Do visual evoked potentials give relevant information to the neuro-ophthalmological examination in optic nerve lesions?

The visual evoked potentials (VEPs) and neuro-ophthalmological examinations of 134 patients were compared. The VEPs were abnormal in 95 % of the eyes with optic neuritis. Defective color vision was found in 99 %, visual field defects in 88 %, decreased vision in 66 % and an afferent pupillary defect in 55 %. 29 patients with optic neuritis were followed up with repeated tests. VEPs and color vision recovered more slowly than visual acuity and visual field.
Abnormal VEPs were observed in 68 % of 50 MS patients. An analysis of symptomatic and asymptomatic eyes showed that testing of color vision, visual field and red-free ophthalmoscopy were equally as useful diagnostic tools as VEPs. 4 (8 %) of the MS patients had abnormal VEPs despite a normal neuro-ophthalmological examination; 94 % of MS patients with symptoms and 47 % of MS patients without visual symptoms had abnormal VEPs.
VEPs were pathological in 59 % of 24 patients with traumatic or compressive optic nerve diseases or optic atrophies of unknown etiology. The neuro-ophthalmological examination was more sensitive than VEPs in the diagnosis of these disorders. A neuro-ophthalmological examination is in most cases sufficient to diagnose optic nerve lesions. VEPs are of diagnostic aid especially in mild optic nerve lesions.     

Early diagnosis of optic glioma in children with neurofibromatosis type 1

Twenty-five asymptomatic patients with neurofibromatosis type 1 (NF 1), aged 6–21 years, underwent the following examinations: intracranial magnetic resonance testing (MRI), visual acuity testing, ophthalmoscopy, and visual field and pattern reversal visual evoked potentials (VEPs). MRI showed enlargement of one or both optic nerves in six children, with bilateral involvement in three. VEPs were normal in all these patients; two of them had abnormalities on other visual examinations, although there were no subjective visual disturbances. These results show that VEPs cannot be considered as a screening test for optic pathway lesions in children with NF 1, as previously stated, and that other types of visual function examination may be more sensitive. These data may contribute to the establishment of more precise guidelines for the evaluation and treatment of children with NF 1.     

Visual wulst influences on flash evoked responses in the ectostriatum of the zebra finch

Anatomical data suggest that visual information from the thalamofugal pathway contributes to visual processing in the tectofugal pathway. We addressed the question of the functionality of anatomically described connections to the visual system of a laterally eyed bird, the zebra finch. The study shows the contribution of visual wulst efferents to visual processing in the ectostriatum by recordings of visually evoked slow field potentials. Suppression of visual wulst activity resulted in a selective reduction of distinct potential components in contralaterally evoked slow field potentials. A clear reduction was observed in the maximum amplitude of short latency components in the negative wave. Long latency components of the negative wave and the entire positive wave of the contralaterally flash evoked potentials were almost abolished. Ipsilateral visual evoked potentials (VEPs) were not significantly affected. Cooling and spreading depression of the optic tectum resulted in a uniform amplitude reduction of the negative wave. The positive wave was almost abolished. Ipsilateral VEPs disappeared completely during suppression of optic tectum activity. The results showed that the visual wulst has a significant, most likely facilitatory, influence on the processing of contralateral visual information in the ectostriatum. Ipsilateral stimulus processing was partly independent from visual wulst activity. A model for thalamo- and tectofugal connectivity in the ectostriatum is suggested.     

Results of static perimetry in subclinical optic neuritis in multiple sclerosis

Static perimetry of the central visual field was performed using Harms apparatus and Friedmann's analyser in 20 M.S. patients with subclinical optic neuritis at least for one eye. Sub-clinical optic neuritis was defined as delayed or absent pattern reversal visual evoked potentials (VEPs) associated with normal routine ophthalmological examination (visual acuity, optic fundi, colour vision, kinetic perimetry). Results in patients were compared to data obtained in 22 control subjects, matched for age. A highly significant loss of mean retinal sensitivity was observed in the 20 central degrees of the visual field of eyes with abnormal VEPs. Central relative scotomata were disclosed in 18 of the 33 eyes with abnormal VEPs. Static perimetry was found to be abnormal, for at least one eye, in 15 in the 20 M.S. patients. Thus abnormal VEPs in M.S. are often associated to a lowered capacity to detect a stationary stimulus in the central visual field. The Friedmann's visual field analyser allows a quick and reliable evaluation of the loss of retinal sensitivity in M.S. patients.     

Early visual processing in neglect patients: A study with steady-state VEPs

Reliable steady-state visual evoked potentials (VEPs) were recorded in a group of 19 right brain-damaged patients with visuospatial hemineglect (Neglect), and two control groups: 15 left brain-damaged (LBD) patients and 12 right brain-damaged (RBD) patients without neglect. Moreover, VEPs were recorded in two rare cases of left brain damage and right visuospatial hemineglect. Stimuli were gratings phase-reversed at various temporal frequencies presented in the left and right visual field. In the Neglect group, VEPs to stimuli displayed in the left visual field (contralesional stimuli) had longer latencies. The delay was not present for the two control groups. As regards the VEP amplitudes, the Neglect group data showed a less distinctive pattern than in the case of latency. VEPs to stimuli contralateral to the lesion were smaller than those recorded for stimuli ipsilateral to the lesion in both Neglect and RBD groups. On the contrary, the VEP amplitudes for the two hemifields were comparable in the LBD group. In the case of left brain damage and neglect, VEPs to right visual field stimuli had longer latencies and lower amplitudes compared to the ipsilesional responses in both patients. Overall, the data support the view that, in most cases, early visual processing is not intact in the neglected hemifield.     

Amplitudes of visually evoked potentials to patterned stimuli: age and sex comparisons

Electrophysiological age and sex differences in visual pattern responsivity were investigated. Pattern reversal evoked potentials (PREPs) and visual evoked potentials (VEPs) to patterned and unpatterned flashes were recorded from 20 normal subjects in each of 4 groups: young females and males aged 25-35 years and older females and males aged 55-70 years. PREP waves N70-P100 and P100-N150 from the older women were significantly larger than those from subjects in the other groups; mean amplitudes for the young females, young males and older males were not different. A similar effect, unusually large potentials for the older women, was obtained for VEPs, but only for VEPs elicited by patterned flashes and recorded from occipital scalp, i.e., an area overlying visual cortex which is sensitive to lines and edges. Our findings suggest that the visual system of older females is unusually responsive to patterned stimuli.     

Electrophysiological findings in patients with nonarteritic anterior ischemic optic neuropathy.

OBJECTIVE: Nonarteritic ischemic optic neuropathy (NAION) is one of the most frequent causes of sudden visual loss in middle-aged or elderly patients. Although several electrophysiological methods are available for an objective evaluation of the visual deficits, these are not generally used in the assessment of the clinical condition of NAION patients. To evaluate the severity of the optic nerve and retinal damage, electrophysiological tests were performed on 8 patients with NAION. METHODS: Visual evoked potentials (VEPs), scotopic, photopic and flicker electroretinograms (ERGs), multifocal ERGs and pattern ERGs were recorded. RESULTS: The results demonstrated that the VEPs fairly reliably reflected the visual loss caused by NAION. The VEPs were extinguished in cases with a serious visual acuity loss, while a decrease in amplitude and a lengthening of the P100 latency were observed in cases with good visual acuity and a severe visual field loss and in the nonattacked fellow eye of the patients with monocular involvement. The pattern ERGs failed to show signs of retrograde degeneration. The photopic, scotopic and flicker ERGs, and the oscillatory potentials (OPs) were close to normal in these NAION patients. CONCLUSIONS: Our observations permit the conclusion that electrophysiological methods can provide an objective indication of the clinical condition of these patients. The new data obtained promote an understanding of the pathomechanism of the disease. SIGNIFICANCE: Electrophysiological tests are suitable for monitoring of the progression of the disease in NAION patients.     

Hemispheric asymmetry in processing visual half-field pattern-reversal stimuli assessed by reaction time and evoked potentials

Reversing checkerboard patterns, like those used to elicit clinical visual evoked potentials (VEPs), were adapted to the study of cerebral lateralization of visual processing in a divided visual field experiment. Seventeen right-handed subjects (9 male, 8 female) provided left- and right-handed responses to pattern-reversal stimuli presented in left, right and both visual half-fields in pseudorandom order. Simple unwarned RTs were shorter for left- compared with right-field stimuli under left-hand response conditions. Parietal VEPs obtained from 9 of the subjects showed larger amplitudes for left compared with right field stimuli at the right hemisphere. The results were consistent with an efficiency model of cerebral dominance incorporating both interhemispheric transfer time and a reduced efficiency for left hemisphere processing of our patterned visual stimuli.     

Visual evoked potentials in idiopathic intracranial hypertension

Objective

Visual evoked potentials (VEPs) are sensitive indicators of optic nerve dysfunction. Since visual loss is a serious complication of idiopathic intracranial hypertension (IIH), we measured VEP in an attempt to evaluate quantitatively the optic nerve damage in patients with chronic IIH.

Methods

We examined 20 consecutive IIH patients fulfilling modified Dandy criteria. VEPs were recorded bilaterally and at midline from occipital electrodes using pattern reversal stimuli to each eye separately. The results were compared to norm values used in our laboratory.

Results

VEP response latencies were usually similar in both eyes. They were delayed in nine patients (45%) bilaterally and in two additional patients unilaterally (55% of patients had abnormal responses in at least one eye). VEP amplitudes were not affected. All three patients with reduced visual acuity in both eyes had prolonged VEP latencies, but abnormal records were seen frequently also in cases with normal visual acuity. Repeated examinations 6–12 months later revealed similar results in clinically stable patients and improvement of VEP latency in parallel to clinical improvement in one.

Conclusions

Clinical visual impairment in IIH is probably preceded by prolongation of VEP responses and the latter may be evidence of optic nerve dysfunction due to demyelination.     

Symptomatic retrochiasmal lesions in multiple sclerosis: clinical features, visual evoked potentials, and magnetic resonance imaging.

We have studied 18 patients with relapsing-remitting multiple sclerosis (MS) who had symptomatic visual field defects due to retrochiasmal lesions. In 17, the lesion responsible was identified by magnetic resonance imaging (MRI), computed x-ray tomography (CT), or both. The lesion responsible involved the posterior optic radiations in eight cases, the optic tract and lateral geniculate nucleus in six, and the posterior limb of the internal capsule in three. The prognosis for recovery of the field defect was good; complete recovery occurred in 14 patients, and only two showed no recovery at all. The striking characteristic of the lesions was that most were unusually large; indeed, many were detectable on CT as well as MRI. Half-field asymmetries of either amplitude or latency of the visual evoked potentials (VEPs), consistent with a postchiasmal lesion, were present in only five out of 13 patients acutely. In only three of these did the abnormality persist at follow-up. We conclude that only large postchiasmal lesions are likely to cause symptomatic homonymous field defects in MS, usually characterized by rapid recovery. Hemifield VEPs have a low sensitivity for the detection of postchiasmal as compared with prechiasmal abnormalities.     

Visual system function in patients after surgery for intracranial tumors

Visual function was studied in patients after operations for brain tumours. The study group comprised 7 cases. Visual acuity, field of vision by kinetic and static methods and visual evoked potentials were studied before and after operations. The follow up time was from 1 to 51 months, mean 20 months. In all patients decreased visual acuity, visual field defects and VEP abnormalities were found, before operation. The first control examination after operation showed improvement of visual acuity in 2 cases after removal of pituitary tumours, and worsening of vision in all the remaining ones. In two cases of tumours spreading to the basis of the frontal lobe blindness of one eye developed. Static and kinetic perimetry showed in all cases enlarged visual field defects. VEP confirmed that removal of pituitary tumours compressing visual tract can improve vision: P100 amplitudes increased and latencies become shorter. Further VEP improvement occurred even 6-20 months after achieving of good visual acuity. No improvement of vision developed if the visual pathway had been damaged during the operation. CONCLUSIONS: Pituitary tumours can be removed without damage to the surrounding structures and vision can improve after that. Meningiomas and gliomas lying in immediate vicinity of optic nerves and their chiasma or growing out from them are usually large and often their removal is associated with damage to the visual pathway leading to visual field defects to blindness. The assessment of vision should be based on static and kinetic perimetry and visual evoked potentials (VEP) since these methods are mutually complementary and only their comparison provides a full result.     

Amplitude asymmetry of hemifield pattern reversal VEPs in healthy subjects.

The amplitudes of transient and steady-state visual evoked potentials (VEPs) were measured during hemifield stimulation of the left eye in 10 healthy adults. Pattern reversal of a checkerboard was produced at 4 stimulation frequencies: 1, 5, 10 and 15 Hz. The amplitudes of pattern VEPs were evaluated using the paired t test to determine significant differences between right and left hemifields. The transient VEP amplitudes from midoccipital, midparietal, ipsilateral occipital and contralateral occipital electrodes were significantly greater with right hemifield stimulation. The steady-state VEP amplitudes from the midoccipital electrode during 15 Hz stimulation were significantly greater with right hemifield stimulation. Our neurophysiological data may be compatible with neuroanatomical asymmetries of the occipital lobes in humans.     

Long-term recovery and fellow eye deterioration after optic neuritis, determined by serial visual evoked potentials

Twelve optic neuritis patients (part of a larger group in whom the effects of intravenous methylprednisolone treatment were previously reported), were followed-up 3 years from the onset of symptoms with visual evoked potentials (VEPs), contrast sensitivity and visual field examination. Findings from the previously “unaffected” eyes, none of which had had symptomatic optic neuritis, were also assessed. Between 6 months and 3 years after the onset of symptoms the VEPs of the affected eyes showed a significant shortening of mean latency (whole field, 131–123 ms; central field, 136–125 ms). Conversely, the responses of the previously unaffected eyes showed a contemporaneous latency prolongation (significant for the whole field, 110–113 ms) which exceeded the expected effect of aging. Contrast sensitivity tests showed no significant change in the affected eyes but a mild deterioration in the unaffected eyes, while the visual fields showed no overall pattern of improvement or deterioration. If the strong tendency for VEP latencies to shorten is due to ongoing remyelination, the lack of significant improvement in visual function may be because the visual deficit at 6 months is due to irreversible axonal loss rather than demyelination. The absence of functional deterioration in the affected eye, while VEPs and contrast sensitivity deteriorated in the unaffected eye, suggests that long-term remyelination may for a while counteract the effects of insidious demyelination and axonal degeneration which affect the visual pathway during clinical remission. Received: 7 April 1998 Received in revised form: 17 December 1998 Accepted: 16 February 1999     

Acutely Administered Haloperidol Has Little Effect on Steady-State Visual Evoked Potentials from Pattern-Reversal Stimulations in Treated Schizophrenics

Abstract: The amplitude changes in steady-state visual evoked potentials (VEPs) from pattern-reversal stimulations at 30 min after an intramuscular injection of haloperidol were examined in 10 treated schizophrenics. The VEP amplitudes to hemi-field or full-field pattern-reversal stimulations with a standard check size were almost unchanged after the haloperidol injection as compared with those before the injection. However, while the VEP amplitudes to the full-field stimulations were significantly higher in the midline occipital portion than in the right occipital portion before the injection, no significant difference was observed after the injection. Further, the VEPs similarly responded to the change in the check sizes used in the full-field stimulations before and after the injection, both showing significantly lower amplitudes only at the large check size of 4.1° in a visual angle than that of 1.0°. These results indicate that acutely administered haloperidol has little effect on steady-state VEPs from pattern-reversal stimulations in treated schizophrenics.     

A fast visual evoked potential method for functional assessment and follow-up of childhood optic gliomas.

OBJECTIVE: To evaluate a fast technique of visual evoked potentials (VEPs) recording, in response to steady-state luminance stimuli (SS-LVEPs), for functional assessment and follow-up of childhood optic gliomas (OGs). METHODS: Eighteen OG patients (age range: 3.5-18 years), with different degrees of optic pathway damage severity, were examined. Sixteen age-matched normal subjects served as controls. Ten of the 18 OG patients were re-tested 1-3 months after the first examination. SS-LVEPs were elicited by a sinusoidally-modulated flickering (8 Hz) uniform field, generated by a light emitting diode (LED)-array and presented monocularly in a mini-ganzfeld. Amplitude and phase of the Fourier-analyzed response fundamental (1F) and second harmonic (2F) were measured. The full VEP protocol had a median duration of 6 min (range: 4-12). RESULTS: When compared to normal control values, median 1F and 2F SS-LVEP amplitudes of OG patients were reduced (P<0.01), with a borderline increase in 2F phase lag (P<0.05). In 11 OG patients with asymmetric optic pathway damage in between-eye comparisons, median 1F amplitude losses were greater (P<0.01) in fellow eyes with more severe damage. No significant interocular difference was observed in control subjects. Median test-retest changes of 1F and 2F component were <20% and 30 degrees for amplitude and phase, respectively. In individual OG patients, 1F and 2F amplitudes were positively correlated (P<0.01) with visual acuity. 1F amplitude losses were correlated (P=0.01) with the severity of optic disc atrophy. Considering both 1F and 2F abnormalities, diagnostic sensitivity of SS-LVEP in detecting OG-induced optic pathways damage was 83.3%. CONCLUSIONS: The present findings support the use of this technique, as an alternative to pattern VEPs, for functional assessment and follow-up of OG in uncooperative children.     

The 20/20 eye in multiple sclerosis

Using clinical and electrophysiologic measures, we evaluated the visual pathway of patients who had multiple sclerosis, 20/20 Snellen acuity, and no history of optic neuritis. Delayed latencies were found in the transient visual evoked potentials (VEPs) of 38% of the patients, and interocular latency differences were abnormal in 67%. Contrast VEPs were abnormal in 46%. Psychophysical determinations of contrast sensitivity were abnormal in 78%. Only 17% of the patients had dyschromatopsia, 36% had afferent pupillary abnormalities, and 59% had optic nerve pallor or nerve fiber layer loss. Psychophysical contrast evaluations and VEP studies were superior to other clinical evaluations in demonstrating visual dysfunction in these patients.     

Early visual selection in near and far space: an event-related potential study

Earlier behavioral studies have shown that near space (within reaching distance) is represented in the brain separately from far space (out of reaching distance), and the relationship between the different spatial coordinates and spatial attention is unclear. The typical event-related potentials of P1 and N1 in the near (viewing distance of 30 cm) and far (140 cm) conditions, with stimuli at a constant visual angle are examined in this study. An early P1 (100-130 ms poststimulus) attention effect at occipital parietal sites increased in response to stimuli at the left visual field only in near space. This suggests that near and far spatial representations are involved in early visual selection.     

Visual evoked potentials in monkeys.

Visual evoked potentials (VEPs) were recorded from 2 cortical sites in stump-tailed macaques. VEPs recorded from striate cortex were basically consistent between animals (especially at low light intensity), remained remarkably stable over time, and compared favorably to VEPs reported by other investigators. We concluded that the VEP recorded from the striate cortex of day-active monkeys consists of 5 major peaks within the first 250 msec. The potentials recorded from post-central gyrus were simpler and more individualized and did not show intensity-related latency changes or increases in inter-subject variability. However, amplitudes of potentials recorded from both electrode placements increased with light intensity apparently reflecting the amplitude of individual potentials rather than the variability of these potentials from which the average VEPs were derived.     

Detection of isolated occipital lobe anomalies during early childhood

The authors report two children with isolated occipital lobe anomalies detected by visual evoked potentials (VEPs) and confirmed by MRI and CT scanning. Both had a markedly asymmetrical occipital distribution of flash and pattern VEPs. One child had acuity reduced to 6/36, and testing on confrontation suggested an homonymous hemianopia. The second child was visually inattentive to one side during infancy. Neither child had band atrophy of the optic disc or an afferent pupillary defect. Isolated abnormalities of the occipital lobes are difficult to detect by clinical examination during infancy and early childhood. Recording VEPs from a horizontal array of occipital electrodes can be helpful in detecting subtle occipital lobe abnormalities.