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At least 775 records · Page 43Linked to original sources
PubMed2003

Neuronal mechanisms for detection of motion in the field of view.

The visual system cannot rely only upon information from the retina to perceive object motion because identical retinal stimulations can be evoked by the movement of objects in the field of view as well as by the movements of retinal images self-evoked by eye movements. We clearly distinguish the two situations, perceiving object motion in the first case and stationarity in the second. The present work deals with the neuronal mechanisms that are likely involved in the detection of real motion. In monkeys, cells that are able to distinguish real from self-induced motion (real-motion cells) are distributed in several cortical areas of the dorsal visual stream. We suggest that the activity of these cells is responsible for motion perception, and hypothesize that these cells are the elements of a cortical network representing an internal map of a stable visual world. Supporting this view are the facts that: (i) the same cortical regions in humans are activated in brain imaging studies during perception of object motion; and (ii) lesions of these same regions produce selective impairments in motion detection, so that patients interpret any retinal image motion as object motion, even when they result from her/his eye movements. Among the areas of the dorsal visual stream rich in real-motion cells, V3A and V6, likely involved in the fast form and motion analyses needed for visual guidance of action, could use real-motion signals to orient the animal's attention towards moving objects, and/or to help grasping them. Areas MT/V5, MST and 7a, known to be involved in the control of pursuit eye movements and in the analysis of visual signals evoked by slow ocular movements, could use real-motion signals to give a proper evaluation of motion during pursuits.

Animals↗
PubMed1994

The otolithic contribution to vertical ocular stability in the cat.

In cats, horizontal (HVOR) and vertical (VVOR) vestibulo-ocular reflexes were studied alone and combined with optokinetic stimulation. The upright VVOR (VVOR O degree) only showed higher gain and smaller phase lead compared to those of HVOR at frequencies below 0.05 Hz. The addition of optokinetic stimulation to the vestibular stimulation increased the gain of the horizontal and vertical ocular responses close to 1. VVOR was also studied in side down position (VVOR 90 degrees). In VVOR 90 degrees the ocular responses were asymmetric. The downward directed eye responses of VVOR 90 degrees showed lower gain and greater phase lead compared to those of VVOR 0 degree for the whole range of tested frequencies (0.01-0.4 Hz), while the upward eye responses only showed a lower gain at the lower range of frequencies tested. In the light the gain of VVOR 90 degrees increased, but the gain of downward directed eye responses was consistently lower than 1 at lower frequencies. The higher gain of the VVOR 0 degree compared to the VVOR 90 degrees and HVOR was attributed to the maculo-ocular reflex (MOR) evoked by the gravity modulation of the otolithic receptors, when the animals were oscillated in the pitch plane. The MOR was isolated from the VVOR 0 degree by plugging all semicircular canals. At very low frequencies the gain of the MOR was 0.3-0.35 and the phase was close to 0 degree. This reflex showed a progressive gain decrease and phase lag by increasing the stimulation frequencies. This suggests a low pass filtering process of the otolithic signal. Furthermore in plugged animals the asymmetry of the vertical optokinetic responses was reduced by adding the MOR. The quick phases (QPs) of the vestibular responses were also different depending upon the stimulation plane. The QPs of VVOR 0 degree were smaller and more delayed than those of HVOR and VVOR 90 degrees. In conclusion the main effects observed during otolithic coactivation in the VVOR 0 of the cat are: 1) the enhancement of gain and reduction of phase lead at low frequency vestibular stimulation, resulting in similar vertical and horizontal gaze stability; 2) the equalization of the upward and downward responses of both vestibulo-ocular and optokinetic responses; 3) the reduction of the amplitude and frequency of vertical quick phases.

Animals↗
PubMedDate not supplied

[EOG findings in patients with multiple sclerosis].

Electroculography (EOG) is useful in the diagnosis of multiple sclerosis (MS), a common disorder. We reviewed the EOG recordings of 192 patients with MS (98 definite, 29 probable, 65 possible diagnoses) to evaluate spontaneous nystagmus, rotation tests, positional tests, vestibulo-ocular reflex visual suppression (VOR), optokinetic nystagmus, saccades and pursuit tracking. The most frequent findings were abnormalities in the pursuit tracking, saccade dysmetria and vestibulo-ocular reflex suppression disorders. Results are discussed and the literature is reviewed.

Adolescent↗
PubMed1994

Factors affecting visual outcome after surgery for bilateral congenital cataracts.

The medical records of 33 patients with dense bilateral congenital cataracts were analyzed for factors affecting visual outcome. The average postoperative follow-up was 6.3 years. Of the 23 patients tested with optotypes (verbal children), 14 had visual acuities of 20/80 or better. Eight patients had binocular vision. Preoperative nystagmus, age at surgery, microphthalmos, and postoperative strabismus were not prognostically significant in visual outcome. Postoperative nystagmus was common and was not indicative of a poor visual outcome. Ocular anomalies, systemic anomalies, and postoperative complications were associated with a lower percentage of good postoperative visual acuities.

Cataract↗
PubMed1985

Bilateral vestibular loss, oscillopsia, and the cervico-ocular reflex.

Oscillopsia during head movement occurs in patients with bilateral vestibular loss and may be transient or persistent. To investigate mechanisms underlying recovery we tested the vestibulo-ocular reflex (VOR), visual-vestibular interaction, and the cervico-ocular reflex (COR); we used a pseudorandom oscillatory stimulus with a frequency band width of 0 to 5 Hz in six patients with bilaterally absent caloric responses and in 10 normal controls. Seven control subjects had low-gain COR responses, but these were anticompensatory with respect to the VOR. Three asymptomatic patients with an absent or grossly deficient VOR had increased oculomotor responses at all frequencies when oscillated in light. Compensatory COR responses were detected in these patients but not in patients with persisting oscillopsia. In some patients with bilateral vestibular loss, augmented cervico-ocular and visual reflexes may compensate, at least partially, for an absent VOR.

Adaptation, Physiological↗
PubMed1987

A survey of electro-oculography.

The vestibulometric examination in the ORL office is done by means of the registration of eye movements of vestibular origin, the electro-nystagmography. With the ENG-equipment one can perform electro-oculography, examining eye movements in general. EOG is quite helpful in neurologic diagnosis and important in ORL practice too. The adjustment of the ENG-equipment to EOG is explained, after some words on the physiology and the clinical examination of ocular motor function. Than a short survey is given of the abnormalities that may be met in EOG.

Electronystagmography↗
PubMed2002

Linearity of canal-otolith interaction during eccentric rotation in humans.

During natural behavior, the head may simultaneously undergo rotation, transduced by the semicircular canals, and translation, transduced by the otolith organs. It has been demonstrated in monkey that the vestibulo-ocular reflexes (VORs) elicited by both endorgans (i.e., the angular and linear VORs, or AVOR and LVOR) sum linearly during combined rotation and translation, but this finding has proven more elusive in humans. To investigate the combined AVOR/LVOR response, six human subjects underwent yaw eccentric rotation at 3 Hz in darkness while displaced from the axis of rotation. Responses to on-center yaw rotation (AVOR alone) and interaural translation (LVOR alone) were also recorded. During eccentric rotation with the subject facing away from the axis of rotation (i.e., nose out), in which a yaw to the right occurs simultaneously with a translation to the right (i.e., translation in phase with rotation), the AVOR and LVOR acted synergistically. Responses were always out of phase with rotation, and became larger in magnitude as vergence increased. For nose-in eccentric rotation, during which translation is out of phase with rotation, the LVOR acted antagonistically to the AVOR. During near viewing, the LVOR often dominated the overall response when eccentricity was sufficiently large, producing eye movements that were in phase with the rotational stimuli. As vergence decreased, the LVOR influence diminished, eventually resulting in responses that were out of phase with rotation at lowest vergence. When the response to pure yaw rotation was vectorially removed from the responses to eccentric rotation, the results proved statistically indistinguishable from the LVOR recorded during interaural translation, suggesting that the ocular response to combined angular and linear motion reflects the linear combination of the AVOR and LVOR.

Adult↗
PubMed1989

Morphometric analysis of T lymphocyte compartmentation in experimental autoimmune uveoretinitis.

Experimental autoimmune uveoretinitis (EAU) in the Lewis rat is characterized by extensive infiltration of inflammatory cells into all compartments of the eye, only some of which become irreversibly damaged. The apparent differences in the pathogenic impact of inflammatory cells within different ocular compartments may suggest that different mechanisms underlie cellular infiltration and selective tissue destruction. In order to investigate the importance of T lymphocyte infiltration, we carried out a precise topographical and temporal analysis of T cell infiltration into five compartments of the eye using an improved method for the fixation of ocular tissue. Our study showed that T cell infiltration began in the ciliary body and was most numerous and sustained in this area during EAU. The peak of T cell infiltration into the retina was comparatively delayed and was of lesser magnitude. Analysis of T cell subsets revealed a tendency for the helper phenotype to predominant during the course of disease in all ocular compartments except the retina where both helper and cytotoxic/suppressor T cells were equally represented at the height of inflammation. We suggest that the pathogenetic impact of autoreactive lymphocytes in EAU depends on the accessibility of relevant tissue antigen and on local microenvironmental features of lymphocytic traffic within different ocular compartments.

Animals↗
PubMed1994

[Superior oblique muscle paralysis and ocular torsion. What is the effect of measuring method on the results?].

BACKGROUND: The rotation of the eye-ball around Fick's Y-axis is called ocular torsion. A precise measurement of the torsional deviation can be clinically as critical in the diagnosis of some complex strabological disorders as in the assessment of some systemic diseases. MATERIALS AND METHODS: We measured the ocular torsion under binocular conditions by five measurement devices on 50 patients with superior oblique palsy. The comparison of the devices was performed using rank tests (Friedman, Wilcoxon signed rank). RESULTS: The 5 methods of measurement do not produce equivalent results. These findings confirm on a population of paretic patients similar published results obtained with healthy subjects. CONCLUSIONS: The simple Maddox rod and the synoptophore are among the most widely used methods to measure cyclotropia; this study reveals that these devices are the least reliable. Harm's tangent scale gives the most reliable results, in all directions of gaze; however, in inferior adduction, the synoptometer also yields a satisfactory measure of ocular torsion. In primary position, the double Maddox glass appears to be the most suitable instrument.

Adolescent↗
PubMed1987

Eye movements in schizophrenia.

Smooth pursuit and other eye movements were quantitatively studied in patients with chronic schizophrenia to characterize the pattern and severity of eye movement abnormalities in this disorder. Twenty-one patients with schizophrenia, 13 patients with other psychiatric disorders (manic-depressive psychosis, schizoaffective disorder, depression and obsessive-compulsive disorder), and 19 normal subjects were studied. Horizontal eye movements were recorded with DC electro-oculography and analyzed by an online computer system. Eye velocity and closed-loop gain of pursuit, optokinetic nystagmus (OKN), vestibulo-ocular response (VOR) and visual-vestibular interactions were calculated. The latency, accuracy and peak velocity-amplitude relationships of voluntary saccades were measured. The group mean gains of pursuit and OKN of the schizophrenic patients were significantly lower than those of the normal subjects. Suppression of the VOR by fixation was impaired, and the latency of saccades was prolonged. However, the differences in group mean values were small in magnitude, and the frequencies of outliers among the schizophrenic patients were low. The patients with other psychiatric disorders had a similar pattern and severity of eye movement abnormalities. The frequency and severity of eye movement abnormalities in schizophrenic patients are lower than those indicated by previous studies that used different techniques of analysis.

Adolescent↗
PubMed1986

Long-term analysis of pigmentary dispersion syndrome and pigmentary glaucoma.

A retrospective, longitudinal study of 129 eyes in 65 patients with pigmentary dispersion syndrome and either ocular hypertension of glaucoma was undertaken. The mean follow-up period was 17 years (range, 5-35 years). Visual acuity, intraocular pressure (IOP), visual field loss, pigment grade, Krukenberg spindle, iris transillumination, medications, and surgeries were analyzed for each patient at 5-year intervals from 1960 through 1983. Disc and field changes developed in 35% of patients with pigment dispersion syndrome and ocular hypertension during the study period. The long-term prognosis of the medical and surgical management of pigmentary glaucoma is discussed.

Adult↗
PubMed1980

Corresponding and disparate retinal points in normal and anomalous correspondence.

Fusional (disparity) vergence requires that the ocular images fall on noncorresponding (disparate) retinal points. Study of the distribution of corresponding retinal points is accomplished by analyzing the locus of object points in space that are seen either singly or in the same direction for each eye. This locus, a horopter, is easily determined for persons with binocular fixation but requires a special tangent plane apparatus (which is described) for persons with strabismus. The identical visual direction horopter for the intermittent exotrope under conditions of bifixation passes through the fixation point and curves sharply toward the eyes, a phenomenon that may produce disparity conflicts between the central and peripheral fields. For squinters with normal anomalous correspondence (where the two foveas correspond), the horopter passes through the intersection of the visual axes, for squinters with anomalous correspondence, it does not; instead, it courses through the space between the visual axes, which indicates correspondence between opposite occipital hemispheres. Additionally, these horopters exhibit a localized central convexity toward the eyes (a notch) that implies correspondence being less anomalous centrally than peripherally. In validating the presence of this horopter notch, a three-light test was developed. Irregular fusional vergence movements of squinters may be attributed in part to their irregular horopters.

Esotropia↗
PubMed2003

Human discrimination of visual direction of motion with and without smooth pursuit eye movements.

It has long been known that ocular pursuit of a moving target has a major influence on its perceived speed (Aubert, 1886; Fleischl, 1882). However, little is known about the effect of smooth pursuit on the perception of target direction. Here we compare the precision of human visual-direction judgments under two oculomotor conditions (pursuit vs. fixation). We also examine the impact of stimulus duration (200 ms vs. ~800 ms) and absolute direction (cardinal vs. oblique). Our main finding is that direction discrimination thresholds in the fixation and pursuit conditions are indistinguishable. Furthermore, the two oculomotor conditions showed oblique effects of similar magnitudes. These data suggest that the neural direction signals supporting perception are the same with or without pursuit, despite remarkably different retinal stimulation. During fixation, the stimulus information is restricted to large, purely peripheral retinal motion, while during steady-state pursuit, the stimulus information consists of small, unreliable foveal retinal motion and a large efference-copy signal. A parsimonious explanation of our findings is that the signal limiting the precision of direction judgments is a neural estimate of target motion in head-centered (or world-centered) coordinates (i.e., a combined retinal and eye motion signal) as found in the medial superior temporal area (MST), and not simply an estimate of retinal motion as found in the middle temporal area (MT).

Discriminant Analysis↗
PubMed1991

Effect of alcohol on VOR compensation after unilateral labyrinthine loss.

It has been reported that alcohol ingestion reduces cerebellar control of the vestibulo-ocular reflex (VOR). To investigate the compensatory processes following labyrinthine loss, we examined gaze function and VOR before and after alcohol ingestion in 10 patients with unilateral lesion. The subjects were rotated sinusoidally in an electrically driven chair under two different visual conditions, i.e., mental arithmetic in the dark, and gaze fixation on a target on the wall. Whereas a control group (17 normal adults) showed no significant change after alcohol ingestion, patients showed a greater difference in gain between rotation to the intact side and affected side under the two conditions. The present study suggested significant cerebellar control of VOR and gaze function during recovery from unilateral labyrinthine dysfunction.

Adult↗
PubMed2000

Long-term optical imaging and spectroscopy reveal mechanisms underlying the intrinsic signal and stability of cortical maps in V1 of behaving monkeys.

Explorations of learning and memory, other long-term plastic changes, and additional cognitive functions in the behaving primate brain would greatly benefit from the ability to image the functional architecture within the same patch of cortex, at the columnar level, for a long period of time. We developed methods for long-term optical imaging based on intrinsic signals and repeatedly visualized the same functional domains in behaving macaque cortex for a period extending over 1 year. Using optical imaging and imaging spectroscopy, we first explored the relationship between electrical activity and hemodynamic events in the awake behaving primate and compared it with anesthetized preparations. We found that, whereas the amplitude of the intrinsic signal was much larger in the awake animal, its temporal pattern was similar to that observed in the anesthetized animals. In both groups, deoxyhemoglobin concentration reached a peak 2-3 sec after stimulus onset. Furthermore, the early activity-dependent increase in deoxyhemoglobin concentration (the "initial dip") was far more tightly colocalized with electrical activity than the delayed increase in oxyhemoglobin concentration, known to be associated with an increase in blood flow. The implications of these results for improvement of the spatial resolution of blood oxygenation level-dependent functional magnetic resonance imaging are discussed. After the characterization of the intrinsic signal in the behaving primate, we used this new imaging method to explore the stability of cortical maps in the macaque primary visual cortex. Functional maps of orientation and ocular dominance columns were found to be stable for a period longer than 1 year.

Anesthesia↗
PubMed1982

Monocular vertical oscillations of amblyopia. The Heimann-Bielschowsky phenomenon.

The Heimann-Bielschowsky phenomenon is an unusual ocular motility pattern which may develop years following uniocular visual loss and may be mistaken as a neuro-ophthalmologic sign pointing to a posterior fossa or brain stem lesion. It consists of strictly monocular coarse, pendular vertical oscillations occurring only in the amblyopic eye. It is noted primarily with distance fixation and is inhibited by convergence or fixation. The oscillations vary between 1-5 cycles/second, and amplitude, often only 2-5 degrees, may be quite large, up to 20-30 degrees (40-60 prism diopters). A faden operation improved the disorder in one patient. The importance of recognizing this characteristic motility pattern is emphasized to ophthalmologists and neurologists.

Adolescent↗
PubMedDate not supplied

Development of normal ocular alignment.

Ocular alignment was examined in a large population of normal infants to determine the prevalence of various motility findings at ages ranging from birth to 10 months. Exodeviations were frequently seen up to the age of 6 months. Esodeviations were occasionally seen in infants who did not go on to develop congenital esotropia, but not after 2 months of age. It is unclear whether precursors of pathologic strabismus, such as congenital esotropia, can be distinguished from these transient ocular deviations seen in normal infants. However, any strabismus persisting after the ages listed above should be considered abnormal and receive ophthalmologic evaluation.

Age Factors↗
PubMed1990

[Stabilization of the gaze in chameleons: visual and vestibular reflexes].

Some visual, vestibular and proprioceptive reflexes which contribute to gaze (head + eye) stabilization were quantified in the chameleon. All the reflexes were analysed in the horizontal plane, and the visual reflexes were also studied in the vertical plane. In restrained-head animals, both the optokinetic nystagmus (OKN) and the vestibulo-ocular reflex (VOR) had low gains. In free-head animals, the head (opto-collic or vestibulo-collic reflex) and eye (OKN or VOR) responses added their effects, thus improving gaze stabilization, especially during vestibular stimulation. Cervical stimulation provoked both a cervico-ocular reflex (COR) in the compensatory direction and a large number of saccades. The saccadic response was especially marked in the presence of patterned visual surroundings.

Animals↗