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To determine the response of human optic nerve head (ONH) blood flow (delta F) to heterochromatic equiluminant flicker modulation (eql-fl) and compare it to the response induced by pure luminance flicker (l-fl).In 5 normal volunteers the ONH blood flow was measured by conventional laser Doppler flowmetry. Stimuli were generated by green and red light emitting diodes and delivered to the eye through a fundus camera illumination optic. Both green and red illuminances were square wave modulated in counter phase at different frequencies between 2 and 40 Hz. delta F was defined as the ratio between the ONH blood flow after 1 min stimulation and a baseline blood flow measured prior to the stimulation.In response to a 2 Hz eql-fl, ONH blood flow increases by 36% in average. delta F versus flicker frequency displayed the characteristics of a low-pass function with a cutoff frequency of 10 Hz for an eql-fl and a band-pass function with broad maximum around 10 Hz for the I-fl.delta F in human ONH can be evoked by heterochromatic equiluminant flicker modulation. The blood flow frequency response to eql-fl and I-fl are similar to the neural activity dominated by the Parvo- and Magno-cellular activity, respectively. These findings offer a new approach to study the neurovascular coupling at the ONH in both physiological and diseased conditions involving predominantly or selectively the Magno- and Parvo-pathways.

To study hemodynamics in the optic nerve head (ONH) in animals and humans using laser Doppler flowmetry (LDF) during physiological stimuli such as flicker light stimulation, variations of the breathing gas (O(2)) concentration, and systemic mean perfusion pressure (PP(m)) variations.LDF is based on the Doppler effect according to which the frequency of the light scattered by a moving particle (i.e., red blood cells in the vessels) is shifted in frequency compared to that of the incident light. The laser light scattered from the tissue and the red blood cells (RBCs) is collected by an optical fiber and fed to photodetector. NeXT computer analysis provides relative measurements of the Vel(ONH) which expresses the mean velocity of the RBCs, the Vol(ONH) representing the number of RBCs and the F(ONH) an expression of the flux of RBCs in the volume sampled by the laser. Modifications of the LDF parameters during physiological stimuli such as modifications of breathing gas (O(2), CO(2)), flicker light stimulation, and variations in the perfusion pressure were studied.The results of these studies demonstrated for the first time a dynamic coupling of blood flow to function and metabolism in the ONH, mediated by an increase in potassium and nitric oxide release. In addition the results of these studies showed that the ONH blood remains constant during variations of the perfusion pressure (PP(m)) induced by an increase in the intraocular pressure or an increase of the systemic blood pressure by isometric exercise. These results confirm an autoregulation in the ONH blood flow in animals and humans.LDF is a powerful technique for investigating changes in blood flow in the ONH of anesthetized animals and humans, induced by physiological stimuli involving the breathing of various gases, neuronal stimulation, and variations in the perfusion pressure. This highly sensitive and reproducible technique opens new avenues in the elucidation of blood flow regulation mechanisms in the ONH.

Previous studies have demonstrated, in the cat, a vasodilatation of retinal vessels in response to neuronal activity induced by diffuse luminance flicker. The aim of this study was to determine whether a similar diameter variation is detectable in humans.Nine normal subjects were exposed to 1 min of sinusoidally varying diffuse luminance flicker (10 Hz, 30 degrees around optic nerve head). Monochromatic fundus pictures before and after the stimulation were taken. The diameter of retinal arteries and veins was measured on the digitised photographs with the NIH-Image software and an own algorythm.The diameter immediately after flicker was significantly larger than the pre-stimulus diameter by 4.2 +/- 2.2% (p0.014) (mean +/- SD) for the retinal arteries and 2.7 +/- 1.7% (p0.001) for the retinal veins. Six seconds after cessation of the flicker, arterial diameter was not significantly different from that of pre-flicker value.Diffuse luminance flicker induces an increase in retinal vessel diameter. This suggest that retinal blood flow is coupled with neuronal activity as previously evidenced by the blue field simulation technique in the macula.

NO is a nonpolar gas, which diffuses across cell membranes in an isotropic fashion. In relatively large arteries NO has been identified as the endothelium-derived releasing factor and the current hypothesis is that NO controls the vascular tone. We are investigating an alternative hypothesis proposing that the retinal tissues surrounding the arterioles contribute in the process of NO production.We performed flicker light stimulation in anesthetized minipigs (hypnodyl 100 mg/hr, tubocurarine 0.1 mg/hr und N2O) in steady-state of normoxia-normocapnia. An NO-microprobe mounted on a micromanipulator was introduced into the eye through the pars plana and positioned on the preretinal space in a zone free of visible vessels. Preretinal NO gradient and recording of NO release variations in response to flicker light stimulation were performed so as periarteriolar microinjections of nitro-L-arginine.When advancing the NO-probe from the vitreous towards the retina we recorded an NO-gradient corresponding to an efflux of 7.1 pMol x min-1 x cm-2 (N = 9). With the microprobe positioned close to the retina and after 60 min dark adaptation we recorded a mean increase in NO release of 1.59 muMol +/- 0.13 SE. After periarteriolar microinjection of nitro-Larginine we recorded a transitory reversible vasoconstriction.These results indicate that a process occurring in the extravascular tissue of the retina modulates the production of NO and that constitutional NO release by the retina is a major determinant of the basal retinal arteriolar tone.

In this review the authors propose to study the impact of antidepressants on attention, memory and motor functions in healthy volunteers and depressed patients on single and long-term administration. After reviewing the principal cognitive functions, we examine the actual investigation means to conclude that the Critical Flicker Fusion Test (CFFT) is one of the most drug-sensitive tests. It permits a categorization in: sedative antidepressants that in single administration lower CFFT; compounds with no effect on CFFT and no deleterious cognitive effect; and finally substances that raise CFFT and may have psychostimulating properties. On single administration amitriptyline is the most sedative antidepressant on attention or motor level. It seems to produce negative effects on memory level. However, experimental trials give contradictory results. Imipramine in single administration also has sedative effects on memory and car driving capacity. However divergent results of experimental trials do not allow any conclusions of a clearcut negative cognitive effect. Memory impairments with imipramine appear at administration levels of 150 mg. Mianserin has a sedative impact on attention and motor level at low doses (10 mg). Among the tricyclics, nortriptyline has a highly dose dependent sedative effect that has been shown on attention tests (Time Reaction:TR, Digit Symbol Substitution Test: DSST). Among non-tricyclic compounds, doxepine lowers attention and motor performances. Maprotiline (75 mg) lowers CFFT and has a dose dependent effect. Trazodone also has a negative impact on attention tests. Finally viloxazine lowers CFFT but does not impair other attention or motor tests on a 100 mg doses. Buspirone, lofepramine, midalcipran and zimelidine are antidepressants with no effect on CFFT and do not have any positive or negative cognitive effect. On the other hand nomifensine, paroxetine and fluoxetine raise CFFT in healthy volunteers on single administration. Improvement of CFFT performances was found in an isolated manner for nomifensine and paroxetine on 30 mg doses with no other memory or motor effects. MAO-Inhibitors do not impair attention or motor function; thus moclobemide has no negative impact on memory, attention or car driving tests. Cognitive impact of antidepressants in depressive patients seems the same with those of healthy volunteers on single administration. In long-term administration antidepressants have different effects in healthy and depressed subjects. In healthy volunteers cognitive effects of most compounds are normalized after the second week of treatment. However, attention and motor performances with amitriptyline are normalized after 3 weeks of treatment. Sedative motor or cognitive effects of imipramine do not exceed 8 days.(ABSTRACT TRUNCATED AT 400 WORDS)

The authors reported their results of flicker visual field in ganzfeld and 17 central points with 3, 8, 15 and 35 Hertz flicker. They tested 4 groups of control subjects and 12 patients with glaucoma. The flicker visual field may be a useful aid in determining campimetric abnormalities for glaucoma patients with normal static perimetry.

In this paper, the authors present the results of Flicker stimulation therapy in functional visual deficits secondary to occipital cortex lesions of miscellaneous origins. They formulate the hypothesis that the functional response obtained is subordinate to a variation or an integration of the macular cortical representation seat. Four cases were examined and the results obtained are significant.

An ocular trauma may be followed only by a decrease in visual acuity without any tissular alteration. The measurement of the flicker sensitivity permits to hypothesize that the origin of the disturbance is in the retina itself. We postulate, therefore, the existence of a trauma of the lateral inhibition and we propose the term contusive intraretinal syndrome.

This study compares and verifies the efficiency of two functional tests based on intermittent light stimulation. One is the De Lange curve, the other flicker E.R.G. recorded in defined photopic conditions and analysed with different methods. The studied cases belong to a reference group and other groups including foveolar lesions, parifoveolar and diffuse retinopathy, ethambutol and quinoline derivative retinal intoxication. The results show that both objective and subjective methods are sensitive and show some parallelism : both methods aid in distinguishing between foveolar and perifoveolar involvements; a possible comparison between the two tests is also possible.

As far back as the second century, Ptolemy reported the apparent immobility of wheel radius at a certain speed. The psychophysical laws of this flicker fusion phenomenon related to the frequency of the light stimulus were established in 1834-1835 by the Englishman Talbot and by the Belgian Plateau, whose thesis in Liège is described as a landmark in the field. CFF is more a measurement of cortical arousal than of visual functions. In psychophysiology, CFF underwent periods of success and oblivion, at the mercy of researcher's enthusiasm or disappointment. At the turn of this century, Pierre Janet measured CFF in the laboratory of physiology of the Salpêtrière Hospital and demonstrated its decrease 'in hysteria, in states of depression, of lowered tension'. All reviewers of CFF literature have overlooked these observations, reported by Henri Piéron in the 'Melanges dedicated to Monsieur Pierre Janet'. When CFF falls into disgrace, it is because of the variability of its results, due to differences in apparatus and designs of the trials as well as the great number and the intrication of the variables which modify CFF thresholds, among them the nonsensory variables. When CFF is reappraised, as it has been the case in psychopharmacology in recent years, the reason is that it represents a brief, easy and economical measure of vigilance which, under certain conditions, seems to be also reliable, valid and sensitive. In the present monograph, the first in French on CFF, the authors try to analyze the most important contributions of the literature from the standpoint of the most relevant variables: characteristics of the stimulus (light intensity, wave form, wavelength, light-dark-ratio, diameter of the flickering point), test procedure (light vs. dark adaptation, visual angle, continuous vs. discontinuous presentation, monocular vs. binocular vision), influence of various physiological or psychological conditions (pupillary diameter, age, training, IQ; anxiety, depression, motivation etc.). The authors summarize the prerequisite for CFF to measure vigilance or aging in psychopharmacological research. The present Monograph is dedicated to the authors' 'Maîtres', who recently became Emeritus Professors, namely the ophthalmologist Roger Weekers, the pioneer of the clinical application of CFF in Belgium, and the psychiatrist Jean Bobon, who pioneered clinical psychopharmacology in Belgium.

Short comparison between psychophysic and electrodiagnostic tests in 20 eyes with macular edema from diabetic retinopathy. De Lange's curve, the critical flicker frequency in central fixation and the macular ERG are compared with the classical EOG and global ERG data. The methodology is briefly described. It allows a new approach of the macula and the macular ERG responses confirms the clinical tests.

Two methods with their instruments are presented. First the measurement of C.F.F. in modified Goldmann perimeter. Secondly the register of the trimodal curve. The term "flicker acuity" is proposed with its mathematical translation. The second method concerns an original papillophotometer which can perhaps explore the color vision mechanism.

The purpose of this study was to find out a simple perceptual visual test that gives the possibility to detect the visual incidence of slight variations of the vitamin A blood rate. The visual function was tested in 30 young subjects without refraction problems at the same time as blood concentration of vitamin A was measured. Visual tests comprised visual acuity at high and low luminance level, contrast sensitivity, glare sensitivity as well as attenuation characteristics of the eye toward flickering stimuli. Among all these tests, only the flicker test showed some relation with the plasma vitamin A levels, which were situated between 35 and 75 mcg/100 ml.

A variety of cells are involved in the pathogenesis of amblyopia : ON, OFF, ON-OFF cells, postsynaptic cells, neurons of striate cortex and the select interest of the macula. The need for stimulation of these cells in treating amblyopia forms the theoretical basis of the Flicker stimulator with red monochromatic light (LED, 655 nm). The authors present a clinical investigation on 35 subjects with anisometropic or strabismic amblyopia, before extensive treatment with classic anti-amblyopic techniques without satisfactory improvement obtaining significant statistical results (p less than 0,001).