterized by involvement of both hemispheres and high level of interhemispheric correlation between the peak latencies of P150 in the posterotemporal and of N180 in the frontal areas. It is suggested that the facial expressions are primarily recognized at the subthreshold level with participation of the posterotemporal areas. The role of the frontal areas is discussed in the completion of this process and making the correct decision about the image.

Adult↗

PubMed1997

Binocular interaction in normal vision studied by pattern-reversal visual evoked potential (PR-VEPS).

Monocular and binocular visual evoked potentials (VEPs) in response to different check size (15-21-38-84 minutes or arc) were studied in 14 subjects with normal visual acuity and stereopsis. The binocular VEP amplitude is slightly higher than the VEP amplitude on stimulation of the "better eye" and significantly higher than the VEP amplitude on stimulation of the "worse eye"; this effect is observed using small checks and almost exclusively involved N75-P100. Both the N75 and P100 peaks occur earlier after binocular than monocular stimulation. The shortening of the N75 mean latency is significantly greater than that of the P100 mean latency when larger check sizes are used. The mean latency of the N145 potential is not significantly different in monocular and binocular stimulus conditions. The slight summation effect and latency shortening in the binocular VEPs are not consistent with the hypothesis that it is the sum of separate monocular signals originating from the visual cortex that gives rise to the response. The early components of both monocular and binocular VEPs are thought to be of post-synaptic origin (outside layer 4c of area 17), where the inputs become mixed so that most cells receive information from both eyes. The amplitude enhancement of binocular VEPs, which mainly occurs when using small checks, may be related to the increase in the total amount of cortical activity representing the macular region; this may account for binocular superiority in fine spatial resolution. The latency shortening in binocular conditions can be explained by considering that the critical determinant of the latency is the fundamental spatial frequency of the pattern. When coarse patterns are used, their effectiveness in parafoveal stimulation may affect the VEPs, with a significant contribution coming from the more peripheral retina. The enlargement of the visual field when the eyes see simultaneously may therefore further reduce the latency of the response when using the larger checks suitable for eccentric stimulation.

Adult↗

PubMed2005

Coupling between visual evoked cerebral blood flow velocity responses and visual evoked potentials in migraneurs.

Neurovascular coupling may be altered in migraneurs. Therefore, visual evoked potentials (VEP) and visually evoked cerebral blood flow velocity responses (VEFR) were simultaneously recorded in 30 healthy controls and 30 migraneurs interictally using a checkerboard stimulus with visual contrasts of 1%, 10% and 100%. The VEFR were measured in the posterior cerebral artery using transcranial Doppler and VEP were recorded from occipital leads. We found an increase in VEFR and VEP in both the healthy and migraneur groups (P < 0.01). VEFR were significantly higher in migraneurs (P < 0.01), while VEP did not significantly differ between the groups (P > 0.05). Regression showed a significant association between VEP and VEFR in both healthy controls (r = 0.66, P < 0.01) and migraneurs (r = 0.63, P < 0.01). The regression coefficient of migraneurs (b = 0.88, SE = 0.08) was significantly higher than that of healthy controls (b = 0.55, SE = 0.07) (P = 0.04). We conclude that neurovascular coupling is increased in migraneurs interictally.

Adult↗

PubMed1994

Pattern reversal visual evoked potentials in minor head injury.

Pattern reversal visual evoked potentials (PR-VEPs) have been recorded in 50 patients with minor head injury (MHI) on days 1 and 30 after trauma and the data compared to 20 normals. None of the patients had visual complaints. The aim was to investigate a possible visual pathway affection in MHI and test the usefulness of PR-VEPs as an objective noninvasive tool in the detection of a possible subclinical affection of the visual system in MHI. P100 latency and amplitude had no significant difference compared to normals. Comparison of patient data on days 1 and 30 after trauma showed a significant latency decrease and amplitude increase on day 30, compared to day 1. These alterations were not age dependent. Our data suggest affection of the human visual pathway in MHI. PR-VEP recording seems to be a useful, objective, noninvasive tool, helping to identify possible subclinical affections of the visual pathway in MHI.

Adolescent↗

PubMedDate not supplied

Visual evoked potentials in encephalopathy induced by galactosamine, ammonia, dimethyldisulfide, and octanoic acid.

Visual evoked potentials were utilized to examine the neuronal transmission changes provoked by galactosamine-induced hepatic encephalopathy and by administration in normal animals of toxins presumably involved in the pathogenesis of hepatic encepalopathy. Separate acute administrations of ammonia, dimethyldisulfide, and octanoic acid induced lethargy, convulsions in the case of the first two, and coma with visual-evoked potential patterns that never resembled the evoked potentials recorded in hepatic coma. By contrast, single and repeated administrations of the three above-mentioned toxins together at lower doses induced lethargy and coma with visual-evoked potential patterns similar to those observed in galactosamine-induced hepatic coma. These observations, together with previously published data, are consistent with the concept that the synergistic interaction of these toxins plays a significant role in the pathogenesis of hepatic encephalopathy.

Ammonia↗

PubMed1993

Application of the spatiochromatic visual evoked potential to detection of congenital and acquired color-vision deficiencies.

Visual evoked potentials were recorded in response to spatiochromatic stimuli modulated in different directions in cone-activation color space from subjects with congenital and acquired color defects. This technique was effective for detection and classification of both mild and severe forms of congenital deficits. Results suggest that the visual evoked potential is useful for early identification of color abnormalities in acquired deficits such as diabetes and that it is sensitive enough to detect regional retinal losses of sensitivity (e.g., as in central serous choroidopathy). The spatiochromatic visual evoked potential provides a systematic and sensitive indication of different color-vision anomalies.

Adult↗

PubMed1983

Abnormal visual evoked potentials in myotonic dystrophy.

Pattern-shift visual evoked potentials (VEPs) were recorded in 17 patients with myotonic dystrophy. Abnormalities of latency or amplitude were found in 10 patients (59%) with no obvious retinal or other significant ocular abnormality. All patients had a visual acuity of 20/30 or better. Since most patients had bilateral VEP abnormalities, localization of the disturbance was not certain.

Adult↗

PubMed1984

Visual evoked potentials in a rabbit model of hepatic encephalopathy. II. Comparison of hyperammonemic encephalopathy, postictal coma, and coma induced by synergistic neurotoxins.

To assess neuronal mechanisms of potential importance in the pathogenesis of hepatic encephalopathy, visual evoked potentials were recorded in rabbits with acute hyperammonemic encephalopathy, postictal coma, and toxin-induced coma resulting from the administration of a combination of subcoma doses of three neurotoxins: ammonia, dimethyldisulfide, and octanoic acid. The patterns of visual evoked potentials in these three syndromes were compared with those of rabbits with hepatic encephalopathy due to galactosamine-induced fulminant hepatic failure. In the absence of seizures, the patterns of visual evoked potentials associated with hyperammonemic encephalopathy and toxin-induced coma were fundamentally different from those associated with any stage of hepatic encephalopathy due to galactosamine-induced fulminant hepatic failure. In contrast, the pattern of visual evoked potentials in early postictal coma induced by four different precipitating factors (including toxin-induced seizures) resembled that of late-stage hepatic encephalopathy due to galactosamine-induced fulminant hepatic failure. These findings suggest that the recording of visual evoked potentials may be of value in experimentally testing hypotheses of the pathogenesis of hepatic encephalopathy due to fulminant hepatic failure. They indicate that acute hyperammonemia is not a satisfactory model of hepatic encephalopathy due to galactosamine-induced fulminant hepatic failure, that the occurrence of seizures may lead to incorrect interpretation of experimental data from models of hepatic encephalopathy, and that the syndromes of hepatic encephalopathy due to galactosamine-induced fulminant hepatic failure and postictal coma may share similar neural mechanisms. Finally, the results of this study do not support the hypothesis that hepatic encephalopathy due to galactosamine-induced fulminant hepatic failure is mediated by the synergistic interaction of ammonia, mercaptans, and fatty acids on the brain.

Ammonia↗

PubMed1988

Visual evoked potentials and changes in serum glycine concentration during transurethral resection of the prostate.

Visual evoked potentials were recorded in 10 patients undergoing transurethral prostatectomy under subarachnoid anaesthesia. They were compared with those obtained in a control group (n = 5) having other operative procedures also under spinal anaesthesia. Serum concentrations of glycine, ammonia, glucose and sodium, and osmolality, were determined during the perioperative period. The prostatectomy group demonstrated a significant prolongation of visual evoked potential P2 latency in the postoperative period when compared with preoperative values (P less than 0.01). No significant changes in latency occurred in the control group when measured at similar times. The prostatectomy group demonstrated a significant increase in serum glycine concentration (P less than 0.01); changes in serum ammonia and sodium concentrations and osmolality were not significant. There was no correlation between visual evoked potential latency and changes in serum glycine concentration. Changes in visual evoked potential during transurethral prostatectomy may be the result of an accumulation of a metabolite of glycine.

Aged↗

PubMed1985

Visual evoked potentials in macular disease.

Although a delayed visual evoked potential is considered to be the hallmark of optic nerve disease, relatively little has been published about VEP delays in macular disease. In this study, 20 patients with either acquired unilateral maculopathy or bilateral maculopathy in which one eye was more affected than the other were evaluated. VEP amplitudes and peak latencies were compared between eyes when recordable. Nine patients (45%) exhibited significant interocular delays in the affected or more affected eye while only four patients (20%) exhibited significant interocular attenuations in amplitude. In the nine patients exhibiting delays, three patients had a visual acuity of 20/30 or better in the affected eye or more affected eye. In the patients exhibiting amplitude attenuations, no patient had a visual acuity better than 20/50 in the affected or more affected eye. Although the mechanism of VEP delays in maculopathy is not clear, a VEP delay, in isolation of other tests, should not be used in the differential diagnosis of macular vs optic nerve disease. The clinician should specifically rule out macular disease in any patient with a delayed VEP before presuming the presence of a visual pathway dysfunction.

Adolescent↗

PubMed1982

Pattern visual evoked potentials in the rat.

Pattern and flash visual evoked potentials (VEPs) were obtained in 25 adult male hooded rats. Different electrode placements were used to detect the origin of the VEPs. The spatial frequency and temporal modulation of the stimulating pattern and the refractive state of the eye were varied to investigate the specificity of these factors in pattern VEPs. Variations in latency, amplitude, and trace morphology were found which were consistent with the characteristics of the visual system of the rat.

Animals↗

PubMed1992

The value of visual evoked potentials in optic neuropathy of Graves' disease.

Visual evoked potentials (VEP) were tested in patients with ophthalmopathy (OP) of Graves' disease (GD) before treatment and half-a-year and 5-7 yr after orbital decompression (7 patients) or retrobulbar irradiation (3 patients). Five patients not requiring treatment for OP and 16 healthy subjects served as controls. Treatment of OP was given on clinical grounds including decreased visual acuity (VA) indicating optic neuropathy. Before treatment VA was decreased in 5 out of 19 eyes whereas VEP were abnormal in all. The mean latency at N60 both in the operated (83.1 +/- 21.6 ms) and in the irradiated groups (80.9 +/- 7.0 ms) was significantly different from that in the untreated group (62.6 +/- 8.2 ms; p < 0.001) and the healthy subjects (58.9 +/- 6.3; p < 0.001). At P120 only the latency of the operated group differed significantly from that of the other groups (p < 0.001). There was a relationship between the eye muscle changes seen on CT scans and the ophthalmopathy score (according to the classification of the American Thyroid Association) and the latency both at N60 and P120. A change from a V-shape to a W-shape of the waves occurred more often in the treated patients before therapy than in the other groups. Two patients had multiphase VEP in both eyes which improved after treatment. After adequate clinical response the visual acuity improved in one of the 5 patients with initially depressed VA. VEP, initially abnormal in all, improved in 7 of the 19 eyes (37%) but further deterioration was observed in 8 (42%).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1995

[Long-term prolongation of direct pupillary light reflex latency and P100 latency of pattern visual evoked potential in unilateral optic neuritis].

We evaluated the visual functions of visual acuity, color sense, direct pupillary light reflex and pattern visual evoked potentials (P100) in five patients with unilateral optic neuritis whose visual acuity improved to 1.0 or better in order to assess the recovery of the impaired optic nerve fibers from the inflammatory process. During follow-up periods the direct light pupillary reflex was electropupillographically recorded and the P100 latency of visual evoked potentials was examined in both eyes. The temporal course of their differences showed a biphasic curve: the acute stage showed a rapid decrease of the differences and the chronic stage showed a flat line analysis of Pearson's correlation coefficient revealed that latency differences were mutually altered although there was a tendency for differences of direct pupillary reflex latency to decrease more rapidly at the acute stage than those of P100 latency. The present study demonstrated that the two different classes of the optic nerve fibers originating from the retinal ganglion cells, pupillary reflex-related fibers and form vision-related fibers, were damaged to the same degree by the inflammation, in spite of their morphological differences.

Adult↗

PubMed1991

Abnormalities of the electroretinogram and visual-evoked potential in vitamin E deficient rats.

Flash electroretinograms, retinal oscillatory and cortical visual-evoked potentials were recorded in 10-month vitamin E deficient rats and in age-matched controls. A significant increase in the latency (P less than 0.0001) and decrease in amplitude (P less than 0.0001) of the electroretinogram a- and b-waves were observed in the vitamin E deficient rats compared with controls. The vitamin E deficient rats also showed a significant delay (P less than 0.002) in early oscillatory potentials. No significant group differences were obtained in the P1 latency or P1-N1 amplitude of the visual-evoked potential; however, the N1 peak was significantly delayed (P = 0.01) in the vitamin E deficient rats. This study shows, for the first time, that the electroretinogram and visual-evoked potential to flash stimulation provide a sensitive index for monitoring the visual effects of vitamin E deficiency in the rat.

Animals↗