Visual Evoked Potentials In Patients Research Articles

Loss of visual function in diabetes mellitus

Background: Diabetes mellitus being a well-known cause for peripheral neuropathy, this study aims to detect visual pathway dysfunction in diabetics using contrast sensitivity as a subjective measure and visual-evoked potential (VEP) as an objective measure of visual pathway function. Aims: To compare contrast sensitivity and VEP in patients with type 2 diabetes mellitus as compared with control and to find the correlation with glycemic level. Materials and Methodology: This was a comparative study conducted at a tertiary eye care center. After detailed ophthalmological evaluation, contrast sensitivity and VEP of 40 patients with diabetes (20 with retinopathy and 20 without retinopathy) were compared with suitable control. Data were analyzed using the SPSS (Statistical Product and Service Solutions) version 18 using the independent sample t-test and ANOVA. Results: There was reduction of mean contrast sensitivity in diabetics as compared to nondiabetics. Contrast sensitivity was better in diabetics without retinopathy as compared to diabetics with retinopathy. There was prolongation of P100 latencies and reduction of P100 amplitudes among diabetics as compared to non-diabetics and among those with diabetic retinopathy as compared to those with normal fundus. Reduced contrast sensitivity and reduction of P100 amplitudes were seen among those with poor glycemic control. Conclusion: There was evidence of reduction of contrast sensitivity and alteration of VEP in patients with diabetes even before reduction in visual acuity giving evidence of visual pathway dysfunction in diabetes mellitus. This may also be affected by the glycemic status of the patient.

Need for Visual Pathway Examination of the Patient Prior to Bone Marrow Transplantation

Aim: Bone Marrow Transplantation is a treatment procedure usually applied for the patients suffering from leukemia. It is observed that some of these patients complain from partial vision loss few months after the operation whereas the routine visual examination of these patients are normal, therefore the aim of present work is to examine the visual pathway of these patients to search for the probable visual pathway degeneration of these patients using visual evoked potential (VEP). Method: 10 patients following bone marrow transplantation were selected randomly. These patients had this operation for at least one year before. Routine ophthalmological examination of them was normal or at most they had refractive error problem which could be corrected by suitable spectacles. Visual evoked potential was recorded in these patients. Latency (msec) and amplitude (μv) of VEP, P100 Peak was noted for each patient. Beside these patients, 10 people with healthy visual system were selected to compare the result of VEP in patients with healthy group following VEP recording. Result: It is observed that 4 patients had abnormal VEP pattern which was reflected either in latency or amplitude of VEP, P100 Peak. Conclusion: From the result of present work, one can conclude that VEP examination of patients following bone marrow transplantation is necessary prior to operation so that if any unexplained visual loss is observed after operation, the medical staff can follow the case for the probable reason for this malfunction.

Continuous Positive Airway Pressure Treatment May Improve Optic Nerve Function in Obstructive Sleep Apnea: An Electrophysiological Study.

Obstructive sleep apnea (OSA) is a sleep disorder frequently associated with optic nerve diseases. Moreover, untreated patients with severe OSA may show optic nerve dysfunction as documented by electrophysiological studies using visual evoked potentials (VEP). Because continuous positive airway pressure (CPAP) treatment has proved to restore the physiologic nocturnal breathing, thus preventing nocturnal hypoxemia and reducing inflammation, in this study we tested whether 1-year CPAP treatment may modify VEP responses in patients with severe OSA. VEP were recorded at baseline and after 1 year of CPAP treatment in 20 patients with severe OSA, divided in two groups on the basis of CPAP adherence, and compared to a healthy control group. Patients with good adherence to CPAP therapy (CPAP+; n = 10) showed VEP P100 amplitude significantly higher than patients with poor adherence to CPAP therapy (CPAP-; n = 10). Moreover, the CPAP+ group showed VEP responses similar to those in the control group (n = 26). Considering the mean difference of VEP responses between baseline and follow-up, the CPAP+ group showed a significant increase in VEP P100 amplitude and a significant decrease in VEP P100 latency compared to the CPAP- group. This study documented that CPAP therapy significantly improves VEP in patients with OSA who are adherent to the treatment. We hypothesize that CPAP treatment, minimizing the metabolic, inflammatory and ischemic consequences of OSA, may normalize the altered VEP responses in patients with OSA by restoring and preserving optic nerve function.

Does Rifaximin Improve EEG and VEP in Egyptian Cirrhotic Patients with Minimal Hepatic Encephalopathy?

Background: Minimal hepatic Encephalopathy (MHE) is defined as HE without symptoms on clinical/neurological examination, but with deficits in some cognitive areas that can only be measured by neuropsychometric testing. However, numerous studies have shown that, although the neurological symptoms are slight, affected patients are markedly impaired in their quality of life and ability to work. Various treatment modalities that have been shown to reverse MHE include lactulose/lactitol, probiotics/synbiotics, L-carnitine but rifaximin has shown a general trend toward better efficacy and better tolerability in patients with overt hepatic encephalopathy (OHE). Objective: Our objective is to assess the diagnostic role of minimental state examination (MMSE), electroencephalography (EEG) and visual evoked potential (VEP) in detection of MHE and to evaluate the efficacy of rifaximin in improving EEG and VEP in patients with MHE. Patients and Methods: Sixty cirrhotic patients were enrolled in the study depending on clinical evidence of stigmata of chronic liver disease, laboratory investigations including liver function tests, ultrasonographic features of liver cirrhosis and with no evidence of overt hepatic encephalopathy. Diagnois of MHE was made depending on minimental state examination (MMSE) and neurophysiological tools including EEG and VEP. A control group of sixty healthy volunteers with age and sex matched were included. The patient group received Rifaximin 550 mg twice daily for 8 weeks then follow up EEG and VEP studies were done. Results: MHE was detected in 36.7%, 48.3%, 51.7% of our series based on MMSE, EEG and VEP respectively. Child Pouph A, B, C was found in 51.7%, 35%, 13.3% respectively. Rifaximin was well tolerated. At the end of treatment, EEG and VEP studies were done which showed signficant changes between pre and post treatment results (P value = 0.03, 0.001, Conclusion: MMSE as well as EEG and VEP were reasonable diagnostic tools for early detection of MHE particularly in countries with low level of education. Rifaximin significantly improves both EEG and VEP in cirrhotic patients with MHE.

Anamnestic headache in patients with cervical artery dissection: clinical characteristics and pathogenetic mechanisms

To study the frequency and characteristics of headache which is in the past history (HPH) of patients with cervical artery dissection (CeAD) and evaluate with the help of EEG and visual evoked potentials (VEP) the role of central mechanisms in its development. Two hundred and twenty-seven patients with CeAD verified by neuroimaging were studied. All patients were interviewed about the presence of a headache in the past history and its features. The comparison group comprised 35 patients (mean age - 32,3±8,9 years, 77% female) with migraine. Thirty-five patients with HPH and 35 patients of the comparison group underwent EEG and VEP. HPH was found in 101 patients (average age of 38.5±8.5 years, 70% female) (44.5%) out of 227 patients. In 35 patients (15.4%), HPH met the International Criteria for migraine (with aura - 3.1%, without aura - 12.3%) and in 66 patients (29.1%) did not (non-migraine headache). The latter started at the age of 24.5±10.2 years, had mild/ moderate intensity (95%), diffuse localization (68%), dull/pressing/squeezing character (53%), never accompanied by vomiting and rarely by nausea (8%), photo- phonophobia (11%). HPH, which met the migraine criteria unlike migraine in the comparison group began at a later age (19.9±9.6 vs 16.2±4.4 years, p<0.03), more frequently did not have aura (80% vs 48%, p<0.003), less often was unilateral (31% vs 71%, p<0,004) and had less intensity. The visual EEG analysis less often found rhythmic disorganization in CeAD patients with HPH than in comparison group with migraine. The hyperventilation caused a slight increase in the spectral power of Teta, Delta waves in HPH patients and significant enhancement in comparison group with migraine (p<0.05). Pattern reversal VEP in patients with HPH had a greater latency and smaller amplitude of cortical responses than in comparison group with migraine (p=0.028 and =0.037, respectively). The flash VEP amplitude was lower in HPH patients than in migraine (p=0.01). HPH in patients with CeAD meets criteria of migraine in 15.4% (with aura - 3.1%, without aura - 12.3%), 29.1% patients have nonmigraine HPH. Central mechanisms, namely, the hypersensitivity of the cerebral cortex playing the main role in migraine pathogenesis, are not significant in HPH genesis. The main role appears to have peripheral mechanisms - dysplastic changes in the wall of extra- and intracranial arteries that predispose both to headache and dissection.

EFFECTS OF HEMODIALYSIS ON VISUAL PATHWAYS ASSESSED BY VISUAL EVOKED POTENTIALS (VEPs)

Uremia is a metabolic disorder that affects the functions of the central nervous system (CNS). Visual evoked potentials (VEPs) can be used to demonstrate uremia-induced effects on the CNS. Data on VEPs of patients with chronic renal failure (CRF) are limited. The purpose of this study was to examine the effects of renal failure and the ultrafiltration rate (UFR) on CNS functions in patients undergoing hemodialysis (HD) using VEPs. The study consisted of 30 CRF patients undergoing HD, and a control group of 28 individuals, matched in terms of age and gender. Patients with mental retardation, diabetes mellitus, demyelinating disease, stroke, use of neurotoxic drugs, and ophthalmologic diseases were excluded from the study. The pattern VEP (PVEP) parameters recorded were latencies to N75 (N1), P100 (P1) and N135 (N2) waves, and the peak-to-peak amplitude of a P100 wave. The PVEP was taken twice just before and 24 h after HD, and the PVEP parameters were compared. Additionally, the effect of the UFR on the PVEP parameters was examined. There was no difference between the HD group and control group in terms of gender and age (mean ages of 49.56±12.52 and 48.53±13.28 years, respectively). The average HD period was 87.53±56.34 months. The P1 latencies between the two eyes the patients with CRF were prolonged when compared to those of the controls (right eye p=0.002; left eye p=0.019). A single HD session significantly shortened the latency of the P1 waves compared to that of the baseline waves (p<0.000). Additionally, there was a positive correlation between the difference in the P1 latency before and after HD and the UFR (right eye p=0.03, r=0.525; left eye p=0.022, r=0.417, respectively). We conclude that VEP, which is an easy, cheap, and simple electrophysiological method, can be used to determine subclinical CNS dysfunction in patients with CRF and show the effect of fluid removal during HD on the visual pathways, and to show the corrective effect of effective fluid imaging on the visual pathways.

Transorbital sonography in acute optic neuritis: a case-control study.

Acute unilateral optic neuritis is associated with a thickening of the retrobulbar portion of the optic nerve as revealed by transorbital sonography, but no comparison has been made between nerve sheath diameter and optic nerve diameter in patients with acute optic neuritis versus healthy controls. We evaluated optic nerve sheath diameter and optic nerve diameter in patients with acute optic neuritis and healthy controls and compared optic nerve sheath diameter and optic nerve diameter with visual-evoked potentials in patients. A case-control study was performed in 2 centers. Twenty-one consecutive patients with onset of visual loss during the prior 10 days and established acute noncompressive unilateral optic neuritis were compared with 21 healthy controls, matched for sex and age (±5 years). Two experienced vascular sonographers performed the study by using B-mode transorbital sonography. Visual-evoked potentials were performed on the same day as the transorbital sonography and were evaluated by an expert neurophysiologist. Sonographers and the neurophysiologist were blinded to the status of the patient or control and to clinical information, including the side of the affected eye. The median optic nerve sheath diameter was thicker on the affected side (6.3 mm; interquartile range, 5.9-7.2 mm) compared with the nonaffected side (5.5 mm; interquartile range, 5.1-6.2 mm; P < .0001) and controls (5.2 mm; interquartile range, 4.8-5.5 mm; P < .0001). The median optic nerve diameter was 3.0 mm (range, 2.8-3.1 mm) on the affected side and 2.9 mm (range, 2.8-3.1 mm) on the nonaffected side (P = not significant.). Both sides were thicker than those in controls (2.7 mm; interquartile range, 2.5-2.8 mm; P = .001 and .009). No correlation was found between optic nerve sheath diameter and optic nerve diameter and amplitude and latency of visual-evoked potentials in patients with optic neuritis. Transorbital sonography is a promising tool to support the clinical diagnosis of acute optic neuritis. Further studies are needed to define its specific role in the diagnosis and follow-up of optic neuritis.

Visual-evoked potentials in patients with brain circulatory problems

Purpose: The aim of this study was to find out if local brain circulatory problems may influence visual-evoked potentials (VEP). Patients and methods: Thirty-eight patients were divided into the following groups: (I) those with hemianopsia or quadrantanopsia and hemiparesis after brain stroke; (II) those with hemianopsia or quadrantanopsia without paresis after brain stroke; and (III) those with amaurosis fugax. The control group consisted of 38 patients. The VEP pattern (PVEP) and flash VEP (FVEP) were examined monocularly using two electrodes placed at O1 and O2. Latency and amplitude of the N75, P100 and N2, P2 waves were measured. The Newman–Keuls test was used for statistical analysis. Results: In PVEP, no differences between the groups were observed. In FVEP, the mean P2 latency was significantly longer in group I than in group III, and the P2 amplitude was significantly lower in all examined groups when compared with the control group. PVEP and FVEP revealed differences in P latency over 3 ms between brain hemispheres and differences in P amplitude over 30% in all examined groups. In the control group, there were no differences in latency between brain hemispheres and only a small difference in amplitude. Conclusion: Local brain circulatory problems that may lead to brain ischemia cause differences in VEP amplitude and latency between brain hemispheres. Changes in VEPs observed in patients with amaurosis fugax may be considered the result of recurrent brain ischemia.

Correlation between circumpapillary and macular retinal nerve fiber layer thickness measured by spectral domain optical coherence tomography and multifocal visual evoked potential in patients with primary open-angle glaucoma

Purpose This study attempts to examine the relationship between the function of postsynaptic activity of the visual pathway at the level of the striate cortex [multifocal visual evoked potential (mfVEP) responses] and the structural integrity of the retinal nerve fiber layer (RNFL) (by measuring the macular and circumpapillary RNFL thickness). Design This was a prospective nonrandomized interventional clinical study. Patients and methods Patients with controlled primary open-angle glaucoma were included in this study. They underwent complete ophthalmic examination, visual field testing, and macular and peripapillary RNFL thickness measurement by a spectral domain optical coherence tomography (OCT) and mfVEP testing. All similar quadrants on OCT macular and glaucomatous modes were compared with the opposite ones on mfVEP testing (e.g. nasal circumpapillary and macular RNFL thicknesses were compared with the temporal ones on mfVEP testing). Results The mean circumpapillary RNFL thickness showed a significant reduction in each quadrant among the three studied stages of glaucoma ( P l0.001), except the nasal one. The mean macular RNFL thickness showed a significant reduction in the inferior and temporal quadrant among the three stages of glaucoma studied ( P l0.001). The decrease in RNFL thickness in different studied quadrants by OCT correlated positively with the decrease in P1 amplitude ( P l0.0001) and correlated negatively with the increase in P1 latency ( P l0.0001) in the comparable quadrants of the visual field studied by mfVEP. Conclusion The circumpapillary RNFL thickness is a more sensitive detector of glaucoma than the macular one; however, both are affected by glaucoma and can be used for structural evaluation of the RNFL. Both circumpapillary and macular RNFL thickness correlated well with visual field loss detected by mfVEP. mfVEP can be used for functional evaluation and follow-up of the visual pathway of the central 30π of the macula in glaucomatous eyes.

Visual sensory processing deficits in schizophrenia: Is there anything to the magnocellular account?

Visual processing studies have repeatedly shown impairment in patients with schizophrenia compared to healthy controls. Electroencephalography (EEG) and, specifically, visual evoked potential (VEP) studies have identified an early marker of this impairment in the form of a decrement in the P1 component of the VEP in patients and their clinically unaffected first-degree relatives. Much behavioral and neuroimaging research has implicated specific dysfunction of either the subcortical magnocellular pathway or the cortical visual dorsal stream in this impairment. In this study, EEG responses were obtained to the contrast modulation of checkerboard stimuli using the VESPA (Visual Evoked Spread Spectrum Analysis) method. This was done for a high contrast condition and, in order to bias the stimuli towards the magnocellular pathway, a low contrast condition. Standard VEPs were also obtained using high contrast pattern reversing checkerboards. Responses were measured using high-density electrical scalp recordings in 29 individuals meeting DSM-IV criteria for schizophrenia and in 18 control subjects. Replicating previous research, a large (Cohen's d=1.11) reduction in the P1 component of the VEP was seen in patients when compared with controls with no corresponding difference in the VESPA response to high contrast stimuli. In addition, the low-contrast VESPA displayed no difference between patients and controls. Furthermore, no differences were seen between patients and controls for the C1 components of either the VEP or the high-contrast VESPA. Based on the differing acquisition methods between VEP and VESPA, we discuss these results in terms of contrast gain control and the possibility of dysfunction at the cortical level with initial afferent activity into V1 along the magnocellular pathway being intact when processing is biased towards that pathway using low contrast stimuli.

Evaluation of pattern-reversal visual evoked potential in patients with neuromyelitis optica

Background: The visual evoked potential (VEP) is used in the evaluation of multiple sclerosis (MS) patients, showing a delay in P100 wave latency with no changes in amplitude in 60–100% of cases. In the last decade, the recurrent form of neuromyelitis optica (NMO) has been recognized, and clinically characterized by acute events of transverse myelitis (TM) and optic neuritis (ON), differing from MS in clinical and laboratory criteria. Despite these differences, so far, the VEP parameters described in MS have been used in the evaluation of patients with NMO. The objective of this study was to investigate VEP responses in NMO. Methods: Patients with NMO underwent pattern-reversal visual stimulation. Nineteen patients were selected for the study. Results: Among the 38 eyes examined, 18 (47.4%) had no visual evoked responses and 13 (34.2%) had a reduction of P100 wave amplitude with normal latency. Only two (5.3%) had the pattern described in MS and five (13.2%) were normal. Conclusion: Evaluation of VEP in patients with definite NMO revealed a pattern that is different from that of MS in 81.6% of eyes examined, characterized by the absence of responses, or decreased amplitude with normal latency.

B12 Vitamini Eksikliğinde Görsel Uyandırılmış Potansiyeller: Ön Çalışma Sonuçları

Objective: Aim of this study was to investigate the possible relationship between serum vitamin B12 levels and P100 latency and amplitudes with visual evoked potentials (VEP) in patients with B12 vitamin deficiency without optic neuritis (ON). Material and Methods: Patients who presented to the outpatient neurology clinic of Canakkale Onsekiz Mart University Research Hospital underwent initial evaluation. Among those, complete blood count, full biochemistry (blood glucose, liver and kidney function tests, electrolites) and thyroid function tests were performed to the patients with serum B12 vitamin levels l200 pg/dl and without optic neuritis who accepted to participate. Electrophysiological evaluations included VEP. Data were organized in SPSS 15.0 programme and statistical analysis were performed in this programme. Non-parametric correlation test and Spierman's rho tests were used for statistical analysis. Results: Patients enrolled the study consisted of 13 (68.4%) men and 6 (31.6%) women. Mean age was 52.68p15.10 years (range=19-75 years). Mean vitamin B12 levels were160.41p44.59 pg/ml (range=78-230 pg/ml). There was no statistically significant correlation between serum vitamin B12 levels and P100 latency and amplitudes (pg0.05). Conclusion: Our results reveals that there is no correlation between the VEP values and the severity of vitamin B12 deficiency in the absence of ON in patients with vitamin B12 deficiency. Study still continues, but results of the preliminary study are shared in order to discuss the value of VEP in patients with vitamin B12 deficiency without ON. Key words: Vitamin B12 Deficiency; Optic Nerve; Visual Evoked Potentials.

Relationship between optical coherence tomography and visual evoked potentials in patients with parasellar tumors without chiasmal compression

AbstractPurpose To evaluate the relationship between retinal nerve fiber layer (RNFL) thickness measured by optical coherence tomography (OCT) and visual evoked potentials (VEP) in patients with parasellar tumors without chiasmal compression on MRI examination.Methods 32 eyes of 16 patients suffering from tumor of sella turcica without any chiasmal compression were included to the study and compared to 59 eyes of 30 healthy patients. Exclusion criteria were any other ophthalmic or general condition that can affect both VEP and OCT measurements. All patients underwent MRI of the head to confirm the diagnosis, retinal nerve fiber thickness measurements with OCT and visual evoked potentials.Results VEP of patients with parasellar tumors without any chiasmal compression showed no P100 latency prolongation (OD=101,9 ± 6,3ms, OS= 101,2 ± 6,3 ms) in comparison to control group (102,1 ± 4,5ms and 102,5 ± 4,2ms). There was noticed a reduced P100 amplitude in examined patients (OD=10,9 ± 4,8µV, OS=11,6 ± 5,6µV) comparing to healthy subjects (12,3±6,5 µV and 12,1±6,3 µV respectively), however it was not statistically significant (p=0,5 and p=0,8 respectively). Average RNFL thickness in our patients was lower (OD=102,2±8,9µm, OS=101,8 ± 11,5µm) than in control group (104,7 ± 10µm and 104,5 ± 15µm respectively), but the difference was not statistically significant (p=0,8 and p=0,95 respectively).Conclusion In patients with parasellar tumors without any chiasmal compression both visual evoked potentials and RNFL thickness measurements in OCT showed no significant differences in comparison to healthy subjects.

Multifocal visual-evoked potentials in patients with schizophrenia during treatment.

Aim: Investigation of responses of multifocal visual-evoked potentials (mfVEPs) in schizophrenic patients under treatment in whom no abnormality was detected on the conventional perimetry.Methods: Recordings of mfVEPs were performed in 31 schizophrenic patients and 30 normal subjects using a VERIS Junior Science recording apparatus (Mayo, Aichi, Japan). Responses from eight sites in each subject were divided into four quadrants (superior and inferior temporal quadrants, and superior and inferior nasal quadrants). In each quadrant, two response waves were grouped and averaged, and the latency and amplitude of main waveforms that appeared near 100 ms were evaluated.Results: The peak latency was about 7–9 ms prolonged and the amplitude was reduced by about 2–5 nV/deg2 in the schizophrenic patient group compared to those in the normal subject group, and significant differences were noted in both parameters in all quadrants.Conclusion: In schizophrenic patients under treatment with psychotropic agents, prolongation of the latency and amplitude reduction were noted in mfVEPs even though no abnormality was detected on the conventional perimetry.

Pattern-reversal visual-evoked potential in patients with occult macular dystrophy

Purpose:Occult macular dystrophy (OMD) is a hereditary retinal disease characterized by a normal fundus, normal full-field electroretinograms (ERGs), progressive decrease of visual acuity, and abnormal focal macular ERGs. The purpose of this study was to report pattern-reversal visual-evoked potential (pVEPs) findings in OMD patients.Patients and method:The pVEPs recorded from four patients with OMD (aged 42–61 years; 2 men and 2 women) were reviewed. The visual acuities ranged from 20/200 to 20/30. The amplitudes of the N-75 and P-100 (P2 amplitude) and the latency of the N-75 components (N1 latency) were analyzed.Results:The mean (±SD) P2 amplitude was 2.7 ± 1.9 μV for the 5′, 4.8 ± 2.9 μV for the 10′, 3.2 ± 2.1 μV for the 20′, and 4.4 ± 3.5 μV for the 40′ checkerboard stimuli. The N1 latency was 122.2 ± 6.4 ms for the 5′, 105.0 ± 11.5 ms for the 10′, 97.7 ± 10.0 ms for the 20′, and 91.0 ± 13.7 ms for the 40′ checkerboard stimuli. The mean P2 amplitude was reduced and the N1 latency was delayed in comparison with the laboratory standard for the Keio University Hospital.Conclusions:The delayed latency and reduced amplitude suggest a major contribution of the central cone pathway to the pVEPs.

Differential Changes in Color and Motion-Onset Visual Evoked Potentials from Both Eyes in Early- and Late-Onset Strabismic Amblyopia

To examine changes in color- and motion-related visual function in patients with strabismic amblyopia. Motion-onset and color visual-evoked potentials (VEPs) were recorded in 16 adult patients with strabismic amblyopia which had an early onset, before 18 months of age, and 14 patients with amblyopia of later onset. The results are compared with those from 21 normal adults. The peak times of motion-onset VEPs in the amblyopic eye were longer those than in the fellow eye in patients with both early- and late-onset strabismic amblyopia, but peak times in both amblyopic and fellow eyes were shorter than those in normal eyes. In patients with late- but not early-onset amblyopia, the peak times for color VEPs were significantly longer in amblyopic than in fellow and normal eyes. The patterns of abnormality for motion-onset and color VEPs in patients with strabismic amblyopia are different, probably indicating differential changes in function in magno- and parvocellular pathways. These abnormalities affect both the amblyopic and fellow eyes and are different in patients with an onset of amblyopia before or after 18 months of age.

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.

Simulated nystagmus suppresses pattern-reversal but not pattern-onset visual evoked potentials

Objective: The aim of this study is to quantify and compare the effects of simulated horizontal nystagmus on pattern-reversal and pattern-onset visual evoked potentials (VEPs). Methods: In eight visually normal subjects with normal oculomotor behaviour, we monitored eye movements and recorded pattern-reversal and pattern-onset VEPs from occipital electrodes. Subjects viewed the stimulus monocularly via a mirror, which was placed close to the eye and driven by a scanner at four different amplitudes (0, 1, 2, and 3°) with a 4 Hz saw-tooth waveform to simulate horizontal jerk-nystagmus. Results: Retinal image motion nearly abolished the pattern-reversal VEPs (maximal reduction by 85%; mean reduction by 72%, P<0.001), while there was a non-significant reduction (mean reduction by 15%) of the pattern-onset VEPs. Conclusions: The differential effect of simulated nystagmus on pattern-reversal and pattern-onset VEPs resembles that reported in studies on nystagmus patients. We conclude that the interaction of retinal image motion with the stimulus is sufficient to explain the reduction of pattern-reversal VEPs in patients with nystagmus and propose simulated nystagmus as a useful tool to test the influence of nystagmus on the efficiency of VEP stimuli. Significance: This study demonstrates how horizontal jerk-nystagmus can be simulated and suggests possible mechanisms by which nystagmus reduces VEP responses.

Photopic and scotopic VEPs in patients with congenital stationary night-blindness

Extended set of visual evoked potentials (VEPs) using pattern-reversal (PREPs), linear motion-onset and radial (expansion) motion-onset stimuli (M-VEPs) (detailed specification at http://www.lfhk.cuni.cz/elf) was used to verify congenital stationary night-blindness (CSNB) characteristics in 7 patients (compared to 7 age matched controls) in photopic conditions (luminance of 17 cd/m2). No differences were found in any of the M-VEPs, whilst PREPs displayed prolonged latencies in 3 of 7 CSNB patients. Additionally, the PREPs and M-VEPs were tested in 3 normal and 3 CSNB subjects (the only available ones from the original group) over large range of scotopic, mesopic and photopic luminances (from 0.0001 to 65.4 cd/m2). Both types of low luminance VEPs had distinctly increased luminance threshold needed for reliable VEPs eliciting in CSNB patients (0.06 cd/m2) when compared with controls (0.003 cd/m2); the VEP appearance threshold was almost identical with the perceptual threshold in both groups. Thus, our pilot study proved that CSNB can be objectively detected also via scotopic VEP examination. Since the prolonged PREP latencies at 17 cd/m2 normalised with luminance increase, it indicates that the lower luminance stimuli (compared to the standard recommended by ISCEV) can be more sensitive for some visual disorders detection.

A study on visual evoked responses in childhood epilepsy with occipital paroxysms

As some apparently idiopatic epilepsies may occasionally pose diagnostic difficulties in regard to their precise status of etiology, evoked potentials, particularly visual evoked potential (VEP), may contribute to the diagnosis of childhood epilepsy with occipital paroxysms (CEOP) as a subsidiary method of evaluation. This study includes 19 children (10 boys 52.6%; 9 girls 47.4%) ranging in age from 5 to 17 years (mean SD = 9.68 3.28) suffering from CEOP and a control group of 30 normal children, matched for chronological age and sex. Peak amplitudes and latencies of the P100 component for pattern-shift VEP (PVEP) and of major positivity for flash VEP (FVEP) are measured, respectively. The results from this study demonstrate that amplitude and latency values in patients with CEOP differs insignificantly when compared with controls. Although, non-significantly, mean values of amplitudes for both PVEP and FVEP were higher in the patients than in the normal children, whereas latencies in FVEP were somewhat longer. There may be some tendency for the amplitudes to increase and the latencies to be delayed in VEPs in patients with CEOP, when an overall interpretation of our and similar studies are considered. In certain cases of diagnostic difficulty, VEP values may provide further information for the clinician, regarding either a symptomatic or an idiopathic nature of the underlying disorder.