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Results for “Evoked Potentials, Visual”

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PubMed2003

Visual evoked potentials in patients with Graves' ophthalmopathy complicated by ocular hypertension and suspect glaucoma or dysthyroid optic neuropathy.

The study compared visual evoked potentials of patients with uncomplicated Graves' ophthalmopathy, patients with ophthalmopathy and elevated intraocular pressure or suspect glaucoma, and patients with dysthyroid optic neuropathy (DON). The aim of the study was to investigate the clinical potential for the visual evoked potentials (VEP) in the differential diagnosis among the groups. The VEPs were obtained from 43 subjects with endocrine ophthalmopathy. Group I included patients with uncomplicated ophthalmopathy (30 eyes); group II included patients with ophthalmopathy, intraocular pressure > or = 23 mmHg with and without early visual field defects, and no evidence of apical crowding on coronal computed tomography scan (28 eyes); group III included patients with DON (28 eyes). Amplitude and latency of major component of pattern VEP were obtained at three visual angles (60', 30', 15'). Data from each group was compared with data from age-matched normal subjects. Disturbances of VEP were found mainly in patients of Group II and Group III. Control Group had normal VEP. About the differential diagnosis between Group II and Group III the most important parameter was the N75-P100 amplitude for 15' of pattern stimulation. Only for this visual angle, Group II and Group III had not overlapped N75-P100 amplitude. This study shows that VEP detect visual function abnormalities noninvasively in patients with complicated Graves' ophthalmopathy. Results also indicate the clinical potential for VEP in the differential diagnosis between patients suffering from ophthalmopathy complicated by ocular hypertension or suspect glaucoma and patients with dysthyroid optic neuropathy.

Adult↗
PubMed1989

Visual adaptation to a spatial contrast enhances visual evoked potentials.

The effects of adaptation to the visual contrast of a counterphase grating were studied with visual evoked potentials (VEPs). The spatial frequency of the grating was 4 cpd, and its temporal frequency was 4 or 12 Hz. Steady-state VEPs were analyzed through an FFT (fast Fourier transform) algorithm. In the first experiment, contrast thresholds rose strongly just after the end of adaptation and declined regularly over time. The VEPs recorded in the medio-occipital lead showed an initial decrease in amplitude after adaptation, followed by an enhancement well above the preadaptation level and then a return to that level. The paradoxical enhancement of the VEP was found at both high and low contrast in both the medio-occipital lead and the right temporal lead of a right-handed subject. The left temporal leads showed a VEP enhancement at high contrast and a decline at a low value.

Attention↗
PubMed1988

Visual evoked potentials in Negro carriers of the gene for tyrosinase positive oculocutaneous albinism.

Visual evoked potential testing was performed on 15 Negro carriers of the gene for tyrosinase positive oculocutaneous albinism in order to detect whether they have the same visual pathway decussation anomalies as do homozygotes. No subject showed 01-02 asymmetry on monocular testing, indicating that decussation follows the normal pattern. It is concluded that visual evoked potential testing is probably not useful in the detection of Negroes heterozygous for the gene for tyrosinase positive oculocutaneous albinism.

Adolescent↗
PubMedDate not supplied

[Visual evoked potentials and the time of motor reaction to visual stimuli in chronic metallic mercury poisoning].

In a group of 10 patients with diagnosed occupational chronic poisoning with metallic mercury a correlation was sought between the parameters of the visual evoked potentials and the results of the psychological test evaluating the rapidity of motor response to the visual stimuli. The analysis suggest a cerebral dysfunction of the visual neurons and reduced rate of visual information transformation to the motor effector at the level of the cortical association centre.

Adult↗
PubMed1984

Visual evoked potentials and ibuprofen (Motrin) toxicity.

A patient taking ibuprofen (Motrin) for the relief of osteoarthritis developed, after two months, decreased visual acuity and decreased color vision. Initially the Visual Evoked Potentials, showed decreased wave amplitudes, and increased conduction times in both eyes. After stopping the drug, the Visual Evoked Potentials returned to normal one month before the visual acuity improved. We feel that Visual Evoked Potentials are useful for screening patients on ibuprofen, and prognosticating their recovery, when a secondary toxic optic neuritis develops.

Aged↗
PubMed1992

Pattern electroretinograms and visual evoked potentials in idiopathic intracranial hypertension.

A subclinical visual dysfunction can be detected by psychophysical methods in early-stage papilledema associated with idiopathic intracranial hypertension (IIH). We recorded steady-state pattern electroretinograms (PERGs) and visual evoked potentials (VEPs) to sinusoidal gratings of variable spatial frequency [0.6, 1.0, 1.4, 2.2 and 4.8 cycles/degree (cpd)] in 18 patients with IIH and early papilledema and in 21 age-matched controls. Spatial frequency selective reductions in the mean PERG (at 1-4.8 cpd) and VEP (at 4.8 cpd) amplitudes were found in patients in comparison with controls. The response functions of amplitude versus spatial frequency of patients' PERG and VEP displayed a low-pass shape, whereas in normal subjects PERG and VEP functions showed a band-pass and a high-pass shape, respectively. PERG and VEP abnormalities were found in 14 (77.7%) and 10 (55.5%) out of 18 patients, respectively. Most of these abnormalities involved only selected spatial frequencies (1.4-4.8 cpd). These results indicate spatial-frequency-dependent functional losses on both PERG and VEP in early papilledema, and suggest a potential value of these responses for detecting subtle visual abnormalities in IIH.

Adult↗
PubMed1989

Hemi-field pattern visual evoked potentials: a comparison of display and analysis techniques.

Three methods for analyzing the spatial organization of visual evoked potentials were compared. Pattern reversal visual evoked potentials were obtained from a single subject under three viewing conditions: stimulation of the left, right, and both visual fields. The scalp distribution of the VEP to 1 deg checks was displayed using three recording and analysis techniques: a conventional horizontal occipital array of electrodes, topographic mapping, and 3-dimensional evoked potentials. All three techniques revealed "paradoxical" lateralization of P100. The relative merits of each technique are discussed.

Brain Mapping↗
PubMedDate not supplied

Visually evoked potentials: theory, techniques and clinical applications.

The visually evoked potential (VEP), the recording of which has recently been made possible by the development of computer averaging techniques, is a gross electrical signal generated by the occipital region of the cortex in response to visual stimulation. It is more specific than the electroencephalogram (EEG) and more sensitive to changes in the visual stimulus; thus, it can provide ophthalmologists and vision researchers with information about the human visual system that is unavailable by other methods. Clinically, the VEP is of special value in the areas of refraction, infant acuity, diseases of the optic nerve, color blindness, amblyopia and field defects. Theory, techniques and instrumentation are described, and applications of the VEP to clinical situations and to vision research are discussed.

Adult↗
PubMed1985

Pattern-reversal visual evoked potentials in patients with hydrocephalus.

Pattern-reversal visual evoked potentials (VEP's) in response to whole- and half-field stimulation were studied in 10 patients with hydrocephalus. Abnormalities consistent with optic nerve dysfunction were recorded in four patients. Two patients had response asymmetry to half-field stimulation, which suggested dysfunction of the visual pathway in the right hemisphere. The remaining four patients had normal responses. Measurement of VEP's was repeated after the surgical treatment of hydrocephalus in four patients, and showed marked improvement in two of the three patients with preoperative abnormalities. This study suggests that, in patients with hydrocephalus, VEP's are more sensitive than clinical methods in detecting visual pathway dysfunction and that they can be useful in the follow-up monitoring of surgically treated hydrocephalic patients.

Adult↗
PubMed1991

Hemisphere asymmetry of the visually evoked potentials elicited by gratings of varying spatial frequency.

Visually evoked potentials (VEP) were recorded upon hemifield stimulation with sinusoidal gratings of varying spatial frequency (SF). Recording was bipolar from 0.1-0.2. The gratings were presented randomly in the left, in the right or in both visual hemifields. No systematic VEP asymmetry was observed at low SF. At SFs above 1.5-2 cpd, however, the early wave peaking at about 100 msec after grating onset was usually of greater amplitude when the grating was presented in the left visual field. In previous experiments of our, contrast sensitivity was almost the same in both hemifields. Thus, the VEP data suggest right-hemisphere specialization in processing high SFs and their comparison with the contrast sensitivity data suggests that this specialization occurs at a level higher than stimulus detection or is evident at suprathreshold contrast levels only.

Electroencephalography↗
PubMed1987

Analysis of visual evoked potentials through Wiener filtering applied to a small number of sweeps.

We introduce a method for processing visual evoked potentials, on the basis of a Wiener filter algorithm applied to a small number of consecutive responses. The transfer function of the filter is obtained by taking into account both the average of 99 sweeps (as an estimate of the true signal) and the EEG signal just before the stimulus onset (as an estimate of the noise superimposed on each individual response). The process acts as a sweep-by-sweep filter (in the sense of the mean square error) which considers the possible non-stationarities of the EEG signal during a complete clinical procedure. The average of a small number of consecutive filtered sweeps reveals variations in the morphology of the evoked responses which produce a change in the principal latencies. Applications are foreseen in neurophysiological studies of visual evoked potential responses, and in the clinic, where it is important to evaluate adaptive mechanisms, dynamic changes in single groups of visual evoked potentials and cognitive responses.

Algorithms↗
PubMed1992

Flicker visual evoked potential differentiation of glaucoma.

We have been recording visual evoked potentials (VEP's) produced by a series of increasing rate flicker stimuli to find early neuronal loss in chronic open-angle glaucoma patients and suspects. This technique has demonstrated selective early signal losses in high flicker frequency responses (25 and 31 Hz). This signal loss can precede the characteristic arcuate losses found with automated perimetry. In this retrospective study, 428 visual fields were graded and grouped with their associated cup/disk ratios, peak recorded intraocular pressures (IOP's), and flicker VEP measures in a population of patients either diagnosed with glaucoma or at risk for glaucoma (glaucoma suspects). The correlation of selective high frequency (31 Hz) flicker VEP amplitude loss with visual field damage was confirmed. More severe VEP losses correlate well with optic cup size and visual field grade, but not with peak recorded IOP. Phase angle data did not differentiate between populations separated by visual field losses and VEP amplitude measurements.

Analysis of Variance↗
PubMed1996

[Correspondence of depth sensitivity and visually evoked potential amplitude in retinal eccentricity].

It is believed that an enhancement of visual evoked potential (VEP) amplitude in response to stereograms is due to the activity of disparity-sensitive neurons in the visual center. However, it is unclear whether the enhancement works only on retinal disparity cues or on other depth cues as well, which are derived from the mental process of recognizing a depth. The aim of this study is to analyze this relationship by comparing the degree of amplitude increase in the VEP with that of the magnitude in depth perception by viewing a stereopair with a stereoscope. The reduction of the retinal disparity sensitivity in increasing retinal eccentricity was confirmed by psychophysical measurement tests and visual evoked potential measurement. However, the reduction rate of the sensitivity curve was greater in the VEP than in the psychophysiological curve. This means that changes in the VEP, when responding to a sterogram, are mainly due to factors in the disparity sensitive neurons rather than in the mental process of recognizing a depth.

Adult↗
PubMedDate not supplied

Sex differences in averaged visual evoked potentials during food intake in rats.

Averaged visual evoked potentials (AVEP's) were recorded in unrestrained male and female rats during alert wakefulness (baseline condition), feeding and drinking. The rats had been deprived of food and water for 23 hr prior to testing. Peak-to-peak amplitude of the AVEP's was measured between the slow negative and the preceding positive component. Under baseline conditions females had higher amplitude AVEP's than males. It is suggested that sex differences in adrenal steroid secretion could account for this observation. During feeding and drinking, AVEP's increased significantly in amplitude in both sexes, and high-voltage, slow EEG activity was observed to appear in most animals. During feeding, these increases in AVEO amplitude were significantly larger in males than in females. These findings support recent views on sex differences in the regulation of feeding behavior.

Animals↗
PubMed1981

Visual evoked potentials, auditory evoked potentials and EEG in shunted hydrocephalic children.

Visual evoked potentials (VEP) and auditory evoked potentials (AEP) were studied together with the EEG, in 15 hydrocephalic children who had been shunted previously, and in a control group of 10 normal children. From the control group normal VEP's, AEP's and EEG's were obtained. In all 15 hydrocephalic children the EEG was abnormal. AEP's were normal in 9 and abnormal in 6 cases. VEP's were normal in 7 and abnormal in 8 cases. Only 4 patients showed both abnormal VEP's and AEP's. No relation could be demonstrated between the severity of EEG disturbances and evoked response abnormalities.

Auditory Pathways↗
PubMed1982

Voluntary alteration of visual evoked potentials.

Fifteen normal adults had pattern-shift visual evoked potentials (PSVEPs) using monocular checkerboard pattern reversal. Subjects were instructed to concentrate on the pattern in the first set of trials and then to avoid perceiving it in the second set. Direct, continuous visual observation ensured that the eye remained open and fixed on the pattern. Nonetheless, a third of the subjects could spontaneously alter or obliterate the PSVEP using several maneuvers, including meditation, daydreaming, and convergence. Several could produce shifts in apparent PSVEP latency. With explicit instruction, most subjects could learn to alter their PSVEP by maneuvers that are inapparent even to an observent technician.

Adult↗