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At least 613 records · Page 34Linked to original sources

PubMed1999

[Effect of levodopa therapy on visual evoked potentials and visual acuity in amblyopia].

Amblyopia represents the most common form of visual impairment in children, affecting approximately 2% of the population. To determine the efficacy of the dopamine agonist levodopa for childhood amblyopia, a double-masked, placebo-controlled randomised study was performed on 32 amblyopic children with central fixation between 4 and 17 years. Subjects received 2 mg/kg levodopa benzeraside or placebo 3 times per day over a 1 week period. Estimates of visual acuity for each eye (Snellen visual acuity) were obtained, and pattern-shift visually evoked potentials (VEP) were examined by an opthalmologist and a neurologist. At the end of dosing regimens, the levodopa group was significantly improved in visual acuity by 1.4 lines and pattern VEP amplitudes. No changes could be detected after placebo administration. One week after the termination of the treatment, Snellen line acuity and pattern VEP amplitude were decreased to pretreatment levels. The transient effect of levodopa points to a long-term treatment with the substance. Our results should therefore encourage further long-term clinical trials investigating the therapeutic potential of levodopa in amblyopia.

Adolescent↗

PubMedDate not supplied

Pattern visual evoked cortical potentials predict postoperative visual acuity after cataract surgery in patients with glaucoma.

Visual acuity after cataract surgery in patients with glaucoma cannot be predicted accurately. We studied preoperative recordings of pattern visual evoked cortical potentials (PVECPs) to evaluate postoperative vision in patients with glaucoma and cataract. Fifty patients with glaucoma and no cataract and 31 patients with glaucoma and cataract who underwent phacoemulsification were included in this study. Age and P100 component significantly correlated with postoperative visual acuity with multiple linear regression analysis. A significantly greater number of patients with glaucoma, cataract, and a P100 component preoperatively showed a visual acuity of 0.7 or better postoperatively, as compared to those without a P100 component. PVECP before cataract surgery was able to predict postoperative good visual acuity in patients with glaucoma and cataract.

Adolescent↗

PubMed1975

Two visual systems in clinical neurology: readaptive role of the primitive system in visual agnosic patients.

In six patients with visual agnosia syndromes there was a striking dissociation between a preserved possibility of recognition of letters or objects in movement versus the recognition by simple visual static presentation. After a review of the literature it is concluded that at least two visual systems may be individualized in humans, i.e. a more recent one (the geniculo-calcarine) and an older one (the tectal-pulvinar-occipito-temporal system). Both from a physiological and clinical point of view, the most primitive system has two parts, i.e. a tectal and a telencephalic part. In visual agnosia, parts of the preserved primitive system remained as single support to compensate the loss of visual recognition for static patterns. The recognition of these two systems has both a theoretical and a practical value.

Adaptation, Physiological↗

PubMed1998

Multimodality visual evoked potentials in evaluating visual dysfunction in optic neuritis.

Visual information is processed via multiple, parallel channels. The present study examined the clinical feasibility of multimodality visual evoked potentials (VEPs) in optic neuritis. We recorded transient VEPs to 30' checkerboard patterns, chromatic and achromatic sinusoidal gratings and apparent motion, and steady-state VEPs to achromatic gratings in 15 normal controls and 14 patients. VEPs to 30' checks were abnormal in 10 eyes (7 patients); however, considering all five modalities, abnormal responses were seen in 20 eyes (12 patients). Abnormality rates were not equal among the visual stimuli, which thus suggested possible dysfunction of individual subdivisions in the visual pathways. We conclude that use of multimodality VEPs may increase both understanding of the pathophysiology of the visual pathways and diagnostic yield.

Adult↗

PubMed1982

Visual masking with presentations in same and opposite visual fields: evidence for contralateral masking.

Three experiments were conducted in a preliminary attempt to study the effects of presentations of an informational target stimulus to the right or left visual fields when the target was either preceded or followed by a noninformational masking stimulus and when the mask was presented to the same or opposite visual field of the target. Results indicated that masking was more effective in the same than in the opposite visual field but that masking of the opposite visual field was feasible for both forward and backward masking. Laterality effects were also found for forward and backward masking, with a modest advantage of the right visual field (left hemisphere) in both cases. Limitations of the data and directions for future research were discussed.

Discrimination Learning↗

PubMed1996

Accumulation of VDT work-related visual fatigue assessed by visual evoked potential, near point distance and critical flicker fusion.

To confirm daily accumulation of visual fatigue induced by work with visual display terminals (VDT), visual evoked potential (VEP), near point distance (NPD) and critical flicker fusion (CFF) were measured in three VDT workers and three sex- and age-matched controls (non-VDT workers) in the morning, noontime and evening for five consecutive days (Monday to Friday), totally 15 times per subject. The workers had been engaged in wireless handling operation, with VDTs, of an unmanned power shovel (Worker 1), an unmanned 78-ton dump truck (Worker 2) and mobile monitor-cameras (Worker 3), for 10 months. Their working hours were about 6.5 hours per day; but, the Worker 2 could take a 10-minute recess (a period without VDT work) per about 30 minutes during working hours. Significant daily variations in the VEP latency, NPD and CFF were found in the Worker 1 or Worker 3 despite the absence of any significant daily or diurnal variations in the non-VDT workers; the trends in the variations were getting worse from Monday to Friday. The NPD in the VDT workers was significantly longer than that in each of the matched controls; also, the CFF in the Workers 1 and 3 was significantly depressed. The changes in the VEP latency from morning to noontime and in the NPD and CFF from noontime to evening were significantly larger in the VDT worker than in the matched control. These findings suggest that VDT work probably affects visual function assessed by the VEP, NPD and CFF. Visual fatigue due to long-term VDT work may tend to be accumulated day by day.

Adult↗

PubMed1979

Effect of altered central and peripheral visual field stimulation on correct recognition and visual evoked response.

Hemispheric asymmetry was assessed using combined electrophysiological (visual evoked response) and behavioral (percentage-correct-recognition) techniques. Right-handed, right-eyed, male undergraduates who viewed tachistoscopically exposed CVCs and random shapes in both central and peripheral visual fields were scored for their ability to recognize the stimuli correctly. Latency and amplitude of visual evoked responses were compared with correct recognition. Central and peripheral stimuli produced significant results. Superiority of the left hemisphere for verbal stimulus processing was supported. Small but consistent positive peak latencies of visual evoked responses also indicated language specialization of the left lobe. Results were interpreted as supporting hemispheric functional asymmetry. Additional findings of "cognitive masking" and marked reduction in intersubject variance in postive peak latencies of visual evoked responses by a central stimulus occurring at approximately 300 msec were also obtained. Mechanisms of iconic image storage, neuropsychological attentional theories, and differential hemispheric structural organization were discussed in interpreting results.

Adolescent↗

PubMed2000

[Changes to visual acuity and the visual field in a case of meningioma operated at the anterior level].

It's presented a midline meningioma of anterior level case which preoperative has an importance affectation of the visual acuity and visual field, and postoperative in dynamic is founded the important improvement of visual acuity and visual field. It's discussed visual field topography and atrophy optic pathophysiology. It's a neuro-ophthalmology case example, where the cooperation neurosurgery-ophthalmology permit medical solution and restored in social life of the patient.

Female↗

PubMed1997

[Objective assessment of visual acuity with visual evoked potential].

PURPOSE: To study the technique for objectively assessment of visual acuity with Pattern Visual Evoked Potential (PVEP) and Discrete Fourier Transform (DFT). METHOD: Thirty-three normal eyes were tested in this study. Reversal square-wave gratings of eight different sizes (30, 20, 18, 12, 10, 6, 4, 2 min. of arc) were used as stimuli. The reversal rate of the stimuli was 10 times/sec. The harmonic amplitudes of VEP at 10 Hz were calculated with Discrete Fourier Transform. A relation curve between the harmonic amplitude and the size of grating was plotted from the data of each tested eye. Regression line was fitted to the data points in the approximately linear section of the curve which is near the threshold of zero amplitude. The threshold of the grating size was obtained by extrapolating of the regression line to zero amplitude, and the visual acuity was assessed with the threshold. RESULT: In seventy percent of tested eyes, the visual acuities assessed with VEPs were consistent with those measured with the International Standard Test Chart. CONCLUSION: The VEP technique for visual acuity assessment is reliable.

Adolescent↗

PubMed2000

[Monitor visual function with flash visual evoked potential during orbital surgery].

OBJECTIVE: To evaluate the feasibility and reliability of monitoring visual function with flash visual evoked potential (FVEP) during orbital surgery. METHOD: The visual function of 82 cases was monitored during orbital surgery with FVEP. Of these cases, the intraoperative and postoperative visual functions (IOVF and POVF) were compared. RESULTS: Sixty-nine cases were successfully monitored. Sixty-seven cases obtained the accordance of IOVF and POVF, and there were false positive in 1 case and false negative in 1 case. CONCLUSION: Intraoperative monitoring of visual function with FVEP can show the surgical injury of the optic nerve and unsuitable procedures, and decrease the surgical blind rate.

Adolescent↗

PubMed2002

[Evaluation of the developing human visual system using flash-visual evoked potential].

Flash visual evoked potential (Flash-VEP) is easily recorded in preterm infants. However, its clinical application has not been established due to its great variability in response. Our longitudinal studies on the two components of the N1 wave facilitated peak definition and established normal ranges that are clinically valuable. The N1a (early component of the N1) peak latency decreases at about 4.6 msec/week between 30 and 40 weeks postmenstrual age. A flash-VEP study in the preterm period enables us to observe the neuronal development in the human visual system that normally proceeds in utero. Flash-VEP analyses on preterm infants demonstrated that the decrease in the N1a peak latency reflects the progress of myelination in the visual pathway according to the developmental program irrespective of preterm birth. The developmental changes of the N1 wave configuration reflect the maturation of the neuronal networks in the visual cortex, which is accelerated by extrauterine visual experience. Using improved methodology and peak denomination that we proposed, flash-VEP can be applied to preterm infants safely, and should provide us with neuro-developmental information of the human cerebrum.

Cerebral Hemorrhage↗

PubMed1991

Temporal interactions in the cat visual system. I. Orientation-selective suppression in the visual cortex.

The perception of a visual contour depends on the spatial and temporal context in which it is viewed. Interactions between visual contours are believed to underlie a wide range of perceptual phenomena, including geometric illusions and aftereffects, contrast adaptation, and visual masking. The physiological mechanisms that might underlie such interactions were studied in the visual cortex of the cat by recording responses of single neurons to pairs of brief stationary stimuli that were separated in time. The results revealed a long-lasting, orientation-selective suppression, termed "paired-pulse suppression," which was strongest at the cell's preferred orientation, but which was more broadly tuned for orientation than the excitatory response of the cell. Although the strength and duration of the suppression varied widely, some degree of response reduction was present in most cells studied. The function of this suppression may be to regulate the gain with which visual inputs are transmitted to cortical neurons, thus preventing response saturation and positive feedback.

Anesthesia↗

PubMed1989

[Long-term follow-up of deterioration of the visual field in visual acuity in retinitis pigmentosa].

The first part of this presentation is devoted to the problem of determining the precise time of onset of retinitis pigmentosa (RP). For the purpose of this discussion we will stay with the definition of the beginning of RP as that date on which the decrease in dark adaptation is first noticed, rather than visual field loss, which is subject to even greater uncertainty. The cases selected demonstrate that the period between the first sign of night-blindness and a noticeable narrowing of the visual field can vary greatly. A latent period of slow progress is followed by marked decrease in visual function. In a third period the area loss proceeds linearly. The course of the disease was observed over periods of up to 16 years using the Goldmann perimeter. Several stages of visual field deterioration are presented over periods of up to 65 years. The mode of visual field loss depends on the diameter of the test objects employed.

Adult↗

PubMed1984

[Effect of visual deprivation on the development of mediator receptors in the visual system of the rat].

Effect of monocular deprivation (unilateral closure of the eye on the 11th postnatal day) and life in darkness (birth, development and killing of animals proceeded under complete exclusion of light) on the development of beta-adrenergic, serotoninergic, M-cholinergic, glutaminergic and benzodiazepin receptors in primary visual structures (visual cortex, lateral geniculate body, superior calliculi of lamina quadrigemina, retina) was studied in experiments with rats. A technique of mediators binding with ligands was used for quantitative estimation of mediator receptors. It is shown that monocular deprivation influences development of beta-adrenergic, serotoninergic and glutaminergic receptors mainly in the lateral geniculate body and retina, while life in darkness--mainly development of serotoninergic receptors in superior colliculi of lamina quadrigemina. Development of cholinergic mediator system receptors under visual deprivation is disturbed only temporarily. The detected changes in development of receptors after visual deprivation testify to the altered activity of different neuronal mediator systems in the respective visual structures.

Animals↗

PubMed1984

[Visual scanning in patients with unilateral visual neglect due to right-sided cerebro-vascular lesion].

The characteristics of visual scanning in patients with unilateral visual neglect (UVN) were studied. Forty-one patients who showed UVN in the figure finding test and 21 patients who showed to UVN in the test were selected from 176 patients with the right-sided cerebro-vascular lesion. They ranged in age from 46 to 78 years. The severity of UVN in each subject was determined by the number of the figures neglected unilaterally in the figure finding test in which a subject was asked to circle the designated figures scattered among the other figures on the test paper. The following two tests were administered to each subject. Test 1 examined binocular peripheral vision by tachistoscopic method in which a white circle of 1 degree was presented for 1/8 sec at 15 degrees from the central fixation point either unilaterally or bilaterally. Test 2 investigated the movement of gazing point while a subject was searching a target on a screen with his or her head stabilized. It was recorded on 16 mm movie film with Eye-Mark Recorder Model IV (Nac Co.) and converted into a series of position coordinates from which a visual scan path was reproduced and values of variables representing characteristics of visual scanning were computed. Six of 19 subjects who demonstrated "mild" UVN were found their peripheral vision intact. The characteristics of their visual scan path did not differ from the ones of the other 9 subjects who demonstrated "no" UVN as well as intact peripheral vision.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗

PubMed1983

Organization of the visual thalamus: corticothalamic projections from the primary visual area in the opossum.

The projections from the visual cortex to thalamic nuclei in the opossum were investigated by degeneration and radioautographic methods. Efferent axons from the striate cortex course from the internal capsule to the thalamus in two bundles, one of which innervates the reticular and dorsal lateral geniculate nuclei, while the other bundle innervates the external layer of the ventral lateral geniculate nucleus. Both bundles course along and through terminal fields found in the lateral posterior nucleus. The visuotopic organization inferred from the corticofugal pathway shows that projection lines in the dorsal lateral geniculate nucleus (DLGN) run along medio-lateral strips including both the beta and alpha segments, across the quasi-laminae of retino-geniculate projection, and that naso-temporal axes in the visual field run in a dorso-ventral direction through the DLGN. The external layer of the ventral lateral geniculate nucleus receives a projection from the striate cortex and bilateral projections from the retina, and naso-temporal axes in the visual field are represented along a dorso-ventral direction in this layer. The striate cortical projections cover approximately the lateral two-thirds of the lateral posterior nucleus, overlapping a small retinal terminal field, and naso-temporal axes in the visual field are represented onto the cortico-recipient zone in a mirror-symmetric direction to that of the adjoining DLGN. In all these three cortico-recipient zones, dorso-ventral axes in the visual field are represented in a rostro-caudal direction.

Animals↗

PubMed2005

Objective perimetry using the multifocal visual evoked potential in central visual pathway lesions.

AIMS: To examine the ability of the multifocal pattern visual evoked potential (mVEP) to detect field loss in neurological lesions affecting the visual pathway from the chiasm to the cortex. METHOD: The mVEPs recorded in the clinic were retrospectively reviewed for any cases involving central neurological lesions. Recordings had been performed with the AccuMap V1.3 objective perimeter, which used an array of four bipolar occipital electrodes to provide four differently oriented channels for simultaneous recording. 19 patients with hemianopias were identified. Of these there were 10 homonymous hemianopias with hemifield type loss, two bitemporal hemianopias, and seven homonymous hemianopias with quadrantanopic distribution. A comparison with subjective field results and CT/MRI findings was done to determine the relation between the two methods of visual field mapping and any relation with the anatomical location of the lesion and the mVEP results. RESULTS: In all hemianopic type cases (12) the defect was demonstrated on the mVEP and showed good correspondence in location of the scotoma (nine homonymous and two bitemporal). The topographic distribution was similar but not identical to subjective testing. Of the seven quadrantanopic type hemianopias, only four were found to have corresponding mVEP losses in the same areas. In the three cases where the mVEP was normal, the type of quadrantanopia had features consistent with an extra-striate lesion being very congruous, complete, and respecting the horizontal meridian. CONCLUSIONS: The mVEP can detect field loss from cortical lesions, but not in some cases of homonymous quadrantanopia, where the lesion may have been in the extra-striate cortex. This supports the concept that the mVEP is generated in V1 striate cortex and that it may be able to distinguish striate from extra-striate lesions. It implies caution should be used when interpreting "functional" loss using the mVEP if the visual field pattern is quadrantic.

Adult↗

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↗