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Multifocal Visual Evoked Potential (multifocal + visual_evoked_potential)

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Medical Sciences100%

Selected Abstracts

Clinical application of the multifocal visual evoked potential

CLINICAL AND EXPERIMENTAL OPTOMETRY, Issue 3 2004
David P. Crewther PhD
Background: Measures of visual function thresholds such as visual acuity and visual fields are generally dependent on subjective responses and assume maintenance of fixation, attention and motivation. In the young, elderly, cognitively impaired or malingering populations, such measures may be inaccurate or difficult to obtain. The Visual Evoked Response Imaging System (VERIS) has been claimed to give more objective topographic recordings of retinal and cortical function. This paper aims to explore the adequacy of this technique in four unusual, unrelated, clinically difficult cases. Methods: Multifocal visual evoked potentials (mfVEPs) recorded on the VERIS System 3.01 are used to assess visual function in four cases with contradictory clinical findings or unreliable subjective responses. Results: Patient 1 had sustained a head injury and had normal ocular and pupil examination but light perception in the right eye and 6/5 acuity in the left. Multifocal VEPs showed a marked depression of the right visual field with little macular response. Patient 2 had sustained a head injury, had a left field hemianopia, possible macular sparing and loss of much of the right field, reduced but variable visual acuities, good near vision and normal ocular fundi. Multifocal VEPs showed a severe depression in both visual fields (L more than R) with little macular response. Patient 3 had a left optic nerve meningioma and experienced great difficulty with visual field assessment. mfVEPs showed a bilateral depression in the superior field particularly the left field, with a larger deficit in the left eye. Patient 4 had unexplained visual acuity and peripheral field deficits. mfVEP results were inconclusive in this case. Discussion: Where there is difficulty performing traditional techniques or conflicting clinical findings, mfVEPs may provide additional objective information to aid in the assessment of patients. [source]

Multifocal objective perimetry compared with Humphrey full-threshold perimetry in patients with optic neuritis

CLINICAL & EXPERIMENTAL OPHTHALMOLOGY, Issue 6 2006
Nima Pakrou MBBS(Hons)
Abstract Background:, The aim of the study is to compare multifocal visual evoked potential (mfVEP) objective perimetry with Humphrey full-threshold visual field (HVF) perimetry, in the assessment of patients with optic neuritis (ON). Methods:, We assessed 16 patients with clinically diagnosed ON. A comparison was made between the HVF and mfVEP, based on the global severity indices of both tests and number and topography of significant abnormalities detected. The latency data and inter-eye asymmetry findings on the mfVEP were also evaluated. Results:, From a total of 128 quadrants analysed in the 16 patients (100 affected, 28 unaffected eyes), HVF perimetry identified a scotoma in 39/128 (30.5%) quadrants, all of which were in affected eyes; the mfVEP detected a scotoma in 68/128 (53.1%) quadrants using amplitude and/or asymmetry data (XV2 = 7.2485, P = 0.0071). Latency plots on the mfVEP identified a significant latency deviation cluster in 20/25 (80%) affected eyes. Abnormalities were also detected in 4/7 (57%) unaffected eyes. The global severity indices in the affected eyes showed a high correlation between the two tests (r = 0.73). Conclusions:, The mfVEP detected more abnormalities in patients with ON than HVF perimetry. The use of latency recordings as well as combined amplitude and asymmetry plots is advantageous and has the potential to detect abnormalities not otherwise detected on HVF perimetry. [source]

Effect of fixation tasks on multifocal visual evoked potentials

CLINICAL & EXPERIMENTAL OPHTHALMOLOGY, Issue 5 2005
Alessandra Martins MB BS
Abstract Purpose:, This study investigated the effects of cognitive influence on the multifocal visual evoked potential (mVEP) at different levels of eccentricity. Three different foveal fixation conditions were utilized involving varying levels of task complexity. A more complex visual fixation task has been known to suppress peripheral signals in subjective testing. Methods:, Twenty normal subjects had monocular mVEPs recorded using the AccuMap objective perimeter. This allowed simultaneous stimulation of 58 segments of the visual field to an eccentricity of 24°. The mVEP was recorded using three different fixation conditions in random order. During task 1 the subject passively viewed the central fixation area. For task 2 alternating numbers were displayed within the fixation area; the subject on viewing the number ,3' in the central fixation area indicated recognition by pressing a button. Throughout task 3, numbers were displayed as in task 2. The subject had the cognitive task of summating all the numbers. Results:, Analysis revealed that the increased attention and concentration demanded by tasks 2 and 3 in comparison with task 1 resulted in significantly enhanced central amplitudes of 9.41% (Mann,Whitney P = 0.0002) and 13.45% (P = 0.0002), respectively. These amplitudes became reduced in the periphery and approached those of task 1, resulting in no significant difference between the three tasks. Latencies demonstrated no significant difference between each task nor at any eccentricity (P > 0.05). As the complexity of each task increased the amount of alpha rhythm was significantly reduced. Conclusions:, Our findings indicate that task 1 required a minimal demand of cognition and was associated with the greatest amount of alpha rhythm. It was also the most difficult to perform because of loss of interest. The other two tasks required a greater demand of higher order cognitive skills resulting in significantly enhanced amplitudes centrally and the attenuation of alpha rhythm. Therefore, amplitudes are increased around the area of attention. [source]

Clinical application of the multifocal visual evoked potential

CLINICAL AND EXPERIMENTAL OPTOMETRY, Issue 3 2004
David P. Crewther PhD
Background: Measures of visual function thresholds such as visual acuity and visual fields are generally dependent on subjective responses and assume maintenance of fixation, attention and motivation. In the young, elderly, cognitively impaired or malingering populations, such measures may be inaccurate or difficult to obtain. The Visual Evoked Response Imaging System (VERIS) has been claimed to give more objective topographic recordings of retinal and cortical function. This paper aims to explore the adequacy of this technique in four unusual, unrelated, clinically difficult cases. Methods: Multifocal visual evoked potentials (mfVEPs) recorded on the VERIS System 3.01 are used to assess visual function in four cases with contradictory clinical findings or unreliable subjective responses. Results: Patient 1 had sustained a head injury and had normal ocular and pupil examination but light perception in the right eye and 6/5 acuity in the left. Multifocal VEPs showed a marked depression of the right visual field with little macular response. Patient 2 had sustained a head injury, had a left field hemianopia, possible macular sparing and loss of much of the right field, reduced but variable visual acuities, good near vision and normal ocular fundi. Multifocal VEPs showed a severe depression in both visual fields (L more than R) with little macular response. Patient 3 had a left optic nerve meningioma and experienced great difficulty with visual field assessment. mfVEPs showed a bilateral depression in the superior field particularly the left field, with a larger deficit in the left eye. Patient 4 had unexplained visual acuity and peripheral field deficits. mfVEP results were inconclusive in this case. Discussion: Where there is difficulty performing traditional techniques or conflicting clinical findings, mfVEPs may provide additional objective information to aid in the assessment of patients. [source]

Effect of fixation tasks on multifocal visual evoked potentials

CLINICAL & EXPERIMENTAL OPHTHALMOLOGY, Issue 5 2005
Alessandra Martins MB BS
Abstract Purpose:, This study investigated the effects of cognitive influence on the multifocal visual evoked potential (mVEP) at different levels of eccentricity. Three different foveal fixation conditions were utilized involving varying levels of task complexity. A more complex visual fixation task has been known to suppress peripheral signals in subjective testing. Methods:, Twenty normal subjects had monocular mVEPs recorded using the AccuMap objective perimeter. This allowed simultaneous stimulation of 58 segments of the visual field to an eccentricity of 24°. The mVEP was recorded using three different fixation conditions in random order. During task 1 the subject passively viewed the central fixation area. For task 2 alternating numbers were displayed within the fixation area; the subject on viewing the number ,3' in the central fixation area indicated recognition by pressing a button. Throughout task 3, numbers were displayed as in task 2. The subject had the cognitive task of summating all the numbers. Results:, Analysis revealed that the increased attention and concentration demanded by tasks 2 and 3 in comparison with task 1 resulted in significantly enhanced central amplitudes of 9.41% (Mann,Whitney P = 0.0002) and 13.45% (P = 0.0002), respectively. These amplitudes became reduced in the periphery and approached those of task 1, resulting in no significant difference between the three tasks. Latencies demonstrated no significant difference between each task nor at any eccentricity (P > 0.05). As the complexity of each task increased the amount of alpha rhythm was significantly reduced. Conclusions:, Our findings indicate that task 1 required a minimal demand of cognition and was associated with the greatest amount of alpha rhythm. It was also the most difficult to perform because of loss of interest. The other two tasks required a greater demand of higher order cognitive skills resulting in significantly enhanced amplitudes centrally and the attenuation of alpha rhythm. Therefore, amplitudes are increased around the area of attention. [source]