Seventy years since the invention of the averaging technique in Neurophysiology: Tribute to George Duncan Dawson / 70 anos da invenção da técnica de promediação na Neurofisiologia: Tributo a George Duncan Dawson

ABSTRACT In 1951, the physiologist George Duncan Dawson presented his work with the averaging of the signal in the evoked potentials (EPs), opening a new stage in the development of clinical neurophysiology. The authors present aspects of Professor Dawson's biography and a review of his work on the EPs and, mainly, the article reveals the new technique in detail that would allow the growth of the clinical application of the visual, auditory, and somatosensory EPs.

RESUMO Em 1951 o fisiologista George Duncan Dawson apresentou seu trabalho com a promediação de sinal nos potenciais evocados, abrindo uma nova etapa no desenvolvimento da neurofisiologia clínica. Os autores apresentam aspectos da biografia do professor Dawson e uma revisão de seus trabalhos sobre os potenciais evocados, principalmente do artigo que mostrava a nova técnica, que viria a permitir o crescimento da aplicação clínica dos potenciais evocados visual, auditivo e somatossensitivo.

Noninvasive intracranial pressure monitoring methods: a critical review / Métodos de monitorização não invasivos da pressão intracraniana: uma revisão crítica

ABSTRACT Background: Intracranial pressure (ICP) monitoring has been used for decades in management of various neurological conditions. The gold standard for measuring ICP is a ventricular catheter connected to an external strain gauge, which is an invasive system associated with a number of complications. Despite its limitations, no noninvasive ICP monitoring (niICP) method fulfilling the technical requirements for replacing invasive techniques has yet been developed, not even in cases requiring only ICP monitoring without cerebrospinal fluid (CSF) drainage. Objectives: Here, we review the current methods for niICP monitoring. Methods: The different methods and approaches were grouped according to the mechanism used for detecting elevated ICP or its associated consequences. Results: The main approaches reviewed here were: physical examination, brain imaging (magnetic resonance imaging, computed tomography), indirect ICP estimation techniques (fundoscopy, tympanic membrane displacement, skull elasticity, optic nerve sheath ultrasound), cerebral blood flow evaluation (transcranial Doppler, ophthalmic artery Doppler), metabolic changes measurements (near-infrared spectroscopy) and neurophysiological studies (electroencephalogram, visual evoked potential, otoacoustic emissions). Conclusion: In terms of accuracy, reliability and therapeutic options, intraventricular catheter systems still remain the gold standard method. However, with advances in technology, noninvasive monitoring methods have become more relevant. Further evidence is needed before noninvasive methods for ICP monitoring or estimation become a more widespread alternative to invasive techniques.

RESUMO Introdução: O uso da monitorização da pressão intracraniana (PIC, em sua sigla em inglês) é adotado há décadas no manejo de diversas condições neurológicas. O padrão ouro atual é a monitorização invasiva intraventricular, que está relacionada a inúmeras complicações. Apesar dessas limitações, até o momento nenhum método de monitorização não invasiva (niPIC, em sua sigla em inglês) conseguiu substituir a técnica invasiva. Objetivos: Revisar os métodos não invasivos de monitorização da PIC. Métodos: As diferentes modalidades e abordagens foram agrupadas de acordo com o mecanismo utilizado para detectar elevação da PIC ou suas consequências. Resultados: As técnicas descritas foram: o exame físico, neuroimagem (tomografia computadorizada e ressonância magnética de crânio), estimativas indiretas da PIC (fundoscopia, deslocamento da membrana timpânica, elasticidade craniana), avaliação do fluxo cerebral (doppler transcraniano e doppler da artéria oftálmica), alterações metabólicas (Espectroscopia próxima do infravermelho) e estudos neurofisiológicos (eletroencefalograma, potencial evocado visual e emissões otoacústicas). Conclusão: Considerando a acurácia, confiabilidade e opções terapêuticas, o sistema de cateteres intraventricular ainda permanece como padrão ouro. No entanto, com os avanços tecnológicos, os métodos não invasivos têm se tornados mais relevantes. Mais evidências são necessárias antes que essas modalidades de monitorização ou estimativas não invasivas se tornem uma alternativa mais robusta às técnicas invasivas.

Grating visual acuity impairment assessed by sweep visually evoked potentials in children with optic pathway tumors unable to perform optotype acuity tests / Deficiência na acuidade visual de grades avaliada pelos potenciais visuais evocados de varredura em crianças com tumores da via óptica incapazes de informar a acuidade de optotipos

ABSTRACT Purpose: To determine visual impairment due to optic pathway tumors in children unable to perform recognition acuity tests. Methods: Grating visual acuity scores, in logMAR, were obtained by sweep visually evoked potentials (SVEP) in children with optic pathway tumors. The binocular grating visual acuity deficit was calculated by comparison with age-based norms and then assigned to categories of visual impairment as mild (from 0.10 to 0.39 logMAR), moderate (from 0.40 to 0.79 logMAR), or severe (≥0.80 logMAR). Interocular differences were calculated by subtraction and considered increased if >0.10 logMAR. Results: The participants were 25 children (13 boys; mean ± SD age, 35.1 ± 25.9 months; median age, 32.0 months) with optic pathway tumors (24 gliomas and 1 embryonal tumor), mostly located at the hypothalamic-chiasmatic transition (n=21; 84.0%) with visual abnormalities reported by parents (n=17; 68.0%). The mean grating acuity deficit was 0.60 ± 0.36 logMAR (median, 0.56 logMAR). Visual impairment was detected in all cases and was classified as mild in 10 (40.0%), moderate in 8 (32.0%), and severe in 7 (28.0%) children, along with increased interocular differences (>0.1 logMAR) (n=16; 64.0%). The remarkable ophthalmological abnormalities were nystagmus (n=17; 68.0%), optic disc cupping and/or pallor (n=13; 52.0%), strabismus (n=12; 48.0%), and poor visual behavior (n=9; 36.0%). Conclusion: In children with optic pathway tumors who were unable to perform recognition acuity tests, it was possible to quantify visual impairment by sweep-visually evoked potentials and to evaluate interocular differences in acuity. The severity of age-based grating visual acuity deficit and interocular differences was in accordance with ophthalmological abnormalities and neuroimaging results. Grating visual acuity deficit is useful for characterizing visual status in children with optic pathway tumors and for supporting neuro-oncologic management.(AU)

RESUMO Objetivo: Determinar o grau de deficiência visual em crianças com tumores da via óptica incapazes de informar a acuidade visual de reconhecimento. Método: A acuidade visual de grades, em logMAR, foi estimada por potenciais visuais evocados de varredura em crianças com tumores das vias ópticas. O déficit da acuidade visual de grades binocular foi calculado em relação ao valor mediano normativo esperado para a idade e a deficiência visual, classificada como leve (0,10 a 0,39 logMAR), moderada (0,40 a 0,79 logMAR) ou grave (≥0,80 logMAR). Diferenças inter-oculares foram calculadas por subtração e consideradas aumentadas se >0,10 logMAR. Resultados: Foram avaliadas 25 crianças (13 meninos; média de idade ± DP=35,1± 25,9 meses; mediana=32,0 meses) com tumores da via óptica (24 gliomas e 1 tumor embrionário) localizados particularmente na transição hipotalâmico-quiasmática (n=21; 84,0%) e com anormalidades visuais detectadas pelos pais (n=17; 68,0%). A média do déficit da acuidade de grades foi 0,60 ± 0,36 logMAR (mediana=0,56 logMAR). Observou-se deficiência visual leve em 10 (40,0%), moderada em 8 (32,0%) e grave em 7 (28,0%), além de aumento da diferença interocular da acuidade visual (n=16; 64,0%). As principais alterações oftalmológicas encontradas foram: nistagmo (n=17; 68,0%), aumento da escavação do disco óptico e/ou palidez (n=13; 52,0%), estrabismo (n=12; 48,0%) e comportamento visual pobre (n=9; 36,0%). Conclusão: Em crianças com tumor da via óptica e incapazes de responder aos testes de acuidade visual de reconhecimento, foi possível quantificar deficiência visual por meio dos potenciais visuais evocados de varredura e avaliar a diferença interocular da acuidade visual de grades. A gravidade do déficit da acuidade visual de grades relacionado à idade e a diferença interocular da acuidade visual de grades foram congruentes com alterações oftalmológicas e neuroimagem. O déficit da acuidade visual de grades foi útil à caracterização do estado visual em crianças com tumores da via óptica e ao embasamento da assistência neuro-oncológica.(AU)

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.

Clinical and electrophysiological correlation in patient with optic neuritis

A descriptive and traverse study was performed in patients with diagnosis of optic neuritis, that attended to the neuro ophthalmology service of the ophthalmological center, at the Santiago General Hospital Dr. Juan Bruno Zayas Alfonso , from the province of Santiago de Cuba, with less than a week of evolution of the disease, and visual acuity greater than 0.3, cooperatives and without refractive opacities, or neuro ophthalmologic diseases, during the period from December 2017 to November 2018. Ophthalmological clinical evaluations and electrophysiological studies of visual evoked potentials to pattern reversal, at diagnosis and eight weeks of evolution were carried out. Objective: To identify the relationship possible between the electrophysiological parameters obtained by visual evoked potentials with the ophthalmological clinical evaluation. Results: alterations predominantly of the parameters of latency and duration of the visual evoked potentials, in relation to the impairment of the clinical evaluations explored. Conclusions: The visual evoked potentials are an effective tool in diagnosis, and complement the clinical evaluation of patients with optic neuritis(AU)

Evaluación piloto de la reducción de niveles séricos de productos de glicación avanzada (AGEs) sobre la electrofisiología de la visión, en pacientes con diabetes mellitus tipo 2 / Pilot evaluation of the serum levels reduction of advanced glication products (AGEs) on the vision electrophysiology in type 2 diabetic patients

BACKGROUND: Diabetic vascular complications are associated with elevated concentrations of advanced glycation end-products (AGEs). These substances can be originated endogenously by hyperglycaemia and oxidative stress, but also by dietary intake. There is indirect evidence suggesting that these complications can be prevented by lowering AGEs levels by dietary or pharmacological interventions, however its clinical benefits are still not clear enough because this would require long periods of treatment. Specific neuro-ophthalmologic tests like Multifocal Electroretinogram (MFERG) and visual evoked potentials (VEP) can detect retinal and myelinic nerve early changes, and thus could represent good methods to study the results of certain interventions in shorter lapses. The aim of this preliminary study was to evaluate the effects of a pharmacological intervention designed to lower AGEs levels, on these variables. PATIENTS AND METHODS: We included 7 patients with type 2 diabetes (DM2), with more than 5 and less than 10 years of disease, without clinically evident micro and macrovascular disease, without renal failure, hypothyroidism nor vitamin B12 deficiency, whose AGEs dietary intake was moderately elevated or high (according to dietary recalls). Upon admission, a clinical evaluation, urine and blood samples were obtained for routine labs, plus ultrasensitive C Reactive Protein (usCRP) as an inflammatory marker, and carboxymethyl-lysine (CML) as representative of AGEs. Then a complete ophthalmologic evaluation was performed, including fundus, MFERG and VEP. After the initial evaluation, placebo capsules were prescribed (12 daily capsules, 4 with each main meal) during 3 months, repeating the same initial evaluation at completion of this period. Then the active treatment followed, with capsules containing cholestyramine (4 capsules containing 500 mg each, totaling 6 g per day). Patients were cited each month, to register adverse events and repeating the same evaluation after this second 3 months period. RESULTS: The sample was composed of 2 male patients, mean age was 55.1 ± 3.8 years, and diabetes was managed with metformin plus other oral agents or o insulin (4 cases). In addition, 4 patients received lipid lowering and 4 antihypertensive drugs. Metabolic control and lipid levels were variable (ranges of HbA1c 6.2-8.4%, LDL cholesterol 45-141 mg/dL, triglycerides 70-220 mg/dL). AGEs levels represented by CML were highly variable (median 31.7, range min-max 3.4-58.9 ug/uL). Basal usCRP was also variable (median 405.9, range min-max 265.6-490.7 mg/L). The treatment was well tolerated, except for mild constipation associated with cholestiramine intake. No significant changes in electroretinography or evoked potentials were observed when comparing the initial placebo period with cholestyramine treatment. A significant increase in triglyceride levels and decrease of vitamin D levels after cholestyramine treatment was observed. No changes were detected in serum concentrations of CML, usCRP or glycemic control, after treatment. The latter variables were not correlated with neurophthalmologic studies. DISCUSSION: In this preliminary study we did not observe changes in MFERG nor VEP after 6 g/day cholestyramine treatment, which did not induce lowering of CML levels. This could be attributed to the many limitations of a pilot study, such as a small sample size, short duration of treatment, reduced doses. However this design allowed to evaluate the patients´ tolerance to the drug and rule out adverse effects, in order to plan further studies using the necessary doses to obtain lowering of AGEs

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)

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.

Hallazgos clínicos y oftalmológicos en niños con neurofibromatosis 1 / Clinical and ophthalmological findings in children with type 1 neurofibromatosis

Este trabajo tuvo por objetivos determinar la incidencia en nuestro medio de los criterios diagnósticos del National Institutes of Health (NIH) en niños con Neurofibromatosis 1 (NF1), comparar con estadísticas publicadas, analizar los hallazgos oftalmológicos, el valor de los estudios complementarios y establecer criterios de seguimiento. Métodos: Se trata de un estudio retrospectivo que incluyó 245 pacientes que ingresaron al Hospital de Pediatría Garrahan entre los años 1988 y 2010. Se diagnosticó NF1 en la primera consulta multidisciplinaria, utilizando los criterios de NIH, efectuándose en algunos niños neuroimágenes y potencial evocado visual (PEV). Resultados: El 92% de los pacientes presentó manchas café con leche; 40.8% neurofibromas, 75.5% nódulos de Lisch; 38.8% efeliloides; 16.3% glioma del nervio óptico; 16.3% displasia esquelética y 49% fueron hereditarios. Evidenciamos 1.76 miopías por cada hipermetropía. Conclusiones: Las frecuencias halladas coinciden con reportes previos, a excepción de las efeliloides, con incidencia menor. Realizamos de elección resonancia magnética nuclear (RMN), aún en pacientes asintomáticos, repitiéndolas bianualmente y examen oftalmológico cada seis meses hasta los ocho años. No indicamos actualmente PEV (AU)

The objective of this study was to determine the incidence of the National Institutes of Health (NIH) diagnostic criteria in children with Neurofibromatosis type 1 (NF1) in our setting, to compare them with the published statistical data, ophthalmological findings, the importance of complementary studies, and to establish follow-up criteria. Methods: We conducted a retrospective study including 245 patients that were admitted to the Pediatric Hospital Garrahan between 1988 and 2010. NF1 was diagnosed at the first multidisciplinary visit, using the NIH criteria. Neuroimaging and visual evoked potentials (VEP) were performed in some of the children. Results: 92% of the patients had café au laity spots; 40.8% neurofibromas; 75.5% Lisch nodules; 38.8% ephelides; 16.3% optic-nerve glioma; and 16.3% skeletal dysplasia. The disorder was hereditary in 49%. For each hypermetry,1.76 myopias were observed. Conclusions: These rates found were according to previous reports, except for ephelides, which were less common. Elective magnetic resonance imaging (MRI ) was performed, even in asymptomatic patients, and was repeated biannually and ophthalmological examination was done every six months until nine years of age. Currently, we do not indicate VEP

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. .

Applications of visual evoked potentials and Fourier-domain optical coherence tomography in Parkinson's disease: a controlled study / Potenciais evocados visuais e tomografia de coerência óptica com domínio de Fourier na doença de Parkinson: um estudo controlado

Purpose: The goal of this cross-sectional observational study was to quantify the pattern-shift visual evoked potentials (VEP) and the thickness as well as the volume of retinal layers using optical coherence tomography (OCT) across a cohort of Parkinson's disease (PD) patients and age-matched controls. Methods: Forty-three PD patients and 38 controls were enrolled. All participants underwent a detailed neurological and ophthalmologic evaluation. Idiopathic PD cases were included. Cases with glaucoma or increased intra-ocular pressure were excluded. Patients were assessed by VEP and high-resolution Fourier-domain OCT, which quantified the inner and outer thicknesses of the retinal layers. VEP latencies and the thicknesses of the retinal layers were the main outcome measures. Results: The mean age, with standard deviation (SD), of the PD patients and controls were 63.1 (7.5) and 62.4 (7.2) years, respectively. The patients were predominantly in the initial Hoehn-Yahr (HY) disease stages (34.8% in stage 1 or 1.5, and 55.8 % in stage 2). The VEP latencies and the thicknesses as well as the volumes of the retinal inner and outer layers of the groups were similar. A negative correlation between the retinal thickness and the age was noted in both groups. The thickness of the retinal nerve fibre layer (RNFL) was 102.7 μm in PD patients vs. 104.2 μm in controls. Conclusions: The thicknesses of retinal layers, VEP, and RNFL of PD patients were similar to those of the controls. Despite the use of a representative cohort of PD patients and high-resolution OCT in this study, further studies are required to establish the validity of using OCT and VEP measurements as the anatomic and functional biomarkers for the evaluation of retinal and visual pathways in PD patients. .

Objetivo: Este estudo observacional transversal controlado visou quantificar os potenciais evocados visuais com estímulo de padrões alternantes (PEV), a espessura e o volume das camadas retinianas com tomografia de coerência óptica (TCO) num grupo de pacientes com doença de Parkinson (DP). Métodos: Quarenta e três pacientes com DP e 38 controles. Procedimentos: pacientes e controles foram submetidos a exames neurológico e oftalmológico detalhados, sendo incluídos pacientes com DP idiopática e excluídos casos com glaucoma ou aumento da pressão intraocular. Todos os participantes foram estudados com PEV e TCO de Fourier, sendo quantificadas as latências de P100, a espessura e o volume das camadas retinianas interna e externa. Resultados: A média das idades e desvio-padrão dos pacientes com DP e controles foram respectivamente 63,1(7,5) e 62,4 (7,2) anos. Os pacientes com DP situaram-se predominantemente nos estágios iniciais de Hoehn-Yahr (34.8% no estágio 1 ou 1.5; 55.8 % no estágio 2). Não foram observadas diferenças entre os dois grupos quanto às latências dos PEV, a espessura e o volume das camadas retinianas. Observamos uma correlação negativa entre a espessura das camadas retinianas e a idade em ambos os grupos. Não se observou diferença significativa quanto à espessura da camada retiniana das fibras do nervo óptico (CRFNO), que foi de 102,7 μm nos pacientes e 104,2 μm nos controles. Conclusões: A espessura das camadas retinianas, os PEV e a espessura da CRFNO foi semelhante nos pacientes com DP e controles. Apesar desse grupo representativo de pacientes com DP e da alta resolução da TCO utilizada neste estudo, mais estudos são necessários para estabelecer o papel da TCO e dos PEV como biomarcadores anatômico e funcional na avaliação ...

Contrast sensitivity of pattern transient VEP components: contribution from M and P pathways

The purpose of this study was to compare contrast sensitivity estimated from transient visual evoked potentials (VEPs) elicited by achromatic pattern-reversal and pattern-onset/offset modes. The stimuli were 2-cpd, achromatic horizontal gratings presented either as a 1 Hz pattern reversal or a 300 ms onset/700 ms offset stimulus. Contrast thresholds were estimated by linear regression to amplitudes of VEP components vs. the logarithm of the stimulus contrasts, and these regressions were extrapolated to the zero amplitude level. Contrast sensitivity was defined as the inverse of contrast threshold. For pattern reversal, the relation between the P100 amplitude and log of the stimulus contrast was best described by two separate linear regressions. For the N135 component, a single straight line was sufficient. In the case of pattern onset/offset for both the C1 and C2 components, single straight lines described their amplitude vs. log contrast relations in the medium-to-low contrast range. Some saturation was observed for C2 components. The contrast sensitivity estimated from the low-contrast limb of the P100, from the N135, and from the C2 were all similar but higher than those obtained from the high-contrast limb of the P100 and C1 data, which were also similar to each other. With 2 cpd stimuli, a mechanism possibly driven by the M pathway appeared to contribute to the P100 component at medium-to-low contrasts and to the N135 and C2 components at all contrast levels, whereas another mechanism, possibly driven by the P and M pathways, appeared to contribute to the P100 component at high contrast and C1 component at all contrast levels...

Effect of contrast and gaps between Vernier stimulus elements on sweep visual evoked potential measurements of human cortical Vernier responses

The present paper focuses on a classic hyperacuity, Vernier acuity-the ability to discriminate breaks in the collinearity of lines or edges on the order of only arcseconds of visual angle. We measured steady-state sweep visual evoked potentials (sVEPs) in response to 6 Hz periodic breaks in collinearity (Vernier offsets) in horizontal squarewave gratings. Vernier thresholds, estimated by extrapolating the amplitude of the first harmonic (1F) to 0 µV, were measured for gratings with 4%, 8%, 16%, 32%, 64%, and 80% contrast, with gaps of 0, 2, or 5 arcmin introduced between neighboring bar elements that formed the Vernier offsets. Thresholds for the 2F response component provided an estimate of motion thresholds. The data confirmed and extended evidence that the odd- and even-harmonic components reflect cortical activity of different neurons (i.e., neurons that respond asymmetrically to the periodic breaks in alignment and neurons that respond symmetrically to the local relative motion cue of the stimulus). Suprathreshold data (peak amplitude, response slope, and response phase at the peak amplitude) provided additional independent evidence of this notion. Vernier thresholds decreased linearly as contrast increased, with a slope of approximately -0.5 on log-log axes, similar to prior psychophysical results. The form of contrast dependence showed more similarity to measures of magnocellular ganglion cell spatial precision than measures from parvocellular ganglion cells. Our data thus support the hypothesis that magnocellular ganglion cell output from the retina has the requisite properties to support cortical calculation of Vernier offsets at a hyperacuity level...

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.

Visual evoked potentials (VEP) and visual acuity improvement after cytidine 52 -diphosphocholine (CDP-Choline) therapy in amblyopic patient / Melhora do potencial evocado visual (PEV) e da acuidade visual em paciente amblíope tratado com citidina difosfato colina

Citicoline may be used in many neurological disorders. Combined treatment of citicoline with patching in amblyopia has previously been researched. The purpose of this paper is to illustrate the effect of citicoline in non-patching amblyopic patient. A 11-year-old amblyopic boy underwent complete ophthalmological examinations, including VEP with flash and pattern stimulus. Two averages of 100 sweep were performed for flash stimulus. Pattern reversal stimulus obtained with high contrast was performed with 60', 30' and 15' checks stimuli. The VEP was repeated 90 days later after a therapy with citicoline and vitamin and the results compared with the responses of the previous recording session. The visual acuity (VA) was 0,7 in the RE and 1,0 in the LE. The VEP pattern amplitude was normal in both eyes. Delayed in latency was detected for all spatial frequency stimulus (SFS) in the RE. Delay in latency was detected only for high SFS in the LE. After the treatment, the VA was 1,0 in both eyes. The latency was normalized with low SFS on the RE and with high SFS on the LE. The flash VEP was normal before and after the therapy. In conclusion, the citicoline demonstrated that it was effective in the treatment of amblyopic eye without patching. The VA and the VEP latency improvement demonstrated that the citicoline enhance the transmission of the electric impulse from retina to visual cortex. Further research is required to understand the immediate and long-term effect of coline treatment in amblyopic patients.

A citicolina pode ser utilizada em vários problemas neurológicos. O tratamento combinado de citicolina e oclusão na ambliopia já foi previamente relatado. O objetivo deste estudo é ilustrar o efeito da citicolina em paciente amblíope sem o tratamento oclusivo. Um menino de 11 anos de idade foi submetido a um exame oftalmológico completo incluindo PEV do tipo flash e do tipo padrão reverso. Para o PEV tipo flash, foram analisadas duas médias de 100 estímulos cada uma. Para o PEV do tipo padrão reverso, foram utilizados estímulos de alto contraste de 60', 30' e 15'. O PEV foi repetido 90 dias depois do tratamento com citicolina e vitaminas e os resultados comparados com os exames antes do tratamento. A acuidade visual era de 0,7 no olho direito e 1,0 no olho esquerdo. A amplitude do PEV era normal em ambos os olhos. Era presente um aumento da latência a todas as frequências espaciais de estimulação (FEE) no olho direito e somente à alta FEE no olho esquerdo. Após o tratamento, a acuidade visual era de 1,0 em ambos os olhos. A latência se normalizou à baixa FSS no olho direito e à alta FSS no olho esquerdo. O PEV tipo flash era normal antes e depois do tratamento. Em conclusão, a citicolina demonstrou ser eficaz no tratamento de olhos amblíopes sem oclusão. A melhora da acuidade visual e da latência do PEV demonstraram que a citicolina restaura a transmissão elétrica do impulso da retina ao cortex visual. Pesquisas futuras são necessárias para entender o efeito imediato e a longo prazo da citicolina no tratamento de pacientes amblíopes.

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.

Comparative neurophysiology of spatial luminance contrast sensitivity

The luminance contrast sensitivity function has been investigated using behavioral and electrophysiological methods in many vertebrate species. Some features are conserved across species as a shape of the function, but other features, such as the contrast sensitivity peak value, spatial frequency contrast sensitivity peak, and visual acuity have changed. Here, we review contrast sensitivity across different classes of vertebrates, with an emphasis on the frequency contrast sensitivity peak and visual acuity. We also correlate the data obtained from the literature to test the power of the association between visual acuity and the spatial frequency of the contrast sensitivity function peak.