A High-Resolution LED Stimulator for Steady-State Visual Stimulation: Customizable, Affordable, and Open Source.

Visually evoked steady-state potentials (SSVEPs) are neural responses elicited by visual stimuli oscillating at specific frequencies. In this study, we introduce a novel LED stimulator system explicitly designed for steady-state visual stimulation, offering precise control over visual stimulus parameters, including frequency resolution, luminance, and the ability to control the phase at the end of the stimulation. The LED stimulator provides a personalized, modular, and affordable option for experimental setups. Based on the Teensy 3.2 board, the stimulator utilizes direct digital synthesis and pulse width modulation techniques to control the LEDs. We validated its performance through four experiments: the first two measured LED light intensities directly, while the last two assessed the stimulator's impact on EEG recordings. The results demonstrate that the stimulator can deliver a stimulus suitable for generating SSVEPs with the desired frequency and phase resolution. As an open source resource, we provide comprehensive documentation, including all necessary codes and electrical diagrams, which facilitates the system's replication and adaptation for specific experimental requirements, enhancing its potential for widespread use in the field of neuroscience setups.

The Impact of the Wavelength and Its Transmittance on the Visual Evoked Potentials, at Baseline, and under the Effect of Six Monochromatic Filters Used for Visual Treatments.

PURPOSE: This is an observational, non-invasive study which measures the VEPs of twelve individuals, at baseline, and under the effect of six monochromatic filters used in visual therapy, to understand their effect on neural activity to propose successful treatments. METHODS: Monochromatic filters were chosen to represent the visible light spectrum, going from red to violet color, 440.5-731 nm, and light transmittance from 19 to 89.17%. Two of the participants presented accommodative esotropia. The impact of each filter, differences, and similarities among them, were analyzed using non-parametric statistics. RESULTS: There was an increase on the N75 and P100 latency of both eyes and a decrease was on the VEP amplitude. The neurasthenic (violet), omega (blue), and mu (green) filter had the biggest effects on the neural activity. Changes may primarily be attributable to transmittance (%) for blue-violet colors, wavelength (nm) for yellow-red colors, and a combination of both for the green color. No significant VEPs differences were seen in accommodative strabismic patients, which reflects the good integrity and functionality of their visual pathway. CONCLUSIONS: Monochromatic filters, influenced the axonal activation and the number of fibers that get connected after stimulating the visual pathway, as well as the time needed for the stimulus to reach the visual cortex and thalamus. Consequently, modulations to the neural activity could be due to the visual and non-visual pathway. Considering the different types of strabismus and amblyopia, and their cortical-visual adaptations, the effect of these wavelengths should be explored in other categories of visual dysfunctions, to understand the neurophysiology underlying the changes on neural activity.

Características clínicas y los resultados de los Potenciales Evocados Visuales por Flash en niños menores de 5 años

Introducción: Los potenciales evocados visuales (PEV) evalúan la vía visual mediante pequeñas respuestas neuroeléctricas de la corteza occipital. Constituyen un examen no invasivo para determinar la función visual en prematuros, recién nacidos, lactantes, niños con malformaciones cerebrales enfermedades metabólicas o retraso mental. Objetivo: Describir las características clínicas y los resultados de los Potenciales Evocados Visuales por Flash en niños menores de 5 años en el periodo de diciembre de 2017 a diciembre de 2018. Materiales y Métodos: Diseño observacional, descriptivo, ambispectivo con componente analítico. Los pacientes incluidos niños de 0 a 5 años de edad que se realizaron PEV en el Hospital Pediátrico en el período de diciembre de 2017 a diciembre de 2018. Muestreo no probabilístico de casos consecutivos. Variables principales: Edad, sexo, procedencia, profesional que solicitó el estudio, motivo de solicitud del estudio, datos maternos y perinatales, resultados del PEV. Los datos fueron analizados con SPSSv 21, utilizando estadística descriptiva. Resultados: Se estudiaron 110 pacientes que se realizaron PEV, la mediana de edad fue de 32 meses, predominó el sexo masculino, procedieron del departamento Central (63,6%). La mayoría de los pacientes presentaban Parálisis cerebral infantil (PCI), los neurólogos solicitaron mayormente el estudio. De los antecedentes perinatales, se evidenció que, a menor edad gestacional, menor peso de nacimiento, menor Apgar y antecedente de hospitalización perinatal, los valores de latencia y amplitud para la onda P100 en ambos ojos presentaban alteraciones, siendo esta relación estadísticamente significativa. Conclusión: Aunque en su mayoría los resultados de PEV fueron normales existe una relación importante entre los antecedentes perinatales y la alteración del resultado especialmente con respecto al Apgar a los 1 min mostrando una relación inversa.

Introduction: Visual evoked potentials (VEP) evaluate the visual pathway through small neuroelectric responses from the occipital cortex. They constitute a non-invasive test to determine visual function in premature babies, newborns, infants, children with brain malformations, metabolic diseases or mental retardation. Objective: To describe the clinical characteristics and the results of Flash Visual Evoked Potentials in children under 5 years of age during the time period from December 2017 to December 2018. Materials and Methods: This was an observational, descriptive and ambispective design with an analytical component. The patients included children from 0 to 5 years of age who underwent VEP at the Pediatric Hospital in the period from December 2017 to December 2018. We used non-probabilistic sampling of consecutive cases. Main variables: Age, sex, place of residence, professional who requested the study, reason for requesting the study, maternal and perinatal data, VEP results. Data were analyzed with SPSSv 21, using descriptive statistics. Results: 110 patients who underwent VEP were studied, the median age was 32 months, the male sex predominated, most lived in the Central department (63.6%). Most of the patients had infantile cerebral palsy (ICP), neurologists most frequently requested the study. Using the perinatal history, we determined that a lower gestational age, lower birth weight, lower Apgar score, and a history of perinatal hospitalization were associated with alterations in the latency and amplitude values for the P100 wave in both eyes, this relationship was statistically significant. Conclusion: Although the majority of the VEP results were normal, there is an important relationship between the perinatal history and the alteration of the result, especially with respect to the Apgar at 1 min, which shows an inverse relationship.

Combined therapy of bilateral transcranial direct current stimulation and ocular occlusion improves visual function in adults with amblyopia, a randomized pilot study.

Background: Amblyopia is the interocular visual acuity difference of two lines or more with the best correction in both eyes. It is treated with ocular occlusion therapy, but its success depends on neuroplasticity, and thus is effective in children but not adults. Transcranial Direct Current Stimulation (tDCS) is suggested to increase neuroplasticity. Objective: To determine if combined intervention of bilateral tDCS and ocular occlusion improves visual function in adults with amblyopia. Methods: A double-blind randomized, controlled pilot trial was conducted in 10 volunteers with amblyopia. While applying ocular occlusion and performing a reading task, participants received bilateral tDCS (n = 5) or sham stimulation (n = 5), with the anodal tDCS electrode in the contralateral visual cortex and the cathodal in the ipsilateral visual cortex in relation to the amblyopic eye. Visual function (through visual acuity, stereopsis, and contrast sensitivity tests) and visual evoked potential (with checkerboard pattern stimuli presentation) were evaluated immediately after. Results: A total of 30 min after treatment with bilateral tDCS, visual acuity improved by 0.16 (± 0.025) LogMAR in the treatment group compared with no improvement (-0.02 ± 0.02) in five controls (p = 0.0079), along with a significant increase in the amplitude of visual evoked potentials of the amblyopic eye response (p = 0.0286). No significant changes were observed in stereopsis and contrast sensitivity. No volunteer reported any harm derived from the intervention. Conclusion: Our study is the first to combine anodal and cathodal tDCS for the treatment of amblyopia, showing transient improved visual acuity in amblyopic adults.

Comparison of sweep visual evoked potential of visual acuity and Snellen visual acuity in healthy and amblyopic children / Comparação da acuidade visual por potenciais evocados visuais de varredura e pelo teste de Snellen em crianças saudáveis e ambliópicas

ABSTRACT Purpose: To evaluate the visual acuity of healthy and amblyopic children using sweep visual evoked potential and compare the results with those of Snellen visual acuity testing. Methods: A total of 160 children aged 6-17 years were included in the study. Of these, 104 (65%) were aged 7-17 years old, able to verbally communicate, and did not have any systemic or ocular pathology (Group 1). Group 2 included 56 (35%) children aged 6-17 years, able to verbally communicate, and had strabismus or anisometropic amblyopia whose best corrected visual acuity was between 0.1 and 0.8. All subjects underwent a detailed ophthalmological examination and sweep visual evoked potential measurement. Demographic characteristics, ocular findings, best corrected visual acuity, and sweep visual evoked potential results were recorded. Results: In Group 1, the mean and maximum visual acuity values for sweep visual evoked potential were lower than the Snellen best corrected visual acuity (p<0.001, for both, respectively). Bland-Altman analysis revealed that in Group 1, the distribution of the differences between the Snellen best corrected visual acuity and mean sweep visual evoked potential visual acuity was ±0.11 logMAR, and the distribution of the differences between the Snellen best corrected visual acuity and maximum sweep visual evoked potential visual acuity was ±0.023 logMAR. In Group 2, the mean and maximum sweep visual evoked potential visual acuity were lower than the Snellen best corrected visual acuity (p<0.001 and p=0.009, respectively). Bland-Altman analysis revealed that the distribution of the differences between the Snellen best corrected visual acuity and mean sweep visual evoked potential visual acuity was ±0.16 logMAR, and the distribution of the differences between the Snellen best corrected visual acuity and maximum sweep visual evoked potential visual acuity was ±0.19 logMAR. Conclusions: Sweep visual evoked potential visual acuity measurements have comparable results with Snellen visual acuity measurements. This technique is an objective and reliable method for evaluating visual acuity in children.

RESUMO Objetivo: Avaliar a acuidade visual através de po­tenciais evocados visuais de varredura em crianças saudáveis e ambliópicas, comparando-a com a acuidade visual pelo teste de Snellen. Métodos: Foram incluídas no estudo 160 crianças com idades entre 6 e 17 anos. Desse total, 104 crianças (65%) estavam entre 7 e 17 anos de idade, eram capazes de comunicação verbal e não tinham nenhuma patologia ocular ou sistêmica (Grupo 1). O grupo 2 incluiu 56 crianças verbais (35%) com idades entre 6 e 17 anos e portadoras de estrabismo ou ambliopia anisometrópica, com a melhor acuidade visual corrigida entre 0,1 e 0,8. Todos os pacientes foram submetidos a um exame oftalmológico detalhado e a uma medição do potencial evocado visual por varredura. Registraram-se as características demográficas, os achados oculares, a melhor acuidade visual corrigida e os resultados do potencial evocado visual por varredura. Resultados: No Grupo 1, os valores médios e máximos da acuidade visual pelo potencial evocado visual por varredura mostraram-se menores que a melhor acuidade visual corrigida medida através do teste de Snellen (p<0,001 para ambas as medições). Uma análise de Bland-Altman revelou que no grupo 1, a distribuição das diferenças entre a melhor acuidade visual corrigida pelo teste de Snellen e a média do potencial evocado visual por varredura foi de ± 0,11 logMAR, enquanto a distribuição das diferenças entre a melhor acuidade visual corrigida pelo teste de Snellen e o valor máximo do potencial evocado visual por varredura foi de ± 0,023 logMAR. No Grupo 2, os valores médio e máximo do potencial evocado visual por varredura mostraram-se menores que a melhor acuidade visual corrigida pelo teste de Snellen (respectivamente, p<0,001 e p=0,009). A análise de Bland-Altman revelou que a distribuição das diferenças entre a melhor acuidade visual corrigida pelo teste de Snellen e a média do potencial evocado visual por varredura foi de ± 0,16 logMAR, enquanto a distribuição das diferenças entre a melhor acuidade visual corrigida pelo teste de Snellen e o valor máximo do potencial evocado visual por varredura foi de ± 0,19 logMAR. Conclusões: As medidas da acuidade visual através do potencial evocado visual por varredura mostram resultados comparáveis às medidas da acuidade visual pelo teste de Snellen. Essa técnica é um método objetivo e confiável de se avaliar a acuidade visual em crianças.

Contribution of objectively measured grating acuity by sweep visually evoked potentials to the diagnosis of unexplained visual loss.

PURPOSE: To investigate the diagnostic contribution of grating visual acuity (GVA) measured by sweep pattern-reversal visually evoked potentials (SPRVEP) in unexplained visual loss (UVL). METHODS: This case-control study included adult patients under suspicion of UVL referred to SPRVEP and transient pattern-reversal visually evoked potentials (TPRVEP) testing. Optotype visual acuity (OVA) was measured by ETDRS 4-meter chart and GVA by SPRVEP. UVL patients were assigned into three distinctive categories, according to the presence of ocular disease, motivation, and electrophysiological evaluation, as follows: exaggerators, malingerers, and psychogenic. Healthy controls and patients with organic visual loss were also tested. Receiver operating characteristic (ROC) curve was constructed to evaluate the diagnostic performance of GVA and TPRVEP parameters. RESULTS: A total of 76 patients with UVL were analyzed: 60 (79.0%) exaggerators, 11 (14.4%) malingerers, and 5 (6.6%) psychogenic. Controls were 49 subjects evaluated for TPRVEP and 28 subjects for SPRVEP. There were 13 patients with organic visual loss enrolled. Mean difference between OVA and GVA was 1.19±0.67 (median=0.84; 95% CI: 1.04 to 1.34) in UVL and 0.14 ±0.09 (median= 0.14; 95% CI: 0.08 to 0.20) in organic visual loss. The area under the ROC curve (AUC) of GVA to distinguish UVL from healthy controls was 0.998 with a cutoff of 0.09 logMAR showing specificity of 100% and sensitivity of 96.0%. CONCLUSIONS: GVA measured by SPRVEP had good diagnostic validity to discriminate patients with unexplained visual loss from healthy controls and patients with organic visual loss, demonstrating its contribution to the diagnosis of this condition.

Solving the SSVEP Paradigm Using the Nonlinear Canonical Correlation Analysis Approach.

This paper presents the implementation of nonlinear canonical correlation analysis (NLCCA) approach to detect steady-state visual evoked potentials (SSVEP) quickly. The need for the fast recognition of proper stimulus to help end an SSVEP task in a BCI system is justified due to the flickering external stimulus exposure that causes users to start to feel fatigued. Measuring the accuracy and exposure time can be carried out through the information transfer rate-ITR, which is defined as a relationship between the precision, the number of stimuli, and the required time to obtain a result. NLCCA performance was evaluated by comparing it with two other approaches-the well-known canonical correlation analysis (CCA) and the least absolute reduction and selection operator (LASSO), both commonly used to solve the SSVEP paradigm. First, the best average ITR value was found from a dataset comprising ten healthy users with an average age of 28, where an exposure time of one second was obtained. In addition, the time sliding window responses were observed immediately after and around 200 ms after the flickering exposure to obtain the phase effects through the coefficient of variation (CV), where NLCCA obtained the lowest value. Finally, in order to obtain statistical significance to demonstrate that all approaches differ, the accuracy and ITR from the time sliding window responses was compared using a statistical analysis of variance per approach to identify differences between them using Tukey's test.

Visual Evoked Potentials in Neuromyelitis Optica Spectrum Disorders.

BACKGROUND: Neuromyelitis optica spectrum disorders (NMOSDs) are rare antibody-mediated disorders of the central nervous system, with a predilection for the spinal cord and optic nerves. The clinical utility of evoked potential recordings (EPs) has already been established for multiple sclerosis, in particular, that of the abnormal visual evoked potentials (VEP), a key criterion in the McDonald diagnostic criteria for MS. However, there have been few reports on EPs in patients with NMOSD. AIM: The aim of our study was to assess the possible involvement of the optical pathway through VEP responses in patients with NMOSD. METHODS: VEPs were prospectively performed in 13 patients with NMOSD. All the patients were recruited from the outpatient clinic of a demyelinating diseases center. The recording was done as recommended by the International Federation of Clinical Neurophysiology. RESULTS: We evaluated the eyes of 12 women with a mean age of 42 years and of one man who was 25 years old. In 6 of the examined eye samples, a response was not obtained, while in the remaining 20 eye samples, we found a significant increase in P100 latency without amplitude change. CONCLUSION: VEPs showed a significant increase in P100 latency. VEP assessment is a non-invasive, painless, fast, and low-cost exam that provides neurophysiological data for diagnosis of NMOSD.

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)

Relation of Structural and Functional Changes in Auditory and Visual Pathways after Temporal Lobe Epilepsy Surgery.

Auditory and visual pathways may be affected as a consequence of temporal lobe epilepsy surgery because of their anatomical relationships with this structure. The purpose of this paper is to correlate the results of the auditory and visual evoked responses with the parameters of tractography of the visual pathway, and with the state of connectivity between respective thalamic nuclei and primary cortices in both systems after the surgical resection of the epileptogenic zone in drug-resistant epileptic patients. Tractography of visual pathway and anatomical connectivity of auditory and visual thalamus-cortical radiations were evaluated in a sample of eight patients. In general, there was a positive relationship of middle latency response (MLR) latency and length of resection, while a negative correlation was found between MLR latency and the anatomical connection strength and anatomical connection probability of the auditory radiations. In the visual pathway, significant differences between sides were found with respect to the number and length of tracts, which was lower in the operated one. Anatomical connectivity variables and perimetry (visual field defect index) were particularly correlated with the latency of P100 wave which was obtained by quadrant stimulation. These results demonstrate an indirect functional modification of the auditory pathway and a direct traumatic lesion of the visual pathway after anterior temporal lobectomy in patients with drug resistant epilepsy.

Caracterización de la Lámpara Flash-LED: EBNeuro Usada para Adquirir Potenciales Evocados Visuales en Ratas / Characterization of the Flash-LED Lamp: EBNeuro Used to Acquired Visual Evoked Potentials in Rats

Resumen: La señal de la amplitud en análisis de Potenciales Evocados Visuales (PEVs) es una variable que depende del tipo y posición de los electrodos, de la fuente, del estímulo y por consecuente, de la intensidad luminosa por lo que es fundamental reportarla para cada diseño experimental y así, garantizar su reproducibilidad. El objetivo de este trabajo es caracterizar una lámpara con 96 LEDs para la adquisición de PEVs en ratas. Se midió la iluminancia y la intensidad luminosa promedio en un sistema espacial XYZ de 8 cm3 aplicable a un sistema estereotáxico para la fijación de ratas. Se realizaron desplazamientos cada 2 cm en cada plano. Se observó que debido a la distribución geométrica de los LEDs la distribución de la iluminancia no sigue la ley del inverso cuadrado, ya que aumenta conforme la lámpara se aleja. Finalmente, se seleccionó una coordenada para la colocación del ojo de la rata empleando una intensidad luminosa promedio para la adquisición del PEV de 1.043 cd e iluminancia de 128.77 luxes a una distancia ojo-lámpara de 9 cm. Una vez caracterizada la intensidad luminosa y de acuerdo con los PEVs obtenidos, esta lámpara puede utilizarse para estudios PEV en ratas en investigaciones posteriores.

Abstract: Signal amplitude for recordings of Visual Evoked Potentials (VEPs) is a variable dependent on the type and position of the electrodes, the source, the stimulus and consequently the luminous intensity; therefore, it is relevant to report it to assure experimental reproducibility. The objective of this work is to characterize flash lamp with 96 LEDs in order to perform the acquisition of VEPs in rats. We measure the illuminance and mean light intensity on space system XYZ of 8 cm3 corresponding to a stereotaxic frame for rodents. Displacements were performed every 2 cm in each plane. Because of the geometric distribution of the LEDs in the EBNeuro lamp the spatial distribution of illuminance does not follow the law of the inverse square, because the illuminance increases as the lamp goes away. Finally a spatial coordinate was selected for the rat eye positioning were the mean luminous intensity was 1.043 cd and 128.77 luxes of illuminance at an eye-lamp distance of 9 cm. According to the obtained VEPs and spatial characterization this lamp can be used for acquire of recordings PEV in rats for further investigations.

Caracterización estructural y funcional de la neuropatía óptica inflamatoria autoinmune / Structural and Functional Description of Autoimmune Inflammatory Optic Neuropathy

Introducción: la neuritis óptica es una inflamación del nervio óptico de variada etiología relacionada con algunas entidades como procesos inflamatorios y enfermedades sistémicas. Objetivo: caracterizar la estructura y función en la neuropatía óptica inflamatoria autoinmune. Métodos: estudio descriptivo de serie de casos en el Hospital Clínico Quirúrgico Lucía Iñiguez Landín en el 2012. El universo estuvo constituido por 18 pacientes con neuropatía óptica inflamatoria. La muestra incluyó 12 pacientes con etiología autoinmune. Se distribuyó a los pacientes según diagnóstico etiológico y topográfico. Se realizó funduscopia y tomografía láser confocal. Se realizó valoración funcional del nervio óptico según potenciales evocados visuales. Resultados: predominó la etiología desmielinizante y la forma topográfica anterior, de los ocho pacientes de la variedad topográfica anterior, siete tenían esclerosis múltiple y un caso se debió a lupus eritematoso sistémico. La variedad desmielinizante posterior se observó en dos casos. El mayor número de pacientes presentó aumento del grosor de la capa de fibras nerviosas retinianas según resultado de la funduscopia y la tomografía confocal. Los resultados con tomografía láser coincidieron con los obtenidos por funduscopia, los ocho casos con topografía anterior presentaron grosor aumentado de la capa de fibras nerviosas retinianas y los dos casos de topografía posterior mostraron un grosor normal. El mayor número de pacientes presentó aumento de la latencia y amplitud normal de los potenciales evocados, la mayoría de los casos presentaron latencia aumentada (9 casos para el 75,0%) y tres mostraron latencia muy aumentada (25,0%). La amplitud fue normal en ocho pacientes y en cuatro estaba disminuida. De ellos (34%), dos correspondieron a neuritis óptica anterior. Conclusiones: se corroboró la relación estructura función en el daño del nervio óptico en la neuropatía inflamatoria de causa autoinmune.

Introduction: optic neuritis is an inflammation of the optic nerve of varied etiology related to some conditions such as inflammatory processes and systemic diseases. Objective: to describe structure and function in autoimmune inflammatory optic neuropathy. Methods: a descriptive of a series of cases study at Lucía Iñiguez Landín Surgical Clinical Hospital in 2012 was done. The universe consisted of 18 patients with inflammatory optic neuropathy. The sample included 12 patients with autoimmune etiology. The patients were distributed according to etiological and topographical diagnosis. Funduscopy and confocal laser tomography were performed. Functional evaluation of the optic nerve was performed according to visual Evoked Potentials. Results: demyelinating etiology and anterior topographic etiology predominated, of the eight patients of the topographic variety, seven had multiple sclerosis and one case was due to systemic lupus erythematosus. The posterior demyelinating variety was observed in two cases. The greatest number of patients presented increased thickness of the retinal nerve fiber layer as a result of funduscopy and confocal tomography. The results with laser tomography coincided with those obtained by funduscopy, the eight cases with anterior topography showed increased thickness of the retinal nerve fiber layer and the two cases of posterior topography showed a normal thickness. The greater number of patients presented increased latency and normal amplitude of the evoked potentials, the majority of cases presented increased latency (9 cases for 75.0%) and three showed a very increased latency (25.0%). The amplitude was normal in eight patients and in four it diminished. Of these (34%), two corresponded to anterior optic neuritis. Conclusions: the relationship structure in the optic nerve damage in autoimmune inflammatory neuropathy was corroborated.

Neuroprotective effect of melatonin in experimental optic neuritis in rats.

Optic neuritis (ON) is an inflammatory, demyelinating, and neurodegenerative condition of the optic nerve, which might induce permanent vision loss. Currently, there are no effective therapies for this disorder. We have developed an experimental model of primary ON in rats through a single microinjection of 4.5 µg of bacterial lipopolysaccharide (LPS) into the optic nerve. Since melatonin acts as a pleiotropic therapeutic agent in various neurodegenerative diseases, we analyzed the effect of melatonin on LPS-induced ON. For this purpose, LPS or vehicle were injected into the optic nerve from adult male Wistar rats. One group of animals received a subcutaneous pellet of 20 mg melatonin at 24 hr before vehicle or LPS injection, and another group was submitted to a sham procedure. Melatonin completely prevented the decrease in visual evoked potentials (VEPs), and pupil light reflex (PLR), and preserved anterograde transport of cholera toxin ß-subunit from the retina to the superior colliculus. Moreover, melatonin prevented microglial reactivity (ED1-immunoreactivity, P < 0.01), astrocytosis (glial fibrillary acid protein-immunostaining, P < 0.05), demyelination (luxol fast blue staining, P < 0.01), and axon (toluidine blue staining, P < 0.01) and retinal ganglion cell (Brn3a-immunoreactivity, P < 0.01) loss, induced by LPS. Melatonin completely prevented the increase in nitric oxide synthase 2, cyclooxygenase-2 levels (Western blot) and TNFα levels, and partly prevented lipid peroxidation induced by experimental ON. When the pellet of melatonin was implanted at 4 days postinjection of LPS, it completely reversed the decrease in VEPs and PLR. These data suggest that melatonin could be a promising candidate for ON treatment.

Electrophysiolocal findings in Mohr-Tranebjærg syndrome / Alterações eletrofisiológicas na síndrome de Mohr-Tranebjærg

Mohr-Tranebjærg syndrome (MTS) is an X-liked recessive rare syndrome also known as deafness-dystonia syndrome. The severity of the symptoms may vary, but they progress usually to severe deafness and dystonia and sometimes they are accompanied by cortical deterioration of vision and mental deterioration. The purpose of this paper is to illustrate a very interesting case of Mohr-Tranebjærg syndrome. A 24-year-old italian man with Mohr-Tranebjærg syndrome underwent full field electroretinography (ERG) and visual evoked potentials (VEPs). Fundus examination showed apparently normal retina with pallor of the optic disc. Pattern reversal VEP and flash VEP responses were non-recordable. ERG showed amplitude reduction of the fotopic, scotopic and 30 Hz flicker responses revealing generalized retinal dysfunction with reduction of cone and rod responses. The progressive neurodegeneration in Mohr-Tranebjærg syndrome can be also associated with a retinal degeneration.

A síndrome de Mohr-Tranebjærg é rara, com herança recessiva ligada ao X, conhecida também como síndrome da surdez-distonia. A intensidade dos sintomas pode variar e normalmente, evoluem para uma surdez profunda e a distonia, algumas vezes, vem acompanhados por deterioração visual e mental. O objetivo deste trabalho é ilustrar um caso muito interessante dessa doença. Um homem, italiano, de 24 anos, com a síndrome de Mohr-Tranebjærg, foi submetido ao exame de eletrorretinografia de campo total (ERG) e ao exame de potencial evocado visual (PEV) (padrão e flash). No exame do fundo do olho era presente uma palidez do nervo óptico com retina, aparentemente, sem alterações. No exame do eletrorretinografia de campo total ERG detectou-se redução das amplitudes das respostas fotópicas, escotópicas e ao flicker de 30 Hz, demonstrando uma disfunção generalizada da retina, com redução da função dos cones e bastonetes. A progressiva neurodegeneração da síndrome de Mohr-Tranebjærg pode ser também associada à degeneração da retina.

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. .

Experimental optic neuritis induced by the microinjection of lipopolysaccharide into the optic nerve.

Optic neuritis (ON) is a condition involving primary inflammation, demyelination, and axonal injury in the optic nerve which leads to retinal ganglion cell (RGC) loss, and visual dysfunction. We investigated the ability of a single microinjection of bacterial lipopolysaccharide (LPS) directly into the optic nerve to induce functional and structural alterations compatible with ON. For this purpose, optic nerves from male Wistar rats remained intact or were injected with vehicle or LPS. The effect of LPS was evaluated at several time points post-injection in terms of: i) visual pathway and retinal function (visual evoked potentials (VEPs) and electroretinograms, (ERGs), respectively), ii) anterograde transport from the retina to its projection areas, iii) consensual pupil light reflex (PLR), iv) optic nerve histology, v) microglia/macrophage reactivity (by Iba-1- and ED1-immunostaining), vi) astrocyte reactivity (by glial fibrillary acid protein-immunostaining), vii) axon number (by toluidine blue staining), vii) demyelination (by myelin basic protein immunoreactivity and luxol fast blue staining), viii) optic nerve ultrastructure, and ix) RGC number (by Brn3a immunoreactivity). LPS induced a significant and persistent decrease in VEP amplitude and PLR, without changes in the ERG. In addition, LPS induced a deficit in anterograde transport, and an early inflammatory response consisting in an increased cellularity, and Iba-1 and ED1-immunoreactivity in the optic nerve, which were followed by changes in axonal density, astrocytosis, demyelination, and axon and RGC loss. These results suggest that the microinjection of LPS into the optic nerve may serve as a new experimental model of primary ON.

Visual Evoked Potentials in Infants With Diffuse Periventricular Leukomalacia.

Periventricular leukomalacia (PVL) is characterized by necrosis of the cerebral white matter in the dorsolateral portions of the lateral ventricles. PVL causes motor, sensory, and cognitive deficits. The aim of this study was to analyze the conduction characteristics of the visual pathway in infants with diffuse PVL using visual evoked potentials (VEPs). We studied 11 healthy infants (mean age 3.3 ± 1.3 months) and 17 with diffuse PVL (mean age 2.9 ± 0.8 months and mean gestational age 31.9 ± 3.1 weeks). The N75, P100, and N135 wave latencies; the interwave N75-P100 and P100-N135 latencies; and the N75-P100 and P100-N135 amplitudes were measured in the occipital leads. VEPs were recorded during binocular stimulation at an angle of 120' from the Fz-Oz lead. Healthy children had mean N75, P100, and N135 wave latencies of 84.4 ± 5.8, 143.4 ± 30.6 and 222.9 ± 40.4 ms, respectively. The mean interwave N75-P100 and P100-N135 latencies were 59.0 ± 28.6 and 79.5 ± 13.6 ms, respectively. Compared with the healthy group, infants with PVL had longer N75 and N135 latencies at 92.3 ± 15.3 (P = .05) and 265.0 ms ± 60.3 (P = .05), respectively. The interwave latency P100-N135 (105.5 ± 29.1 ms; P = .017) was longer in children with PVL than in healthy infants. Infants with diffuse PVL had mild alterations in their N75, P100 and, particularly, their N135 latencies. These increases in P100-N135 interwave latencies could be because of damage to the geniculocortical pathways and V2-V3 networks.

Sweep visually evoked potentials and visual findings in children with West syndrome.

BACKGROUND: West syndrome (WS) is a type of early childhood epilepsy characterized by progressive neurological development deterioration that includes vision. AIM: To demonstrate the clinical importance of grating visual acuity thresholds (GVA) measurement by sweep visually evoked potentials technique (sweep-VEP) as a reliable tool for evaluation of the visual cortex status in WS children. METHODS: This is a retrospective study of the best-corrected binocular GVA and ophthalmological features of WS children referred for the Laboratory of Clinical Electrophysiology of Vision of UNIFESP from 1998 to 2012 (Committee on Ethics in Research of UNIFESP n° 0349/08). The GVA deficit was calculated by subtracting binocular GVA score (logMAR units) of each patient from the median values of age norms from our own lab and classified as mild (0.1-0.39 logMAR), moderate (0.40-0.80 logMAR) or severe (>0.81 logMAR). Associated ophthalmological features were also described. RESULTS: Data from 30 WS children (age from 6 to 108 months, median = 14.5 months, mean ± SD = 22.0 ± 22.1 months; 19 male) were analyzed. The majority presented severe GVA deficit (0.15-1.44 logMAR; mean ± SD = 0.82 ± 0.32 logMAR; median = 0.82 logMAR), poor visual behavior, high prevalence of strabismus and great variability in ocular positioning. The GVA deficit did not vary according to gender (P = .8022), WS type (P = .908), birth age (P = .2881), perinatal oxygenation (P = .7692), visual behavior (P = .8789), ocular motility (P = .1821), nystagmus (P = .2868), risk of drug-induced retinopathy (P = .4632) and participation in early visual stimulation therapy (P = .9010). CONCLUSIONS: The sweep-VEP technique is a reliable tool to classify visual system impairment in WS children, in agreement with the poor visual behavior exhibited by them.

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...

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.(AU)