Flash Visual Evoked Potentials Research Articles

Methane rescues retinal ganglion cells and limits retinal mitochondrial dysfunction following optic nerve crush

Secondary degeneration is a common event in traumatic central nervous system disorders, which involves neuronal apoptosis and mitochondrial dysfunction. Exogenous methane exerts the therapeutic effects in many organ injury. Our study aims to investigate the potential neuroprotection of methane in a rat model of optic nerve crush (ONC). Adult male Sprague-Dawley rats were subjected to ONC and administrated intraperitoneally with methane-saturated or normal saline (10 ml/kg) once per day for one week after ONC. The retinal ganglion cells (RGCs) density was assessed by hematoxylin and eosin staining and Fluoro-Gold retrogradely labeling. Visual function was evaluated by flash visual evoked potentials (FVEP). The retinal apoptosis was measured by terminal-deoxy-transferase-mediated dUTP nick end labeling (TUNEL) assay and the expression of apoptosis-related factors, such as phosphorylated Bcl-2-associated death promoter (pBAD), phosphorylated glycogen synthase kinase-3β (pGSK-3β), Bcl-2 associated X protein (Bax) and Bcl-2 extra large (Bcl-xL). Retinal mitochondrial function was assessed by the mRNA expressions of peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α), nuclear respiratory factor 1 (NRF1) and mitochondrial transcription factor A (TFAM), the mitochondrial DNA (mtDNA) copy number, citrate synthase activity and ATP content. Methane treatment significantly improved the RGC loss and visual dysfunction following ONC. As expected, methane also remarkably inhibited the retinal neural apoptosis, such as the fewer TUNEL-positive cells in ganglion cell layer, accompanied by the up-regulations of anti-apoptotic factors (pGSK-3β, pBAD, Bcl-xL) and the down-regulation of pro-apoptotic factor (Bax). Furthermore, methane treatment suppressed up-regulations of critical mitochondrial components (PGC-1α, NRF1 and TFAM) mRNA and mtDNA copy number, as well as improved the reduction of functional mitochondria markers, including citrate synthase activity and ATP content, in retinas with ONC. Taken together, methane treatment promotes RGC survival and limits retinal mitochondrial dysfunction against ONC insult. Methane can be a potential neuroprotective agent for traumatic and glaucomatous neurodegeneration.

Early Methylprednisolone Treatment Can Stabilize the Blood-Optic Nerve Barrier in a Rat Model of Anterior Ischemic Optic Neuropathy (rAION).

We investigated whether methylprednisolone (MP) treatment halting retinal ganglion cell (RGC) death and having anti-inflammatory effect over a narrow therapeutic window affects the integrity of the blood-optic nerve barrier (BOB) in a rat model of ischemic optic neuropathy (rAION). The optic nerve (ON) vascular permeability was determined by Evans blue extravasation. Changes in the levels of TNF-α and IL-1β cytokines were analyzed using quantitative RT-PCR (qRT-PCR) from day 1 to day 5 post-rAION. Rats were treated with MP starting on days 0, 1, 2, and 7 post-rAION. The survival and apoptosis of the RGCs were determined by fluoroGold labeling and TUNEL assay, and the visual function was assessed with flash visual-evoked potentials (FVEPs) 4 weeks postinfarct. Inflammation of the ON was detected by immunohistochemical staining of ED1. Macrophage recruitment in the ON was significantly reduced, which was compatible with the reduction in ON vascular permeability, after MP treatment starting on days 0 and 1 postinsult compared to PBS treatment (both, P < 0.05). There was significant reduction in TNF-α and IL-1β expression in MP-treated rats (all, P < 0.05). The survival number and antiapoptotic effect on RGCs, and the P1-N2 FVEP amplitude significantly improved with MP treatment starting on days 0 and 1 (all, P < 0.05). Early treatment with MP halts RGC death and mitigates macrophage infiltration with decreased expression of proinflammatory cytokines in acute rAION. The very narrow therapeutic window is related to the quick stabilization of the disrupted BOB by early application of MP.

Neuroprotective Effects of Omega-3 Polyunsaturated Fatty Acids in a Rat Model of Anterior Ischemic Optic Neuropathy.

The purpose of this study was to investigate the therapeutic effect of omega-3 polyunsaturated fatty acid (ω-3 PUFA) administration in a rat model of anterior ischemic optic neuropathy (rAION). The level of blood arachidonic acid/eicosapentaenoic acid (AA/EPA) was measured to determine the suggested dosage. The rAION-induced rats were administered fish oil (1 g/day EPA) or phosphate-buffered saline (PBS) by daily gavage for 10 consecutive days to evaluate the neuroprotective effects. Blood fatty acid analysis showed that the AA/EPA ratio was reduced from 17.6 to ≤1.5 after 10 days of fish oil treatment. The retinal ganglion cell (RGC) densities and the P1-N2 amplitude of flash visual-evoked potentials (FVEP) were significantly higher in the ω-3 PUFA-treated group, compared with the PBS-treated group (P < 0.05). The number of apoptotic cells in the RGC layer of the ω-3 PUFA-treated rats was significantly decreased (P < 0.05) compared with that of the PBS-treated rats. Treatment with ω-3 PUFAs reduced the macrophage recruitment at the optic nerve (ON) by 3.17-fold in the rAION model. The M2 macrophage markers, which decrease inflammation, were induced in the ω-3 PUFA-treated group in contrast to the PBS-treated group. In addition, the mRNA levels of tumor necrosis factor-alpha, interleukin-1 beta, and inducible nitric oxide synthase were significantly reduced in the ω-3 PUFA-treated group. The administration of ω-3 PUFAs has neuroprotective effects in rAION, possibly through dual actions of the antiapoptosis of RGCs and anti-inflammation via decreasing inflammatory cell infiltration, as well as the regulation of macrophage polarization to decrease the cytokine-induced injury of the ON.

Multichannel visual evoked potentials in the assessment of visual pathways in children with marked brain abnormalities

To demonstrate how multichannel visual evoked potentials (VEPs) can provide quantitative measures of visual function in children with marked cortical anatomy abnormalities. Four children with marked brain pathology (2 holoprosencephaly, 2 giant interhemispheric cysts with hydrocephalus) underwent pattern reversal and flash VEP recordings from 16 equally distributed electrodes. Voltage maps of the major VEP components were constructed, and their distributions were compared to the magnetic resonance imaging (MRI) findings. No reproducible responses were evident in 1 case, and responses were present, but, as expected based on the MRI finding, not over the occipital electrodes in 3 cases. Thus, the standard clinical VEP electrode placement would not have detected responses. The distribution of responses during monocular testing obtained in 2 cases suggested normal decussation of the visual pathways at the chiasm, and voltage mapping indicated which part of the abnormally positioned brain tissue is functional visual cortex. In children with markedly abnormal brain anatomy, multichannel VEP recordings can provide quantifiable measures of visual pathway function detected in atypical locations. VEPs provide a quantifiable measure of visual function that could be used to assist in determining visual acuity levels, and offered a baseline for monitoring in the context of raised intracranial pressure. These recordings were also able to identify functional anatomical structures that were not apparent on MRI. In a clinical setting, the use of additional recordings from nonstandard electrode placement based on the MRI findings is suggested.

Intraoperative monitoring of flash visual evoked potential under general anesthesia.

In neurosurgical procedures that may cause visual impairment in the intraoperative period, the monitoring of flash visual evoked potential (VEP) is clinically used to evaluate visual function. Patients are unconscious during surgery under general anesthesia, making flash VEP monitoring useful as it can objectively evaluate visual function. The flash stimulus input to the retina is transmitted to the optic nerve, optic chiasm, optic tract, lateral geniculate body, optic radiation (geniculocalcarine tract), and visual cortical area, and the VEP waveform is recorded from the occipital region. Intraoperative flash VEP monitoring allows detection of dysfunction arising anywhere in the optic pathway, from the retina to the visual cortex. Particularly important steps to obtain reproducible intraoperative flash VEP waveforms under general anesthesia are total intravenous anesthesia with propofol, use of retinal flash stimulation devices using high-intensity light-emitting diodes, and a combination of electroretinography to confirm that the flash stimulus has reached the retina. Relatively major postoperative visual impairment can be detected by intraoperative decreases in the flash VEP amplitude.

Effect of ethanol on the visual-evoked potential in rat: dynamics of ON and OFF responses.

The effect of acute ethanol administration on the flash visual-evoked potential (VEP) was investigated in numerous studies. However, it is still unclear which brain structures are responsible for the differences observed in stimulus onset (ON) and offset (OFF) responses and how these responses are modulated by ethanol. The aim of our study was to investigate the pattern of ON and OFF responses in the visual system, measured as amplitude and latency of each VEP component following acute administration of ethanol. VEPs were recorded at the onset and offset of a 500 ms visual stimulus in anesthetized male Wistar rats. The effect of alcohol on VEP latency and amplitude was measured for one hour after injection of 2 g/kg ethanol dose. Three VEP components - N63, P89 and N143 - were analyzed. Our results showed that, except for component N143, ethanol increased the latency of both ON and OFF responses in a similar manner. The latency of N143 during OFF response was not affected by ethanol but its amplitude was reduced. Our study demonstrated that the activation of the visual system during the ON response to a 500 ms visual stimulus is qualitatively different from that during the OFF response. Ethanol interfered with processing of the stimulus duration at the level of the visual cortex and reduced the activation of cortical regions.

Change in flash visual evoked potentials in New Zealand albino rabbits after sub-tenon’s anesthesia

Context: The occurrence of amaurosis during ophthalmic anesthesia is well known. The reason for this manifestation has not been studied.Purpose: To investigate the effect of sub-tenon’s anesthesia on visual conduction in rabbit eyes.Methods: Fifteen right eyes of 15 New Zealand albino rabbits were included. 2% lidocaine hydrochloride and 0.75% bupivacaine hydrochloride (1 ml, 1:1 mixture) was injected in the sub-tenon’s space of 8 eyes while the control group (n = 7) was injected with 1 ml physiological saline. Flash visual evoked potentials (FVEP) were performed with Roland reti-scan system before and, 5 min, 15 min, and 5 days after injection. The natural pupillary diameter and minimal pupillary diameter with light reflex were recorded.Results: In the anesthesia group, N1 latency, P1 latency, and P1 amplitude were 17.13 ± 1.13 ms, 28.25 ± 1.83 ms, 13.45 ± 4.36 μv respectively before injection; 21.75 ± 3.06 ms, 29.63 ± 2.67 ms, 7.24 ± 4.64 μv at 5 min after injection; 22.25 ± 1.39 ms, 29.50 ± 2.51 ms, 7.54 ± 4.47 μv at 15 min after injection, and, 17.75 ± 0.71 ms, 28.13 ± 2.42 ms, 13.17 ± 4.08 μv 5 days after injection. When compared with baseline, N1 latency at 5 min and 15 min after injection showed prolongation (p = 0.019 and p = 0.001, respectively). Likewise, P1 amplitude decreased at 5 min and 15 min after injection (p < 0.001, p < 0.001, respectively). Both N1 latency and P1 amplitude recovered 5 days after the injection. Pupillary light reflex (PLR) constriction amplitude was 35.42% and 0.00% before and at 5 min after injection (p = 0.012). After 5 days it recovered to 33.33%. The FVEP and PLR constriction amplitude did not change significantly after injection in the control group.Discussion: Sub-tenon’s anesthesia was associated with changes in the FVEP and pupullary light reflex in rabbit eyes in our study.Conclusions: The data from this study suggested that sub-tenon’s anesthesia could reversibly block visual conduction in rabbit’s eyes.

Clinical features of neurosyphilis with optic neuritis as an initial finding

Objective: To study the characteristics of neurosyphilis with optic neuritis as an initial finding. Methods: Retrospective analysis of clinical data and laboratory testing results of 16 cases (27 eyes) with optic neuritis as an initial finding of neurosyphilis from October 2010 to March 2015 in General Hospital of People's Liberation Army was made. Results: Six-teen patients (12 males, 4 females) were collected, the median age of patients was 47 (range 33 to 65) years ,the mean age was (49.63±9.05) years. Treponema pallidum particle agglutination assay (TPPA) analysis was positive in all of the patients and rapid plasma reagin (RPR) test was positive in 14 patients (2 patients did not test). Lumbar puncture was requested and performed for all patients. Cerebrospinal fluid (CSF) TPPA analysis was positive in 16 patients and RPR test was positive in 12 patients. The CSF white blood cell counting increased in 9 (56.3%) patients and 10(62.5%)patients presented with increased CSF protein level. Both eyes were involved in 11 patients (68.8%). Relative afferent papillary defect was positive in 11 patients. Twenty-seven eyes were affected in 16 patients, and among them 7 eyes' pupil diameter were 2.5 mm or less. Incipient visual acuity was less than 0.1 in 22 eyes. The slit lamp examination showed vitreous opacity in 12 eyes and visible cells in 6 eyes among 27 eyes. Fundus examination found that 6 eyes had papillary edema and 15 eyes had pallordisc among 27eyes. Electro-retinogram (ERG) was tested in 24 eyes, and 18 eyes were abnormal. Visual evoked potential (VEP) were performed in 26 eyes (flash VEP in 22 eyes, pattern VEP in 4 eyes), and all were abnormal. Fourteen eyes were tested by 30-2 perimetry, and 6 eyes had diffuse visual field defect, 2 eyes had peripheral visual field defect, 4 eyes had quadrant defect and 2 eyes had center scotoma. Fundus fluorescence angiography was done in 16 eyes and choroidal hyper-fluorescent dots were found in posterior pole in 4 eyes. All patients were treated with antibiotic medicines, among them 10 cases in the General Hospital, and 6 cases in the other hospitals. During 15 months follow-up after discharge, visual acuity of 17 eyes recovered to 0.5 and above. Conclusion: Syphilitic optic neuritis is a condition that manifests with severe visual loss and tends to involve both eyes, Some patients have a smaller pupil diameter. Due to the particular infective routes of the disease, patients often conceal their sexual history. The manifestations of ocular syphilis are complicated and easy to misdiagnose or undiagnose. Clinical manifestations combining with the detailed history taking, serum and cerebrospinal fluid examination can guide to an accurate diagnosis and prevent from permanent vision loss. (Chin J Ophthalmol, 2016, 52: 898-904).

Modeling the Chronic Loss of Optic Nerve Axons and the Effects on the Retinal Nerve Fiber Layer Structure in Primary Disorder of Myelin.

PurposeWe determined whether the chronic lack of optic nerve myelination and subsequent axon loss is associated with optical coherence tomography (OCT) changes in the retinal nerve fiber layer (RNFL), and whether this models what occurs in multiple sclerosis (MS) and confers its use as a surrogate marker for axon degeneration.MethodsUsing an animal model of Pelizaeus-Merzbacher disease (shp) bilateral longitudinal measurements of the peripapillary RNFL (spectral-domain OCT), electroretinograms (ERG), and visual evoked potentials (VEP) were performed in affected and control animals from 5 months to 2 years and in individual animals at single time points. Light and electron microscopy of the optic nerve and retina and histomorphometric measurements of the RNFL were compared to OCT data.ResultsOf the shp animals, 17% had an average reduction of OCT RNFL thickness on the superior retinal quadrant compared to controls (P < 0.05). Electroretinograms showed normal photopic A- and B-waves but flash VEPs were disorganized in shp animals. Morphologically, the shp retinas and optic nerves revealed significant RNFL thinning (P < 0.001) without retinal ganglion cell (RGC) loss, decrease total and relative retinal axonal area, and loss of optic nerve axons. There was strong positive correlation between OCT and morphometric RNFL thickness measurements (r = 0.878, P = 0.004).ConclusionThe loss of optic nerve axons demonstrated in the shp model resulted in moderate thinning of the RNFL confirmed by OCT and histology. These results indicate that OCT-derived RNFL measurement can be a useful surrogate biomarker of optic nerve axon loss and potentially disease progression in demyelinating diseases.

Onset‐offset visual evoked potentials in the diagnosis of ocular albinism in infantile nystagmus

PurposeTo study the contribution of onset‐offset visual evoked potentials (VEP) in the diagnosis of ocular albinism in infantile nystagmus.MethodsCase report.ResultsObservations: Two girls aged respectively three‐year old and six‐year old presented with infantile nystagmus. Ophthalmic examination showed visual acuity of 2/10 bilaterally, a brown iris, with positive transillumination and depigmented fundus without any other depigmentation of skin or hair. Flash VEP showed probable crossed asymmetry of P2 amplitude. P100 wave was unrecordable in 60’ Pattern VEP. 60’ onset‐offset VEP were performed and showed evident crossed asymmetry in C1 and C2 waves which confirmed the diagnosis of ocular albinism. SD‐OCT was also performed and showed foveal hypoplasia.ConclusionsOcular albinism is more difficult to diagnose than the oculo‐cutaneous albinism since it is limited to ophthalmic manifestations. Onset‐offset VEP are very useful in nystagmus patients because they are less sensitive to ocular oscillations and showed more evident crossed asymmetry than flash or pattern VEP.

Retinal microcysts associated with optic atrophy in children – visual electrophysiology studies

PurposeRetinal microcysts have been described in adults with chronic or advanced optic atrophy of different aetiologies. We report microcysts in 4 children with visual electrophysiological evidence of optic atrophy.MethodsVisual electrophysiological investigation of 4 children with unexplained poor vision was carried out using flash and pattern ERGs and VEPs. SPECTRALIS® OCT images were taken. Case 1 aged 12 years logMAR VA 0.3, 0.5 was referred to investigate a suspected maculopathy as Ishihara colour vision was also reduced. The discs were described as full and consistent with bilateral drusen. Case 2 aged 4 years LogMAR VA 0.8 R&amp;L had presented in infancy with a strabismus, and had been patched with no improvement. His hearing was also being investigated. Case 3 aged 16 years LogMAR VA BEO 0.54 R&amp;L, was born prematurely, 32/40 weeks, and his discs were described as slightly small. Case 4 LogMAR VA 0.24, 0.1 diagnosed with ADHD presented aged 12 years with headaches. His discs were described as ‘unusual’.ResultsIn all cases flash ERG b: a amplitude ratios were normal, whilst pattern and flash VEPs showed marked dysfunction of macular and generalised pathways. PERG N95 components were subnormal in two cases tested. In all cases RNFL was thinned and OCT showed schitic changes in the inner nuclear layer of the maculae. The markedly abnormal pVEP and fVEPs contrasted with the preserved foveal architecture and indicated schisis was not a primary cause of poor vision. MRI scans were normal in cases 1–3 and genetic results for DOA and mitochondrial disorders are awaited. Case 4 has a heterozygous mutation of FGFR2.ConclusionsOur findings show that retinal microcysts associated with optic atrophy can occur as early as 4 years of age and highlight the value of visual electrophysiology in the differential diagnosis of subnormal vision of children.

EP 139. Cortical maturation during the first years of life as assessed by steady state flicker VEP

Cognitive and motor development are closely coupled to structural and functional brain maturation during the first years of life. During this developmental period brain maturation is dominated by the differentiation and grow of dendritic arbours, forming of synapses and the axons of the cortical neurons get isolated by the myelin shade. Children with learning disabilities often show a delayed functional and structural maturation of their brain early in life. However most of these children are diagnosed only after the clinical symptoms are apparent. In order to diagnose a delayed maturation early quantitative markers are required. Several studies in the past have shown that evoked potentials can be used to assess brain maturation. Recently it was shown (Dubois et al., 2008), that the myelinisation as measured by T2-MR imaging and the latency parameters of flash visual evoked potentials (VEP) closely correlate during early development. Therefore VEPs could function as surrogate marker for myelinisation. However flash VEPs still show a range of variability that makes a conclusive judgment difficult. Most studies so far analyze VEP in the time domain. However the analysis of the VEP in frequency space delivers stable and reproducible results (Pieh et al., 2009). The aim of the study presented her was to establish a method to use steady state flicker VEP in order to assess brain development. We recorded VEP from children aged between 0 days and 12 years. Classical VEP were calculated using time-locked grand averages and the latency of the P100 components were measured. Second, we analyzed the steady state signal of the cortex to the presented visual stimuli. In order to do so the measured signal was transferred to the frequency space using a fast Fourier transformation. We analyzed the power of the first and second harmonic in relation to different visual stimulation frequencies presented. Using this data we could derived a synchronization parameter. We could show that this parameter closely correlates to the maturation of the classical VEP and therefore -according to (Dubois et al., 2008)- also to the maturation of myelinisation in general. To conclude we have derived a technique which delivers an objective and quantitative marker for brain development in young children using VEP.

Flash visual evoked potentials in diurnal birds of prey.

The objective of this pilot study was to evaluate the feasibility of Flash Visual Evoked Potentials (FVEPs) testing in birds of prey in a clinical setting and to describe the protocol and the baseline data for normal vision in this species. FVEP recordings were obtained from 6 normal adult birds of prey: n. 2 Harris’s Hawks (Parabuteo unicinctus), n. 1 Lanner Falcon (Falco biarmicus), n. 2 Gyrfalcons (Falco rusticolus) and n. 1 Saker Falcon (Falco cherrug). Before carrying out VEP tests, all animals underwent neurologic and ophthalmic routine examination. Waveforms were analysed to identify reproducible peaks from random variation of baseline. At least three positive and negative peaks were highlighted in all tracks with elevated repeatability. Measurements consisted of the absolute and relative latencies of these peaks (P1, N1, P2, N2, P3, and N3) and their peak-to-peak amplitudes. Both the peak latency and wave morphology achieved from normal animals were similar to those obtained previously in other animal species. This test can be easily and safely performed in a clinical setting in birds of prey and could be useful for an objective assessment of visual function.

ISCEV standard for clinical visual evoked potentials: (2016 update).

Visual evoked potentials (VEPs) can provide important diagnostic information regarding the functional integrity of the visual system. This document updates the ISCEV standard for clinical VEP testing and supersedes the 2009 standard. The main changes in this revision are the acknowledgment that pattern stimuli can be produced using a variety of technologies with an emphasis on the need for manufacturers to ensure that there is no luminance change during pattern reversal or pattern onset/offset. The document is also edited to bring the VEP standard into closer harmony with other ISCEV standards. The ISCEV standard VEP is based on a subset of stimulus and recording conditions that provide core clinical information and can be performed by most clinical electrophysiology laboratories throughout the world. These are: (1) Pattern-reversal VEPs elicited by checkerboard stimuli with large 1 degree (°) and small 0.25° checks. (2) Pattern onset/offset VEPs elicited by checkerboard stimuli with large 1° and small 0.25° checks. (3) Flash VEPs elicited by a flash (brief luminance increment) which subtends a visual field of at least 20°. The ISCEV standard VEP protocols are defined for a single recording channel with a midline occipital active electrode. These protocols are intended for assessment of the eye and/or optic nerves anterior to the optic chiasm. Extended, multi-channel protocols are required to evaluate postchiasmal lesions.

Promotion of axon regeneration and inhibition of astrocyte activation by alpha A-crystallin on crushed optic nerve.

To explore the effects of αA-crystallin in astrocyte gliosis after optic nerve crush (ONC) and the mechanism of α-crystallin in neuroprotection and axon regeneration. ONC was established on the Sprague-Dawley rat model and αA-crystallin (10(-4) g/L, 4 µL) was intravitreously injected into the rat model. Flash-visual evoked potential (F-VEP) was examined 14d after ONC, and the glial fibrillary acidic protein (GFAP) levels in the retina and crush site were analyzed 1, 3, 5, 7 and 14d after ONC by immunohistochemistry (IHC) and Western blot respectively. The levels of beta Tubulin (TUJ1), growth-associated membrane phosphoprotein-43 (GAP-43), chondroitin sulfate proteoglycans (CSPGs) and neurocan were also determined by IHC 14d after ONC. GFAP level in the retina and the optic nerve significantly increased 1d after ONC, and reached the peak level 7d post-ONC. Injection of αA-crystallin significantly decreased GFAP level in both the retina and the crush site 3d after ONC, and induced astrocytes architecture remodeling at the crush site. Quantification of retinal ganglion cell (RGC) axons indicated αA-crystallin markedly promoted axon regeneration in ONC rats and enhanced the regenerated axons penetrated into the glial scar. CSPGs and neurocan expression also decreased 14d after αA-crystallin injection. The amplitude (N1-P1) and latency (P1) of F-VEP were also restored. Our results suggest α-crystallin promotes the axon regeneration of RGCs and suppresses the activation of astrocytes.

Visual evoked potentials in the horse.

BackgroundElectrical potentials generated in the central nervous system in response to brief visual stimuli, flash visual evoked potentials (FVEPs), can be recorded non-invasively over the occipital cortex. FVEPs are used clinically in human medicine and also experimentally in a number of animal species, but the method has not yet been evaluated in the horse. The method would potentially allow the ophthalmologist and equine clinician to evaluate visual impairment caused by disorders affecting post-retinal visual pathways. The aim was to establish a method for recording of FVEPs in horses in a clinical setting and to evaluate the waveform morphology in the normal horse.MethodsTen horses were sedated with a continuous detomidine infusion. Responses were recorded from electrodes placed on the scalp. Several positions were evaluated to determine suitable electrode placement. Flash electroretinograms (FERGs) were recorded simultaneously. To evaluate potential contamination of the FVEP from retinal potentials, a retrobulbar nerve block was performed in two horses and transection of the optic nerve was performed in one horse as a terminal procedure.ResultsA series of positive (P) and negative (N) peaks in response to light stimuli was recorded in all horses. Reproducible wavelets with mean times-to-peaks of 26 (N1), 55 (P2), 141 (N2) and 216 ms (P4) were seen in all horses in all recordings. Reproducible results were obtained when the active electrode was placed in the midline rostral to the nuchal crest. Recording at lateral positions gave more variable results, possibly due to ear muscle artifacts. Averaging ≥100 responses reduced the impact of noise and artifacts. FVEPs were reproducible in the same horse during the same recording session and between sessions, but were more variable between horses. Retrobulbar nerve block caused a transient loss of the VEP whereas transection of the optic nerve caused an irreversible loss.ConclusionsWe describe the waveform of the equine FVEP and our results show that it is possible to record FVEPs in sedated horses in a clinical setting. The potentials recorded were shown to be of post-retinal origin. Further studies are needed to provide normative data and assess potential clinical use.

Effect of hyperbaric oxygen on lipid peroxidation and visual development in neonatal rats with hypoxia-ischemia brain damage.

The aim of the present study was to investigate the effect of hyperbaric oxygen (HBO) on lipid peroxidation and visual development in a neonatal rat model of hypoxic-ischemic brain damage (HIBD). The rat models of HIBD were established by delayed uterus dissection and were divided randomly into two groups (10 rats each): HIBD and HBO-treated HIBD (HIBD+HBO) group. Another 20 rats that underwent sham-surgery were also divided randomly into the HBO-treated and control groups. The rats that underwent HBO treatment received HBO (0.02 MPa, 1 h/day) 24 h after the surgery and this continued for 14 days. When rats were 4 weeks old, their flash visual evoked potentials (F-VEPs) were monitored and the ultrastructures of the hippocampus were observed under transmission electron microscope. The levels of superoxide dismutase (SOD) and malonyldialdehyde (MDA) in the brain tissue homogenate were detected by xanthine oxidase and the thiobarbituric acid colorimetric method. Compared with the control group, the ultrastructures of the pyramidal neurons in the hippocampal CA3 area were distorted, the latencies of F-VEPs were prolonged (P<0.01) and the SOD activities were lower while the MDA levels were higher (P<0.01) in the HIBD group. No significant differences in ultrastructure, the latency of F-VEPs or SOD/MDA levels were identified between the HBO-treated HIBD group and the normal control group (P>0.05). HBO enhances antioxidant capacity and reduces the ultrastructural damage induced by hypoxic-ischemia, which may improve synaptic reconstruction and alleviate immature brain damage to promote the habilitation of brain function.

Efficacy of Intravitreal Injections of Triamcinolone Acetonide in a Rodent Model of Nonarteritic Anterior Ischemic Optic Neuropathy.

To investigate effects of intravitreal injections of triamcinolone acetonide (IVI-TA) at different times in a rodent model of nonarteritic anterior ischemic optic neuropathy (rAION). After inducing ischemic optic neuropathy, the rats received either IVI-TA (0.32 mg/2 μL) at 1 day (1d-TA), 1 week (7d-TA), 2 weeks (14d-TA), or PBS. The density of retinal ganglion cells (RGCs) was calculated using retrograde Fluorogold labeling. Electrophysiological visual function was assessed by flash visual evoked potentials (FVEPs). Apoptosis assays of the retinal sections and immunohistochemistry of ED1 staining of the optic nerves were performed. Four weeks postinfarct, the 1d- and 7d-TA groups had significantly rescued RGCs in the central (2160 ± 250 mm(2), P = 0.004; 2050 ± 660, P = 0.008, respectively) and midperipheral retinas (1240 ± 130; 1250 ± 220, respectively, both P = 0.004) compared with those of the PBS-treated rats. Flash visual evoked potentials demonstrated improvements in P1 amplitude (μV) in the 1d- and 7d-TA groups (both P < 0.05). Assays of TUNEL showed a decrease in the number of apoptotic cells in the RGC layers of 1d- and 7d-TA-treated retinas compared with the PBS-treated group (both P = 0.004). Cells ED1-positive were significantly decreased in the optic nerve (ON) of the 1d- and 7d-TA groups compared with the PBS group (P = 0.004 and 0.02, respectively). Within 1 week postinfarct of rAION, IVI-TA had neuroprotective effects on RGC survival with an increase in the electrophysiological amplitude of VEPs and a decrease in microglial infiltration in the ONs.

Double function of noninvasive intracranial pressure monitoring based on flash visual evoked potentials in unconscious patients with traumatic brain injury

Intracranial pressure (ICP) monitoring based on flash visual evoked potentials (F-VEP) is a noninvasive method of monitoring ICP. The early diagnosis of traumatic optic neuropathy (TON) in unconscious patients with traumatic brain injury (TBI) is a challenge. The aim of this study was to evaluate the function of F-VEP ICP monitoring in predicting TON and detecting contusion enlargement (CE) in unconscious TBI patients using a modified approach. A series of F-VEP ICP-monitored unconscious TBI patients were included in the study. The interocular differences in N2 wave latency (DL) and amplitude (DA) were obtained through monocular flash stimulation. The increases in ICP (dxP) and interchannel difference (dxDC) across various time points were obtained through binocular flash stimulation. The predictive power of DL and DA on TON, as well as of dxP and dxDC on CE, was assessed by logistic regression and receiver operating characteristic (ROC) curve analysis. Patients with TON had a longer DL and a higher DA than those without TON. The dxP and dxDC of patients with CE were both higher than those of patients without CE. The differences were statistically significant. The logistic regression showed that both DL and DA were predictors of TON, whereas only dxDC was a predictor of CE. However, the ROC curve analysis showed that DL had greater predictive power for TON, and dxDC had greater predictive power for CE. An F-VEP ICP monitoring system with a modified approach is beneficial for early diagnosis of TON and prediction of CE in unconscious TBI patients.

ID 133 – Flash ERG and VEP – Comparison of stimulation by LED and Xenon lamp

Objective Electroretinography (ERG) examines the functional integrity of the retina. Visual evoked potentials (VEP) are electrical responses recorded from occipital cortex which provides information about central visual pathways. The purpose of this study is to compare ERG and VEP results elicited with two different types of flash stimulator. Methods Seven healthy volunteers without any known ocular or neurological diseases were took part in this study. The mean age of participants was 23 (4 female-3 male). ERG and VEP responses were recorded with two different stimulators, Xenon lamp (Flash) stimulator and Light emitting diodes (LED) photic stimulator. Results There was no significant difference in the mean P100 latencies and amplitudes of Flash VEP and LED VEP ( p = 0.213, p = 0.145 respectively). The mean latencies of a-wave and b-wave were longer for LED ERG than Flash ERG but it did not reach a statistical significance ( p = 0.195). Also the amplitude of b-wave (measured from the trough of the a-wave to the peak of the b-wave) had no significant difference between Flash ERG and LED ERG. Conclusions These results taken altogether suggest that we could produce similar VEP and ERG responses with Xenon lamp and LEDs. Key words Visual Evoked Potentials, Electroretinography, Light Emitting Diodes