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At least 307 records · Page 17Linked to original sources
PubMed1977

Neuro-optometry: an evolving specialty clinic.

Neuro-optometry is evolving as an optometric clinical specialty focusing on neurological dysfunctions of the visual system. Initially, we focused upon abnormalities of ocular movements, and our investigations have now broadened to include static and dynamic measurements of eye movements, accommodation, and the pupil. We feel the clinic serves three fundamental purposes: (1) to provide service to the patient, (2) to perform clinical research, and (3) to broaden the scope of the students' clinical experience. Operation of the clinic, technical methods of measurement, the testing protocol, and examples of interesting clinical recordings are described.

Accommodation, Ocular↗
PubMed1991

Selective impairment of smooth-pursuit eye movements due to an ischemic lesion of the basal pons.

Voluntary and reflex-like eye movements were measured in a patient with an ischemic lesion of the right basal pons. Ipsilateral smooth-pursuit eye movements were predominantly impaired and interrupted by saccades. This profound smooth-pursuit deficit contrasted with only minor abnormalities of visually guided saccades and the vestibulo-ocular reflex. A selective disturbance of smooth-pursuit eye movements due to a lesion of the basal pons in this patient concurs with recent work in monkeys suggesting that smooth-pursuit eye movements are mediated by a parietooccipito-ponto-cerebellar pathway.

Brain Ischemia↗
PubMedDate not supplied

Eye movements can control localized image enhancement and analysis.

The eye movements of a reader during interpretation of digital chest radiographs can provide valuable information for lesion detection. Measures of eye movements (e.g., the locations and durations of gaze dwells) are associated with detection accuracy. During image interpretation, the reader's eye movements are tracked unobtrusively with a video camera mounted below the monitor displaying the images. The eye movement information is used to identify regions of prolonged dwell, which are associated with false-positive detection of pulmonary nodules. Based on the locations of the dwell regions, a small, circular region of interest is created within the image. Real-time digital processing can then be performed within this region of interest. Such processing can be performed as the reader is looking at the image or after the image has been interpreted. Readers' eye movements can be used to direct localized image enhancement and analysis during interpretation of digital chest radiographs.

Eye Movements↗
PubMed2003

Retinal slip during active head motion and stimulus motion.

Gaze control in various conditions is important, since retinal slip deteriorates the perception of 3-D shape of visual stimuli. Several studies have shown that visual perception of 3-D shape is better for actively moving observers than for passive observers watching a moving object. However, it is not clear to what extent the improved percept of 3-D shape for active observers has to be attributed to corollary discharges to higher visual centers or whether the improved percept might be due to improved gaze stabilization during active head movements. The aim of this study was to measure binocular eye movements and to make a quantitative comparison of retinal slip for subjects instructed to fixate a visual stimulus in an active condition (subject makes an active head movement, object is stationary) and in a passive condition (the stimulus moves, the subject is stationary) for various movement frequencies, viewing distances, and stimulus diameters. Retinal slip remains below the "acuity threshold" of about 4 deg/s in active conditions, except for the highest frequency tested in this study (1.5 Hz) for nearby targets (0.25 cm). Retinal slip exceeds this threshold for most passive conditions. These results suggest that the enhanced performance in the visual perception of 3-D shape during active head movements can, at least partly, be explained by better fixation by actively moving observers.

Adult↗
PubMed2001

Interaction of the body, head, and eyes during walking and turning.

Body, head, and eye movements were measured in five subjects during straight walking and while turning corners. The purpose was to determine how well the head and eyes followed the linear trajectory of the body in space and whether head orientation followed changes in the gravito-inertial acceleration vector (GIA). Head and body movements were measured with a video-based motion analysis system and horizontal, vertical, and torsional eye movements with video-oculography. During straight walking, there was lateral body motion at the stride frequency, which was at half the frequency of stepping. The GIA oscillated about the direction of heading, according to the acceleration and deceleration associated with heel strike and toe flexion, and the body yawed in concert with stepping. Despite the linear and rotatory motions of the head and body, the head pointed along the forward motion of the body during straight walking. The head pitch/roll component appeared to compensate for vertical and horizontal acceleration of the head rather than orienting to the tilt of the GIA or anticipating it. When turning corners, subjects walked on a 50-cm radius over two steps or on a 200-cm radius in five to seven steps. Maximum centripetal accelerations in sharp turns were ca.0.4 g, which tilted the GIA ca.21 degrees with regard to the heading. This was anticipated by a roll tilt of the head of up to 8 degrees. The eyes rolled 1-1.5 degrees and moved down into the direction of linear acceleration during the tilts of the GIA. Yaw head deviations moved smoothly through the turn, anticipating the shift in lateral body trajectory by as much as 25 degrees. The trunk did not anticipate the change in trajectory. Thus, in contrast to straight walking, the tilt axes of the head and the GIA tended to align during turns. Gaze was stable in space during the slow phases and jumped forward in saccades along the trajectory, leading it by larger angles when the angular velocity of turning was greater. The anticipatory roll head movements during turning are likely to be utilized to overcome inertial forces that would destabilize balance during turning. The data show that compensatory eye, head, and body movements stabilize gaze during straight walking, while orienting mechanisms direct the eyes, head, and body to tilts of the GIA in space during turning.

Acceleration↗
PubMed1997

Medical treatments for abnormal eye movements: pharmacological, optical and immunological strategies.

PURPOSE: To review current medical treatments for nystagmus and saccadic intrusions, and their visual consequences. METHODS: Evaluation of studies that have used reliable measurement of eye movements and visual acuity before and after treatment. Interpretation of results in light of physiological and pharmacological studies in animals, and recent immunological advances. RESULTS: There are many case reports of patients with abnormal eye movements being improved by a variety of drugs, but few double-blind, controlled studies have been carried out. Most promising are agents that mediate their effects through the neurotransmitter gamma-aminobutyric acid; such drugs include baclofen and gabapentin. Botulinum toxin, injected into selected extraocular muscles or the retrobulbar space, can abolish nystagmus for several months, but often produces troublesome side-effects, such as diplopia and ptosis, which limit its value. Optical measures to either reduce nystagmus by manipulating vergence angle, or reduce retinal image motion, help some patients. Opsoclonus occurring in association with cancer may be successfully treated with an immuno-adsorption technique using a protein A column. CONCLUSIONS: There is need for controlled, blinded studies to evaluate the many agents reported to improve visual symptoms in individual patients with abnormal eye movements.

Animals↗
PubMed1982

Identification of abnormal patterns in eye movements of schizophrenic patients.

Using precise infrared recording instrumentation, we measured the eye-movement patterns in six schizophrenic patients who were taking medication and found saccadic intrusions and saccadic smooth-pursuit tracking in three. This defined some of the eye-movement irregularities reported previously by many investigators. A variety of eye-movement functions in addition to smooth pursuit exhibited these abnormalities, including fixation, vergence, and head-eye pursuit. Saccadic intrusions or saccadic pursuit also occurs in a number of neuro-ophthalmologic disorders, and occasionally in healthy normal subjects. Thus, these eye-movement abnormalities do not occur exclusively in schizophrenia.

Adult↗
PubMed2000

Interactions between first- and second-order motion revealed by optokinetic nystagmus.

A previous study has suggested that second-order motion is ineffective at driving optokinetic nystagmus (OKN) when presented alone. First- and second-order motion cues interact in creating the perception of motion. Is there an interaction between first- and second-order cues in the control of eye movements? We presented combinations of first- and second-order cues moving in the same or opposite directions and measured the eye movements evoked, to look for a modification of the oculomotor response to first-order motion by simultaneously presented second-order cues. Dynamic random noise was used as a carrier for first- and second-order drifting gratings (13.4 degrees/s; 0.25 cycles/degree; 64 x 48 degrees screen viewed at 28.5 cm). Second-order gratings were defined by spatial modulation of the luminance flicker frequency of noise pixels of constant contrast (50%). A first-order, luminance-defined grating (13.4 degrees/s; 0.25 cycles/degree; variable contrast from 4-50%) was moved in either the same or the opposite direction. Eye movements were recorded by video-oculography from six subjects as they looked straight ahead. The gain (eye velocity/stimulus velocity) of first-order-evoked OKN increased with contrast. The presence of flicker-defined second-order motion in the opposite direction attenuated this OKN below a first-order contrast of 15%, although it had little effect at higher contrasts. When first- and second-order motion were in the same direction, there was an enhancement of the OKN response. We conclude that second-order motion can modify the optokinetic response to simultaneously presented first-order motion.

Contrast Sensitivity↗
PubMed1986

Vertical visual-vestibular interaction in normal human subjects.

Previous studies have described asymmetrical vertical eye movements when normal human subjects were rotated about a vertical inter-aural axis (with head rolled 90 degrees). We measured vertical eye movements induced by visual, vestibular and visual-vestibular stimuli with a magnetic scleral search coil technique while 10 normal subjects sat upright in a chair designed to rotate about the horizontal inter-aural axis at frequencies and amplitudes of natural head movements. Asymmetries in the gain of upward and downward pursuit and fixation-suppression of the VOR were found in individual subjects. However, there was no significant difference (p greater than 0.05) between the mean gain of up and down slow eye movements induced by vestibular, visual or visual-vestibular stimulation in the group of normal subjects. Systematic up-down asymmetries in vertical eye movements previously observed with testing about the vertical inter-aural axis were probably due to bias introduced by otolith stimulation and/or electro-oculographic eyelid artifact.

Adult↗
PubMed1977

Cerebellar role in smooth pursuit movement.

It is generally believed that pursuit eye movements are unaffected by cerebellar cortical atrophy or cerebellectomy. The present study was performed on patients who underwent partial vermis and hemisphere ablations as a result of severe cranial injury or cerebellar tumors. Eye movements were measured by DC electro-oculography. A clear disparity of the slow phase of the optokinetic nystagmus was observed. When eye movements were contralateral to the ablated side the slow phase of optokinetic nystagmus was statistically slower than drum or visual field velocity. It is suggested that the cerebellum network is involved in the mechanisms of the smooth pursuit movement.

Brain↗
PubMed1993

Eye movement control during reading: fixation measures reflect foveal but not parafoveal processing difficulty.

The main purpose of this study was to determine whether, during natural reading, the difficulty of the upcoming parafoveal word affects eye movement behaviour on the currently fixated word. A model in which visual attention is allocated in parallel over both the fixated and the upcoming parafoveal word predicts such as effect, while a sequential attention allocation model in which attention is directed first to the fixated word and then to the upcoming parafoveal word, does not. The data reported here show that neither the frequency nor the combined length, frequency and class of the upcoming word affect eye movement behaviour on the current word. These data support the sequential attention--parallel programming model of eye movement control in reading.

Adult↗
PubMed1984

Signals in vestibular nucleus mediating vertical eye movements in the monkey.

The action potentials of single neurons were recorded extracellularly throughout the rostral vestibular nuclei and subadjacent reticular formation in three alert, juvenile, rhesus monkeys. Neuronal responses were tested during a) sinusoidal pitch oscillations in darkness, b) cancellation of the vestibuloocular reflex (VOR) during similar oscillations by fixation of a target moving with the head, c) sinusoidal vertical smooth pursuit, d) vertical saccades, and e) fixation with the head stationary. Eye movements were measured using the magnetic field-search coil technique. Of the 527 neurons isolated, 318 responded to pitch oscillation and/or vertical eye movements. The latter cells could be classified into six categories. Of this group, 273 cells were recorded from for sufficient time to allow them to be fully tested and form the basis of this report. Cells were classified as follows: pure-vestibular cells with firing rates modulated only by head velocity (15%), vestibular-pause cells that were similar to the pure-vestibular cells but paused for saccades in all directions (10%), gaze-velocity cells that modulated their rates in proportion to vertical eye velocity in space (7%), position cells with rates modulated by changes in eye position in the head but that did not burst or pause during saccades (33%), position-burst cells that also carried an eye-position signal but did burst during saccades in one direction and paused in the opposite direction (15%), and position-vestibular-pause cells that carried signals proportional to eye position in the head and head velocity and paused during all saccades (20%). Most cells that carried an eye-position signal also carried an eye-velocity signal during pursuit. Position and position-burst cells could be divided into two subcategories. Position cells that also reported head velocity represented 20% of the total sample, while those without head-velocity signals made up the remaining 13%. Position-burst cells were divided into two subcategories based on their behavior during pitch oscillation in darkness. Both carried eye-velocity signals during pursuit, but only one type (8% of the total sample) also carried an eye-velocity signal during vestibular eye movements in the dark, while the other (7%) did not. Some cells in all six categories except the pure-vestibular cells responded antidromically to stimulation of the medial longitudinal fasciculus (MLF). Only the position-vestibular-pause, position-burst, and gaze-velocity cells, however, were judged to be commonly antidromically activated, suggesting that these three cell types are the major contributors to the MLF from the rostral vestibular nuclei.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed2003

Attention maintains mental extrapolation of target position: irrelevant distractors eliminate forward displacement after implied motion.

Observers' judgments of the final position of a moving target are typically shifted in the direction of implied motion ("representational momentum"). The role of attention is unclear: visual attention may be necessary to maintain or halt target displacement. When attention was captured by irrelevant distractors presented during the retention interval, forward displacement after implied target motion disappeared, suggesting that attention may be necessary to maintain mental extrapolation of target motion. In a further corroborative experiment, the deployment of attention was measured after a sequence of implied motion, and faster responses were observed to stimuli appearing in the direction of motion. Thus, attention may guide the mental extrapolation of target motion. Additionally, eye movements were measured during stimulus presentation and retention interval. The results showed that forward displacement with implied motion does not depend on eye movements. Differences between implied and smooth motion are discussed with respect to recent neurophysiological findings.

Adolescent↗
PubMed1997

Open loop optokinetic responses of the turtle.

Turtle eye movements were measured during full-field horizontal optokinetic stimulation under closed and open loop conditions. Because these animals display unyoked slow-phase eye movement behavior, open loop stimulation could not be presented to a paralyzed eye, while monitoring the position of the contralateral eye. The turtle's optokinetic reflex loop was opened electronically by a continuous adjustment of the pattern's position that effectively canceled the effect of the movement of the recorded eye. The highest open loop gains (2-3) were observed at low speeds (< 1 deg/sec), demonstrating a more limited speed range and lower gain in turtle than in the mammalian optokinetic system. These results in the intact animal can be correlated with the visual response properties of the turtle's pretectum and accessory optic system recorded in vitro.

Animals↗
PubMed1989

Fault management in process control: eye movements and action.

Operators controlled a simulated thermal hydraulic system based on Crossman's waterbath task. They were required to keep the system at set points for temperature, level and flow rates. The system was subjected to disturbances and to failures, which the operators were required to manage. Behavioural data were collected in the form of keystroke commands, and in addition eye movements were measured. Evidence for 'cognitive lockup' and for a preference for serial fault management were found. Fixation durations do not change, but faulty subsystems are examined more frequently. During lockup other subsystems may be examined but action on them is delayed. Eye movements give considerable additional insight into the nature of process control information processing compared with traditional measures of operator performance.

Attention↗
PubMed1994

Saccadic responses in patients with hemispheric stroke.

Saccadic characteristics were examined in 15 patients with unilateral hemispheric stroke. Eye movements were measured by a standard electro-oculogram technique. In patients with cortical infarcts, mean gain values were lower than in the control subjects for eye movements directed away from the infarct (contralateral), but higher for eye movements towards the infarct (ipsilateral) (p < 0.025). We suggest that impairment of efferent neural signals from the affected hemisphere of stroke patients may decrease excitation of the contralateral neural circuits and inhibition of the ipsilateral neural circuits of the brainstem saccade generator.

Adult↗