Dark Trough Research Articles

Recovering 21cm Monopole Signals Without Smoothness

We expect the monopole signal at the lowest frequencies below 100MHz to be composed to two components: the deep Rayleigh-Jeans tail of the cosmic microwave background and two distinct features: the dark ages trough at ∼17MHz and the cosmic dawn trough at ∼75Mhz. These are hidden under orders of magnitude brighter foregrounds whose emission is approximately a power-law with a spectral index ≈−2.5. It is usually assumed that monopole signals of interest are separable from foregrounds on the basis of spectral smoothness. We argue that this is a difficult approach and likely impossible for the Dark Ages trough. Instead, we suggest that the fluctuations in the foreground emission around the sky should be used to build a model distribution of possible shapes of foregrounds, which can be used to constrain presence of a monopole signal. We implement this idea using normalizing flows and show that this technique allows for efficient unsupervised detection of the amplitude, width and center of the Dark Ages trough as well as Rayleigh-Jeans tail of the cosmic microwave background for a sufficiently sensitive experiment. We show that achromatic and smooth response significantly helps with foreground separation. We discuss the limitations of the inherent assumptions in this method and the impact on the design of future low-frequency experiments.

Function of the Retinal Pigment Epithelium in Patients With Neurofibromatosis Type 1.

PurposeRetinal and choroidal abnormalities in neurofibromatosis type 1 (NF1) remain poorly studied. It has been reported, however, that the function of the retinal pigment epithelium (RPE) in NF1 was abnormal, with a supra-normal Arden ratio of the electro-oculogram (EOG). This study aims to evaluate the function of the RPE, using EOG, first in patients with NF1 compared to controls and second in patients with NF1 with choroidal abnormalities compared to patients with NF1 without choroidal abnormalities.MethodsThis prospective case-control study included 20 patients with NF1 (10 patients with choroidal abnormalities and 10 patients without) and 10 healthy patients, matched for age. A complete ophthalmologic assessment with multimodal imaging, an EOG, and a full-field electroretinogram were performed for each included patient. The main outcome measured was the EOG light peak (LP)/dark trough (DT) ratio.ResultsThe LP/DT ratio was 3.02 ± 0.52 in patients with NF1 and 2.63 ± 0.31 in controls (P = 0.02). DT values were significantly lower in patients with NF1 than in controls (240 vs. 325 µV, P = 0.02), while light peak values were not significantly different (P = 0.26). No difference was found for peak latencies. No significant correlation between the surface and number of choroidal abnormalities and EOG parameters was demonstrated.ConclusionsThis study confirms the dysfunction of the RPE in patients with NF1, involving a lower DT and a corresponding higher LP/DT ratio. We hypothesize that this pattern may be due to a dysregulation of the melanocytogenesis, inducing a disruption in Ca2+ ion flux and an abnormal polarization of the RPE.

Electrophysiological signs of retinal cone remodeling in geographic atrophy of the pigment epithelium in patients with non-exudative age-related macular degeneration

Testing patients with primary geographic atrophy (GA) requires a multimodal approach and identification of functional biomarkers characterizing retinal structural remodeling.Purpose: to identify the changes in the functional activity of the retinal cone system, which may serve as biomarkers of primary GA in non-exudative age-related macular degeneration (AMD).Material and methods. We tested 22 patients (30 eyes) aged 45–83 (ave. 72.1 ± 10.8 years) with non-exudative AMD and 18 age matched controls (60.2 ± 7.6 years) all of which underwent standard ophthalmological examinations, optical coherence tomography, autofluorescence study, and fundus photography. Standard photopic ERGs, photopic flicker ERGs to stimuli with frequencies of 8.3, 10, 12, and 24 Hz, multifocal ERG (mfERG), and electrooculogram (EOG) were recorded.Results. Electroretinographic signs for GA of retinal pigment epithelium and choriocapillary layer atrophy were described. The results confirm early impairment of the activity of cones in GA and weakening of the functional interaction of M ller cells with the cone bipolar cells. The delayed P1 peak latency of mfERG indicates a decrease in the entire central retina function in non-exudative AMD. A selective reduction in the fovea's mfERG magnitude can serve as a biomarker of primary GA. The spread of the P1 anomaly to adjacent rings may indicate a possible risk of disease progression. A decrease in the dark trough on the EOG and an increase in the Arden ratio can serve as a biomarker of primary GA.Conclusion. We determined electrophysiological signs which can serve as markers of early retinal dysfunction in eyes with primary GA and non-exudative AMD.

Dysfunction in macula, retinal pigment epithelium and post retinal pathway in acute organophosphorus poisoning

Context Organophosphorus (OP) insecticide poisoning is a significant health problem in South Asian countries. Although cholinergic receptors are present at the junction between photoreceptors and the retinal pigment epithelium (RPE), human studies of the effects of OP poisoning on the visual pathways are very few. This study aims to demonstrate the pattern of changes in retina and post retinal pathways in patients with acute OP poisoning using visual electrophysiological tests. Methods This is an observational, cross-sectional study conducted at the Neurophysiology Unit, Teaching Hospital, Peradeniya, Sri Lanka. We tested 16 patients recovered from cholinergic phase, at least 24 h after deatropinization and within 8 weeks of OP ingestion. We assessed the functional integrity of the photoreceptors and ganglion cells of the macula by pattern electroretinography (PERG); RPE by electro-oculography (EOG); and post retinal pathways by pattern reversal visual evoked potentials (PR-VEP). Latencies and amplitudes of PR-VEP and PERG, light peak (LP), dark trough (DT) and Arden ratio of EOG were determined in patients and compared with 16 controls using the Mann–Whitney U test. Results Of the 16 OP-poisoned patients (median age of 37 ± IQR 20 years), six (37.5%) had reduced Arden ratio with reference to the International Society of Clinical Electrophysiology of Vision cut-off value of 1.7. The median Arden ratio in patients (1.69 ± IQR 0.36) was significantly lower compared to controls (1.90 ± IQR 0.4). The median latencies and amplitudes of PR-VEP or PERG were not significantly different between patients and controls. However, three patients had prolonged P100 latencies in PR-VEP and one had prolonged P50 latency in PERG. Conclusions Acute OP poisoning seems to affect the functions of the RPE and the visual electrophysiological changes outlast the cholinergic phase. Limited evidence suggests that photoreceptors of the macula region and post retinal pathway might be affected in some patients.

Best abstract award runner-up. Effect of acute optic neuropathies on Light Peak: Dark trough ratio (Arden ratio) of electro-oculography

Best abstract award runner-up. Effect of acute optic neuropathies on Light Peak: Dark trough ratio (Arden ratio) of electro-oculography

Chapter 33 - The electrooculogram

The electrooculogram (EOG) measures the cornea-positive standing potential relative to the back of the eye. By attaching skin electrodes outside the eye near the lateral and medial canthus, the potential can be measured by having the patient move the eyes horizontally a set distance. The voltage becomes smaller in the dark, reaching its lowest potential after 8-12min, the so-called dark trough. When the lights are turned on, the potential rises, reaching a peak by about 10min. When the size of the light peak is compared to the dark trough, the normal ratio should be near 2:1. A light peak:dark trough ratio of less than 1.7 is considered abnormal. The origin of electrooculographic potentials is the pigment epithelium of the retina interacting with the midretina. The light rise of the potential requires both a normal pigment epithelium and normal midretinal function. The most common use of the electrooculogram is to confirm Best disease. Best disease is identified by the appearance of an egg-yellow fundus and can be confirmed by recording both an electroretinogram (ERG) and electrooculogram (EOG). The ERG will be normal and the EOG will be abnormal. The EOG is also used for tracking eye movement.

The slow light and dark oscillation of the clinical electro‐oculogram

BackgroundThe standing potential of the eye exhibits a slow damped oscillation under light and dark conditions that continues for at least 80 minutes. However, our understanding of the relationship between the slow dark and light oscillation has not been previously studied. The aim of this study was to explore through regression analysis a model of these oscillations in order to establish if they may have the same underlying cellular generators.MethodsHealthy participants undertook recordings of the standing potential using the electro‐oculogram for 100 minutes. To explore the light oscillation, participants (n = 8) were dilated and performed an extended electro‐oculogram protocol consisting of 15 minutes dark adaptation and 85 minutes of white light adaptation at 100 cd/m2. For the dark oscillation, participants (n = 11) undertook the electro‐oculogram for 100 minutes in complete darkness. Both sessions began with pre‐adaptation to 30 cd/m2 of white light for five minutes. Non‐parametric statistics were used to evaluate all data.ResultsRatios of the dark and light oscillations showed a significantly greater dampening of the dark oscillation compared to the light oscillation (p < 0.000). Regression analysis using a five‐factor damped sine function revealed significant differences in the parameters governing the dampening (p = 0.005) and period (p = 0.009) of the functions (R2 > 0.874). There were no significant differences in the dark trough amplitude.ConclusionThe results support a different underlying physiological mechanism for the light and dark oscillation of the clinical electro‐oculogram. Future work will need to establish how the dark oscillation and dark trough of the clinical electro‐oculogram arise.

A meta-analysis of clinical electro-oculography values.

The aim of the meta-analysis was to derive a range of mean normal clinical electrooculogram (EOG) values from a systematic review of published EOG studies that followed the guidelines of the ISCEV standard for clinical electro-oculography. A systematic literature review was performed using four relevant databases limited to peer-reviewed articles in English between 1967 and February 2017. Studies reporting clinical EOG or FO normal values were included when the report used a standard 30° horizontal saccade, a retinal luminance of between 100 and 250cdm-2, and had >10 subjects in their normative values. The search identified 1145 articles after duplicates were removed with subsequent screening of the abstracts excluding a further 1098, resulting in 47 full-text articles that were then assessed by the author (PC) with a final nine articles meeting the inclusion criteria. An overall effect estimate using inverse variance-weighted meta-analysis was performed to estimate the mean values for the light peak/dark trough ratio (LP:DT ratio) (dilated and undilated), the time to the LP, the amplitude of the LP, dark trough (DT) and the fast oscillation (FO) peak-to-trough ratio from the included studies. The mean dilated LP:DT ratio was 2.35 (95% CI 2.28-2.42); undilated LP:DT ratio was 2.37 (95% CI 2.28-2.45); LP amplitude was 835 (95% CI 631-1039)µV and the mean time to the LP being 8.2 (95% CI 7.7-8.7)min. The mean DT amplitude was 358 (95% CI 292-424)µV, and the mean FO peak-to-trough ratio was 1.13 (95% CI 1.11-1.16). The results of the LP/DT ratio are drawn from studies with a mean±standard deviation (SD) age of 34.08±12.93years for dilated and 33.65±12.28years for undilated LP/DT ratios. The meta-analysis of EOG studies has generated a reference range of normal mean values for clinicians to refer to when using the ISCEV clinical EOG. It provides a potential method to generate similar data sets from published normal values in related visual electrophysiology tests.

ISCEV Standard for clinical electro-oculography (2017 update)

The clinical electro-oculogram (EOG) is an electrophysiological test of the outer retina and retinal pigment epithelium (RPE) in which changes in the electrical potential across the RPE are recorded during successive periods of dark and light adaptation. This document presents the 2017 EOG Standard from the International Society for Clinical Electrophysiology of Vision (ISCEV: www.iscev.org). This standard has been reorganized and updated to include an explanation of the mechanism of the EOG, but without substantive changes to the testing protocol from the previous version published in 2011. It describes methods for recording the EOG in clinical applications and gives detailed guidance on technical requirements, practical issues and reporting of results with the main clinical measure (the Arden ratio) now termed the light peak:dark trough ratio. The standard is intended to promote consistent quality of testing and reporting within and between clinical centers.

THE PHYSIOLOGY OF THE RETINAL PIGMENT EPITHELIUM IN DANON DISEASE.

Danon disease is caused by mutations in the lysosome-associated membrane protein-2 gene (LAMP2). In the eye, LAMP2 is expressed only in the retinal pigment epithelium. This study aimed to investigate the previously unreported impact of LAMP2 mutations on the electrooculogram generated by the retinal pigment epithelium. Four members of a family with Danon disease were examined. All have mutations in c294G > A, of the LAMP2 gene on Xq24, by which no, or aberrant, protein will be formed. Electrooculograms to International Society for the Clinical Electrophysiology of Vision (ISCEV) standards were recorded with full-field electroretinography, Goldmann kinetic visual fields, and spectral optical coherence tomography with fundus autofluorescence imaging. Electrooculogram amplitude ratios of light rise:dark trough, the Arden index, fell at low-normal limits (range: 1.68-3.94) but misrepresent retinal pigment epithelium health, because the absolute dark trough voltages were abnormally low (median: 140 μV, range: 72-192 μV) as were the light rise amplitudes (median: 297 μV, range: 198-366 μV), and full-field electroretinograms were normal. Hyperfundus autofluorescence and hypofundus autofluorescence changes became more confluent and florid with increasing age of female patients. Goldmann visual field testing showed constriction of the central field. Low electrooculogram voltages indicate that the retinal pigment epithelium is unable to maintain its tight junctions in Danon disease.

The effects of gender and age on the range of the normal human electro-oculogram.

To define the normal ranges for the slow oscillations (SO) and fast oscillations (FO) of the electro-oculogram (EOG) recorded to International Society for Clinical Electrophysiology of Vision (ISCEV) standards. The effects of age and gender on the EOG ranges were examined. ISCEV standard SOs and FOs were recorded from 121 subjects (51 % male) aged from 7 to 72 years. Study variables for the SO were dark trough (DT) and light peak (LP) amplitudes (µV), times to DT and LP (min), and the Arden ratio (LP/DT amplitude). The FO was fit by a sine wave and peak-to-peak amplitude (µV), phase (°), and peak-to-trough (PT) ratios derived. The effects of age, gender and pupil size on EOG parameters were examined by multiple regression analysis. The average Arden ratio was 2.5. Arden ratio decreased with age at a rate of 0.13 per decade of age (R (2) = 0.14, P < 0.0001). The 5th percentile of the Arden ratio decreased from 2.0 to 1.7 between 10 and 60 years of age. Median time to LP was 9 min (interquartile range 8-9 min). Time to LP was age-dependent and increased by 2 min for subjects over 55 years of age compared with those less than 25 years. EOG amplitudes were greater in women than in men (P < 0.005). The average PT ratio was 1.18, which was not affected by age or gender. Time to reach the light trough of the FO was 40 s, which increased with age (1.1 s/decade). No correlation was observed between Arden ratio and PT ratio. The major strength of this study is the definition of the normal range and associated lower limits of ISCEV standard EOGs based on recordings from 121 subjects balanced by gender and spanning the 1st through 8th decades of life. Decreased Arden ratio and increased time to LP are associated with aging, which is likely due to the intricate mechanisms involved in generation of the light rise. Differences between the FO and SO with respect to the effects of aging are consistent with separate generation of these two EOG signals.

Comparing short‐duration electro‐oculogram with and without mydriasis in controls

AbstractPurpose In order to obtain artefact‐free EOG recordings the subject’s cooperation is necessary. The aim of our study is to evaluate recording characteristics of the short‐duration EOG and to compare the effect of mydriasis on EOG recordings in a cohort of controls.Methods EOG recordings were performed on a LED stimulus screen using a RETI‐port gamma plus2 system (RETIscanTM, Roland Consult). Dark phase included: pre‐adaptation (6min), alternate fixation (4min), fixation‐rest (20sek), 100 sweeps. Light phase included: light adaptation (4min), alternate fixation (10min), fixation‐rest (20sek), 250 sweeps. Amplifier was band pass filtered at 0.1‐50Hz. Background illumination in mydriasis was 100cd/m2 and in miosis 450cd/m2. Fast oscillations were set at 1.5sek (6 cycles; total duration 75sek).Results A total of 55 controls divided in three age‐groups participated (number; mean (years, y); ±SD): group 1: 18‐ 20y (19; 19.49y; ±0.89); group 2: 20‐40y (18; 27.91y; ±5.39) and group 3: 40‐60y (18; 48.66y; ±4.00). Arden ratio (AR), dark‐trough (DT) and light‐peak (LP) did not differ between recordings with or without mydriasis (p=0.885; p=0.860; p=0.776, linear mixed‐effects model). Age did not influence the AR, DT, LP (p= 0.206; p=0.112; p=0.155). AR, DT, LP were comparable between eyes tested (p=0.998; p=0.196; p=0.324).Conclusion Short‐duration EOG allows successful recording, where the application of mydriasis does not influence the quality of the recording.

Rebalancing binocular vision in amblyopia

Humans with amblyopia have an asymmetry in binocular vision: neural signals from the amblyopic eye are suppressed in the cortex by the fellow eye. The purpose of this study was to develop new models and methods for rebalancing this asymmetric binocular vision by manipulating the contrast and luminance in the two eyes. We measured the perceived phase of a cyclopean sinewave by asking normal and amblyopic observers to indicate the apparent location (phase) of the dark trough in the horizontal cyclopean sine wave relative to a black horizontal reference line, and used the same stimuli to measure perceived contrast by matching the binocular combined contrast to a standard contrast presented to one eye. We varied both the relative contrast and luminance of the two eyes' inputs, in order to rebalance the asymmetric binocular vision. Amblyopic binocular vision becomes more and more asymmetric the higher the stimulus contrast or spatial frequency. Reanalysing our previous data, we found that, at a given spatial frequency, the binocular asymmetry could be described by a log-linear formula with two parameters, one for the maximum asymmetry and one for the rate at which the binocular system becomes asymmetric as the contrast increases. Our new data demonstrates that reducing the dominant eye's mean luminance reduces its suppression of the non-dominant eye, and therefore rebalances the asymmetric binocular vision. While the binocular asymmetry in amblyopic vision can be rebalanced by manipulating the relative contrast or luminance of the two eyes at a given spatial frequency and contrast, it is very difficult or even impossible to rebalance the asymmetry for all visual conditions. Nonetheless, wearing a neutral density filter before the dominant eye (or increasing the mean luminance in the non-dominant eye) may be more beneficial than the traditional method of patching the dominant eye for treating amblyopia.

Binocular combination of phase and contrast explained by a gain-control and gain-enhancement model

We investigated suprathreshold binocular combination, measuring both the perceived phase and perceived contrast of a cyclopean sine wave. We used a paradigm adapted from Ding and Sperling (2006, 2007) to measure the perceived phase by indicating the apparent location (phase) of the dark trough in the horizontal cyclopean sine wave relative to a black horizontal reference line, and we used the same stimuli to measure perceived contrast by matching the binocular combined contrast to a standard contrast presented to one eye. We found that under normal viewing conditions (high contrast and long stimulus duration), perceived contrast is constant, independent of the interocular contrast ratio and the interocular phase difference, while the perceived phase shifts smoothly from one eye to the other eye depending on the contrast ratios. However, at low contrasts and short stimulus durations, binocular combination is more linear and contrast summation is phase-dependent. To account for phase-dependent contrast summation, we incorporated a fusion remapping mechanism into our model, using disparity energy to shift the monocular phases towards the cyclopean phase in order to align the two eyes' images through motor/sensory fusion. The Ding-Sperling model with motor/sensory fusion mechanism gives a reasonable account of the phase dependence of binocular contrast combination and can account for either the perceived phase or the perceived contrast of a cyclopean sine wave separately; however it requires different model parameters for the two. However, when fit to both phase and contrast data simultaneously, the Ding-Sperling model fails. Incorporating interocular gain enhancement into the model results in a significant improvement in fitting both phase and contrast data simultaneously, successfully accounting for both linear summation at low contrast energy and strong nonlinearity at high contrast energy.

THE CHARACTERIZATION OF RETINAL PHENOTYPE IN A FAMILY WITH C1QTNF5-RELATED LATE-ONSET RETINAL DEGENERATION

To describe the clinical, spectral-domain optical coherence tomography and electrophysiological features of C1QTNF5-associated late-onset retinal degeneration in a molecularly confirmed pedigree. Five members of a family participated, and affected individuals (n = 4) underwent detailed ophthalmologic evaluation including fundus autofluorescence and spectral-domain optical coherence tomography imaging and electroretinography. Electrooculography was performed in three individuals. The visual acuity was initially normal and worsened with time. Anterior segment abnormalities included peripupillary iris atrophy and long anterior insertion of zonules. Peripapillary atrophy, drusenoid deposition, and scalloped sectorial chorioretinal atrophy were observed in all older individuals (n = 3). Fundus autofluorescence demonstrated hypofluorescent areas corresponding to regions of chorioretinal atrophy. The spectral-domain optical coherence tomography demonstrated multiple areas of retinal pigment epithelium-Bruch membrane separation with intervening homogeneous deposition that corresponded to the drusenoid lesions and areas of chorioretinal atrophy. Electrooculography was normal in one individual and showed abnormally low dark trough measures in older individuals (n = 2). Electroretinography was normal in early stages (n = 1), but showed marked abnormalities in the rod system (n = 3), which was predominantly inner retinal (n = 2) in late stages. Late-onset retinal degeneration is a progressive degeneration, and anterior segment abnormalities present early. The widespread sub-retinal pigment epithelium deposition seen on spectral-domain optical coherence tomography in older individuals appears to be a characteristic in late stages. Electrooculography demonstrates abnormalities only in late stages of the disease.

Is there a dysfunction in the visual system of depressed patients?

BackgroundThe aim of the current study was to identify a possible locus of dysfunction in the visual system of depressed patients.Materials and MethodsFifty Major Depressive patients aged 21–60 years and 15 age-matched controls took part in the study The diagnosis was obtained with the SCAN v 2.0. The psychometric assessment included the HDRS, the HAS, the Newcastle Scales, the Diagnostic Melancholia Scale and the GAF scale. Flash Electroretinogram and Electrooculogram were performed in all subjects. The statistical analysis included ANCOVA, Student's t-test and Pearson Product Moment Correlation Coefficient were used.ResultsThe Electro-oculographic findings suggested that all subtypes of depressed patients had lower dark trough and light peak values in comparison to controls (p < 0.001), while Arden ratios were within normal range. Electroretinographic recordings did not reveal any differences between patients and controls or between subtypes of depression.DiscussionThe findings of the current study provide empirical data in order to assist in the understanding of the international literature and to explain the mechanism of action of therapies like sleep deprivation and light therapy.

Electro-oculographic findings after 360 degrees retinotomy and macular translocation for subfoveal choroidal neovascularisation in age-related macular degeneration.

To evaluate potential electro-oculographic changes after 360 degrees retinotomy and macular translocation for subfoveal choroidal neovascularisation in patients with age-related macular degeneration (AMD) in a randomised comparative (self-controlled) trial. A consecutive series of 30 patients suffering from subfoveal choroidal neovascularisation secondary to age-related macular degeneration underwent 360 degrees retinotomy and macular translocation. The EOG served as the main parameter of the study and was recorded 1 day prior to the translocation surgery and no earlier than 21 days after the silicone oil removal. Postoperatively, a statistically significant decrease in mean dark trough by 64% was found for treated eyes (P<0.001). The mean dark trough of the fellow eye remained stable after surgery (P=0.33). The postoperative difference between the treated und untreated eyes proved to be statistically significant (P<0.001). The Arden ratio remained stable in the treated and untreated eyes with mean values of 204% (P=0.81) and 213% (P=0.18), respectively. A significant correlation between the reduction of the dark trough and the visual acuity at the 1-year follow-up was found. A persistent decrease in the corneofundal potential is associated with 360 degrees retinotomy and macular translocation for exudative AMD. This indicates a substantial postoperative malfunction of retinal pigment epithelial cells and an impaired photoreceptor regeneration. The impeded recovery of the RPE-photoreceptor complex can be interpreted as the result of the surgical trauma on the basis of prediseased RPE. A severe postoperative decrease in dark trough forecasts an incomplete recovery of visual acuity.

Electrophysiology in the Investigation of Acquired Retinal Disorders

Electrophysiological research on acquired retinal disorders, both common and rare, is reviewed. Age is a major factor influencing electroretinogram (ERG) and electro-oculogram (EOG) findings. Bipolar or Müller cell death in the aging retina could account for much of the amplitude decline that is observed with age. In diabetic retinopathy, the oscillatory potentials can monitor the progression of the disease and indicate neuronal alterations rather than diabetic angiopathy of the retina. Human ERG studies on glaucoma concentrated on ERG measures that are dominated by inner retinal contributions. It has been shown that the pattern ERG can serve as a predictor of ocular hypertension's progression to glaucoma. In retinal disorders caused by endogenous intoxication, such as hepatic retinopathy, or exogenous intoxication from chronic lead exposure, ERG changes give an objective measure of the damage and allow to study the pathophysiological mechanisms that are involved. Inflammations of the choroid and the retina affect the standard ERG when they are diffuse. In central serous chorioretinopathy, functional disturbances can be revealed not only in the photoreceptors but also in the middle and inner retinal layers with the use of focal stimuli. Choroidal melanoma leads to large reductions of the EOG light peak–to–dark trough ratio through its influence on the transepithelial potential of the retinal pigment epithelium (RPE). In cancer-associated retinopathy, both the rod and cone ERGs are reduced. However, selective cone dysfunction has been described. In melanoma-associated retinopathy, the long flash ERG may reveal a specific pathophysiological mechanism, namely the affection of the ON-pathway with preservation of the OFF-pathway. ERG measurements can reveal vitamin A deficiency and are altered in cases with a mutation in the gene for the retinol binding protein in which other organs are not affected. Photochemical damage to the retina from light emission by the operating microscope can be assessed by electrophysiological methods.

Serotonin modulation of pain responsiveness in the aged rat

This study was designed to examine differences in basal nociceptive responsiveness between young (3 months) and old (25 months) male Fischer-344 rats and also to evaluate the effects of methysergide and fluoxetine on this behavioral paradigm. The results indicate that the aged animals were less sensitive than young animals to pain responsiveness in simple nociceptive tests such as the tail-flick, hot plate (55°C), and hind-paw pressure tests. In both groups of animals, this behavioral response followed a circadian rhythm, with peak of pain latency during the dark phase and trough occuring in the light phase. In all three analgesic tests, treatment with methysergide, which is a serotonin antagonist, resulted in hyperalgesia in both groups of animals within the first hour, followed by a return to basal response level after 2 h. Fluoxetine treatment resulted in a nonsignificant increase in nociceptive response at 30 min posttreatment which returned to the baseline by 1 h. Moreover, in both young and old animals morphine produced moderate analgesia in the hot plate and hind-paw tests, which was potentiated by simultaneous treatment with fluoxetine. This study shows that noxious response was reduced in the aged male Fischer-344 rats, and the data obtained provide evidence that the serotonergic system modulates pain sensitivity similarly in young and old animals.

The dark trough in clinical electro-oculography. Influence of preadaptation on amplitudes and latencies.

The influence of four different intensities of the preadapting light on amplitude and implicit time of the dark-induced oscillation (dark trough) of the electro-oculogram was tested in 10 healthy individuals. The amplitude of the dark trough (normalized to preadapting baseline) was found to be dependent on the intensity of the preadapting light (analysis of variance: p < 0.0001). No correlation could be proven between preadapting light intensity and the implicit time of the dark trough (p = 0.299). The confidence intervals of the implicit time of the dark trough exceeded 14 minutes in all four intensity settings. There was no significant dependence of the absolute baseline values on preadapting intensities (p = 0.236).