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Results for “Evoked Potentials, Visual”

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At least 235 records · Page 13Linked to original sources

PubMed1988

Evolution of visual evoked potentials in optic neuritis.

The visual evoked potential (VEP) latency was either abnormally prolonged or absent in the involved eye of 47 patients with optic neuritis. Twenty-two of these patients with known multiple sclerosis (MS), had similar abnormalities to 25 patients with no clinical evidence of MS. Follow-up clinical assessment and VEP were done 10 to 42 (mean 22) months later in 34 patients. In 15 of 34 patients with no VEP from the involved eye during initial examination, 6 returned to normal, 8 had prolonged latencies and 1 still had no response at follow up. Of 19 patients who initially had prolonged latencies in the involved eye, 6 returned to normal, 11 had prolonged latencies and 2 had no response at follow up. The VEP is helpful in confirming the diagnosis of ON. The examination must be performed when the patient is symptomatic or soon thereafter as 35% of our patients with an abnormal initial VEP had a normal VEP at follow up. This normalization was not related to the severity of the initial VEP abnormality.

Adult↗

PubMed1993

Visual-evoked potentials in neonates following asphyxia.

Visual evoked potentials (VEPs) are easily recorded in the neonatal intensive care setting using light-emitting diode goggles as the flash stimulus. They are sensitive measures of CNS integrity and are altered or abolished by hypoxia. Prognosis in newborns with birth asphyxia or hypoxia is difficult to predict; however, the VEPs have been shown to be very helpful. Absent VEPs carry a poor prognosis; persistently abnormal, i.e., beyond 1 week, also predict abnormal outcome. Normal VEPs by 1 week have an accuracy rate around 90% for normal outcome.

Age Factors↗

PubMed1990

Steady-state visually evoked potential topography associated with a visual vigilance task.

This paper describes data which demonstrate a correlation between the magnitude of the Steady-State Visually Evoked Potential (SSVEP) and visual vigilance. The SSVEP was recorded from 64 scalp sites and elicited by a 13Hz uniform visual flicker presented continuously while subjects undertook a visual vigilance task. Fifteen right-handed males were required to view three times a series of 180 geometrical shapes comprising a sequence of 60 squares, 60 circles and a further 60 squares. Each viewing of the 180 shapes constituted a trial. Trials 1 and 2 were identical while trial 3 differed from the first two in that one of the circles was modified. Subjects were ignorant as to the location of the modified circle and prior to the third trial, were challenged to identify the modified circle. A comparison of trials 2 and 3 indicated that the appearance of the modified circle was associated with an attenuation of the SSVEP in the occipito/parietal region. The same comparison indicated a pronounced SSVEP attenuation in the centro/parietal region during the interval that subjects were anticipating the appearance of the modified circle. These results suggest a distinction between the cortical activation patterns occurring during different phases of a visual vigilance task.

Adolescent↗

PubMed1987

Are flash-evoked visual potentials useful for intraoperative monitoring of visual pathway function?

Flash-evoked visual potentials (VEPs) recorded from the scalp were used in a series of 35 patients with tumors along the visual pathway: 3 orbital tumors, 25 perisellar tumors, 4 intraventricular tumors, and 3 occipital lesions. Preoperatively, various combinations of impaired visual fields and visual acuity were observed in over 90% of the patients. A postoperative decrease in visual function was observed in 3 cases. Of the 25 perisellar lesions, 13 were operated through a standard frontotemporal craniotomy and 12 were operated through a transnasal-transsphenoidal approach. VEPs were highly susceptible to volatile anesthetics, and there was a significant incidence of spontaneous latency increases and amplitude decreases in a large number of patients. There was an unacceptably high number of cases with significant VEP alteration occurring without concomitant visual function change. During trepanation or the transnasal approach, a reversible potential loss was observed in 11 patients, a profoundly altered wave form was seen in 8 cases, and a loss of single peaks was observed in 15 patients. During dissection of the tumor, a reversible potential loss or a potential with unidentifiable peaks was found in 25 cases; however, the VEPs recovered during closure or in the recovery room. There was no correlation between intraoperative VEP changes and the postoperative changes in visual function. In only 1 patient with an insignificant postoperative decrease in visual acuity from 0.4 to 0.3 was there a concomitant intraoperative potential loss. The major conclusion of our findings is that light-emitting diode flash-evoked VEPs demonstrate intraoperative changes that appear too early and too prominently to be caused solely by manipulation of the optic pathways.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1992

Visual evoked potentials specific for motion onset.

Motion-onset visual evoked potentials were studied in 140 subjects by means of motion-onset stimulation either on a television screen or through back projecting via a moving mirror. The motion-onset visual evoked potentials were characterized in 94% of the population by a dominant negative peak with latency in the range of 135-180 ms. Motion-onset visual evoked potentials with a dominant positive peak, as described in the literature, seemed to be a variant of pattern-off visual evoked potentials, caused by the pattern-disappearance effect at the onset of motion with a high temporal frequency (the multiple of the spatial frequency of the structure and the velocity of motion) of more than 6 Hz. Such visual evoked potentials occur mainly when the stimulus is limited to the macular area only. Additionally, other stimulus and recording conditions were found to be suitable for acquiring the specific motion-onset potentials without their contamination by pattern-related components. These conditions were as follows: an aperiodic moving pattern (e.g., random dots) with a low contrast (less than 0.2); a short duration of motion (less than or equal to 200 ms) and a sufficient interstimulus interval (at least five times longer than the motion duration) to decrease the adaptation to motion; and extramacular stimulation and recording of visual evoked potentials from unipolar lateral occipital leads. Such leads should be used because of the lateralization of these visual evoked potentials (mainly to the right occipital area), which is consistent with their assumed extrastriate origin.

Adult↗

PubMed1991

Postnatal development of the visual-evoked potential in dogs.

Recordings of visual-evoked potentials that were induced by flashes of white light were obtained from 13 Beagle pups to document the development of the response from age 7 to 100 days. Responses were recorded between needle electrodes placed on the nuchal crest and the interorbital line, with ground at the vertex. Five alternating positive (P) and negative (N) peaks were observed in most visual-evoked potentials: P1, N1, P2, N2, and P3. Responses were recorded from 2 pups prior to opening of the eyelids. Recordings were performed without sedation or dark adaptation. Peak latencies were essentially mature (equal to those of adult dogs) by day 11 for P1, and by day 38 for N1 and P2. The latencies to N2 and P3 did not reach adult values by day 100, but did reach plateau values by day 43. The P1-N1 amplitude measurements reached mature levels by day 14, whereas N1-P2 amplitudes were mature by day 32. The P2-N2 and N2-P3 amplitudes reached plateaus that greatly exceeded adult amplitudes by days 50 and 58, respectively. Maturation of visual-evoked potential responses paralleled reported morphologic development of the visual cortex. All of the measured latency and amplitude values had significant (P less than or equal to 0.004) linear regression lines of latency vs age or amplitude vs age.

Animals↗

PubMed2004

[The visual evoked potentials in diabetic retinopathy].

PURPOSE: The recording of Visual Evoked Potential alterations at the patients with diabetic retinopathy. MATERIAL AND METHODS: It was performed the Visual Evoked Potential recordings at 24 patients with diabetic retinopathy in different stages of evolution, with or without complications. The type of Visual Evoked Potential recording was pattern reversal with vertical bars. We followed the diagram alterations in correlation with the evolution stages of diabetic retinopathy and the visual parameter alterations. RESULTS: In all cases we recorded alteration of the Visual Evoked Potential. In nonproliferative diabetic retinopathy was noticed the delay of P100 wave with inconstant presence of the N75 and N135 waves. In proliferative diabetic retinopathy and its complications the alterations of the tract were important. CONCLUSIONS: The gradual alteration of the Visual Evoked Potential tract at the patients with diabetic retinopathy represents a prognosis of the disease.

Aged↗

PubMedDate not supplied

[Visual evoked potentials in disorders of the cerebral circulation].

Visual evoked potentials were analysed in 15 patients before and after operations performed in the acute and cold periods of rupture of cerebral aneurysms. The analysis made it possible to identify the regions of the disturbed latency and shape of the potentials. The location of the aneurysm determines the site of the region of impairment of the visual evoked potentials, whose area correlates with the severity of the patients' condition in the acute period. Diminution of the region of impairment of the evoked potentials was more manifest in patients who were operated on in the acute period of rupture of the aneurysm than in those who underwent operation in the cold period.

Adolescent↗

PubMed1989

Pattern electroretinography in patients with delayed pattern visual evoked potentials due to distal anterior visual pathway dysfunction.

Between March 1983 and January 1988 delayed pattern visual evoked potentials (PVEP) were observed in 67 patients with distal visual pathway dysfunction. Many of these patients had been referred for neurophysiological examination because of possible optic nerve dysfunction. These patients also had pattern electroretinography (PERG) performed which in all cases showed an abnormality of the main positive P50 component. None of these patients had an abnormality confined to the negative N95 component, the type of abnormality usually found if the PERG is abnormal in optic nerve disease. It is suggested that PERG recording should now be a routine adjunct to the PVEP in the assessment of anterior visual pathway dysfunction.

Adolescent↗

PubMed1993

Visual evoked potentials and electroretinography in brain-dead patients.

Visual evoked potentials and electroretinograms were elicited by light-emitting diode stimulation and recorded simultaneously, with cephalic and noncephalic references, in 30 normal subjects and in 30 brain-dead patients. A characteristic pattern was found in the group of patients: when a cephalic reference was used for both visual evoked potentials and the electroretinogram, the a- and b-waves of the electroretinogram were recognized in all patients, and visual evoked responses consisted of waves with inverse polarity, similar morphologic characteristics, the same latency, and less amplitude than those of the electroretinogram. When a noncephalic derivation was chosen for the electroretinogram and visual evoked potentials, electroretinogram did not change in either morphologic features or latency, whereas the visual evoked potential channel showed no response. Only in two cases was it possible to record waves in the visual evoked potential lead with a noncephalic reference, showing a spread of the electroretinogram to the occipital area, with a considerably reduced amplitude. These results suggest that, although contamination of visual evoked potential records by the spread of the electroretinogram to the occipital area could occur, it is easy to confirm the absence of a true cortical visual response in brain-dead patients by means of a noncephalic reference. This pattern clearly confirms that in the visual pathways of brain-dead patients, electrical activity is confined to the retina.

Adolescent↗

PubMed1995

Pattern electroretinogram, visual evoked potential and psychophysical functions in maculopathy.

To compare pattern electroretinograms and visual evoked potentials with psychophysical examinations, such as visual acuity, static (automated) perimetry and color vision in unilateral maculopathies of various origins, 20 patients with unilateral retinal diseases within the macula and the posterior pole were tested. Pattern electroretinography, visual evoked potential testing and static perimetry (Octopus program M1) were performed with three different test field sizes (20 degrees x 20 degrees, 10 degrees x 10 degrees and 6 degrees x 6 degrees). The best correlation in all three test field sizes was found between visual acuity, static perimetry and visual evoked potential. This result is surprising, since central area defined functions (visual evoked potentials, visual acuity) correlated well with a total area integrating function (mean defect in static perimetry. The pattern electroretinogram, which seems to reflect an area-related function as well, showed a correlation to static perimetry only in the smaller 10 degrees x 10 degrees and 6 degrees x 6 degrees fields and not a significant correlation in the 20 degrees x 20 degrees field. Smaller stimulation fields may therefore produce sharper results in pattern electroretinographic testing. There was no correlation between pattern electroretinograms and visual evoked potentials or visual acuity. The pattern electroretinogram was recorded under monocular and binocular viewing conditions. In 60% of the patients, the amplitude of the affected eye was more reduced in the monocular than the binocular viewing condition; the healthy fellow eye controlled stable fixation of the affected eye more readily during binocular pattern electroretinogram registration. The degree of the color vision disturbance (C-index, desaturated panel D-15 test) did not correlate to any of the other examinations.

Adolescent↗

PubMed2003

Pattern reversal visual evoked potentials as a measure of visual pathway pathology in multiple sclerosis.

BACKGROUND: Pattern reversal visual evoked potentials (PRVEPs) have a well-documented role in diagnosis of multiple sclerosis (MS), but their value as a visual function surrogate remains controversial. METHODS: We evaluated PRVEP in 37 patients with MS who were participating in a long-term follow-up study following a phase III trial of interferon beta-1a (Avonex). Patients were examined to determine the Kurtzke Extended Disability Status Score (EDSS), multiple sclerosis functional composite (MSFC), contrast letter acuity (CLA), and had cranial MRI scans to determine whole brain atrophy (BPF). PRVEP was evaluated for P100 latency, amplitude, and waveform morphology. Two summary scores were created: for Score A, abnormal latencies, morphologies, and amplitudes of each individual eye were added; for Score B, abnormal latencies, morphologies, and amplitude ratio between eyes was determined. Sixteen patients in this group also had PRVEP at the time they enrolled in the clinical trial, eight years previously. RESULTS: At the follow-up exam, over 75% of patients had abnormal PVEP parameters while visual acuity (VA) was abnormal only in 59%. Increased PRVEP latency over the eight-year period correlated with deterioration assessed by EDSS (P = 0.006), BPF (P = 0.0001), and MSFC (P = 0.0041). Score A was significantly correlated with EDSS, BPF, CLA, cognitive function, and quality of life assessed with the Sickness Impact profile. No correlation was seen with the MSFC. CONCLUSIONS: The results indicate that PRVEP measures MS-related pathology, and can provide not only diagnostic but also prognostic information during evaluation of MS patients.

Evoked Potentials, Visual↗

PubMed1989

[Visual evoked potentials in diabetics].

The authors investigated visually evoked potentials in 27 patients with diabetes mellitus type I and II. In 77.8% of the patients abnormal values of visually evoked responses were found. The authors did not find a significant relationship between the degree of diabetic retinopathy and the disorder of visually evoked potentials.

Diabetes Mellitus↗

PubMedDate not supplied

Comparison of visual evoked potentials in patients with psychogenic visual disturbance and malingering.

PURPOSE: To verify the efficiency and objectivity of the pattern visual evoked potential (VEP) for organic disorders of the cortical visual system. METHODS: This retrospective study evaluated VEP in 19 patients diagnosed with psychogenic visual disturbance, 7 patients with malingering, and 37 age-matched normal volunteers. Transient (3 reversals per second) and steady-state (12 reversals per second) pattern VEPs for check sizes 15' and 30', with a contrast of 80%, were recorded. RESULTS: The amplitudes of both transient and steady-state pattern VEPs were significantly increased in patients with psychogenic visual disturbance, while patients with malingering had significantly lower amplitudes. P100 peak latency was prolonged in both groups of patients. CONCLUSION: Monitoring of patients' fixation on the stimulus showed those with psychogenic visual disturbance fixated well on the stimulus, while those with malingering did not. This finding produced a VEP amplitude reduction in patients with malingering. The reason for the VEP amplitude in patients with psychogenic visual disturbance is unclear.

Adolescent↗

PubMed1985

The application of flash visual evoked potentials during operations on the anterior visual pathways.

Flash visual evoked potentials (F-VEP's) have been recorded in fifteen patients (thirty eyes) with anterior visual pathway compression lesions before, during and after the operation in relation to clinical visual testing. A grading system for the wide variety of abnormal F-VEP's has been established, based on changes in forty patients (eighty eyes). No significant correlation between change in F-VEP and visual acuity or visual field has been demonstrated. Intraoperative F-VEP's have been found to be sensitive to halothane and to surgical manipulation of the optic nerve and/or chiasm during dissection of the tumour. The technique is considered a useful means of identifying the optic pathway during operation and may assist in prevention of optic damage if the transphenoidal approach is used.

Adult↗

PubMedDate not supplied

Visual evoked potentials in diabetic children and adolescents.

Visual evoked potentials were studied in 30 insulin-dependent diabetic children and adolescents. Thirty percent of the subjects had evidence of significant abnormalities. No correlation was found between visual evoked potentials and age, duration of diabetes, metabolic control, and retinopathy.

Adolescent↗

PubMed1995

Diagnostic value of 33 Hz steady-state visual evoked potentials in low-vision children.

Pattern-reversal visual evoked potentials elicited by patterns of 60' and 20' checks and 33 Hz steady-state flash visual evoked potentials were recorded in low-vision children (visual acuity less than 20/120) with optic atrophy (18 eyes), amblyopia (18 eyes), macular degeneration (7 eyes) and controls (24 eyes). Steady-state visual evoked potentials were non-recordable in 17 out of 18 eyes of optic atrophy patients and normal in other children. Abnormalities of pattern-reversal visual evoked potentials were similar in all groups of patients. 33 Hz steady-state flash visual evoked potentials are recommended for differential diagnosis of optic atrophy with other causes of low vision in children.

Adolescent↗

PubMed1982

Visual evoked potentials: evidence for lateral interactions.

Electrical potentials evoked in the human brain by visual stimulation can easily be recorded by using electrodes attached to the scalp. It is difficult, however, to relate these visual evoked potentials (VEPs) to specific neural processes: scalp electrodes, far removed from the brain, sum potentials from large areas of cortex. We improved identification and localization of lateral interactions by differentially modulating small neighboring parts of a "windmill-dartboard" stimulus pattern-a central disc surrounded by three contiguous annuli, all radially divided into light and dark segments. With temporal contrast reversal of all segments in the pattern, the major component of the VEP is at the second harmonic of the frequency of modulation--as expected. Temporal contrast reversal of the segments in the central disc and second annulus, with contrast of segments held constant in the first and third annuli, unexpectedly amplifies the VEP at the fundamental frequency of modulation and attenuates it at the second harmonic. Slight spatial separation of static and dynamic zones reduces both the amplification of the fundamental and the attenuation of the second harmonic. Thus, both phenomena appear to result from strong lateral interactions over relatively short distances. Nevertheless, different neural mechanisms must be involved; fundamental and second-harmonic components of the VEP are different functions of spatial separation and relative contrast of the segments in contiguous static and dynamic zones.

Animals↗