Search

Aim: Visual evoked potentials (VEP) represent an objective non-invasive and inexpensive dia­gnostic method, particularly in neuro-ophthalmology. A lot of possible dia­gnostic applications are limited because they are only examined with the use of robust equipment which is hardly transportable and immobile and handicapped patients cannot visit the specialized labs. The aim of our research work was the development of a portable inexpensive VEP device that could be used almost anywhere. Methods: All parts of the last prototype of the device (built-in visual stimulator, recording electrodes, 4-channel EEG amplifier, analog-digital converter, and control unit) with a total weight of 390 g are placed in a headset (plastic "shield" with an adjustable strap). The software for VEP recording and evaluation is used on a standard notebook (PC). The parameters of the device fulfill recommendations of the international societies for clinical electrophysiology of vision and clinical neurophysiology also enabling new applications of so far not routinely used variants of evoked potentials. Testing of the device was done so far in 91 control subjects and 135 neuroophthalmological patients. Results: Pilot studies proved comparable parameters of VEP and dia­gnostic sensitivity as in standard devices (equal results in 93% of cases). It was verified that the device is usable in various environments, at the patient's bedside, and also for basic self-examination. Conclusion: The portable device for VEP significantly increases the availability of their examination and thus enables much broader dia­gnostic applications of this method. [ABSTRACT FROM AUTHOR]

Abstract: This review article summarises the research on the motion-onset visual evoked potentials (VEPs) and important motion stimulus parameters which have been clarified. For activation of the visual motion processing system and evocation of the motion-onset specific N2 peak (with latency of 160–200ms) from the extra-striate temporo-occipital and/or parietal cortex, the following stimulus parameters can be recently recommended: low luminance (

The aim of this introductory lecture is to point out that despite the intensive use of modern imagine techniques (MRI, OCT, etc.), the diagnostic applications of visual evoked potentials (VEPs) need not be obsolete, if not preferable in many cases. This objective, fully non-invasive, low-cost electrophysiological method can detect functional problems of the optic pathway and various brain cortical areas even before a development of the first displayable morphological changes. For the increased sensitivity of VEPs, it is necessary to use a larger spectrum of visual stimuli (activating quite selectively different subsystems of the visual pathway and visual cortex) compared to standards recommended by ISCEV or IFCN. It should include not only flash or pattern-related stimuli (pattern-reversal, pattern-on/off) but also motion-related (motion-onset VEPs) and cognitive visual stimulation. Then, not only the early diagnostics of a large spectrum of neuro-ophthalmological and neuro-psychiatric disorders is possible but also the physiological aging of visual information processing or a drug abuse is recognisable. For a better availability of VEPs examination and their long-term monitoring also in home conditions, we have just introduced a “Mobile (wearable), low-cost device for examination of visual evoked potentials (VEPs)”, the use of which will be demonstrated during the lecture. Acknowledgements: Supported by the project of Charles University “Progres Q40/07”. [ABSTRACT FROM AUTHOR]

Introduction: In our previous papers (for review see Kuba et al., Vision Res., 2007, 47, 189–202) we have shown that in adults the motion-onset visual evoked potentials (M-VEPs) represent a useful diagnostic tool in neuro-opthalmology because they enable to test quite selectively the magnocellular system/dorsal stream function. In adults robust M-VEPs with low variability and typical shape with dominant negative N160 peak can be acquired easily, however, it is difficult to record and evaluate this type of VEPs in children. The M-VEPs go through very long maturation (up to 18years of age) accompanied by gradual shortening of main negative peak latencies and also by age dependent shape development (Langrova et al., Vision Res., 2006, 46, 536–544). Moreover, they are unidentifiable to standard moving stimuli in some children. To understand better this problem, we tested 30 normal children aged 7–12years. Methods: We performed the set of standard stimuli used in our lab (https://www.lfhk.cuni.cz/elf) for examination of adults – low contrast translation motion (TM) and expansion/contraction motion (EXCOM). Results: Reliable VEPs were detected in 77% of children to TM and in 83% of children to EXCOM. The dominant peak of the VEPs was negative in all TM VEPs and in 80% of EXCOM VEPs (positive in 20%). In both VEP types there was large inter-individual latency variability (in the range of 176–268ms in TM and 176–290ms in EXCOM). When a high contrast TM stimulus (non-optimal “magno” stimulus) was used, the M-VEP latencies shortened and amplitudes increased in majority of subjects. In contrast to adults, M-VEPs to peripheral stimulation (outside central 20°) were detectable only in 43% of children. Conclusions: Our findings show that maturation of motion perception in children is rather inter-individually variable, which makes a diagnostic use of M-VEPs in children quite complicated. Acknowledgement: Supported by the project PRVOUK - P37/07. [ABSTRACT FROM AUTHOR]

Introduction: The aim of our study was to verify the possibility of early identification of HIV-related neural injury using visual evoked potentials (VEPs) in neurologically asymptomatic HIV seropositives. In the CART (combination antiretroviral therapy) era, the prevalence of neurocognitive impairment remains high, up to 50%, and HIV-associated neurocognitive disorder (HAND) has shifted towards a milder clinical presentation. Such a mild clinical presentation can escape detection [1]. Methods: The examination consisted of the Montreal Cognitive Assessment (MoCA) [2], and VEPs to pattern-reversal, motion-onset stimulation (radial movement), and of visual ERPs recorded during an odd-ball test (http://www.lfhk.cuni.cz/elf). Subjects: 9 homosexual men and 3 heterosexually infected women were examined in this study. All patients had ⩾350×106 CD4 cells/l blood at inclusion. The duration of the HIV infection was 0.5 – 7years, and mean age of the patients was 35 (24–50) years. Results: P100 potential was recorded with no alteration in the VEP amplitude or latency. However, in 5 patients with CD4 counts 350–750×106cells/l, there was prolonged latency of the N160 peak compared to the reference values obtained in our laboratory, which suggests a dysfunction of the motion-processing (magnocellular system or the dorsal cortical stream) [3]. P300 latencies and MoCA results were within the normal range in all HIV patients. Conclusions: Our data suggest that motion-onset VEPs may be a sensitive measure of subclinical visual pathway dysfunction in early HIV-1 infection, however, we did not reveal any cognitive decline in this pilot group. Subsequently, the patients will be investigated using VEPs and visual ERPs at six-month intervals to evaluate the long-term development of the visual pathway involvement in HIV patients. [ABSTRACT FROM AUTHOR]

Purpose: Optical coherence tomography (OCT) and Visual evoked potentials (VEPs) represent non-invasive objective examination of the visual system. While the OCT measures a morphological property of the retina (thickness of the retinal nerve fibre layer – RNFL), the VEP allows assessment a function of the visual system. There are numerous studies describing a mutual involvement of both mentioned aspects in diseases like multiple sclerosis, optic neuritis or glaucoma, however, normative studies of these relationship are missing. In our study we address this issue with an expectation to translate the findings into interpretation of pathological findings. Methods: We examined a group of 20 healthy volunteers (14 females, 6 males) aged 19–23years. For VEPs were used the following stimuli: standard checkerboard reversal stimulation with 60’ and 15’ check size and radial expansion/contraction motion of concentric rings. RNFL thickness was measured for superior, temporal, inferior and nasal retinal sectors in peripapilar circular scan using FD-OCT (Spectralis Heidelberg Engineering, Germany). The RNFL in each sector was compared with latency and amplitude of VEP dominant peaks (MedelecSynergy, Viasys Healthcare, USA). Results: We found highly significant positive correlation between inferior sector of the RNFL thickness with P100-N145 interpeak amplitude for reversal R15’ (r =0.728; p <0.001) and reversal R60′ (r =0.424; p =0.006) and negative relationship to N160 interpeak amplitude (r=−0.498; p =0.01). The only correlation for the RNFL within the papilo-macular bundle was demonstrated for reversal 60′ N75-P100 interpeak amplitude (r =0.496; p =0.001). This correlation was also seen for RNFL in temporal sector (r =0.412; p =0.006). Conclusion: In our study we demonstrated the relationship of some anatomic and function factors of visual system in healthy subjects. However, the interpretation of the relationship between inferior RNFL sector and VEPs amplitudes is not straightforward, as for VEPs recorded above the sulcus calcarinus just the upper hemiretina is dominant and so this topic is opened for further research. This study was supported by Grant Agency of the Czech Republic 309/09/0869 and by the P37/07 (PRVOUK) program. [Copyright &y& Elsevier]