Visual Evoked Cortical Potentials Research Articles

Abnormal late visual responses and alpha oscillations in neurofibromatosis type 1: a link to visual and attention deficits

BackgroundNeurofibromatosis type 1 (NF1) affects several areas of cognitive function including visual processing and attention. We investigated the neural mechanisms underlying the visual deficits of children and adolescents with NF1 by studying visual evoked potentials (VEPs) and brain oscillations during visual stimulation and rest periods.MethodsElectroencephalogram/event-related potential (EEG/ERP) responses were measured during visual processing (NF1 n = 17; controls n = 19) and idle periods with eyes closed and eyes open (NF1 n = 12; controls n = 14). Visual stimulation was chosen to bias activation of the three detection mechanisms: achromatic, red-green and blue-yellow.ResultsWe found significant differences between the groups for late chromatic VEPs and a specific enhancement in the amplitude of the parieto-occipital alpha amplitude both during visual stimulation and idle periods. Alpha modulation and the negative influence of alpha oscillations in visual performance were found in both groups.ConclusionsOur findings suggest abnormal later stages of visual processing and enhanced amplitude of alpha oscillations supporting the existence of deficits in basic sensory processing in NF1. Given the link between alpha oscillations, visual perception and attention, these results indicate a neural mechanism that might underlie the visual sensitivity deficits and increased lapses of attention observed in individuals with NF1.

Abnormal pattern visual evoked response in carotid-cavernous fistula

Abnormal pattern visual evoked response in carotid-cavernous fistula

Visual Evoked Cortical Potential (VECP) Elicited by Sinusoidal Gratings Controlled by Pseudo-Random Stimulation

The contributions of contrast detection mechanisms to the visual cortical evoked potential (VECP) have been investigated studying the contrast-response and spatial frequency-response functions. Previously, the use of m-sequences for stimulus control has been almost restricted to multifocal electrophysiology stimulation and, in some aspects, it substantially differs from conventional VECPs. Single stimulation with spatial contrast temporally controlled by m-sequences has not been extensively tested or compared to multifocal techniques. Our purpose was to evaluate the influence of spatial frequency and contrast of sinusoidal gratings on the VECP elicited by pseudo-random stimulation. Nine normal subjects were stimulated by achromatic sinusoidal gratings driven by pseudo random binary m-sequence at seven spatial frequencies (0.4–10 cpd) and three stimulus sizes (4°, 8°, and 16° of visual angle). At 8° subtence, six contrast levels were used (3.12–99%). The first order kernel (K1) did not provide a consistent measurable signal across spatial frequencies and contrasts that were tested–signal was very small or absent–while the second order kernel first (K2.1) and second (K2.2) slices exhibited reliable responses for the stimulus range. The main differences between results obtained with the K2.1 and K2.2 were in the contrast gain as measured in the amplitude versus contrast and amplitude versus spatial frequency functions. The results indicated that K2.1 was dominated by M-pathway, but for some stimulus condition some P-pathway contribution could be found, while the second slice reflected the P-pathway contribution. The present work extended previous findings of the visual pathways contribution to VECP elicited by pseudorandom stimulation for a wider range of spatial frequencies.

Magno and parvocellular contributions to the cortical visually evoked response – time-frequency and source considerations

Event Abstract Back to Event Magno and parvocellular contributions to the cortical visually evoked response – time-frequency and source considerations David P. Crewther1*, Laila Hugrass1, Alyse Brown1 and Callum Hollis1 1 Swinburne University of Technology, Centre for Human Psychopharmacology, Australia Purpose: The search for cortical evoked responses identifiable as magnocellular (M) or parvocellular (P) in origin is heightened by claims for abnormal magno processing in disorders as disparate as Schizophrenia, Autism, Dyslexia and Dyscalculia. However, in human, the readily available techniques of EEG, MEG, fMRI measure different signals with different technology. Nonlinear Wiener kernel analysis of visual evoked cortical potentials (VEP) and magnetic evoked fields (MEF) offer some distinct advantages in isolating M and P generated activity. Methods: Contrast responses of VEP kernels recorded with 29 normal young adults were compared with Magnetoencephalographic evoked fields (MEF) generated using a similar pseudorandom stimulus developed using a VPixx/DataPIXX combination recorded through the 306 SQUID sensors of an Elekta TRIUX magnetoencephalograph on a (different) population of 15 normal young adults. Results: Contrast response functions were extracted from the major first and second order Wiener kernel peaks of the VEP. Naka-Rushton fits enabled contrast gain and semi-saturation contrasts to be elicited for each peak. A short latency second order response with high contrast gain and a saturating contrast response function mimicking primate magnocellular (M) responses was found. A longer latency non-linearity (P) with lower contrast gain and no evidence of contrast saturation across the full range of stimulus contrasts was also found. MEG nonlinear analysis yielded similar responses, with the added source localization capability indicating that the earliest cortical responses (~50ms) occurred simultaneously over the occipital pole and an extrastriate location (MT/V5). Time-Frequency MEG analysis differentiates the slices of the second order response, with the putative magno response of the first slice of the second order response showing heightened gamma band activity, while the second slice (K2.2 - putative parvocellular response) shows strong beta band activation but little gamma. Conclusion: The cortical VEP and MEF first and second order responses can be decomposed into those with high contrast gain and contrast saturation (M-like) versus those with lower contrast gain and little evidence of saturation (P-like). TF analysis demonstrates higher gamma power in the magno components. The latency of the M-like components is approximately 25 ms less than those of the P-like components. Comparison of MEF with cortical VEP results gives strong confirmation of the M and P origins of the first and second slice major peaks respectively. Acknowledgements National Health and Medical Research Council NHMRC (APP1004740) Keywords: Magnocellular, Parvocellular pathway, nonlinearity, Magnetoencephalography (MEG), visual evoked potential (VEP) Conference: ACNS-2013 Australasian Cognitive Neuroscience Society Conference, Clayton, Melbourne, Australia, 28 Nov - 1 Dec, 2013. Presentation Type: Poster Topic: Sensation and Perception Citation: Crewther DP, Hugrass L, Brown A and Hollis C (2013). Magno and parvocellular contributions to the cortical visually evoked response – time-frequency and source considerations. Conference Abstract: ACNS-2013 Australasian Cognitive Neuroscience Society Conference. doi: 10.3389/conf.fnhum.2013.212.00007 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 15 Oct 2013; Published Online: 25 Nov 2013. * Correspondence: Prof. David P Crewther, Swinburne University of Technology, Centre for Human Psychopharmacology, Hawthorn, VIC, 3122, Australia, dcrewther@swin.edu.au Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers David P Crewther Laila Hugrass Alyse Brown Callum Hollis Google David P Crewther Laila Hugrass Alyse Brown Callum Hollis Google Scholar David P Crewther Laila Hugrass Alyse Brown Callum Hollis PubMed David P Crewther Laila Hugrass Alyse Brown Callum Hollis Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Objective assessment of chromatic and achromatic pattern adaptation reveals the temporal response properties of different visual pathways

The aim was to investigate the temporal response properties of magnocellular, parvocellular, and koniocellular visual pathways using increment/decrement changes in contrast to elicit visual evoked potentials (VEPs). Static achromatic and isoluminant chromatic gratings were generated on a monitor. Chromatic gratings were modulated along red/green (R/G) or subject-specific tritanopic confusion axes, established using a minimum distinct border criterion. Isoluminance was determined using minimum flicker photometry. Achromatic and chromatic VEPs were recorded to contrast increments and decrements of 0.1 or 0.2 superimposed on the static gratings (masking contrast 0-0.6). Achromatic increment/decrement changes in contrast evoked a percept of apparent motion when the spatial frequency was low; VEPs to such stimuli were positive in polarity and largely unaffected by high levels of static contrast, consistent with transient response mechanisms. VEPs to finer achromatic gratings showed marked attenuation as static contrast was increased. Chromatic VEPs to R/G or tritan chromatic contrast increments were of negative polarity and showed progressive attenuation as static contrast was increased, in keeping with increasing desensitization of the sustained responses of the color-opponent visual pathways. Chromatic contrast decrement VEPs were of positive polarity and less sensitive to pattern adaptation. The relative contribution of sustained/transient mechanisms to achromatic processing is spatial frequency dependent. Chromatic contrast increment VEPs reflect the sustained temporal response properties of parvocellular and koniocellular pathways. Cortical VEPs can provide an objective measure of pattern adaptation and can be used to probe the temporal response characteristics of different visual pathways.

Low-contrast multifocal visual evoked potentials

For 40 years, visual evoked cortical potentials (VEPs) have been used to aid in the diagnosis of demyelinating optic neuropathy.1 Early studies demonstrated an increased latency of the positive peak normally seen at about 100 msec—the P100—in patients with optic neuritis.1 Since the P100 often remains prolonged following recovery from the acute episode, the VEP is useful to detect optic nerve involvement in patients with suspected multiple sclerosis (MS).2 One might posit that the VEP would be useful in the identification of subclinical optic neuropathy, in which the demyelination is so …

Chromatic visual evoked potential responses in preschool children

The purpose of the study was to analyze chromatic visual evoked potential (VEP) responses to isoluminant red-green (R-G) and blue-yellow (B-Y) stimuli in 30 preschool children (1.5-6 years). The predominant part of the response consisted of a positive (P) wave, which showed age-related latency changes (linear decrease). P wave latency was shorter when using 21° compared to 7° R-G (p=0.004) and B-Y (p=0.044) stimulus and also when using 21° R-G compared to 21° B-Y stimulus (P=0.000). P wave amplitude did not show age-related changes. However, a lower amplitude was recorded when using 7° R-G stimulus (p=0.0013) and also when using B-Y compared to R-G stimulus. We may conclude that chromatic VEP to R-G and B-Y stimuli is reliably recorded in preschool children and that P wave to R-G stimulation shows a higher amplitude and shorter latency than to B-Y stimulus.

Monitorización continua de los potenciales evocados visuales corticales mediante electrodos subdurales en la cirugía de la vía óptica posterior. Caso clínico y revisión de la bibliografía

Intraoperative monitoring of functional language and motor areas is a commonly used technique which makes it possible to minimise the post-operative sequelae and to perform an optimal resection of lesions in these areas. Monitoring of the visual cortex, however, is not usually carried out nowadays. The scarce spatial resolution and its sensitivity to anaesthesia are some of the technical difficulties that reduce its clinical usefulness. The study reports a case of resection of an occipital lesion under general anaesthetic, with intraoperative monitoring of the cortical visual evoked potentials (VEP) by means of subdural electrodes. A 50-year-old female who underwent surgery involving the resection of an occipital lesion that was suggestive of radionecrosis. The VEP were monitored by administering flashing light at 4.1 Hz and recording with subdural strip electrodes on the occipital cortex. During the operation, a progressive lowering of the amplitude of the cortical VEP was observed when 50% of the baseline amplitude was exceeded, and thus the resection was finished. The increase in latency was below 10% of the baseline value. The patient recovered well during the post-operative period and her sight did not present any changes with respect to the baseline values. In our case, monitoring the cortical VEP by cortical recordings produced stable recordings with a good correlation with the post-operative visual function. Cortical recordings performed either directly or by means of subdural electrodes make it possible to achieve adequate spatial resolution and response intensity. Further studies need to be conducted with a greater number of patients in order to obtain decisive conclusions.

Multiple mtDNA deletions in Kearns‐Sayre syndrome associated with macular dystrophy

AbstractPurpose Kearns‐Sayre syndrome (KSS) is a rare disorder resulting from a mitochondrial dysfunction. Classical triad includes chronic progressive external ophthalmoplegia (CPEO), tapetoretinal degeneration and complete heart block. A 48‐year‐old woman with a clinically and histopathologically confirmed KSS developed a maculopathy resembling an adult‐onset vitelliform macular dystrophy in her right eye.Methods The patient underwent optical coherence tomography (OCT), fluorescein angiography (FA),electroretinogram (ERG), electrooculogram (EOG), visually evoked cortical potentials (VEP)and muscle enzymes determination. A sartorius muscle biopsy was performed. DNA was submitted to Southern blot analysis.Results The foveal vitelliform lesion remained hypofluorescent because the accumulation of vitelliform material blocks fluorescence. OCT revealed a retinal pigment epithelium (RPE)detachment in the right macula. ERG, EOG and VEP were normal. Serum lactate value was 3.3 mg/dL (normal: 0.63‐2.44). Muscle enzymes were normal. Muscle biopsy demonstrated "ragged red fibres" on Gomori‐trichome staining. On electron microscopy abnormal aggregation of large and atypical mitochondria were observed. DNA analysis identified the presence of multiple deletions in the mtDNA of a muscle sample, with the common deletion of 4977 bp the most abundant.Conclusion The retina, in particular RPE, is highly vulnerable to mtDNA defects and decreased oxidative phosphorylation. This is the first report associating KSS to multiple mtDNA deletions and there have been no previous reports of such macular lesion occurring in association with KSS.Ohthalmologists should be aware of the mitochondrial ocular myopathies.

EEG alpha rhythms and transient chromatic and achromatic pattern visual evoked potentials in children and adults

Transient chromatic pattern visual evoked potentials (VEPs) have been found to be less repeatable in morphology in children than in adults at low to moderate chromatic contrasts. The purpose of this study is to investigate whether low repeatability of VEP components can be associated with high alpha power, in a comparison of alpha activity in children and adults. Transient chromatic contrast and achromatic resolution VEPs were recorded in children (n=14, mean 9.6years) and adults (n=12, mean 21.8years) with normal vision and assessed for repeatability. Isoluminant chromatic (magenta-cyan) and luminance-modulated achromatic grating stimuli were presented at and above psychophysical threshold levels, in pattern onset-offset at 2Hz temporal frequency. EEGs (eyes closed and open) were recorded as single sweeps (1s long) over three 30s periods while facing a uniform computer display. An index of VEP detectability by observation was developed based on VEP component repeatability. The index was examined for correlations with alpha-wave parameters. Alpha power was calculated as the sum of the powers of 8-13Hz frequencies of the EEG sweeps (using the discrete Fourier transform). Alpha power variability was calculated using the standard deviation of the powers of each sweep in a 30s time period. The children had significantly higher alpha powers than the adults for both the eyes-open and eyes-closed conditions. Alpha power variability was significantly higher for the eyes-open condition only. There was no relationship between alpha power parameters and index of VEP detectability by observation for both the chromatic and achromatic grating stimuli. Poor repeatability of transient pattern VEPs is not associated with high alpha power or its variability in EEG measurements in older children or young adults at Oz.

Cortical visual evoked potentials recorded after optic tract near field stimulation during GPi-DBS in non-cooperative patients

Object Neurophysiologic monitoring during deep brain stimulation (DBS) interventions in the globus pallidus internum (Gpi) for the treatment of Parkinson's disease or primary dystonia is generally based upon microelectrode recordings (MER); moreover, MER request sophisticated technology and high level trained personnel for a reliable monitoring. Recordings of cortical visual evoked potentials (CVEPs) obtained after stimulation of the optic tract may be a potential option to MER; since optic tract lies just beneath the best target for Gpi DBS, changes in CVEPs during intraoperative exploration may drive a correct electrode positioning. Patients and methods Cortical VEPs from optic tract stimulation (OT C-CEPs) have been recorded in seven patients during GPi-DBS for the treatment of Parkinson's disease and primary dystonia under general sedation. OT C-VEPs were obtained after near-field monopolar stimulation of the optic tract; recording electrodes were at the scalp. Cortical responses after optic tract versus standard visual stimulation were compared. Results After intraoperative near-field OT stimulation a biphasic wave, named N40–P70, was detected in all cases. N40–P70 neither change in morphology nor in latency at different depths, but increased in amplitude approaching the optic tract. The electrode tip was positioned just 1 mm above the point where OT-CVEPs showed the larger amplitude. No MERs were obtained in these patients; OT CVEPs were the only method to detect the Gpi before positioning the electrodes. Conclusions OT CVEPs seem to be as reliable as MER to detail the optimal target in Gpi surgery: in addition they are less expensive, faster to perform and easier to decode.

Combined OCT retinal nerve fibre layer analysis and VEP in neuro‐ophthalmic disease

Abstract Purpose Ocular Coherence Tomography (OCT) has become a valuable tool in assessing retinal nerve fibre layer thickness (RNFL) in Patients with optic nerve disease. This study is designed to compare RNFL thickness n with Visual Evoked Cortical Potentials (VECP)in patients with known optic nerve disease and comparing these to a group of patients with primary open angle glaucoma (POAG). Methods Twenty Patients (37 eyes) with clinically determined optic nerve disease underwent pattern reversal VECP and also OCT using a Spectralis OCT system. Assessment of global and segmental RNFL was made. Six Patients were diagnosed as Dominant Optic atrophy, 3 with Lebers Optic Neuropathy (LHON), 6 with Nutritional amblyopia, 3 with Anterior Ischaemic Optic Neuropathy (AION), and 2 with Demyelinating disease. These Patients were also compared to a group of 10 patients (20 eyes) with Primary Open Angle Glaucoma POAG. Results Pattern reversal VECP were abnormal in 32/37 eyes (86%): 26/32 (81%) of these being of reduced amplitude, and 20/32 (62%) being delayed. Amongst the patients with POAG only 4/20 eyes (20%) had abnormal VECP, and none were delayed. Thinning of the RNFL occurred in 36/37 eyes (97%) with optic nerve disease; 24 (65%) had global thinning, and the remainder segmental thinning only. All of the eyes with POAG had RNFL thinning but only 6/20 eyes (30%) had global thinning. Bipolar cell thinning of the central retina was noted in 6 eyes with optic nerve disease. Conclusion OCT is a valuable tool in the assessment of patients with optic nerve disease. Thinning of the RNFL was a more consistent finding than delay of the VECP in optic nerve disease, and a combination of VECP and OCT is helpful in the differential diagnosis of low tension glaucoma and optic nerve disease.

Cone contrast influence on components of the pattern onset/offset VECP

Transient visual evoked cortical potentials (VECP) were recorded from the scalp of healthy normal trichromats (n = 12). VECPs were elicited by onset/offset presentation of patterned stimuli of two kinds: isochromatic luminance-modulated, and equiluminant red-green modulated, sine wave gratings. The amplitude and latency of the major onset components of the onset/offset VECP were measured and plotted as a function of the logarithm of pooled cone contrast. The early onset components, achromatic C1 and chromatic N1, increase linearly with log contrast, but N1 has a higher contrast gain than C1. The late onset components, achromatic C2 and chromatic N2, have similar contrast gain, and similar response as a function of contrast level: both increase in the low-to-medium range of contrasts and saturate at high contrast levels. In the range of pooled cone contrast tested, C1 and N1 show similar latencies, whilst C2 shows shorter latencies than N2. We suggest that C1 and N1 are generated by the same visual mechanism with high red-green contrast gain and low luminance contrast gain, whilst C2 and N2 are generated by different visual mechanisms.

Course of pattern-reversed visual evoked cortical potentials in 30 eyes after bony orbital decompression in dysthyroid optic neuropathy

AimTo investigate optic nerve function using the pattern-reversed visual evoked cortical potentials (VECP) before and after bony orbital decompression in dysthyroid optic neuropathy (DON) due to Graves' disease.MethodsA total of...

Intraoperative monitoring of cortically recorded visual response for posterior visual pathway

Intraoperative monitoring of visual evoked potentials (VEPs) has been regarded as having limited significance for the preservation of visual function during neurosurgical procedures, mainly due to its poor spatial resolution and signal-to-noise ratio. The authors evaluated the usefulness of cortically recorded VEPs, instead of the usual scalp VEPs, as intraoperative monitoring focusing on the posterior visual pathway. In 17 consecutive patients who underwent microsurgical procedures for lesions near the posterior visual pathway, cortical responses were recorded using 1-Hz flashing light-emitting diodes and subdural strip electrodes after induction of general anesthesia with sevoflurane or propofol. The detectability and waveform of the initial response, stability, and changes during microsurgical manipulations were analyzed in association with the position of electrodes and postoperative changes in visual function. Initial VEPs were detected in 82% of all patients. The VEPs were detected in 94% of patients without total hemianopia in whom electrodes were placed sufficiently near the occipital pole; in these cases the recordings were not significantly affected by anesthesia. The detectability rates of the negative peak before 100 msec (N1), positive peak approximately 100 msec (P100), and negative peak after 100 msec (N2) were 36, 50, and 100%, respectively. The mean latencies and amplitudes of N1, P100, and N2 were 90.0 +/- 15.9 msec and 61.0 +/- 64.0 microV, 103.9 +/- 13.5 msec and 34.3 +/- 38.6 microV, and 125.7 +/- 12.2 msec and 44.9 +/- 48.9 microV, respectively, showing great variability. In 11 patients, the initial waveforms of VEP remained stable during microsurgical procedures, and the visual status did not change postoperatively, while it disappeared in 2 patients who presented with postoperative hemianopia. Direct recording from the visual cortices under general anesthesia achieved satisfactory detectability of the visual response to a light-emitting diode flashing light. Although the initial waveforms varied greatly among patients, they were stable during microsurgical procedures, and the changes were consistent with postoperative visual function. Intraoperative cortical VEP monitoring is a potentially useful procedure to monitor the functional integrity of the posterior visual pathway.

Statistical test of VEP waveform equality

The aim of the study was to describe a theory and method for inferring the statistical significance of a visually evoked cortical potential (VEP) recording. The statistical evaluation is predicated on the pre-stimulus VEP as estimates of the cortical potentials expected when the stimulus does not produce an effect, a mathematical transform to convert the voltages into standard deviations from zero, and a time-series approach for estimating the variability of between-session VEPs under the null hypothesis. Empirical and Monte Carlo analyses address issues concerned with testability, statistical validity, clinical feasibility, as well as limitations of the proposed method. We conclude that visual electrophysiological recordings can be evaluated as a statistical study of n = 1 subject using time-series analysis when confounding effects are adequately controlled. The statistical test can be performed on either a single VEP or the difference between pairs of VEPs.

Changes in chromatic pattern-onset VEP with full-body inversion

Intra-ocular pressure (IOP) increases to double that of its normal level under full-body inversion, in part simulating high IOPs found in glaucoma and ocular hypertension. Inversion also simulates negative g-forces experienced in aerobatic maneuvers such as those produced during aerial combat. Studies using achromatic pattern-reversal visual evoked potentials (VEPs) have shown losses in response amplitude when subjects are inverted and IOP is increased. In other studies, chromatic, pattern-onset VEPs have been shown to be a sensitive and objective indicator of ocular and systemic pathology. Thus, chromatic pattern-onset VEPs may also show changes in amplitude and/or latency when subjects are subjected to full-body inversion. In this study we employed chromatic, pattern-onset VEPs to determine if there were changes in response latency for the different visual pathways with healthy subjects during full-body inversion. Stimuli were 1 cpd horizontal sine-wave patterns presented in an onset mode (100 ms on/400 ms off). Subjects (n = 7) were tested at low to medium contrast levels, which were subjectively equated across chromatic pathways (S, LM, and achromatic). Patterns were presented using LCD goggles. All subjects showed a small but statistically significant increase in latency in the large negative component (CII) for both L - M and S - (L + M) pathways during inversion. The achromatic pathway also showed a statistically significant increase in latency to the positive component (CI) during inversion. These results demonstrate that changes in ocular and/or systemic physiology during full-body inversion can result in increased latencies of chromatic and achromatic pattern-onset VEPs.

Optic neuritis in different strains of mice by a recombinant HSV-1 expressing murine interleukin-2.

The authors have shown previously that a recombinant HSV-1 that constitutively expresses two copies of murine IL-2 (HSV-IL-2) induces demyelination by activated CD8(+) T cells in the brain and spinal cord of ocularly infected female BALB/c mice. The present study was conducted to determine whether the ocular infection with this recombinant virus induces optic neuritis independent of virus dose, major histocompatibility complex (MHC) background, or sex. Female BALB/c, C57BL/6, SJL/6, and 129SVE mice and male BALB/c mice were ocularly infected with different doses of recombinant HSV-IL-2 virus. Demyelination of optic nerves in infected mice was monitored histologically using Luxol fast blue staining and by measurement of visual-evoked cortical potentials (VECPs). Both focal and diffuse regions of demyelination of the optic nerves were observed in the HSV-IL-2-infected mice as early as day 10 after infection and as late as day 60 after infection (the final experimental time point) in all strains of mice tested. Optic nerve demyelination was not observed in control mice ocularly infected with HSV-IL-4 or wild-type HSV-1. VECP responses were delayed significantly in the HSV-IL-2-infected mice compared with mice infected with control viruses. The results demonstrate for the first time that a combination of viral infection and constitutive expression of IL-2, but not IFN-gamma or IL-4, can result in demyelination and visual impairment in the optic nerves of ocularly infected mice.

Severe Optic Neuropathy Caused by Dichloromethane Inhalation

In this paper, we report a case of severe optic neuropathy caused by dichloromethane inhalation. A 65-year-old man fell unconsciousness while cleaning a dichloromethane tank containing a small amount of dichloromethane (purity greater than 99%) and was transported to the emergency department of our hospital, after which he was treated with hyperbaric oxygen therapy. After 1 month, narrowing of the visual field in both eyes was noted and the patient was referred to our department for additional examinations. Visual acuity was 0.3 in both eyes, which demonstrated normal reactions to light, while the critical flicker frequency (CFF) values were 30 and 25 Hz in the right and left eye, respectively. There were no abnormal findings shown in slit-lamp and fundus examinations, except for a mild cataract. Concentric contractions of the visual field by 10 degrees in both eyes were shown by a Goldmann perimetry examination, while an electroretinogram (ERG) and visual evoked cortical potential (VECP) examination exhibited nearly normal results. We diagnosed the condition as optic neuropathy caused by organic solvent poisoning, based on the decreased visual acuity, decreased CFF values, and visual-field narrowing. Although the patient was treated with vitamin B(12), visual disturbance, optic nerve atrophy, and results of VECP examinations worsened in both eyes, whereas ERG examination results were normal. Based on our findings, we considered that the central nervous system, including the optic nerve, was more severely damaged than the retina due to the normal findings in the ocular fundus and ERG examinations. Since dichloromethane produces carbon monoxide when catabolized in the liver, carbon monoxide toxicity together with the direct toxic effect of dichloromethane were considered to contribute to optic neuropathy in this case. The outcome for the present patient was poor.

Objective assessment of chromatic and achromatic pattern adaptation reveals the temporal response properties of different visual pathways

Abstract Purpose To investigate the temporal response properties of magnocellular, parvocellular and koniocellular pathways using contrast increment/decrement visual evoked potentials (VEPs). Methods Static achromatic and isoluminant chromatic gratings were generated on a monitor (Michelson contrast 0.05 to 0.6). Chromatic gratings were modulated along R/G or subject‐specific tritanopic confusion axes, established using a minimum distinct border criterion. Isoluminance was determined using minimum flicker photometry for a 1‐degree field. Achromatic and chromatic VEPs were recorded to contrast increments and decrements of 0.1 superimposed on the static gratings. Field size for Tritan gratings was restricted to 3‐degrees to minimize the effects of luteal pigment. Results Achromatic increment/decrement VEPs were positive in polarity and largely unaffected by high levels of static contrast at low spatial frequencies. Responses to finer achromatic gratings showed marked attenuation as static contrast was increased. Chromatic VEPs to R/G or Tritan chromatic contrast increments were of negative polarity and showed progressive attenuation as static contrast was increased. Chromatic contrast decrement VEPs were of positive polarity and less sensitive to pattern adaptation. Conclusion The relative contribution of sustained and transient response mechanisms to achromatic processing is spatial‐frequency dependent. Chromatic contrast increment VEPs are highly sensitive to pattern adaptation consistent with high stimulus selectivity and the sustained temporal response properties of the parvocellular and koniocellular pathways.