Effect of central scotomata on pattern reversal visual evoked potentials in patients with maculopathy and healthy subjects

Unusual visual evoked potentials in patients with age-related macular degeneration

Among a series of patients with age-related macular degeneration (ARMD), a few individuals could be identified showing larger amplitudes of pattern reversal visual evoked potentials (prVEP) after stimulation of a central 3 degrees field compared to stimulation of a 13 degrees field although in the majority of ARMD patients and in normals, VEP amplitudes increased with increasing field size. An analysis of prVEPs recorded after stimulation of different macular zones showed that the 3 degrees central area and the perifoveal zone contributed differently to the 13 degrees response or macular response. Perifoveal activity in this subgroup of ARMD patients seemed to mask the foveal contribution to the macular prVEP. The cortical magnification factor in ARMD may be higher than in normal controls. Small-field stimulation techniques are therefore also recommended in patients with central retinal pathology.

Effects of check size on pattern reversal visual evoked magnetic field and potential

The effects of different check sizes on the 100m component of pattern reversal visual evoked magnetic fields (VEF) and the P100 component of visual evoked potentials (VEP) in terms of latency, amplitude and source localization were analyzed. Half field stimuli with or without central occlusion with check sizes of 15', 30', 60', 90' and 180' of visual arc were given to 7 healthy subjects. VEF and VEP were recorded simultaneously. The effect of the check size on the peak latency of both 100m and P100 was significant (P<0.01, ANOVA). The latencies for the smaller checks were significantly longer than those for the larger checks. The effect of the check size on the amplitude of the 100m to the stimulation with central occlusion was significant (P<0.05, ANOVA), but was not to the stimulation without central occlusion. That is, the amplitudes for the smaller checks were significantly smaller than those for the larger checks when using the stimulation with central occlusion, but not the stimulation without central occlusion. The effect of the check size on the P100 amplitude was not significant to the stimulation with and without central occlusion. The equivalent current dipoles were located around the calcarine fissure and did not differ significantly in location with check size. In conclusion, check size significantly affects the latency and amplitude of the 100m and/or P100, but not the receptive areas for the stimulation.

Frontal negativity of pattern-reversal visual evoked potentials in humans

We investigated the nature of negative potential in the frontal region with an approximate latency of 100 ms ('frontal negativity') as a component of pattern-reversal visual evoked potential (PVEP) in healthy human subjects. It was recorded by stimulation of one-half of the visual field, with different reference electrodes and with experimental manipulations of the stimulating visual field ('central scotomata' and 'peripheral constriction'). A negative potential field was demonstrated to be localized in the frontal region, and its physiological properties detected by the visual field manipulations were shown to be different from those of the occipital positive (P100) and negative (N105) components of PVEP. We conclude, therefore, that frontal negativity of PVEP is an actual electrical event generated in the frontal region, independent of P100 and N105.

Visual evoked potentials in macular hole

Pattern reversal visual evoked potentials (VEPs) with checks of 50' and 12' were recorded in 15 patients with idiopathic unilateral macular hole. VEPs from the affected eyes were reduced in amplitude compared with those from the fellow eyes, especially with checks of 12' (percentage of the amplitude in the affected eye to that in the fellow eye was 86% +/- 19% with checks of 50' and 61% +/- 35% with checks of 12'). The latencies showed no statistically significant difference between the affected and the fellow eyes, although a marked interocular delay was found in a few patients. The degree of amplitude reduction and interocular delay had no relation to the size of the macular hole or visual acuity. The effects of experimental scotomata of various sizes on the VEPs, which were evaluated in nine normal subjects, were also variable among the subjects. We conclude that although the macula predominantly participates in the pattern VEP, an estimation of the extent of macular pathology from the VEP changes may be difficult because the VEP changes induced by a macular hole have wide individual variation and have no relation to the size of the hole.

Handedness and hemispheric asymmetry of pattern reversal visual-evoked potentials

Pattern reversal visual-evoked potentials (EP) from temporal leads in the two hemispheres of 26 right-handed (14 right-eye-dominant and 12 left-eye-dominant) and 10 left-handed (left-eye-dominant) adults were recorded. Checkerboard patterns (check sizes: 5.7 and 17 min of arc) at 1 and 8 Hz were reversed. Stimuli (a) subtended 6 degrees of visual field, (b) subtended 1 degree of visual field (foveal condition), and (c) were restricted to the annular portion of the visual field around the fovea (peripheral condition). Larger EP amplitudes in right or left hemisphere in relation to handedness, temporal frequency, and visual field condition were recorded. Eye dominance of dextrals appeared to play a role in determining the hemispheric asymmetry. Previous literature data and present results in relation to the hypothesis of different hemispheric specialization for basic visual information are discussed.

The effects of visual field size on hemispheric asymmetry of pattern reversal visual evoked potentials

Visual evoked potentials (VEPs) were recorded in 17 females (10 right-handers and 7 left-handers) and 17 males (10 right-handers and 7 left-handers). The stimulus was a checkerboard pattern phase-reversed at a rate of 1 Hz, binocularly viewed by the subject. Two experimental conditions were tested: field size (the stimulus was enlarged from 1 to 30 degrees of visual angle) and occlusion (the central part of the stimulus was occluded by experimental scotomata of various size--from 1 to 16 degrees). Responses recorded at occipital and temporal leads of the two hemispheres were compared. The P100-N145 amplitude was larger at occipital than at temporal leads, it augmented increasing the size of the stimulus and diminished occluding progressively larger portions of the central field. Hemispheric asymmetries emerged with large field sizes and were not abolished by the presence of experimental scotomata. The hemispheric asymmetry was related to handedness (left-handers had larger amplitudes in the right hemisphere, right-handers in the left hemisphere), but not to sex. Hemispheric asymmetries in VEPs latency were not present. In comparison to males, females showed larger amplitudes and shorter latencies. These results point out that hemispheric asymmetries are found also for the processing of elementary visual stimuli like checkerboards, and they depend both on stimulus parameters (field size) and subject variables (handedness).

Metastatic malignant meningioma

The onset of a rapidly progressive abducens and trigeminal neuropathy, third-order neuron Horner's syndrome, and decreased lacrimation clinically suggest a malignant lesion at the base of the middle cranial fossa, commonly a metastatic process. A case is reported in which computed tomography and magnetic resonance imaging failed to image the lesion but a bone scan clearly depicted the abnormal area. A malignant meningioma (en plaque) was evident on biopsy, and pulmonary metastases later ensued. Common histological patterns of meningioma (often thought of as a benign tumor) include meningothelial, fibrous, and transitional types. The association of cellular atypia, nuclear pleomorphism, marked mitoses, and brain invasion warrants the designation of malignant meningioma. The incidence of malignancy in meningioma ranges from 2 to 10% with reported metastases occurring in 0.1%.

Alteration of the visual evoked potential by macular holes: comparison with optic neuritis

Nine patients with maculopathy (macular holes, macular cysts, and lamellar holes) and ten patients with optic neuritis were examined in order to determine changes in the visual evoked potential (VEP) in response to pattern-reversal stimulation. Eyes with lamellar holes had normal P100 latency, but eyes with macular cysts and macular holes had prolonged P100 latency. Eyes with optic neuritis exhibited greater prolongation of the P100 latency than eyes with macular holes. In contrast, eyes with macular holes had a greater reduction in the steady-state VEP amplitude than eyes with optic neuritis. The prolonged latency occurring in maculopathy may be due to a peculiar amplitude summation noted with half-field VEP, rather than to a true conduction delay like that seen in eyes with optic neuritis. The amplitude slope, which is usually positive in normal controls, was negative for 85.7% of eyes with macular holes and 69.2% of eyes with optic neuritis. The negative amplitude slope may represent a subtle defect in retinal ganglion X cells. Eyes with significantly lower values for four or more of the nine central test points on quantitative automated perimetry had negative amplitude slopes and prolonged P100 latency.

Hemispheric asymmetry of pattern reversal visual evoked potentials in healthy subjects

Pattern reversal visual evoked potentials were recorded from temporal leads of both hemispheres in 3 right-handed and 3 left-handed subjects. The stimuli subtended 6 degrees of visual field (full field condition), or 1 degree of visual field (foveal condition), or were restricted to the peripheral portion of the visual field (annular condition). Check sizes varied from 16 to 2.8 min of arc. The stimuli were phase-reversed at 1 or 8 Hz. Remarkable hemispheric asymmetries were found, depending on the portion of the visual field and temporal frequency. In right-handed subjects the amplitude of visual evoked potentials recorded over the left hemisphere was larger for stimuli phase-reversed at 8 Hz in full-field and annular conditions, whereas the amplitude of visual evoked potentials recorded over the right hemisphere was larger for stimuli phase-reversed at 1 Hz in the foveal condition. Different patterns of hemispheric asymmetries were observed in left-handed subjects.