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PubMed2003

Effect of chronic exposure to methylmercury on eye movements in Cree subjects.

OBJECTIVES: To examine the effect of chronic exposure to methylmercury on eye movements (pursuit, fixation and dynamic saccades) in Cree subjects from Northern Quebec. METHODS: Eye movements were recorded in a group of Cree subjects ( n=36) exposed chronically to methylmercury, a group of patients with Parkinson's disease (PD) ( n=21), and a group of control subjects ( n=30) by use of an infrared eye-movement recording system. Pursuit, fixation, and prompted and remembered saccades were recorded twice for both eyes in the horizontal and vertical axes. Blinks were removed, and data were calibrated. RESULTS: Analyses of variance revealed significant differences for all characteristics examined for fixation and pursuit, and for some characteristics in dynamic saccades. These differences arose sometimes from the Cree group, sometimes from the PD group and sometimes from both groups. CONCLUSIONS: The results suggest that eye movements of Cree subjects exposed to methylmercury are qualitatively different from those of both control subjects and patients with PD. Comparisons between more-exposed and less-exposed Cree subjects matched for age with control subjects also showed significant differences for fixation, pursuit and dynamic saccades. The average scores of the more-exposed group were clearly separated from those of the less-exposed and control groups for characteristics of fixation and pursuit, and for accuracy and sharpness of prompted saccades. This trend was less clear in other results where a possible effect of mercury exposure could not be distinguished from a possible cultural effect. Further studies should focus on the most discriminating characteristics for the Cree group, such as measures of accuracy and coherence in all tests and sharpness of saccades.

Adult↗
PubMed2006

Eye movements and the control of actions in everyday life.

The patterns of eye movement that accompany static activities such as reading have been studied since the early 1900s, but it is only since head-mounted eye trackers became available in the 1980s that it has been possible to study active tasks such as walking, driving, playing ball games and ordinary everyday activities like food preparation. This review examines the ways that vision contributes to the organization of such activities, and in particular how eye movements are used to locate the information needed by the motor system in the execution of each act. Major conclusions are that the eyes are proactive, typically seeking out the information required in the second before each act commences, although occasional 'look ahead' fixations are made to establish the locations of objects for use further into the future. Gaze often moves on before the last act is complete, indicating the presence of an information buffer. Each task has a characteristic but flexible pattern of eye movements that accompanies it, and this pattern is similar between individuals. The eyes rarely visit objects that are irrelevant to the action, and the conspicuity of objects (in terms of low-level image statistics) is much less important than their role in the task. Gaze control may involve movements of eyes, head and trunk, and these are coordinated in a way that allows for both flexibility of movement and stability of gaze. During the learning of a new activity, the eyes first provide feedback on the motor performance, but as this is perfected they provide feed-forward direction, seeking out the next object to be acted upon.

Activities of Daily Living↗
PubMed2001

Closed-loop and open-loop accommodative vergence eye movements.

We examined accommodative vergence eye movements under conditions in which feedback about retinal-image slip was and was not present (i.e. closed-loop and open-loop conditions). We found that (a) in both conditions the two eyes started to move at the same time; (b) in the open-loop condition, vergence continued in both eyes; and (c) in the closed-loop condition, vergence continued in the occluded eye only, and the magnitude and velocity exceeded that of the occluded eye in the open-loop condition by a factor of two.

Accommodation, Ocular↗
PubMed2005

The relationship between eye movement and brain structural abnormalities in patients with schizophrenia and their unaffected relatives.

Schizophrenia is associated with subtle eye movement and brain structural abnormalities, but the extent to which these abnormalities occur in the same individuals is unclear. The relationship between quantitative measures of eye movement task performance (smooth pursuit and antisaccade) and MRI volumetric measurements (whole brain volume, prefrontal region, lateral ventricles, third ventricle, hippocampus, and cerebellum) was assessed in 70 patients with schizophrenia or schizoaffective disorder, 105 of their unaffected first-degree relatives and 68 controls. There was a lack of correlation between eye movement and morphometric abnormalities suggesting largely separable neurobiological pathways underlying the morphological and the eye movement deviations that have previously been identified in these patients. However, in the total sample, smaller prefrontal lobe volume was significantly associated with longer latency of correct antisaccades (partial correlation r=-0.22, p=0.01) in line with previous studies demonstrating the importance of frontal lobe structures in performance of the antisaccade task. Also larger third ventricular volume was associated with larger mean amplitude of intrusive saccades during smooth pursuit (r=0.28, p=0.01). There were no significant between-group differences in the relationship between measures of eye movement and morphometry.

Adolescent↗
PubMed2003

Cortical inhibitory circuits in eye-movement generation.

The role inhibitory circuits play in target selection with saccadic eye movements was examined in area V1, the frontal eye fields (FEF) and the lateral intraparietal sulcus (LIP) of the Rhesus Macaque monkey by making local infusions of the GABA agonist muscimol and antagonist bicuculline. In V1, both agents greatly interfered with target selection and visual discrimination of stimuli placed into the receptive field of the affected neurons. In the FEF, bicuculline facilitated target selection without affecting visual discrimination and generated many spontaneous saccades. Muscimol in the FEF interfered with saccadic eye-movement generation. In the LIP, bicuculline was ineffective and muscimol had only a small effect. These findings suggest that in the FEF GABAergic inhibitory circuits play a central role in eye-movement generation whereas in V1 these circuits are essential for visual analysis. Inhibitory circuits in the LIP do not appear to play a central role in target selection and in visual discrimination.

Anesthetics, Local↗
PubMed1991

Disjunctive eye movement evoked by microstimulation in an extrastriate cortical area of the cat.

Slow disjunctive eye movement similar to ocular convergence was evoked by microstimulation in parts of the lateral suprasylvian area (LSA) in alert cats. A tungsten-in-glass microelectrode was used for stimulation, and eye movement was monitored using the magnetic search coil method. The velocity-versus-amplitude relationship of disjunctive eye movement evoked by microstimulation was comparable to that of ocular convergence evoked by presenting a visual target. It is suggested that the LSA plays a role in controlling convergence eye movement.

Animals↗
PubMed1994

Characteristics of antidromically identified oculomotor internuclear neurons during vergence and versional eye movements.

1. Previous studies have shown that midbrain near response cells that increase their activity during convergent eye movements project to medial rectus motoneurons, which also increase their activity during convergence. Most neurons in the abducens nucleus decrease their firing rate during convergence, and the source of this vergence signal is unknown. Oculomotor internuclear neurons (OINs) in monkeys project primarily from the medial rectus subdivisions of the oculomotor nucleus to the contralateral abducens nucleus, although there is a smaller ipsilateral projection as well. Because of these anatomic connections, it has been suggested that the OIN input may be responsible for the vergence signal seen on abducens neurons. The behavior of the OINs during eye movements and their synaptic drive are not known. Thus the goal of this study is to determine the behavior of these neurons during conjugate and disjunctive eye movements and to determine if these neurons have an excitatory or inhibitory drive on the abducens neurons. 2. Single-unit recording studies in alert rhesus monkeys were used to characterize the behavior of OINs. Eighteen OINs were identified by antidromic activation and collision testing. The recorded OINs displayed a burst-tonic pattern of activity during adducting saccades, and the majority of these cells displayed an increase in tonic activity with convergent eye movements. 3. Identified OINs were compared with a large sample of non-activated and untested horizontal burst-tonic cells in the medial rectus subdivisions of the oculomotor nucleus. The results indicate that the OINs behave similarly to medial rectus motoneurons during vergence and versional eye movements. None of the OINs displayed vertical eye position sensitivity. 4. Microstimulation of the oculomotor nucleus where both the OINs and medial rectus motoneurons were located resulted in a large adducting twitch of the ipsilateral eye and a smaller abducting twitch of the contralateral eye. The latter effect was presumed to be the result of OIN innervation of the contralateral abducens nucleus. This result suggests that the crossed OIN pathway is predominately, if not entirely, excitatory. 5. Injection of 10% lidocaine HCl into the medial rectus subdivision of the oculomotor nucleus caused a reversible inactivation of the medial rectus motoneurons and OINs. As expected, the inactivation of medial rectus motoneurons resulted in an exophoria and weakness of adduction for the eye ipsilateral to the lidocaine injection. In addition, the lidocaine injection resulted in hypometric and slowed abducting saccades in the eye contralateral to the injection site. This result also suggest that the crossed OIN pathway is excitatory.(ABSTRACT TRUNCATED AT 400 WORDS)

Abducens Nerve↗
PubMed1994

[Disorganized eye movements and visuospatial dysfunctions in an early stage of the patients with Alzheimer's disease--the effects of language and visual information processing on constructional performances].

In Alzheimer's disease higher brain function disorders such as geographical disorientation, visual agnosia and constructional disability are frequently observed in addition to the progressive memory loss. Visual information processing was studied through newly developed technology, vision analyzer, since visuospatial functions play an important role in the pathophysiology underlying these neuropsychiatric symptoms and dementia itself. We found characteristic findings as to eye movements of focus indicating visual cognitive disorders. Language or language functions, however, are considered to be essentially involved in visuospatial functions. We examined eye movements of patients suffering from Alzheimer's disease (15 cases), MID (5 cases), Parkinson's disease (5 cases) and 10 control subjects during constructional behavior under various conditions in terms of visual information processing. 1. Alzheimer's disease (n = 15): All patients showed constructional disabilities when copying geometrical figures. 1) Three dimensional drawing was possible following verbal instructions in 7 out of 15 patients. 2) Three dimensional drawing was successful when the model figure to be copied was covered in 4 out of these 7 patients. 3) Three dimensional drawing was possible following verbal instruction in a dark room, although they were not so accurate but better than those when copied in 4 out of 7 patients. 4) The analysis of eye movements revealed that typical eye movements were confirmed during copying geometric figures. The distribution of the gazing points of focus, and the average eye movement velocity distribution were also distinctive. But these disorganized eye movements in description of graphic figures following verbal instruction became more similar to those of healthy controls when compared to those in the copying graphic figures. 2. MID (n = 5), Parkinson disease (n = 5), healthy controls (n = 10): 1) No subject showed constructional disability when copying a graphic figure. They were also capable to describe a graphic figure both in the dark and following verbal instruction. 2) No remarkable change was observed in the distribution of the eye movement, or in the average eye movement velocity on these subjects. 3. These results indicate that in an early stage of the patients with Alzheimer's disease, primary or fundamental disorders seem to lay in the verification process of visual information, which results in the difficulties in categorization process of the visual objects. The categorization process is involved with language function, which was preserved in a certain period at an early stage of the disease.(ABSTRACT TRUNCATED AT 400 WORDS)

Alzheimer Disease↗
PubMed1977

Eye-movement asymmetry and hemispheric function: an examination of individual differences.

The relationship between lateral eye movements and selected individual characteristics was examined in a group of 81 right-handed adult males. Ss answered 20 verbal and 20 visuospatial questions in one of three experimental conditions while their eye movements were being recorded electrically. Multiple regression analyses were used to predict the proportion of eye movements to the right on the basis of spatial and verbal test scores, questionnaire responses concerning imagery and verbal processes, a self-report measure of values and interests, and choice of academic major. No significant relationships were found. Even the most consistent "left movers" and "right movers" did not differ in the manner suggested by a model of eye-movement asymmetry based upon individual differences in cerebral function.

Career Choice↗
PubMed1994

Relationship of eye movement to computed tomographic findings in patients with Graves' ophthalmopathy.

To elucidate the relationship between eye movement and computed tomographic findings, 101 patients with Graves' ophthalmology were studied. Eye movements were scaled 0 to 3 according to movability. Extraocular muscle width and area were calculated from the largest portion of each muscle from the orbital coronal CT sections. Muscle widths were measured manually and muscle areas were calculated by a digitizer. The width and area of each rectus muscle were significantly correlated with limitation of eye movement. The muscle widths and areas were also significantly correlated to each other (r = 0.91 to 0.77, p < 0.001). Limitations of supraduction and abduction from enlargement of the inferior and medial rectus muscles were the most common clinical findings (46.5% and 39.6%, respectively). In conclusion, this study establishes a relationship between limitation of eye movement and extraocular muscle enlargement. Calculation of the width from the largest portion of the muscle manually from orbital coronal section is a simple method for clinical assessment of the severity of extraocular muscle involvement.

Adolescent↗
PubMed1984

Vergence eye movements and visual suppression.

Visual sensitivity was measured during vergence eye movements in order to determine whether a suppression of vision similar to that associated with saccades is also present during vergence. Suppression was evaluated psychophysically by determining sensitivity to briefly presented, full-field decrements of light in a Ganzfeld. Subjects were rougly 0.5 log unit less sensitive when stimuli were presented at the beginning of a 2-3 deg convergent or divergent eye movement, than during steady fixation. Thus, the concept of saccadic suppression must be broadened to include visual suppression that also accompanies nonsaccadic eye movements. These results support the hypothesis that vision is affected by signals that accompany initiation of oculomotor activity.

Electrooculography↗
PubMed1997

Vergence eye movements in response to binocular disparity without depth perception.

Primates use vergence eye movements to align their two eyes on the same object and can correct misalignments by sensing the difference in the positions of the two retinal images of the object (binocular disparity). When large random-dot patterns are viewed dichoptically and small binocular misalignments are suddenly imposed (disparity steps), corrective vergence eye movements are elicited at ultrashort latencies. Here we show that the same steps applied to dense anticorrelated patterns, in which each black dot in one eye is matched to a white dot in the other eye, initiate vergence responses that are very similar, except that they are in the opposite direction. This sensitivity to the disparity of anticorrelated patterns is shared by many disparity-selective neurons in cortical area V1, despite the fact that human subjects fail to perceive depth in such stimuli. These data indicate that the vergence eye movements initiated at ultrashort latencies result solely from locally matched binocular features, and derive their visual input from an early stage of cortical processing before the level at which depth percepts are elaborated.

Convergence, Ocular↗
PubMed1998

Normal reading despite limited eye movements.

Many investigators have demonstrated that poor readers exhibit abnormal eye movements during reading. An association between defective vergence, accommodation, and poor reading skills has also been noted by some investigators. Children who are poor readers have been subjected to therapeutic interventions on the basis of the assumption that improving their eye movements, as part of a multifaceted program of "vision therapy," will yield commensurate improvement in reading performance. This approach has been controversial, and other authors have expressed opposing views. We report the ophthalmologic and reading assessments of two children with Möbius' syndrome who were average to above-average readers despite essentially absent horizontal eye movements.

Adolescent↗
PubMed1992

Smooth-pursuit eye movements: alterations in Alzheimer's disease.

Smooth-pursuit eye movements induced by targets moving at constant velocities (from 5 to 100 deg/sec) were recorded from 13 patients with Alzheimer's disease (AD) and from 11 healthy subjects. Four variables were evaluated to quantify the patients' response to the eye movement tests: (1) average peak velocity of smooth-pursuit; (2) percent target matching index after saccade removal (percent ratio between the area of the velocity curve of smooth-pursuit eye movement after saccade removal and the area of target velocity) which is related to the eye performance for each value of target velocity; (3) total amplitude of anticipatory saccades; (4) total number of anticipatory saccades. Compared to the controls, AD patients were found to have significantly lower values of average peak velocity of smooth pursuit and of percent target matching index and a significantly increased number and amplitude of anticipatory saccades. A discriminant stepwise analysis indicated that 5 oculographic variables were significantly associated with the patient's clinical condition (healthy volunteer or AD patient). These statistics yielded an equation for predicting the patient's status according to which the percentage of cases classified correctly was 82.6% in the overall group (n = 23). The predictive performance was similar between the healthy volunteers subgroup (81.8%, n = 11) and the AD subgroup (83.3%, n = 12). The discriminant score was significantly correlated with the score resulting from the MiniMental test (r = 0.67). A significant correlation was also found between the MiniMental score and the number of anticipatory saccades (r = -0.61). No significant correlation was present between the gain of smooth pursuit and the patients' cognitive decline.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1986

Saccadic eye movements in determination of the residual effects of flunitrazepam.

Saccadic eye movements and the subjective assessments of the volunteers were used in the determination of the residual effects of a single evening dose of flunitrazepam 0.5 mg, 1 mg and 2 mg or placebo. Sleep inducing and maintaining effects were subjectively assessed, too. Flunitrazepam at all three dose levels possessed sleep inducing and increasing effects (n = 9), but in the number of nocturnal awakenings and sedation in the morning (10 hrs after drug intake), no significant differences between placebo and the active medications were reported. However, saccadic eye movement recording could differentiate the residual effects produced by placebo or the active medication. No correlation was detected between the serum levels (radioreceptor assay) and saccadic eye movement recordings.

Adult↗
PubMed1989

Neurological aspects of vergence eye movements.

This review of vergence eye movements emphasizes the importance of performing a more rigorous examination of vergence at the bedside. Furthermore, recent experimental studies have better defined the physiological organization of brain-stem neurons that generate immediate premotor vergence commands. We emphasize analogies with the saccadic system and suggest that there are common organizational features of models for the generation of saccadic and of vergence movements. Finally, using the paradigm of spectacle-corrected anisometropia, we have demonstrated a remarkable adaptive capability that assures proper ocular alignment with changes of gaze.

Animals↗
PubMed1979

Effect of eye movement on perception of flicker.

With 3 experienced subjects CFF during eye movements was higher than that obtained by fixing a line of sight. CFF increased with a moving line of sight. With additional subjects CFF during eye movements was related to various factors such as target size and conditions of eye movement. More thorough study is required.

Adult↗
PubMed1979

Vestibulo-ocular function during co-ordinated head and eye movements to acquire visual targets.

1. Experiments have been conducted on human subjects in an attempt to establish the role of the vestibulo-ocular reflex in the co-ordination of head and eye movements during visual target acquisition. 2. When the subject moved head and eyes to acquire visual targets in the horizontal plane, the eye movement consisted of an initial saccade in the direction of head movement followed by a slower return towards orbital centre which compensated for remaining head movement. 3. When the head was moved either voluntarily or passively in the dark the pattern of eye movement was very similar to that seen during target acquisition. 4. The mean latency between the start of head acceleration and the onset of the saccadic eye movement was greater in the dark (108 msec, S.D. 85 msec) than for the visually induced responses (14 msec, S.D. 59 msec), in which eye movement often preceded head movement when moving to small ( less than 45 degrees) target offset angles. 5. In all experimental conditions gaze displacement at the end of the initial saccade was normally related in a predictive manner to final head position, but when fixating visual targets offset by more than 60 degrees from the central position there were often large errors, 22% of responses undershooting the target by more than 15 degrees. 6. A highly significant (P less than 0.001) linear relationship was found between gaze displacement and head velocity under all experimental conditions. During target acquisition head velocity was normally positively correlated with amplitude of target offset. The large errors in gaze displacement in response to the larger target offsets occurred at levels of head velocity lower than normally associated with such target offsets. 7. The results have led to the suggestion of a dual mode of control for head-eye co-ordination. In one mode, normally associated with small target offsets (less than 45 degrees), control is mediated by retinal error information. In the other mode, associated with larger target offsets, gaze displacement is generated as an automatic response to head turning. 8. The observation of similar relationships between head and eye movement during passive head turning implicates the vestibulo-ocular reflex in the secondary mode of control, and provides support for the hypothesis that the role of the vestibular saccade is to induce a rapid offset of the eyes in the direction of head movement, thus facilitating rapid search and target location.

Eye Movements↗