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.     

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.     

The rapid assessment of visual dysfunction in multiple sclerosis.

A consecutive series of patients with normal activity and a diagnosis of multiple sclerosis (10 male and 31 female) underwent extensive ophthalmological examination including visual evoked potentials (VEPs) and a new test of contrast sensitivity, which is described in detail. Seventy three per cent of patients had abnormal contrast sensitivity and 83% had abnormal VEPs. There was no association between abnormalities of the two types, but patients who had impaired contrast sensitivity and normal VEPs were younger than those whose contrast sensitivity was normal but whose VEPs were not. The test of contrast sensitivity (which took less than 5 minutes to administer) was the only examination to reveal visual abnormalities in all nine patients with a history of optic neuritis, and would be a useful supplementary test in the examination of patients with suspected multiple sclerosis.     

Optic neuritis: a prospective study

We studied 20 patients with acute optic neuritis prospectively for 12 months. Visual fields, color vision, and VEPs to 15' checks were initially abnormal in all patients. Visual acuity was abnormal in 90% and contrast sensitivity in 95% of patients. We devised a graded visual impairment scale (GVIS) to include all visual functions tested. Complete recovery of visual function occurred in 65% of cases. Recovery in the majority of patients was rapid and complete within the first 2 months. In some patients, improvement continued over 6 months. The initial classification on the GVIS was significantly correlated with the final outcome. Patients initially classified as having moderate visual impairment recovered completely or improved to near normal vision. Sixty percent of patients initially classified as total or severe blindness had permanent visual impairment. VEP latency remained prolonged in 19 patients, even when their vision had returned to normal, and is a reliable indicator of resolved optic neuritis.     

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.     

Pattern visual evoked potentials and flash electroretinogram in clinically definite multiple sclerosis

The authors have studied, by means of pattern visual evoked potential (VEP) and flash electroretinogram (ERG) recordings, a group of 15 patients affected by definite multiple sclerosis. All of the subjects examined presented a clinical history indicating involvement of the visual pathways; VEPs were altered in a high percentage of eyes examined (93.3%), while a lower percentage of abnormal ERGs was seen (20% of eyes examined). The only type of ERG alteration found consisted of a pathologic b wave voltage increase, observed mainly with red flash stimuli. This finding could be attributed to an involvement of centrifugal optic nerve fibers having inhibitory functions on retinal cells.     

Visual evoked potentials in neurosyphilis.

The visual evoked potential (VEP) to pattern reversal was recorded in 79 patients with neurosyphilis. Sixteen patients (20%) had abnormal VEP latencies with a predominance of pathological VEP values in the group of tabes dorsalis (50%) as compared to general paresis (18%) or meningovascular forms (13%). A comparison of the frequency of abnormal VEPs with that of other ophthalmological tests (visual acuity, visual field, central campimetry, pupillary reactions, dark adaptation, optic fundus) yielded no diagnostic superiority of VEP.     

Equiluminant red-green and blue-yellow VEPs in multiple sclerosis.

The primate visual system is composed by two color-opponent pathways--red-green (R-G) and blue-yellow (B-Y)--subserved by the so-called parvo- and koniocellular streams respectively. The authors' aim was to compare the relative involvement of chromatic visual subsystems in multiple sclerosis (MS). In 30 MS patients with different forms of MS they recorded visual evoked potentials (VEPs) to onset (300 msec) and offset (700 msec) of equiluminant R-G and B-Y sinusoidal gratings of different contrast (90% and 25%). Equiluminance was established psychophysically by establishing the R-G and the B-Y color ratio at which chromatic gratings alternating at 15 and 10 Hz respectively had minimum visibility. The negative wave at stimulus onset with a peak latency of 120 to 160 msec was evaluated. Ordinary VEPs to luminance (LUM) contrast (black-white reversing checkerboards of 15' check size and 50% contrast) were also recorded for comparison. Latencies of R-G VEPs were abnormal in 53.3% and 58.3% of patients at 90% and 25% contrast respectively, whereas abnormal B-Y VEPs were 56.6% and 48.3%. Latencies of LUM VEPs were abnormal in 45% of patients. Interocular latency asymmetries were abnormal in 59.2% and 33.3% of patients for R-G, and 51.8% and 62.9% for B-Y. Latency asymmetries for LUM VEP were abnormal in 46.4% of patients. The higher rate of VEP abnormalities found with equiluminant chromatic stimuli compared with achromatic stimuli confirms the general vulnerability of color-opponent visual pathways in MS, even if the number of patients with abnormal findings was not significantly different when both test conditions were compared. VEPs to R-G and B-Y equiluminant stimuli appear to be involved approximately to the same extent.     

Visual electroencephalographic computer analysis (VECA). A new electrophysiologic test for the diagnosis of optic nerve lesions

The function of optic pathways was studied by visual electroencephalographic computer analysis (VECA). Pattern and flash stimuli were used. The VECA profile was abnormal in two types of lesions: pathology involving the eye, and pathology involving the optic nerve. When ocular pathology is excluded, an abnormal profile indicates optic nerve dysfunction. Of the multiple sclerosis patients tested, 77 percent had an abnormal VECA profile. The test was always abnormal in patients with optic neuritis. Delayed visual evoked responses occurred in 18 of 29 multiple sclerosis patients judged to be clinically without visual deficits. VECA is reliable and sensitive for detecting clinical and subclinical optic nerve pathology.     

Visual evoked potential abnormalities in Charcot-Marie-Tooth disease and comparison with Friedreich's ataxia

Pattern-reversal visual evoked potentials (VEPs), recorded in 15 visually asymptomatic patients fulfilling the clinical and electrophysiological criteria of Charcot-Marie-Tooth disease (CMTD), were abnormal in 5 and possibly abnormal in another 3. Five patients showed a prolongation of P100 latency, one a reduction of amplitude and one a possibly abnormal "scotomatous" waveform. In 9 cases abnormalities were detected on neuro-ophthalmological examination. These were poorly correlated with VEP abnormalities, except for patients with 2 or more clinical eye signs. Relative central scotomata were found in the patient with an abnormal waveform. VEP abnormalities, where present, were usually fairly comparable in the 2 eyes. In comparison with a group of Friedrich's ataxia cases there was a lower overall incidence of VEP abnormalities in CMTD, but little to suggest a qualitative difference in the nature of the visual pathway pathology. All 4 patients with unequivocally abnormal VEPs had experienced atypical symptoms suggestive of CNS involvement. In none of these was it possible to sustain an alternative diagnosis. It is concluded that a minor degree of visual pathway involvement may be present in many CMTD cases, in spite of the fact that optic atrophy is only rarely reported, and that the VEP latency may reflect the degree to which other parts of the CNS are involved.     

Visual evoked potentials in the detection of subclinical optic toxic effects secondary to ethambutol

In 14 patients with tuberculosis treated with ethambutol hydrochloride, pattern-reversal visual evoked potentials (VEPs) were recorded to monocular, whole-field stimulation before the commencement of treatment and one month and three months subsequently. In six subjects, the VEPs showed changes in the latency and amplitude of the P100 component at the one- or three-month interval. In three cases, the VEP changes reversed after cessation of treatment. In five of the six cases, changes were not associated with a change in visual function, as measured by clinical neuro-ophthalmologic examination. Our findings confirm the usefulness of VEPs in the detection of subclinical optic nerve disease and suggest their use in routine monitoring of ocular function in patients treated with ethambutol.     

Visually evoked potentials in respiratory chain disorders

OBJECTIVES: Little is known about the frequency of abnormal visually evoked potentials (VEPs) in patients with respiratory chain disorders (RCDs). We thus wanted to investigate the frequency of abnormal VEPs in RCDs, how often VEPs are abnormal despite normal visual acuity, and which of the VEP variables are most often abnormal. MATERIAL AND METHODS: Reversal checkerboard VEPs of 26 patients with RCDs, aged 32-74 years, were evaluated. RESULTS: VEPs were abnormal in 17 of the 26 cases (65%). The P100 latency was prolonged at least unilaterally in 16 patients. The P100/N145 amplitude was decreased in a single patient. VEPs were abnormal without visual impairment in 9 cases (53%). CONCLUSION: VEPs prove useful to detect clinical or subclinical impairment of the optical tract in patients with RCDs. In the majority of the cases, the P100 latencies are prolonged while the P100/N145 amplitude remains normal.     

Late onset multiple sclerosis

Multiple sclerosis (MS) with clinical onset after 50 years old is unusual and frequently misdiagnosed. Clinical presentation and course seem also to be different that in MS occurring between 20 and 50 years old. The aim of this study was to evaluate the clinical and paraclinical characteristics of late onset MS. We respectively studied MS patients older than 50 years at the onset of the disease. We evaluated demographical data, clinical symptoms, cerebrospinal fluid (CSF), visual evoked potentials (VEPs) and MRI of these patients. We also studied clinical data during the follow-up with the occurrence of new symptoms and the evolution of the disease by the index of progression (EDSS unit per year). In a population of 1 417 MS, 3.4 p.cent had their first symptoms at 50 years old or older and 0.45 p.cent after 59 years old. At the time of the study patients had more frequently a progressive form: 37 p.cent had a primary progressive form and 35 p.cent a secondary progressive MS. None of the patients with onset after 60 years old had relapsing remittent MS. Motor symptoms were the most common neurologic presentation (54 p.cent of patients). Very few patients had a clinical optic nerve involvement during the follow-up. The mean progression index was 1 suggesting a most severe evolution in this subgroup of MS patients. 76 p.cent of patients had oligoclonal banding detected by CSF electrophoresis. The VEPs were abnormal in 81 p. cent of patients tested. 71 p.cent of the brain MRI were consistent with the diagnosis of MS. 60 p.cent of patients had spinal cord MRI abnormal. This study highlights the differences between the late onset MS and earlier onset. As previously reported, our study underlines the high frequency of progressive course, motor function involvement and poor prognosis.     

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.     

Visual and auditory evoked potentials in the early diagnosis and follow-up of neurosarcoidosis

Visual and brainstem auditory evoked potentials (VEPs, BAEPs) were recorded in 23 patients with neurosarcoidosis. Eight patients (35%) had abnormal BAEPs, and 10 (43%) had abnormal VEPs. Four of the 8 patients with abnormal BAEPs had facial paresis, one had impaired memory and only 3 had symptoms and signs compatible with brainstem lesion. Seven of the patients with abnormal VEPs had no visual symptoms. These findings suggest that BAEP and VEP can reveal subclinical nervous system involvement in sarcoidosis and can also help in the early diagnosis of neurosarcoidosis. Successive recordings of 5 patients showed that BAEP and VEP were useful in the follow-up of these patients.     

Recovery from optic neuritis is associated with a change in the distribution of cerebral response to visual stimulation: a functional magnetic resonance imaging study

OBJECTIVES: Recovery to normal or near normal visual acuity is usual after acute demyelinating optic neuritis, despite the frequent persistence of conduction abnormalities as evidenced by the visual evoked potential (VEP). This raises the possibility that cortical adaptation to a persistently abnormal input contributes to the recovery process. The objective of this study was to investigate the pattern of cerebral response to a simple visual stimulus in recovered patients in comparison to normal subjects. METHODS: Functional magnetic resonance imaging (fMRI) was used to study the brain activation pattern induced by a periodic monocular 8Hz photic stimulus in seven patients who had recovered from a single episode of acute unilateral optic neuritis, and in seven normal controls. VEPs and structural optic nerve MRI were performed on patients. RESULTS: Stimulation of either eye in controls activated only the occipital visual cortex. However, in patients, stimulation of the recovered eye also induced extensive activation in other areas including the insula-claustrum, lateral temporal and posterior parietal cortices, and thalamus; stimulation of the clinically unaffected eye activated visual cortex and right insula-claustrum only. The volume of extraoccipital activation in patients was strongly correlated with VEP latency (r = 0.71, p = 0.005). CONCLUSIONS: The extraoccipital areas that were activated in patients all have extensive visual connections, and some have been proposed as sites of multimodal sensory integration. The results indicate a functional reorganisation of the cerebral response to simple visual stimuli after optic neuritis that may represent an adaptive response to a persistently abnormal input. Whether this is a necessary part of the recovery process remains to be determined.     

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     

Visual impairment in children with epilepsy treated with vigabatrin

Vigabatrin is an anti-epileptic drug particularly useful for drug-resistant partial seizures and infantile spasms. Recently, vigabatrin-induced visual field constriction (VFC) and abnormal ocular electrophysiological studies were reported. In this study, we assessed visual fields, visual evoked potentials (VEPs), and electroretinography (ERG) in children treated with vigabatrin. Twenty-four visually asymptomatic children underwent a clinical ophthalmological examination, perimetry when appropriate, and VEP and ERG. Thirteen patients had at least one abnormal study. VFC was seen in 11 of 17 patients who had perimetry; 5 of 15 patients who underwent VEP testing and 4 of 11 who underwent ERG testing had abnormal examinations. For the most part, abnormal VEPs and ERGs were found in children who also had VFC. There was a consistent trend for longer treatment periods to correlate with VFC, abnormal ERGs, and VEPs. In summary, over half of the children treated with vigabatrin demonstrated VFC or abnormal ocular electrophysiological studies. Perimetry seemed to be the most sensitive modality for identifying vigabatrin toxicity. Abnormal ERGs and VEPs were primarily seen in children with VFC and may be useful in monitoring children who are not appropriate candidates for perimetry. Although the incidence of vigabatrin-induced VFC is worrisome, in the context of intractable seizures or infantile spasms, therapeutic benefits must be weighed against risks.     

Chromatic modulation of luminance visual evoked potential latencies in healthy subjects and patients with mild vision disorders.

OBJECTIVE: To study whether and how color modulates luminance visual evoked potentials (VEPs). METHODS: We studied pattern-reversal luminance VEPs to red/black and blue/black checkerboards with identical luminance contrast values (mixed luminance and chromatic components) (isocontrast color VEP, in brief, IVEPs) in 25 healthy subjects and two groups of patients with mild vision disorders (23 with glaucoma and 25 with optic neuritis). We then compared these with the standard color VEPs to pure chromatic contrast red/green and blue/yellow gratings (CVEPs). RESULTS: In healthy subjects, VEPs to red/black checkerboards and red/green gratings were slower than those obtained with blue/black checkerboards and blue/yellow gratings. Both procedures (IVEPs and CVEPs) differentiated patients with vision disorders from healthy subjects and distinguished between the two different vision disorders. Red/black checkerboards and red-green gratings elicited slower VEPs in patients with optic neuritis and blue/black checkerboards and blue/yellow gratings elicited slower VEPs in patients with glaucoma. IVEPs appeared more stable and ample than CVEPs. The contrast indices normalized CVEP and IVEP latencies in the same subject and showed a positive correlation between CVEP and IVEP latencies in healthy subjects and in patients with optic neuritis, but not in patients with glaucoma. CONCLUSIONS: Our study confirms the usefulness of CVEPs in detecting and differentiating mild vision disorders. IVEPs to colored pattern-reversal luminance checkerboards are equally effective in distinguishing between various vision disorders possibly because colors can modulate VEP latencies to luminance contrast stimuli. SIGNIFICANCE: IVEPs can be useful in differentiating the various vision disorders and are easier than CVEPs to test in a routine clinical setting.     

Frequency and clinical significance of Lyme seropositivity in patients with isolated optic neuritis

We evaluated antibody reactivity against Borrelia burgdorferi in 20 consecutive patients with newly diagnosed isolated optic neuritis who resided in a region endemic for Lyme disease. Four (20%) patients had positive serology. All three patients who had follow-up serologies showed rising convalescent levels of Borrelia-specific IgM. One patient refused lumbar puncture, one had normal CSF constituents except for an elevated Lyme antibody index, and two had CSF lymphocytic pleocytosis that remained unexplained after extensive evaluations for causes other than Lyme disease. We treated both patients who had CSF pleocytosis with intravenous ceftriaxone; the pleocytosis and optic nerve function improved. The other two patients received oral antibiotics and showed excellent recovery of visual acuity. We believe that serologic testing for Lyme disease is warranted for individuals with optic neuritis who reside in an endemic region, and patients with rising convalescent antibody levels or unexplained CSF pleocytosis should receive antibiotic treatment for Lyme disease.