Prolonged Visual Evoked Potentials Latencies Research Articles

Prolonged visual evoked potential latency predicts longitudinal worsening of fatigue in people with multiple sclerosis

BackgroundFatigue is a common problem experienced by people with multiple sclerosis (PwMS) and can impact physical, cognitive, and psychosocial aspects of daily living and quality of life. The tracking of meaningful longitudinal change in subjective fatigue that occurs as a result of MS activity may be enhanced by incorporating objective neurophysiological measures into longitudinal assessment. To examine this possibility, we examined the longitudinal relationship between visual evoked potential (VEP) measures and a variety of fatigue measures over an approximately two-year period in PwMS. MethodsVEP measures were obtained using a checkerboard pattern-reversal paradigm. Fatigue was assessed with the Modified Fatigue Impact Scale (MFIS Global, Physical, Cognitive, and Psychosocial subscales) and the Fatigue Severity Scale (FSS) questionnaires. Multiple linear regression analyses were conducted in which the change in each fatigue scale score from baseline to follow-up (T1-to-T2) served as the outcome variables for separate models. Predictor variables included the peak latency of the P100 component of the VEP (maximum peak among the two eyes) and the inter-ocular latency (IOL) at T1, the T1-to-T2 change score for maximum VEP latency and IOL, and the fatigue score at T1 that corresponded to each outcome measure. ResultsProlonged baseline VEP latency was a significant predictor of the T1-to-T2 increase in MFIS Global score, and increased VEP latency from baseline to follow-up was significantly associated with MFIS Cognitive score over the same time period. Furthermore, VEP latency measures in these two models were better predictors of changes in fatigue than baseline fatigue scores were, based on the magnitude of the standardized beta coefficients. Subsequent post-hoc analyses revealed that the relationship between change in VEP latency and change in MFIS Cognitive score was evident primarily for PwMS that had elevated MFIS Cognitive score at baseline. ConclusionThe present study provides novel evidence that prolonged VEP latency is predictive of worsening of global and cognitive fatigue in PwMS. VEP latency measures may therefore provide clinical utility for monitoring changes in fatigue in PwMS, when used in conjunction with other clinical tools.

The relationship between cognitive impairment, cognitive fatigue, and visual evoked potential latency in people with multiple sclerosis

Background: Fatigue in people with multiple sclerosis (PwMS) can impact physical, cognitive, and psychosocial domains of daily life. The experience of fatigue in PwMS is thought to originate from the central nervous system, particularly for the domain of cognitive fatigue. Here, we tested the hypothesis that fatigue scores in PwMS would be significantly associated with an index of neural activity - the latency of the P100 of the visual evoked potential (VEP) - in line with the notion of a centralized origin of fatigue. We predicted that prolonged VEP latency would be associated with greater fatigue, and that this relationship would be the most pronounced within the domain of cognitive fatigue. Methods: PwMS (n=249) completed the Modified Fatigue Impact Scale (Global, Physical, Cognitive, and Psychosocial scales of the MFIS) and Fatigue Severity Scale. VEP latency was obtained using an alternating checkerboard paradigm. We also examined the influence of depression (Beck Depression Inventory, second edition, BDI-II) and cognitive functioning (NeuroTrax testing battery) on the VEP/fatigue relationship. Results: Surprisingly, we observed that earlier (not later) VEP latency was significantly associated with higher MFIS Cognitive score. The negative relationship between VEP latency and cognitive fatigue was evident in PwMS that had poor cognitive performance as measured by a latent variable that reflected attention, executive function, information processing speed, and motor skills; but a significant relationship was not observed in PwMS that exhibited good performance on this measure. Conclusions: These findings can be interpreted within a metacognitive framework – greater fatigue may be perceived when neural performance and the level of mental effort expended does not translate to efficient cognitive performance. Cognitive fatigue may be particularly salient in PwMS when neural resources are unable to compensate for cognitive difficulties. The mismatch between the expectation of what ought to occur and what does occur during cognitive performance may be a key feature of the experience of cognitive fatigue for some PwMS.

Impact of Hyperventilation and Sleep Deprivation Upon Visual Evoked Potentials in Patients with Epilepsy.

The diagnosis of epilepsy can cause many problems, especially when the routine electrophysiological tests are inconclusive. The aim of the present study was to assess the visual evoked potential (VEP) in patients with epilepsy using various kinds of stimulation and activation tests. The VEP parameters were also presented with reference to the type of seizure and abnormalities in electroencephalogram (EEG), including the response to the activation tests. This study comprised 81 patients with newly diagnosed epilepsy of unknown etiology before initiation of the treatment. The VEP tests were performed at rest, after hyperventilation, and deprivation of sleep. Visual stimulation included an alternating checkerboard pattern and a uniform flash light (FL) with a frequency of 1.88 and 15 Hz. The VEP parameters obtained with the stimulation of a checkerboard pattern did not differ significantly between the patients and controls. Neither the presence of seizure activity in EEG nor the type of seizure significantly affected the VEP parameters. Using the FL stimulation, a significantly prolonged VEP latency was found at the FL frequency of 1.88 Hz and shortened at the frequency of 15 Hz. These changes were augmented after activation tests. In case of the patients with positive intermittent photic stimulation response in EEG, a significant prolongation of P100 latency was shown at rest and after FL stimulation at the frequency of 1.88 Hz. Standard activation methods significantly affect the VEP parameters in patients with epilepsy. Changes in the VEP parameters depend on the frequency and the type of the stimulus, as well as the activation method used. These findings suggest a disturbed balance between the glutamatergic and GABAergic systems in the visual excitability of neuronal networks in case of patients with epilepsy.

Pattern- and motion-related visual evoked potentials in HIV-infected adults.

The goal of the current study was to explore visual function in virally suppressed HIV patients undergoing combined antiretroviral therapy (cART) by using pattern-reversal and motion-onset visual evoked potentials (VEPs). The pattern-reversal and motion-onset VEPs were recorded in 20 adult HIV+ patients with a mean age of 38years and CD4 cell counts ≥230×106 cells/L of blood. Nine out of 20 patients displayed VEP abnormalities. Pattern-reversal VEPs pathology was observed in 20% of subjects, and 45% HIV patients had impaired motion-onset VEPs. Five out of 16 neurologically asymptomatic HIV patients had prolonged motion-onset VEP latencies in both eyes. Four neurologically symptomatic patients displayed simultaneously abnormal motion-onset and pattern-reversal VEP latencies: monocular involvement was observed in two patients with Lyme and cytomegalovirus unilateral optic neuritis. Binocular involvement was noted in two patients with cognitive deficits. Correlation analysis between disease duration, CD4 cell count, HIV copies in plasma, MoCA and electrophysiological parameters did not show any significant relationships. The functional changes of the visual system in neurologically asymptomatic virally suppressed HIV patients displayed higher motion-onset VEP sensitivity than in standard pattern-reversal VEP examinations. This promising marker, however, has no significant association with clinical conditions. Further exploration is warranted.

Afferent Visual Pathway Affection in Patients with PMP22 Deletion-Related Hereditary Neuropathy with Liability to Pressure Palsies.

BackgroundThe PMP22 gene encodes a protein integral to peripheral myelin. Its deletion leads to hereditary neuropathy with liability to pressure palsies (HNPP). PMP22 is not expressed in the adult central nervous system, but previous studies suggest a role in CNS myelin development. The objective of this study was to identify potential structural and functional alterations in the afferent visual system in HNPP patients.MethodsTwenty HNPP patients and 18 matched healthy controls (HC) were recruited in a cross-sectional study. Participants underwent neurological examination including visual acuity, visual evoked potential (VEP) examination, optical coherence tomography (OCT), and magnetic resonance imaging with calculation of brain atrophy, regarding grey and white matter, and voxel based morphometry (VBM), in addition answered the National Eye Institute’s 39-item Visual Functioning Questionnaire (NEI-VFQ). Thirteen patients and 6 HC were additionally examined with magnetic resonance spectroscopy (MRS).ResultsAll patients had normal visual acuity, but reported reduced peripheral vision in comparison to HC in the NEI-VFQ (p = 0.036). VEP latency was prolonged in patients (P100 = 103.7±5.7 ms) in comparison to healthy subjects (P100 = 99.7±4.2 ms, p = 0.007). In OCT, peripapillary retinal nerve fiber layer thickness RNFL was decreased in the nasal sector (90.0±15.5 vs. 101.8±16.5, p = 0.013), and lower nasal sector RNFL correlated with prolonged VEP latency (Rho = -0.405, p = 0.012). MRS revealed reduced tNAA (731.4±45.4 vs. 814.9±62.1, p = 0.017) and tCr (373.8±22.2 vs. 418.7±31.1, p = 0.002) in the visual cortex in patients vs. HC. Whole brain volume, grey and white matter volume, VBM and metabolites in a MRS sensory cortex control voxel did not differ significantly between patients and HC.ConclusionPMP22 deletion leads to functional, metabolic and macro-structural alterations in the afferent visual system of HNPP patients. Our data suggest a functional relevance of these changes for peripheral vision, which warrants further investigation and confirmation.

Effects of albendazole combined with TSII-A (a Chinese herb compound) on optic neuritis caused by Angiostrongylus cantonensis in BALB/c mice.

BackgroundAngiostrongylus cantonensis (A. cantonensis) infection can lead to optic neuritis, retinal inflammation, damage to ganglion cells, demyelination of optic nerve and visual impairment. Combined therapy of albendazole and dexamethasone is a common treatment for the disease in the clinic, but it plays no role in vision recovery. Therefore, it has been necessary to explore alternative therapies to treat this disease. Previous studies reported the neuro-productive effects of two constituents of Danshen (a Chinese herb)-tanshinone II-A (TSII-A) and cryptotanshinone (CPT), and this study aims to evaluate the impacts of TSII-A or CPT combined with albendazole on optic neuritis caused by A. cantonensis infection in a murine model.MethodsTo assess the effects of TSII-A or CPT combined with albendazole on optic neuritis due to the infection, mice were divided into six groups, including the normal control group, infection group and four treatment groups (albendazole group, albendazole combined with dexamethasone group, albendazole combined with CPT group and albendazole combined with TSII-A group). The infection group and treatment groups were infected with A. cantonensisand the treatment groups received interventions from 14 dpi (days post infection), respectively. At 21 dpi, the visual acuity of mice in each group was examined by visual evoked potential (VEP). The pathologic alteration of the retina and optic nerve were observed by hematoxylin and eosin (H&E) staining and transmission electronic microscopy (TEM).ResultsInfection of A. cantonensis caused prolonged VEP latency, obvious inflammatory cell infiltration in the retina, damaged retinal ganglions and retinal swelling, followed by optic nerve fibre demyelination and a decreasing number of axons at 21 dpi. In treatment groups, albendazole could not alleviate the above symptoms; albendazole combined with dexamethasone lessened the inflammation of the retina, but was futile for the other changes; however, albendazole combined with CPT and albendazole combined with TSII-A showed obvious effects on the recovery of prolonged VEP latency, destruction and reduction of ganglion cells, optic nerve demyelination and axon loss. Compared with albendazole-CPT compound, albendazole combined with TSII-A was more effective.ConclusionsThe current study demonstrates that albendazole combined with TSII-A plays a more effective role in treating optic neuritis caused by A. cantonensis in mice than with dexamethasone, as applied in conventional treatment, indicating that albendazole combined with TSII-A might be an alternate therapy for this parasitic disease in the clinic.

Temporal aspects of visual perception in demyelinative diseases

The study aims to test whether impaired conduction velocities following optic neuritis (ON) serve as a limiting factor on various temporal, as compared to static, aspects of vision. Critical Flicker fusion frequency (CFFF), two motion perception tasks (object and number-from-motion extraction tasks), high and low contrast acuities, and visual evoked potentials (VEPs) were assessed in 23 ON patients. Strong correlations were found between the various dynamic visual function scores. Furthermore, regression models revealed that each of the dynamic visual functions significantly predicted VEP latencies. These findings were specific to patients' affected eyes and were not evident for static visual functions. Fellow eyes' VEP latencies were best predicted by the VEP latencies of the affected eyes. The similar impact of VEP latencies on various dynamic visual functions suggests conduction velocity to be the common limiting factor for temporal-related visual perceptual abilities. The specificity of these findings to the patients' affected eyes and to dynamic visual functions highlights the precision of dynamic visual functions for identifying demyelinative attack. Prolonged VEP latencies in the fellow eyes seem to stem from different patho-physiological processes. The hypothesis that inter-eye synchronization in conduction latencies is important to accomplish visual processing (binocular vision) is further discussed.

The pathogenesis of optic neuritis caused by Angiostrongylus cantonensis in BALB/c mice.

BackgroundOne of the most common causes of meningitis in South East Asia is angiostrongyliasis or infection by the parasitic nematode Angiostrongyliasis cantonensis. Although this nematode usually resides in the pulmonary arteries of rats, its incidental occurence in other hosts such as humans can cause optic neuritis and lead to serious vision sequelae. Nevertheless, there are currently no systematic studies conducted in this area.MethodsIn order to study the pathogenesis of optic neuritis, mice were tried as a new animal model to study and challenge with A. cantonensis on 7d, 14d and 21d, respectively. Electroretinogram (ERG), visual evoked potential (VEP), ophthalmoscopy and histology were examined on day 7d, 14d and 21d and tribendimidine (TBD) was later used to treat optic neuritis on day 14d for a week to evaluate its therapeutic effects.ResultsInfection of A. cantonensis caused obvious inflammatory cell infiltration in the retina and optic nerve adventitia in day 14d and 21d followed by optic nerve fiber demyelination and retinal ganglion swelling at day 21d in the challenged mice. Prolonged VEP latency and decreased ERG amplitude were also observed on day 21. After treatment of TBD in the infected mice, retinal and optic nerve inflammation were alleviated, but VEP latency and ERG amplitude did not improve on day 21d and 28d.ConclusionsThe current study provides evidence that A. cantonensis can cause optic neuritis along with optic nerve demyelination and retinal ganglion cell damage in a mouse model. TBD alone treatment can improve the symptoms of optic neuritis, but does not aid in vision recovery, suggesting that both neuroprotective agents and Dexamethasone should be administered, along with treatment for the infection, to protect the optic nerve and ganglion cells. Furthermore, as the symptoms of optic neuritis caused by A. cantonensis in mice are similar to the optic neuritis in multiple sclerosis (MS) human patients, we suggest that the BALB/c mouse model provided in this study may be useful to explore therapies of optic neuritis in MS patients.

The role of nitric oxide on visual-evoked potentials in MPTP-induced Parkinsonism in mice

The present study aimed to elucidate visual evoked potentials (VEP) changes in MPTP induced Parkinson’s disease (PD) and investigate the possible benefical effects of neuronal (n) and inducible (i) nitric oxide synthase (NOS) inhibitors on altered VEPs, lipid peroxidation and apoptosis. 3months old C57BL/6 mice were randomly divided into 6 groups which included control (C), 7-nitra indazole treated (7-NI), S-methylisothiourea (SMT) treated, 1,2,3,6-tetrahydropyridine (MPTP) treated, 7-NI+MPTP treated and SMT+MPTP treated. Motor activity of mice was evaluated via the pole test. At the end of the experimental period VEPs were recorded, brain and retina tissues were removed for biochemical analysis. Dopaminergic neuron death at substantia nigra (SN) was determined by immunohistochemical analysis of tyrosine hydroxylase (TH). Immunohistochemical staining was also performed to determine iNOS and nNOS in all tissue sections. Mice with experimental PD exhibited decreased motor activity. Dopaminergic cell death at pars compacta of SN (SNpc) was significantly increased in MPTP treated group compared to control. Diminished Parkinsonism symptoms were observed in 7-NI+MPTP and SMT+MPTP groups. Treatment with 7-NI and SMT decreased dopaminergic cell death in MPTP treated mice. Caspase-3 activity, nitrite/nitrate and 4-hydroxynonenal (4-HNE) levels were significantly increased in SN of MPTP treated mice compared to control. Treatment with 7-NI and SMT significantly decreased elevated caspase-3 activity, nitrite/nitrate and 4-HNE levels in SN of MPTP treated mice. No significant difference in above parameters were observed in the retina. VEP latencies were significantly prolonged in MPTP group compared to control group. 7-NI and SMT treatment caused a significant decrease in VEP latencies in MPTP treated mice compared to none treated MPTP group. This data shows that 7-NI and SMT improves prolonged VEP latencies. The protective effects of 7-NI and SMT on VEP alterations can be related to decreased dopaminergic cell death and reduced lipid peroxidation.

1089 Visual Evoked Potentials in Term and Preterm Infants

Background and AimsEvoked potentials are a useful non-invasive method for the assessment of neurological status in term and preterm infants at risk for perinatal CNS damage. The present study intended...

The effect of sodium metabisulfite on visual evoked potentials in rats with hypercholesterolemia

This study aimed to investigate the effects of hypercholesterolemia on visual evoked potentials (VEPs) and sulfite additional effects. Rats were assigned as follows: control (C), sulfite (S), hypercholesterolemia (H), vitamin E (E), sulfite + vitamin E (SE), hypercholesterolemia + sulfite (HS), hypercholesterolemia + vitamin E (HE), and hypercholesterolemia + sulfite + vitamin E (HSE). Hypercholesterolemic diet led significant increase in plasma cholesterol levels of rats. Brain thiobarbituric acid reactive substances (TBARS) levels were significantly increased in S, E, SE, HE and HSE groups compared with C. TBARS levels were increased in HE and HSE groups as compared to HS group. Nitrite levels were decreased in S, SE, H, HS and HSE groups compared with C. Nitrite level was notably increased in the HE group compared with H group. Sulfite exposure prolonged N1 and P3 latencies of VEP in group S compared with C. Prolonged VEP latencies by sulfite were significantly decreased by vitamin E in SE group. Cholesterol rich diet increased VEP latencies in comparison with control latencies. Sulfite gave rise to an additional increase in P3 latency in HS group compared with H group. Vitamin E-treated animals had notably shortened latencies of VEP components in HE and HSE groups according to the H and HS groups, respectively.

The Effect of Docosahexaenoic Acid on Visual Evoked Potentials in a Mouse Model of Parkinson’s Disease: The Role of Cyclooxygenase-2 and Nuclear Factor Kappa-B

This study aimed to investigate the effect of docosahexaenoic acid (DHA) on visual evoked potentials (VEPs) in a mice model of Parkinson's disease (PD). Mice model was created by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and DHA was given by gavage. Cyclooxygenase-2 (COX-2), caspase-3 activities, nuclear factor kappa-B (NF-κB) and prostaglandin E2 (PGE2) levels were determined in substantia nigra (SN) and retina. Cyclooxygenase-2 intensities were also determined immunohistochemically. The tyrosine hydroxylase (TH) immunolabelling was significantly decreased in MPTP group compared to control. Docosahexaenoic acid decreased dopaminergic neuron death in MPTP+DHA group when compared to MPTP group. Mice treated with MPTP showed motor deficits as compared to control. Significant improvement was observed in MPTP+DHA group when compared to MPTP group. Treatment with MPTP significantly increased the activity of COX-2 and total COX in SN when compared to the control group. Docosahexaenoic acid caused a significant decrease in total COX and COX-2 activity in SN of mice given MPTP. Cyclooxygenase-2 showed strong immunostaining in MPTP group when compared to other groups in SN. Levels of PGE2 increased in MPTP group when compared to control in SN. Docosahexaenoic acid treatment in MPTP group reduced PGE2 in SN. Nuclear factor kappa-B levels were found to be decreased in SN of MPTP group. The mean latencies of P1, N1, P2, N2, P3, N3, P4, N4, and P5 VEP components were significantly prolonged in MPTP group when compared to control. In MPTP+DHA group, the mean latencies of all components except P5 returned to control values. Current data shows that DHA treatment improves prolonged VEPs latencies and locomotor activity.

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.

Clinical, MRI, CSF and electrophysiological findings in different stages of multiple sclerosis

Effective therapy in the earliest stages of multiple sclerosis (MS) demands early correct diagnosis. Retrospective analysis included 130 patients (90 women) with a median age of 35.5 years, median duration of the disease of 2 years and median EDSS score of 3.0. Twenty-seven patients had clinically isolated syndrome (CIS) suggestive of MS, 66 relapsing-remitting (RR) MS, 19 secondary progressive (SP) MS and 18 primary progressive (PP) MS. The predominant symptoms were sensory in 52% of the patients with CIS compared to 27% in patients with RRMS, whereas they were more often motor in patients with PPMS. Patients with CIS had higher CSF cell counts than patients diagnosed in later stages of the disease and oligoclonal bands were found in 89% of all patients without statistically significant differences between the subgroups. Prolonged latencies of visual evoked potentials (VEP) were found in only 29% of patients with CIS compared to 66% in RRMS, 75% in SPMS and 65% of PPMS patients. Fifty-six percent of patients with CIS, 88% with RRMS, 74% with SPMS and 78% of patients with PPMS fulfilled modified the Barkhof et al. MRI criteria at the time of diagnosis. Patients in early MS often present with sensory symptoms. Brain MRI can be inconclusive in over 40% of patients with CIS but the elevated CSF cell count and positive oligoclonal bands are helpful in establishing the diagnosis of CIS suggestive of MS. In later stages of the disease the combination of clinical features, MRI, prolonged VEP latencies and positive CSF oligoclonal bands secures the correct diagnosis.

Visual evoked potentials study in chronic idiopathic inflammatory demyelinating polyneuropathy

Background: The frequency of the association between chronic demyelinating inflammatory polyneuropathy (CIDP) and central nervous system (CNS) demyelinating lesions is probably underestimated. Objective: To investigate the occurrence of combined central and peripheral demyelination in CIDP patients and to correlate visual evoked potential (VEP) abnormalities with CNS demyelinating lesions, observed on brain magnetic resonance imaging, and antibodies against glycolipids. Methods: Nerve conduction studies, brain MRI and antibodies against glycolipids were prospectively studied in 17 patients who fulfilled the diagnostic criteria proposed for CIDP (Cornblath DR, Asbury AK, Albers JW, Feasby TE, Hahn AF, McLeod JG, Mendell JR, Parry GJ, Pollard JD, Thomas PK. Ad Hoc Subcommittee of the American Academy of Neurology AIDS Task Force. Research criteria for diagnosis of chronic inflammatory demyelinating polyneuropathy. Neurology, 1991;41:617–618). VEPs were performed in each case before and after 6 months treatment with either intravenous immunoglobulins (IVIG) or steroids. Results: Eight patients (47%) had increased latencies in at least one eye or showed increased interocular latency difference. Four patients (23%) presented a significant high signal intensity on T2-weighted brain MRI images. Of these 4 patients, 3 had prolonged VEP latency. Two patients with delayed VEP latency had antibodies against GM1, and SGLPG and anti-sulfatides, respectively. One patient with normal VEPs also had antibodies to GM1. VEP results were not significantly modified after treatment, either with steroids or IVIG. Conclusion: This study confirmed the high frequency of abnormal VEPs in CIDP patients, and found that they are poorly correlated with CNS demyelinating lesions and antibodies against glycolipids. The VEP abnormalities of these patients may be explained by the susceptibility to immune-mediated damage of both the peripheral nervous system and the optic nerve.

Long term decline of P100 amplitude in migraine with aura

OBJECTIVESTo investigate visual function in migraine using visual evoked potentials.METHODSElectroretinograms (ERGs) and visual evoked potentials (VEPs) to single flash (SF) and pattern reversal (PR) stimuli were studied in 92 migraine...

EFFECTS OF THYROID HORMONE ON THE LATENCY OF EVOKED POTENTIAL AND ELECTRORETINOGRAM IN ADULT RATS

To analyze effects of thyroid hormone on the central nervous system, we recorded visual evoked potentials (VEPs) by photic and electrical stimulations in normal, thyroidectomized (Tx) and T3 or T4-supplemented (Tx-T3, T4) adult rats under pentobarbital anesthesia. The latencies of VEPs recorded in the visual cortex (VC) and lateral geniculate nucleus (LGN) and b-wave of electroretinogram (ERG) were compared in these three groups. A significant prolongation of latency in the visual system of Tx rats 14 to 28 days after operation was observed compared with that in intact control rats. The prolonged VEP latencies in the LGN and the VC showed a positive correlation with the prolonged b-wave latency of ERG between the three groups. These prolonged latencies observed in the VC, the LGN and ERG were partially normalized 24 hours after T3 supplement (50μg/kg, sc) and completely restored to normal levels by 48 hours after T4 injection (100μg/kg, sc). There was a positive correlation between recovered latencies to observed in the LGN and VC and those in b-wave of ERG. When electrical stimulation was delivered to the optic chiasma or the LGN, and evoked potential were recorded in the VC and LGN, neither latencies recorded in the VC nor those in the LGN were significantly different in intact and Tx rats. Moreover, there was no significant difference between optic nerve conduction velocities in these two groups.These results suggest that the prolongation of latency of VEPs observed in hypothyroid rats are mainly attributed to that occurring in the retina, indicating the essential role of thyroid hormone in maintaining retinal function in adult animals.

Correlation of visual evoked potentials, ophthalmological and neurological findings after unilateral optic neuritis.

Forty-two patients were tested with pattern reversal visual evoked potentials (VEPs) 1--8 years after an episode of acute unilateral optic neuritis. The stimulation was produced by dot as well as checker-board pattern. An unexpectedly large proportion (12 cases) showed normal VEP latencies from the affected eye. In these patients the initial visual acuity was on the average significantly better than in cases with prolonged VEP latencies. They also had significantly fewer remaining ocular signs than the patients with abnormal VEPs. On the other hand, no correlation was found between the VEP findings and the incidence of CSF abnormalities, multiple sclerosis and HLA types. In 14 patients of which 13 belonged to the group above, repeated VEP tests were performed from the acute onset of the disease and up to 2 years afterwards confirming that a considerable normalization of VEP latencies occurs.

THE INCIDENCE AND NATURE OF VISUAL PATHWAY INVOLVEMENT IN FRIEDREICH'S ATAXIA

Pattern-reversal visual evoked potentials (VEP) were recorded from 22 patients (mean age 33.7 years) with Friedreich's ataxia, 15 of whom also had a detailed neuro-ophthalmological assessment prior to the VEP examination. None had noted symptomatic visual impairment. Eleven of the 15 (73 per cent) examined clinically had one or more neuro-ophthalmic abnormality and 14/22 (64 per cent) had an abnormal VEP study which was always binocular and comprised absent responses, or most commonly, increased P100 component latencies. The maximum P100 latency was 143 ms and the group mean was 118 ms. The P100 amplitude was also generally reduced particularly in those patients with latencies less than 115 ms (upper limit of normal), while in those with latencies above the normal range there was a significant inverse correlation between the P100 amplitude and latency. The waveform, temporal dispersion and interocular differences were normal in almost all patients with identifiable responses, including those with prolonged VEP latencies. Electroretinograms recorded from three selected patients were either normal or minimally abnormal and suggested secondary rather than primary retinal involvement. The only VEP parameter to correlate with either the duration of the generalized disease or the visual acuity was the P100 amplitude. A good correlation was found between the VEP and the clinical neuro-ophthalmic findings. Temporal pallor of the optic disc was most often associated with an abnormal VEP result and impaired visual acuity or colour vision were uncommon in the absence of VEP abnormalities. The VEP changes and those obtained from 24 age- and acuity-matched cases of demyelinating optic neuritis are contrasted and the probable pathophysiology is discussed. Two main conclusions emerge from this study. First, there is a high incidence of asymptomatic visual pathway involvement in Friedreich's ataxia which can be demonstrated by both clinical and VEP examination. Secondly, the VEP changes in Friedreich's ataxia differ from those found in typical demyelinating optic neuropathy and are consistent with progressive nerve fibre loss and associated slowing of conduction, indicating that the visual pathway is affected by the same widespread process of axonal degeneration found throughout the nervous system.

Visual evoked potentials and the visuogram in multiple sclerosis

Visual evoked potential (VEP) latency to a sinusoidal grating pattern was measured in each eye of 103 patients with multiple sclerosis (MS) and compared with results in a control group of 56 patients hospitalized for other neurological conditions. Of the 50 patients classified as having definite MS, 90% showed prolonged latency (over 131 msec) in one or both eyes. In each eye of 24 of the MS patients, psychophysical measurement of the detectability of grating patterns was obtained. This test was abnormal in 11 of 13 patients with definite MS, 3 of 4 with probable MS, and 5 of 7 with possible MS. There was no concordance between prolonged VEP latency and visual impairment as revealed by the psychophysical test. Apparently pathways determining VEP latency and spatial contrast detection may be unequally affected in MS.