Respuestas evocadas visuales mediante estimulación con diodos emisores de luz montados en gafas / Visual evoked responses to light-emitting diodes in goggles

Introducción: El potencial evocado visual es una técnica que permite la evaluación de la integridad funcional de la vía visual; su aplicación en niños pequeños resulta de gran dificultad. Objetivo: Caracterizar desde el punto de vista fisiológico el potencial evocado visual en niños menores de 5 años. Métodos: Estudio descriptivo transversal, donde se registran respuestas visuales obtenidas con diodos (montados en gafas) en 112 niños sanos (65 varones, 47 hembras) con rango de edad entre 3 meses y 5 años. Se calcularon los valores medios y desviación estándar de latencias y amplitudes de cada componente de la respuesta y se estimaron sus dinámicas madurativas en función de la edad. Se utilizó un análisis de componentes principales para explicar la variabilidad morfológica (complejo N1-P1-N2) y, se calculó una ecuación discriminante (con indicadores de replicación y relación señal/ruido), para evaluar la contribución en su mejor detección. Resultados: La morfología típica encontrada resultó consistente, replicable y mostró un nivel de detección visual > 90 por ciento (para cada componente), con 85 por ciento de acierto global (clasificaciones correctas) mediante la ecuación discriminante. El complejo N1-P1-N2, consigue explicar > 70 por ciento de la varianza de esta respuesta. Se demostró un acortamiento significativo de latencia con la edad (regresión, p≤ 0,05) para los componentes N1, P1 (marginal, N2). Los valores de amplitud resultaron de mayor dispersión y su tendencia al incremento no alcanzó significación. Conclusiones: El registro del potencial evocado visual mediante diodos/gafas demuestra la obtención de respuestas fisiológicas consistentes y replicables (alta detectabilidad) con una variabilidad morfológica controlable(AU)

Introduction: The Visual Evoked Potentials is a neurophysiological technique to provide an objective assessment of the functional integrity of the visual pathway. However, the young children population is a particularly difficult (uncooperative) group to obtain visual responses. Objective: The purpose of this study was to describe electrophysiological characteristics of the visual response in children. Methods: Descriptive, cross-sectional study. Transient visual evoked potentials with goggles were recorded from 112 healthy children (65 males, 47 females) aged between 3 months to 5 years old. The mean (and standard deviations) for latencies and amplitudes of each component was calculated and both statistical significance in function of age was analyzed (linear regression model). Principal component analysis is use to explain the visual waveform variability. A discriminant equation (with indicators of reliability and noise/signal ratio) is calculate to evaluate contribution in detectability. Results: The typical waveform of (N1, P1, N2, components) is consistent and reliable and showed a visual detection level >90 percent (for each component) and 85 percent of global success (good classifications) with the discriminant equation. N1-P1-N2 complex is able to explain >70 percent of the visual response variance. A significant reduction of N1, P1 (N2, marginal) latencies with increasing age is demonstrated (linear regression, p≤0.05). There was no significant difference for age-dependent increased pattern of amplitude data (high variability). Conclusions: The visual evoked potentials/goggles obtained in infants and young children are consistent and reliable physiological responses (high detectability) with recognizable morphological variability(AU)

Diferencias en procesamiento cerebral visual temprano en niños con trastorno del déficit de atención / Differences in early visual cerebral processing in children with attention deficit / hyperactivity disorders with predominance of no attention

Para evaluar los procesos atencionales a estímulos visuales que no requieren repuesta motora, se llevó a cabo un estudio con potenciales evocados a 17 niños con trastornos del déficit de atención/ hiperactividad (TDAH-I) con predominio inatento y a 15 controles de edades entre 7 y 11 años. Se analizó la latencia y localización de fuentes de los potenciales evocados visuales tempranos P100 y N100 durante la realización de una tarea oddball visual (20% rayas horizontales y 80% verticales) en que las rayas verticales no exigían respuesta motora. Los resultados indican que los niños con TDAH-I procesan la información visual que no requiere respuesta motora con un mayor aumento de la actividad cerebral y mediante la vía temporal ventral mientras que el grupo control lo hace mediante la vía parietal dorsal. Este proceso neurobiológico de procesamiento de la información visual vía temporal ventral de los niños con TDAH-I podría deberse a alteraciones en los procesos emocionales que influyen directamente en el reconocimiento visual o a un déficit en el control de los procesos atencionales por parte de la vía parietal dorsal.

To evaluate attentional processes to visual stimuli that do not require motor response, a study with evoked potentials was carried out on 17 children with attention deficit disorder predominantly inattentive (ADDH-I) and 15 controls between the ages of 7 and 11 years. The latency and localization of sources of the early visual evoked potentials P100 and N100 were analyzed during the performance of a visual oddball task (20% horizontal and 80% vertical lines) where the vertical lines did not require motor response. The results indicate that ADDH-I group process visual information that does not require motor response with a greater increase in brain activity and through the ventral temporal pathway, while the control group does so by means of the dorsal parietal stream. This neurobiological process of visual information processing by ventral temporal pathway of ADDH-I group could be due to alterations in emotional processes that directly influence visual recognition or as consequence of deficit in the control of attentional processes by the dorsal parietal pathway.

Potencial evocado visual em cães e ovinos / Visual evoked potential in dogs and sheep

O potencial evocado visual (PEV) é técnica eletrodiagnóstica que permite avaliação das vias visuais. O PEV de 20 cães e 20 ovinos adultos, de ambos os sexos, foram obtidos para estudo normativo. Foram utilizados eletrodos de agulha monopolar posicionados em O1 e O2 (ativos), em Fpz (referência comum) e em Cz (terra). O estímulo foi na forma de flash a 1Hz. Dezessete cães e 17 ovinos foram incluídos no estudo, pois apresentaram potenciais auditivos com boa qualidade técnica. Os resultados da avaliação dos dois olhos foram agrupados, totalizando 34 exames em cada espécie. O achado mais consistente em todos os exames foi uma deflexão eletropositiva, com latência média de 55,4ms em cães (P55) e 63,75ms em ovinos (P63). Outras duas ondas eletronegativas também foram identificadas: N31 e N75 em cães; e N42 e N86 em ovinos. A metodologia utilizada neste estudo permitiu obtenção de potenciais visuais com pequena variabilidade, sendo útil para avaliação de animais com suspeita de alteração nas vias visuais centrais.(AU)

The visual evoked potential (VEP) is an electro-diagnostic technique that allows assessment of visual pathways. The VEP from 20 adult dogs and 20 adult sheep of both gender was obtained for normative study. Monopolar electrode needles were placed in O1 and O2 (active), Fpz (common reference) and Cz (ground). The stimuli were flash at 1Hz. Seventeen dogs and 17 sheep were included in the study because they had auditory potentials with good technical quality. The results from both eyes were grouped, totaling 34 results in each species. The most consistent result in all tests was an electropositive deflection, with a mean latency 55.4ms in dogs (P55) and 63.75ms in sheep (P63). Two negative deflections were also identified: N31 and N75 in dogs, and N42 and N86 in sheep. The methodology used in this study allowed to obtain potential similar to those described in other studies, with little variability, and is useful for evaluation of animals with suspected changes in the central visual pathways.(AU)

Contrast Visual Evoked Potentials under Pattern Stimulus in Ocular Trauma / 法医学杂志

OBJECTIVES@#To study the characteristic of contrast visual evoked potentials （CVEP） in patients with ocular trauma.@*METHODS@#Sixty patients defined as ocular trauma by forensic clinical examination in our center were selected, and split into 0.2-0.3 （Group A）, 0.3-0.5 （Group B） and ≥0.5 （Group C） according to the best corrected visual acuity. The variation characteristics of wave amplitude and latency of CVEP under 100%, 25% and 10% contrast were observed and analyzed statistically.@*RESULTS@#（1） Under the same contrast, the wave amplitude of P₁₀₀ decreased with the decrease of stimulus perspective. （2） Under the same stimulus perspective, the wave amplitude of P₁₀₀ decreased with the decrease of contrast （P<0.05）. （3） Under the contrast of 100% and 25% with the same stimulus perspective （except 100% 7' perspective stimulus）, the difference between group A and group B had no statistical significance （P>0.05）. Between group A and group C, group B and group C, the wave amplitude of P₁₀₀ gradually increased with the increase of vision （P<0.05）. Under the contrast of 10% with 15' stimulus perspective, the wave amplitude of P₁₀₀ increased with the increase of vision （P<0.05）. （4） Under the same contrast with the same stimulation perspective, the latency of P₁₀₀ wave shortened with the increase of vision, while the difference had no statistical significance （P>0.05）. Under the same stimulus perspective, the latency of P₁₀₀ wave was prolonged with the decrease of contrast （P>0.05）.@*CONCLUSIONS@#CVEP may become one of the possible methods for the evaluation of contrast visual acuity.

Dysfunction in the fellow eyes of strabismic and anisometropic amblyopic children assessed by visually evoked potentials / Alterações dos potenciais visuais evocados nos olhos contralaterais de crianças com ambliopia estrabísmica e anisometrópica

ABSTRACT Purpose: To evaluate visual acuity and transient pattern reversal (PR) visual evoked potentials (VEPs) in the fellow eyes of children with strabismic and/or anisometropic amblyopia. Methods: Children diagnosed with strabismic and/or anisometropic amblyopia were recruited for electrophysiological assessment by VEPs. Monocular grating and optotype acuity were measured using sweep-VEPs and an Early Treatment Diabetic Retinopathy Study chart, respectively. During the same visit, transient PR-VEPs of each eye were recorded using stimuli subtending with a visual angle of 60', 15', and 7.5'. Parameters of amplitude (in μV) and latency (in ms) were determined from VEP recordings. Results: A group of 40 strabismic and/or anisometropic amblyopic children (22 females: 55%, mean age= 8.7 ± 2.2 years, median= 8 years) was examined. A control group of 19 healthy children (13 females: 68.4%, mean age= 8.2 ± 2.6 years, median= 8 years) was also included. The fellow eyes of all amblyopes had significantly worse optotype acuity (p=0.021) than the control group, regardless of whether they were strabismic (p=0.040) or anisometropic (p=0.048). Overall, grating acuity was significantly worse in the fellow eyes of amblyopes (p=0.016) than in healthy controls. Statistically prolonged latency for visual angles of 15' and 7.5' (p=0.018 and 0.002, respectively) was found in the strabismic group when compared with the control group. For the smaller visual stimulus (7.5'), statistically prolonged latency was found among all fellow eyes of amblyopic children (p<0.001). Conclusions: The fellow eyes of amblyopic children showed worse optotype and grating acuity, with subtle abnormalities in the PR-VEP detected as prolonged latencies for smaller size stimuli when compared with eyes of healthy children. These findings show the deleterious effects of amblyopia in several distinct visual functions, mainly those related to spatial vision.

RESUMO Objetivo: Avaliar a acuidade visual e os potenciais visuais evocados transientes por reversão de padrões no olho contralateral de crianças com ambliopia estrabísmica e/ou anisometrópica. Métodos: Foram avaliados os potenciais visuais evocados de crianças com ambliopia estrabísmica e/ou anisometrópica. As acuidades visuais monoculares de grades e de optotipos foram mensuradas utilizando o PVE de varredura e a tabela EDTRS, respectivamente. Na mesma visita, foram registrados os PVERP transients de cada olho usando estímulos de ângulo visual de 60'; 15' e 7,5'. Parâmetros de amplitude (em microvolts) e latência (em milissegundos) foram determinados para os registros dos potenciais visuais evocados. Resultados: Um grupo de 40 crianças amblíopes estrábicas e/ou anisometrópicas (22 meninas - 55%, media idade= 8,7 ± 2,2, mediana= 8) foi examinado. Um grupo de 19 crianças saudáveis (13 meninas 68,4%, media idade= 8,2 ± 2,6, mediana= 8) de controle também foi incluído. A acuidade visual por optotipos foi significativamente pior (p=0,021) nos olhos contralaterais de todos os amblíopes, quando comparado com o grupo controle, independentemente se estrábico (p=0,040) ou anisometrópico (p=0,048). No geral, a acuidade visual por grades foi significativamente pior nos olhos contralaterais dos amblíopes (p=0,016), quando comparados com o grupo controle. Foi encontrada latência estatisticamente prolongada para ângulos visuais de 15' (p=0,018) e 7,5' (p=0,002) no grupo estrábico, quando comparado com o grupo controle. Para o menor estímulo visual (7,5') foi encontrada latência estatisticamente prolongada nos olhos contralaterais de todas crianças amblíopes (p<0,001). Conclusões: Os olhos contralaterais de crianças amblíopes mostraram pior acuidade visual de optotipo e de resolução de grades, com alterações sutis nos PVERP, detectadas pelas latências prolongadas para estímulos de menor tamanho, quando comparados com os olhos de crianças saudáveis. Estes resultados mostram os efeitos deletérios da ambliopia em várias funções visuais distintas, principalmente relacionadas à visão espacial.

Pattern-reversal visual evoked potentials as a diagnostic tool for ocular malingering / Potenciais visuais evocados por padrões reversos como uma ferramenta diagnóstica de simulação

ABSTRACT Purpose: To investigate the contributions of transient pattern-reversal visual evoked potentials in the diagnosis of ocular malingering at a Brazilian university hospital. Methods: Adult patients with suspected malingering in one or both eyes were referred for visual evoked potential testing. Data from patients' medical records were reviewed and analyzed retrospectively. Data analysis included the distance optotype visual acuity based on a ETDRS retro-illuminated chart and the transient pattern-reversal visual evoked potential parameters of latency (milliseconds) and amplitude (microvolts) for the P100 component, using checkerboards with visual subtenses of 15' and 60'. Motivations for malingering were noted. Results: The 20 subjects included 11 (55%) women. Patient ages ranged from 21 to 61 years (mean= 45.05 ± 11.76 years; median= 49 years). In 8 patients (6 women), both eyes exhibited reduced visual acuity with normal pattern-reversal visually evoked potential parameters (pure malingerers). The remaining 12 patients (7 men) exhibited reduced vision in only 1 eye, with simulated reduced vision in the contralateral eye (exaggerators). Financial motivation was noted in 18 patients (9 men). Conclusion: Normal pattern-reversal visually evoked potential parameters with suspected ocular malingering were observed in a 20 patient cohort. This electrophysiological technique appeared to be useful as a measure of visual pathway integrity in this specific population.

RESUMO Objetivo: Investigar a contribuição dos potenciais visuais evocados por padrões reversos no diagnóstico de simulação de baixa de visão em um hospital universitário do Brasil. Métodos: Um grupo de pacientes adultos com suspeita de simulação de baixa de visão em um ou ambos os olhos foi avaliado e os dados analisados retrospectivamente. Foram medidos: acuidade visual de optotipos informada para longe utilizando a tabela ETDRS, parâmetros dos potenciais visuais evocados por padrões reversos de latência (milissegundos) e amplitude (microvolts) para o componente P100 com estímulos de ângulos visuais de 15' e 60'. A motivação do paciente para a simulação foi anotada. Resultados: Os participantes foram 20 indivíduos com 11 (55%) do sexo feminino. A idade variou de 21 a 61 anos (média= 45,05 ± 11,76 anos; mediana= 49 anos). Em 8 pacientes (6 mulheres) ambos os olhos tinham acuidade visual reduzida com parâmetros dos potenciais visuais evocados por padrão reverso normais para ambos os olhos (simuladores puros). Uma subsérie separada de 12 pacientes (7 homens) tinha visão reduzida em apenas um olho e estavam simulando redução da visão no outro olho (exacerbadores). A motivação financeira foi observada em 18 pacientes (9 homens). Conclusões: Parâmetros dos potenciais visuais evocados por padrões reversos normais foram encontrados neste grupo de 20 pacientes com suspeita de simulação. Esta técnica eletrofisiológica pode ser útil como uma medida da integridade do sistema visual nesta população de doentes.

The Effects of Alcohol on Visual Evoked Potential and Multifocal Electroretinography

The aim of this study was to investigate the acute effects of ethanol administration on pattern-reversal visual evoked potential (VEP) and multifocal electroretinography (mfERG). Fifteen healthy subjects with no ocular or general disease were recruited. VEP (0.25° pattern sizes) and mfERG with 19 elements in two recording segments were performed before ethanol administration to obtain baseline for each participant. A few days later, the participants visited again for VEP and mfERG measurements after ethanol administration. Ethanol (0.75 g/kg) was administered orally over the course of 30 minutes. VEP and blood alcohol concentration were evaluated one hour after ethanol administration, and mfERG was conducted after pupil dilation. The Wilcoxon signed-rank test was used to compare parameter changes after randomized eye selection. The mean blood alcohol concentration was 0.034% ± 0.05% by volume. VEP revealed a P100 latency delay (109.4 ± 5.3; 113.1 ± 8.2; P = 0.008) after alcohol administration. The P1 implicit time of ring 1 on mfERG showed a trend of shortening after alcohol administration (37.9 ± 1.0; 37.2 ± 1.5; P = 0.048). However, the changes did not show statistical significance after Bonferroni correction. In conclusion, orally administrated ethanol (0.75 g/kg) appears to suppress the central nervous system, but it is not clear whether alcohol intake affects the retina.

Comparison of Pattern-pulse and Pattern-reversal Multifocal Visual Evoked Potentials in Normal Individuals / 法医学杂志

OBJECTIVE@#To compare pattern-pulse multifocal visual evoked potential (PPmfVEP) with pattern-reversal multifocal visual evoked potential (PRmfVEP), and to investigate the symmetry of mfVEP between both eyes in normal individuals.@*METHODS@#The multifocal Vision Monitor was used to observe the mfVEP. T-test and ANOVA were used to analyze P1 wave, amplitude and signal noise ratios (SNR) of two mfVEPs.@*RESULTS@#The SNR and the P1 amplitude reached the maximum at the central visual field and decreased with the increase of eccentricity, and then decreased slowly. The amplitude of the PPmfVEP was significantly smaller than the PRmfVEP in the central retina, while in the peripheral retina the result was exactly the opposite. SNR and amplitude of the PRmfVEP showed no statistical difference in both eyes (P > 0.05). The variance of the amplitude at the same side of visual field was larger than that at the symmetrical visual quadrant.@*CONCLUSION@#mfVEP can reflect the visual function in different parts of retina objectively and exactly. PPmfVEP reflect the vision function of the central retina better than PRmfVEP. The stability of PPmfVEP is better than PRmfVEP in the central retina, while the result is opposite in the peripheral retina. The mfVEP is symmetrical in both eyes of the same individual.

Visual evoked potentials show strong positive association with intracranial pressure in patients with cryptococcal meningitis / Potenciais evocados visuais mostram correlação positiva forte com a pressão intracraniana em pacientes com meningite criptocócica

Objective : To verify the relationship between intracranial pressure and flash visual evoked potentials (F-VEP) in patients with cryptococcal meningitis. Method The sample included adults diagnosed with cryptococcal meningitis admitted at a reference hospital for infectious diseases. The patients were subjected to F-VEP tests shortly before lumbar puncture. The Pearson’s linear correlation coefficient was calculated and the linear regression analysis was performed. Results : Eighteen individuals were subjected to a total of 69 lumbar punctures preceded by F-VEP tests. At the first lumbar puncture performed in each patient, N2 latency exhibited a strong positive correlation with intracranial pressure (r = 0.83; CI = 0.60 - 0.94; p < 0.0001). The direction of this relationship was maintained in subsequent punctures. Conclusion : The intracranial pressure measured by spinal tap manometry showed strong positive association with the N2 latency F-VEP in patients with cryptococcal meningitis. .

Objetivo : Verificar a relação entre pressão intracraniana e potencial evocado visual por flash (PEV-F) em pacientes com meningite criptocócica. Método A amostra incluiu pacientes admitidos em um hospital de referência para doenças infecciosas. Realizou-se PEV-F antes de cada punção lombar. Calculou-se o coeficiente de correlação de Pearson e a equação de regressão linear entre as variáveis latência N2 e pressão intracraniana inferida através de raquimanometria. Resultados Dezoito pacientes foram submetidos a um total de 69 punções lombares. A latência N2 mostrou correlação positiva forte com a pressão de abertura verificada na primeira punção lombar a que cada paciente foi submetido (r = 0,83; IC = 0,60 – 0,94; p < 0,0001). A positividade da correlação foi mantida nas aferições subsequentes. Conclusão Houve associação positiva forte entre a latência N2 do PEV-F e pressão intracraniana em pacientes com meningite criptocócica. .

Forensic Application of Microperimetry and Visual Evoked Potential in Macular Disease / 法医学杂志

OBJECTIV@#e To find the correlation between real best corrected visual acuity (BCVA) and testing results of microperimetry and visual evoked potential (VEP) and to explore a new method in recording BCVA in macular disease.@*METHODS@#Sixty-two patients with macular disease (macular disease group, 62 eyes) and eighteen healthy volunteers (control group, 36 eyes) had BCVA, microperimetry and VEP recorded.@*RESULTS@#(1) By microperimetry, the values of retinal mean sensitivity and fixation percentage in macular disease group were lower than that in control group. The bicurve ellipse area in macular disease group was higher than that in control group. By VEP, P100 amplitude under 0.5 cpd and 2 cpd in macular disease group were significantly higher than that in control group and the latency was prolonged (P < 0.05). (2) In macular disease group, BCVA had significant positive correlation with retinal mean sensitivity, bicurve ellipse area, macular central 2 degrees and 4 degrees fixation percentage, respectively (P < 0.05). There was a significant correlation between retinal mean sensitivity and P100 amplitude (P < 0.05). (3) Multiple linear regression equation was y = 0.053 x1+0.008 x3+3.897 (y was BCVA, while x1 was retinal mean sensitivity and x3 was P100 amplitude under 2 cpd).@*CONCLUSION@#Combined use of microperimetry and VEP is useful in the assessment of BCVA in macular disease.

Correlation between contrast vision and sweep visual evoked potential acuity / 法医学杂志

OBJECTIVE@#To compare the correlation between contrast vision (LV) and sweep visual evoked potential acuity (SVEP-A) among people with emmetropia, mild myopia, and moderate myopia.@*METHODS@#The CV and SVEP-A were tested individually in 96 eyes from healthy young volunteers, including 37 eyes of emmetropia, 27 eyes of mild myopia, and 32 eyes of moderate myopia. The statistic analysis was done by ANOVA analysis and rank sum test.@*RESULTS@#(1) With the decrease of contrast, CV and SVEP-A decreased in every group. (2) At 100% contrast, the difference of CV between emmetropia and mild myopia had statistical significance (P<0.05). At 100%, 25% and 10% contrast, the difference of CV between emmetropia and moderate myopia had statistical significance (P<0.05). (3) In the same group, the difference of 100% and 25% contrast had statistical significance (P < 0.05). So was between 100% and 10% contrast. (4) At 100% and 10% contrast, the difference of CV and SVEP-A had statistical significance (P < 0.05).@*CONCLUSION@#The CV of myopia relates to many factors including ametropia and fundus lesions. The correction of ametropia is important to the values of CV and SVEP-A.

Lateral Geniculate Body Evoked Potentials Elicited by Visual and Electrical Stimulation

PURPOSE: Blind individuals who have photoreceptor loss are known to perceive phosphenes with electrical stimulation of their remaining retinal ganglion cells. We proposed that implantable lateral geniculate body (LGB) stimulus electrode arrays could be used to generate phosphene vision. We attempted to refine the basic reference of the electrical evoked potentials (EEPs) elicited by microelectrical stimulations of the optic nerve, optic tract and LGB of a domestic pig, and then compared it to visual evoked potentials (VEPs) elicited by short-flash stimuli. METHODS: For visual function measurement, VEPs in response to short-flash stimuli on the left eye of the domestic pig were assessed over the visual cortex at position Oz with the reference electrode at Fz. After anesthesia, linearly configured platinum wire electrodes were inserted into the optic nerve, optic track and LGB. To determine the optimal stimulus current, EEPs were recorded repeatedly with controlling the pulse and power. The threshold of current and charge density to elicit EEPs at 0.3 ms pulse duration was about ±10 microA. RESULTS: Our experimental results showed that visual cortex activity can be effectively evoked by stimulation of the optic nerve, optic tract and LGB using penetrating electrodes. The latency of P1 was more shortened as the electrical stimulation was closer to LGB. The EEPs of two-channel in the visual cortex demonstrated a similar pattern with stimulation of different spots of the stimulating electrodes. We found that the LGB-stimulated EEP pattern was very similar to the simultaneously generated VEP on the control side, although implicit time deferred. CONCLUSIONS: EEPs and VEPs derived from visual-system stimulation were compared. The LGB-stimulated EEP wave demonstrated a similar pattern to the VEP waveform except implicit time, indicating prosthetic-based electrical stimulation of the LGB could be utilized for the blind to perceive vision of phosphenes.

Evaluation of Hemifield Sector Analysis Protocol in Multifocal Visual Evoked Potential Objective Perimetry for the Diagnosis and Early Detection of Glaucomatous Field Defects

PURPOSE: Multifocal visual evoked potential (mfVEP) is a newly introduced method used for objective visual field assessment. Several analysis protocols have been tested to identify early visual field losses in glaucoma patients using the mfVEP technique, some were successful in detection of field defects, which were comparable to the standard automated perimetry (SAP) visual field assessment, and others were not very informative and needed more adjustment and research work. In this study we implemented a novel analysis approach and evaluated its validity and whether it could be used effectively for early detection of visual field defects in glaucoma. METHODS: Three groups were tested in this study; normal controls (38 eyes), glaucoma patients (36 eyes) and glaucoma suspect patients (38 eyes). All subjects had a two standard Humphrey field analyzer (HFA) test 24-2 and a single mfVEP test undertaken in one session. Analysis of the mfVEP results was done using the new analysis protocol; the hemifield sector analysis (HSA) protocol. Analysis of the HFA was done using the standard grading system. RESULTS: Analysis of mfVEP results showed that there was a statistically significant difference between the three groups in the mean signal to noise ratio (ANOVA test, p < 0.001 with a 95% confidence interval). The difference between superior and inferior hemispheres in all subjects were statistically significant in the glaucoma patient group in all 11 sectors (t-test, p < 0.001), partially significant in 5 / 11 (t-test, p < 0.01), and no statistical difference in most sectors of the normal group (1 / 11 sectors was significant, t-test, p < 0.9). Sensitivity and specificity of the HSA protocol in detecting glaucoma was 97% and 86%, respectively, and for glaucoma suspect patients the values were 89% and 79%, respectively. CONCLUSIONS: The new HSA protocol used in the mfVEP testing can be applied to detect glaucomatous visual field defects in both glaucoma and glaucoma suspect patients. Using this protocol can provide information about focal visual field differences across the horizontal midline, which can be utilized to differentiate between glaucoma and normal subjects. Sensitivity and specificity of the mfVEP test showed very promising results and correlated with other anatomical changes in glaucoma field loss.

Evaluation of Hemifield Sector Analysis Protocol in Multifocal Visual Evoked Potential Objective Perimetry for the Diagnosis and Early Detection of Glaucomatous Field Defects

PURPOSE: Multifocal visual evoked potential (mfVEP) is a newly introduced method used for objective visual field assessment. Several analysis protocols have been tested to identify early visual field losses in glaucoma patients using the mfVEP technique, some were successful in detection of field defects, which were comparable to the standard automated perimetry (SAP) visual field assessment, and others were not very informative and needed more adjustment and research work. In this study we implemented a novel analysis approach and evaluated its validity and whether it could be used effectively for early detection of visual field defects in glaucoma. METHODS: Three groups were tested in this study; normal controls (38 eyes), glaucoma patients (36 eyes) and glaucoma suspect patients (38 eyes). All subjects had a two standard Humphrey field analyzer (HFA) test 24-2 and a single mfVEP test undertaken in one session. Analysis of the mfVEP results was done using the new analysis protocol; the hemifield sector analysis (HSA) protocol. Analysis of the HFA was done using the standard grading system. RESULTS: Analysis of mfVEP results showed that there was a statistically significant difference between the three groups in the mean signal to noise ratio (ANOVA test, p < 0.001 with a 95% confidence interval). The difference between superior and inferior hemispheres in all subjects were statistically significant in the glaucoma patient group in all 11 sectors (t-test, p < 0.001), partially significant in 5 / 11 (t-test, p < 0.01), and no statistical difference in most sectors of the normal group (1 / 11 sectors was significant, t-test, p < 0.9). Sensitivity and specificity of the HSA protocol in detecting glaucoma was 97% and 86%, respectively, and for glaucoma suspect patients the values were 89% and 79%, respectively. CONCLUSIONS: The new HSA protocol used in the mfVEP testing can be applied to detect glaucomatous visual field defects in both glaucoma and glaucoma suspect patients. Using this protocol can provide information about focal visual field differences across the horizontal midline, which can be utilized to differentiate between glaucoma and normal subjects. Sensitivity and specificity of the mfVEP test showed very promising results and correlated with other anatomical changes in glaucoma field loss.

Chromatic spatial contrast sensitivity estimated by visual evoked cortical potential and psychophysics

The purpose of the present study was to measure contrast sensitivity to equiluminant gratings using steady-state visual evoked cortical potential (ssVECP) and psychophysics. Six healthy volunteers were evaluated with ssVECPs and psychophysics. The visual stimuli were red-green or blue-yellow horizontal sinusoidal gratings, 5° × 5°, 34.3 cd/m2 mean luminance, presented at 6 Hz. Eight spatial frequencies from 0.2 to 8 cpd were used, each presented at 8 contrast levels. Contrast threshold was obtained by extrapolating second harmonic amplitude values to zero. Psychophysical contrast thresholds were measured using stimuli at 6 Hz and static presentation. Contrast sensitivity was calculated as the inverse function of the pooled cone contrast threshold. ssVECP and both psychophysical contrast sensitivity functions (CSFs) were low-pass functions for red-green gratings. For electrophysiology, the highest contrast sensitivity values were found at 0.4 cpd (1.95 ± 0.15). ssVECP CSF was similar to dynamic psychophysical CSF, while static CSF had higher values ranging from 0.4 to 6 cpd (P < 0.05, ANOVA). Blue-yellow chromatic functions showed no specific tuning shape; however, at high spatial frequencies the evoked potentials showed higher contrast sensitivity than the psychophysical methods (P < 0.05, ANOVA). Evoked potentials can be used reliably to evaluate chromatic red-green CSFs in agreement with psychophysical thresholds, mainly if the same temporal properties are applied to the stimulus. For blue-yellow CSF, correlation between electrophysiology and psychophysics was poor at high spatial frequency, possibly due to a greater effect of chromatic aberration on this kind of stimulus.

Multifocal visual electrophysiology in visual function evaluation / 法医学杂志

Multifocal visual electrophysiology, consisting of multifocal electroretinography (mfERG) and multifocal visual evoked potential (mfVEP), can objectively evaluate retina function and retina-cortical conduction pathway status by stimulating many local retinal regions and obtaining each local response simultaneously. Having many advantages such as short testing time and high sensitivity, it has been widely used in clinical ophthalmology, especially in the diagnosis of retinal disease and glaucoma. It is a new objective technique in clinical forensic medicine involving visual function evaluation of ocular trauma in particular. This article summarizes the way of stimulation, the position of electrodes, the way of analysis, the visual function evaluation of mfERG and mfVEP, and discussed the value of multifocal visual electrophysiology in forensic medicine.

Comparison of the reliability of multifocal visual evoked cortical potentials generated by pattern reversal and pattern pulse stimulation

This study compared the effectiveness of the multifocal visual evoked cortical potentials (mfVEP) elicited by pattern pulse stimulation with that of pattern reversal in producing reliable responses (signal-to-noise ratio >1.359). Participants were 14 healthy subjects. Visual stimulation was obtained using a 60-sector dartboard display consisting of 6 concentric rings presented in either pulse or reversal mode. Each sector, consisting of 16 checks at 99% Michelson contrast and 80 cd/m² mean luminance, was controlled by a binary m-sequence in the time domain. The signal-to-noise ratio was generally larger in the pattern reversal than in the pattern pulse mode. The number of reliable responses was similar in the central sectors for the two stimulation modes. At the periphery, pattern reversal showed a larger number of reliable responses. Pattern pulse stimuli performed similarly to pattern reversal stimuli to generate reliable waveforms in R1 and R2. The advantage of using both protocols to study mfVEP responses is their complementarity: in some patients, reliable waveforms in specific sectors may be obtained with only one of the two methods. The joint analysis of pattern reversal and pattern pulse stimuli increased the rate of reliability for central sectors by 7.14% in R1, 5.35% in R2, 4.76% in R3, 3.57% in R4, 2.97% in R5, and 1.78% in R6. From R1 to R4 the reliability to generate mfVEPs was above 70% when using both protocols. Thus, for a very high reliability and thorough examination of visual performance, it is recommended to use both stimulation protocols.

Characteristics and distribution of ERP by different field stimulation / 法医学杂志

OBJECTIVE@#To study the variation of latency and amplitude of the event related potential (ERP) and its distribution in human scalp when the normal subjects were stimulated with different visual fields.@*METHODS@#The ERP recorded in scalp with the stimulation of 10 degrees visual field and 60 degrees visual field respectively in 20 healthy volunteers with normal visual function.@*RESULTS@#Two different visual field stimulation may evoke the different exogenous components P1 (70-125 ms), N1 (90-170 ms), P2 (140-220 ms) and endogenous components N2 (190-280 ms) and P3 (290-430 ms). The latencies of all the components evoked by 10 degrees visual field were shorter than that of the 60 degrees visual field while the amplitudes of N1 and N2 were lower and appeared over the extensive encephalic region; and the amplitudes of the P1, P2 and P3 were higher and appeared in occipitotemporal, prefrontal and occipital region, respectively.@*CONCLUSION@#Two different visual field stimulation may evoke all the ERP components with significant differences in the latency, amplitude and distribution. The differences may reflect the different visual information integration and processing in human brain during the different visual field stimulation.

Axonal electrovisiogram as an electrophysiological test to evaluate optic nerve and inner retina electrical potentials: findings in normal subjects / Eletrovisuograma axonal como teste eletrofisiológico na avaliação dos potenciais de ação do nervo óptico e da retina interna: achados em indivíduos normais

PURPOSES: To standardize and validate the technique of axonal electrovisiogram (AxEvg), defining its normative values and parameters and characterizing its findings in normal individuals. METHODS: We enrolled 140 normal individuals (280 eyes) divided into seven groups according to age, each one with 10 males and 10 females. The technique was based on monocular visual stimulation by a 0 dB intensity bright flash on Ganzfeld bowl at a presentation rate of 1.4 Hz. Golden cup electrodes were used and electrical waves were acquired after artifact rejection. For each amplitude and implicit time peak we calculated the mean, median, pattern deviation, minimum and maximum values and 95 percent confidence interval. RESULTS: Monocular visual stimulation with bright flash under mesopic conditions was the standard technical procedure established. The normal AxEvg waveform consists of an initial positive wave (named P1, with mean amplitude of 2.0 mV and mean implicit time peak of 23.1 ms) followed by a negative wave (named N1, with mean amplitude of -3.9 mV and mean implicit time peak of 41.4 ms). No significant differences were observed between males and females or between right and left eyes, but there was an increased P1 and N1 implicit time peaks according to age. Implicit time characteristics suggest that P1 wave represents an optic nerve electrical potential and N1 wave represents an inner retinal layers potential. CONCLUSIONS: AxEvg can be considered a pre-chiasmatic visual evoked potential capable to reliably record the electrical activity of optic nerve and inner retina. The findings suggest that AxEvg may be useful as an electrophysiological test in the diagnosis of neuroretinal diseases.

OBJETIVOS: Padronizar e validar a técnica de realização do eletrovisuograma axonal (EVA), definir seus valores normativos e caracterizar os achados em indivíduos normais. MÉTODOS: Estudo descritivo com 140 indivíduos (280 olhos) normais. Os participantes foram divididos em sete grupos de acordo com a idade, cada qual com 10 indivíduos do sexo masculino e 10 do sexo feminino. Definiu-se como técnica de exame a estimulação monocular por flash luminoso com intensidade de 0 dB na cúpula de Ganzfeld a uma frequência de 1,4 Hz. Foram utilizados eletrodos com cúpula de ouro e foram analisados os traçados elétricos obtidos após rejeição de artefatos. Para cada amplitude e tempo de culminação foram calculados a média, a mediana, o desvio-padrão, os valores mínimo e máximo e o intervalo de confiança de 95 por cento representando uma faixa de normalidade para os valores. RESULTADOS: A técnica de exame padronizada foi a estimulação visual monocular por flash em condições mesópicas. O traçado normal do eletrovisuograma axonal consistiu numa onda positiva inicial (P1, com amplitude média de 2,0 mV e tempo de culminação médio de 23,1 ms) seguida de uma onda negativa (N1, com amplitude média de -3,9 mV e tempo de culminação médio de 41,4 ms). Não foram observadas diferenças significativas entre os sexos e entre os olhos direito e esquerdo, mas os tempos de culminação de P1 e de N1 aumentaram proporcionalmente com a idade. CONCLUSÕES: O eletrovisuograma axonal é um exame de potencial visual evocado pré-quiasmático, capaz de registrar de forma confiável e reprodutível a atividade elétrica do nervo óptico e da retina interna, podendo ser utilizado na propedêutica eletrofisiológica na investigação de lesões neurorretinianas.