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Results for “Evoked Potentials, Visual”

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At least 883 records · Page 49Linked to original sources
PubMed1988

Simultaneous recording of visual evoked potentials and electroretinograms in patients with unilateral opaque media.

We studied the correlation between preoperative visual evoked potentials (VEPs) and postoperative visual acuities in patients with unilateral opaque media. The fellow eye was used as the control. The filtering effect due to opaque media could be assessed on the basis of the difference of the electroretinogram (ERG) threshold in the two eyes. 'Modified VEPs' were then calculated by eliminating the assessed filtering effects, which improved our ability to detect the potential for visual recovery. In the normal eye, the stimulus threshold for VEP is lower than that for ERG by 2 or 3 log units. Therefore should a higher stimulus threshold be found for VEP than ERG, severe optic nerve damage is highly probable in eyes with media opacties.

Electroretinography↗
PubMed2006

Multifocal visual evoked potential latency analysis: predicting progression to multiple sclerosis.

OBJECTIVE: To monitor the difference in conversion rates to multiple sclerosis (MS) in 46 patients with optic neuritis between patients with multifocal visual evoked potential latency delay and those with normal latency. DESIGN: Prospective case series. SETTING: Metropolitan neuro-ophthalmology clinic. PARTICIPANTS: Forty-six patients with optic neuritis who did not have a diagnosis of MS on enrollment in the study. MAIN OUTCOME MEASURES: Conversion to MS according to the McDonald criteria. RESULTS: Analysis revealed that only 22 subjects had multifocal visual evoked potential latency delay. Over 1 year, 36.4% of patients with optic neuritis with latency delays progressed clinically to MS compared with 0% of those with normal latencies (P = .03, chi2). CONCLUSION: This may indicate that multifocal visual evoked potential latency delay can assist in predicting progression to future MS.

Analysis of Variance↗
PubMed1990

[Drusen papilla with vision disorder and pathologic visual evoked potentials].

Six cases of optic nerve head drusen ophthalmoscopically are reported. Five of these had pathological latencies of the P 100 potentials on VEP examination. Only three of the patients had subjective visual complaints; all six, however, had variable visual field defects. Optic nerve head drusen are an important differential diagnosis, which can be readily established especially in those younger patients who need neurological and ophthalmological examination because of visual disturbances and pathological VEP responses.

Adult↗
PubMed1987

[Visual evoked potentials in glaucoma and ocular hypertension].

In 60 patients affected by primary open angle glaucoma, in 30 patients with isolated ocular hypertension and in 30 healthy patients visual evoked potentials were studied. Amplitudes and latencies of P100 of the pattern reversal visually evoked potential were recorded and compared between the three groups. A new method is presented. A significant increase in VEP latency could only be demonstrated in the pathological groups. The reasons of these findings are discussed.

Age Factors↗
PubMed2002

Visual field defects and multifocal visual evoked potentials: evidence of a linear relationship.

OBJECTIVE: To determine the relationship between spatially localized multifocal visual evoked potentials (mfVEPs) and Humphrey visual fields (HVFs) in patients with unilateral field defects. METHODS: Humphrey visual fields and mfVEPs were obtained from 20 patients with unilateral field losses due to either ischemic optic neuropathy or glaucoma. Monocular mfVEPs were obtained for each eye. The amplitude of the mfVEP responses was calculated using root-mean-square and signal-noise ratio measures. Estimates of the HVF loss in the same regions of the field used for the mfVEP were obtained by interpolating the 24-2 HVF data. RESULTS: Monocular mfVEP amplitude decreased with HVF loss, although small mfVEP signals were not uniquely associated with poor fields. On average, the monocular mfVEP was indistinguishable from noise for field losses between -5 and -10 dB, and good monocular mfVEP amplitudes were never associated with extensive visual field loss. The interocular ratio of the mfVEP amplitudes correlated well with the difference between the HVF values of the 2 eyes, and this correlation improved with increased signal-noise ratio. CONCLUSIONS: The monocular and interocular results were consistent with a linear relationship between the amplitude of the signal portion of the mfVEP response and linear HVF loss. One way to produce this relationship would be if both the signal in the mfVEP and linear HVF loss were linearly related to the percentage of local ganglion cells lost. The clinical limitations of the mfVEP technique can be understood by taking the signal-noise ratio, and the linear model proposed herein, into consideration.

Adult↗
PubMed2002

Fomepizole therapy for reversal of visual impairment after methanol poisoning: a case documented by visual evoked potentials investigation.

PURPOSE: To illustrate the safety and efficacy of fomepizole in a case of methanol poisoning with initial visual impairment. DESIGN: Interventional case report. METHODS: A 60-year-old man was admitted with blurred vision and changes in color perception 18 hours after ingesting 100 ml methanol. Fomepizole was chosen for antidotal therapy in combination with hemodialysis. Flash electroretinogram (fERG) and flash visual evoked potentials (fVEPs) examinations were obtained at the bedside 2 hours after admission and on days 1 and 8. The monocular pattern-reversal visual evoked potentials (pVEPs) were investigated on days 1 and 8. RESULTS: A complete reversal of visual impairment was achieved within 20 hours. An abnormal b-wave amplitude and an increased peak III latency at VEPs were present on admission and recovered within 24 hours. CONCLUSIONS: Fomepizole appeared safe and effective for a patient who had severe methanol poisoning presenting with visual impairment.

Alcohol Dehydrogenase↗
PubMed1997

Comparison of the mechanisms of latency shift in pattern reversal visual evoked potential induced by blurring and contrast reduction.

Reduction of visual acuity or of the contrast of the stimulus induces a prolongation of the pattern reversal visual evoked potential (PR-VEP) latencies, perhaps because these conditions cause deterioration of the visual capacity to recognize objects and may preferentially activate the slower central retina channel. The PR-VEP was obtained with a video stimulator and 3 kinds of stimuli: total video field, video with a central scotoma and a restricted central stimulus. The subjects were tested under conditions of normal (20/20) and reduced visual acuity (20/200) with 14' and 56' checks and 60% contrast, and under conditions of normal visual acuity (20/20) with 14' checks and with stimulus contrast of 60% and 25%. Blurring increased latencies and decreased amplitudes only with the 14' checks stimulus but no with 56' checks, and the amplitudes obtained with the central stimulus became greater than those obtained with a central scotoma. Reducing contrast increased only latency, and there was not difference between amplitudes obtained with a central stimulus or a central scotoma. We conclude that blurring small checks induces a preferential stimulation of receptors in the central retina, but the same effect was not observed when stimulus contrast was reduced.

Adult↗
PubMedDate not supplied

Pattern reversal visual evoked potentials in migraine with aura and migraine aura without headache.

Pattern reversal visual evoked potentials (PVEPs) were recorded in 20 patients with migraine with aura (MA), 19 patients with migraine without headache (migraine equivalent; ME) during interictal periods, and 34 normal subjects. All migraine patients had hemianopsia or fortification spectra during attacks. In both MA and ME patients of less than 49 years of age, there were significant (p<0.01) differences in amplitude of PVEPs at the mid-occipital and contralateral to visual aura electrode sites compared to normal subjects. Amplitude of PVEPs in MA and ME showed significant (p<0.001) increases when recorded soon after attacks, especially within 10 days. There was a significant (p<0.01) correlation between percentage asymmetries and the duration of illness in both MA and ME. We conclude from our PVEP findings that cortical spreading depression remains the most likely explanation for the migraine visual aura.

Adult↗
PubMed1995

Behavior-dependent and drug-induced changes of rat visual evoked potential: relation to the EEG spectral power.

The relation between EEG spectral power and alterations of the visual evoked potential (VEP) during different behavioral states and after intraperitoneal application of neuroactive drugs have been investigated in Long-Evans rats. FFT power and field potential maps were made in five behavioral states of the unrestrained rat: exploratory sniffing, face washing, relaxed waking immobility, slow wave sleep, and during cortical high-voltage spindling. Fourteen epidural electrodes were implanted in the bulbus olfactorius, in the frontal areas Fr2 and Fr1, in the visual areas 18 and 17, and in the cerebellum of the right hemisphere. Two regions in the investigated cortex were found to be the probable origins of slow delta and theta waves: the frontal cortex and the anterior area 18. Area 17 does not express prominent EEG frequencies that contribute to the cortical EEG in any of the investigated behavioral states. The VEP was found to originate in area 17. The neural activity of the occipital cortex is reflected in the VEP whereas the occipital EEG possibly reflects the hippocampal activity in some behavioral states. This may be a reason for partly independent changes of VEP and EEG during different behavioral states and after application of neuroactive drugs.

Animals↗
PubMed1994

Visual evoked potentials to flash and pattern reversal stimulation after administration of systemic or topical scopolamine.

It has previously been shown that 0.6 mg of scopolamine produces a delay in the flash visual evoked potential of young normal volunteers, while the pattern-reversal response does not change in latency. Recent work has shown that this drug differentially affects parvocellular and magnocellular systems. To investigate this effect, two studies were performed. In the first study, 0.4 mg of scopolamine was injected intramuscularly into 11 young, healthy male volunteers who had fasted overnight. The visual evoked potential was recorded to both binocular flash stimulation and monocular pattern-reversal stimulation by means of a checker-board consisting of 56' checks in a 28 degrees field. Responses were recorded before administration of the drug and then 1, 2, 4 and 6 hours after administration. The scopolamine produced a slowing of the flash P2 latency of approximately 6 ms (p < 0.05) two hours after drug administration. There was no effect on the latency of the flash N2 or pattern-reversal N75 or P100. There was an increase in amplitude of the flash N2-P2 component 6 hours after drug administration and an increase in the amplitude of the N75 and P100 2, 4 and 6 hours after the drug. Further subjects were investigated with the use of topical administration of 0.125% scopolamine applied monocularly. In all studies the other eye acted as a control. The subjects were again young healthy volunteers. The visual evoked potential was recorded to both flash and pattern-reversal stimulation with a checkerboard consisting of 60' checks counterphasing at 2 Hz within a 5 degrees field. Results suggest that systemic scopolamine affects the tectal pathway but has no peripheral effect.

Administration, Topical↗
PubMed2004

Determining abnormal interocular latencies of multifocal visual evoked potentials.

PURPOSE: To describe methods for measuring interocular latency differences of multifocal visual evoked potentials (mfVEP) and for determining regions with abnormal interocular latencies in patients. METHODS: The mfVEPs from 100 individuals with normal visual fields and normal fundus examinations were analyzed. Individuals ranged in age from 21.6 to 92.4 years. The stimulus was a 60 sector, pattern-reversing dartboard display. Each sector had 16 checks, 8 white (200 cd/m2) and 8 black (< 1 cd/m2). Interocular latency was measured as the temporal shift producing the best cross-correlation value between the corresponding responses of each eye. The 'corrected interocular latency' was defined as the difference between this shift and the mean interocular latency (shift) for a particular sector and recording channel. RESULTS: The variability of the corrected interocular latency decreased as the signal-to-noise ratio (SNR) of the mfVEP responses increased. For example, the 95% confidence intervals decreased from over 16 ms to under 4 ms as SNR increased. Grouping and summing the responses also lead to an increase in SNR and a decrease in the confidence interval. The results of various cluster criteria were also derived. A cluster criterion (e.g. two or more contiguous points within a hemisphere exceeding a given confidence interval), can serve to increase the specificity for detection of eyes or individuals with abnormal interocular latencies. For example, while 21% of the eyes had 3 or more points exceeding the 5% confidence interval, only 1.8% of the eyes had a cluster of 3 or more of these points. Finally, interocular latency was only weakly correlated with age (r = 0.26). CONCLUSION: In testing for abnormalities in interocular latencies, the confidence interval should be based upon the SNR of the response. Grouping and summing responses to increase SNR or employing a cluster test may also prove useful.

Acute Disease↗
PubMed1982

Eye patching and visual evoked potential acuity in children four months to eight years old.

The monocular visual acuities of six children aged 4 months to 8 years were measured using visual evoked potentials (VEP's) before and during patching therapy. A seventh child had both Snellen and VEP monocular acuities determined before patching. In a cooperative child, it was estimated that VEP acuity was within 0.25 octaves (one line on an eye chart) of Snellen acuity. In the four children less than 3 years of age, patching resulted in a 1.8-octave decrease in acuity of the patched eye and a 2.0-octave improvement in the unpatched eye. After cessation of patching therapy, acuity of the previously patched eye improved 2.0 octaves and that of the abnormal eye declined 1.75 octaves. In the two children older than 4 years, patching resulted in 1.25-octave acuity decrease in the patched eye. Cessation of patching resulted in a 1.25-octave improvement in acuity of the patched eye. No permanent deleterious effects of patching on acuity were observed.

Age Factors↗
PubMed1996

Value of visual evoked potential monitoring during trans-sphenoidal pituitary surgery.

The visual outcome of 22 patients undergoing trans-sphenoidal excision of pituitary macroadenomas with intraoperative flash visual evoked potential (VEP) monitoring (Group A), was compared with a non-randomized group of 14 patients who had undergone similar operations without VEP monitoring (Group B). Tumour size, preoperative visual acuity, peripheral fields, and latencies and amplitudes of P1 and P2 were analysed to ascertain the best predictor of postoperative visual function. It was found that patients in Group A had a significantly greater improvement in field defects than those in Group B. There was no difference in postoperative improvement in visual acuity between the two groups. None of the variables analysed were good predictors of visual outcome.

Adenoma↗
PubMed1987

Visual evoked potentials, intracranial pressure and ventricular size in hydrocephalus.

Hydrocephalus in the newborn is frequently seen associated with perinatal asphyxia, birth trauma, or intracranial hemorrhage. Hydrocephalus produces enlargement of the cerebral ventricles and raised intracranial pressure secondary to increases in the amount of cerebrospinal fluid. In this study the relationship between the visual evoked potential and ventricular size in infantile hydrocephalus was investigated. Statistical analysis was used to define them and the role of the visual evoked potential in the clinical and structural assessment of infantile hydrocephalus. The results of these investigations demonstrated a significant relationship between ventricular size and evoked potential parameters and confirmed the usefulness of the flash visual evoked potential examination in the assessment of infants with hydrocephalus.

Cerebral Ventricles↗
PubMed1989

A PC-based system for visual evoked potential studies.

An interactive PC-based computer controlled system is described that can be used for collection and analysis of data of Visual Evoked Potentials (VEPs). Visual stimuli are generated on a high-resolution color monitor driven by an Enhanced Graphics Adaptor (EGA). The VEP waveforms are digitized by an A/D converter at a sampling rate of 1 KHz and stored on a hard disk for further analysis. The analysis software includes both time and frequency analysis routines as well as some innovative techniques for the use of the VEPs as a diagnostic measure for various diseases.

Computer Systems↗