Biomedical subjects

S Ron

Publications and source records attributed to S Ron.

10 recordsLinked to original sources

PubMed1992

Does work with visual display units impair visual activities after work?

It is well established that visual display unit (VDU) operators complain of visual fatigue and visual stress during after-work hours. The present study was divided into two parts. In the first part, standard eye examinations were performed on a group of VDU workers (n = 32) and a control group (n = 15); those subjects who were found to have correct vision (n = 16 and 13, respectively) participated in the second part. The eye examinations revealed that on the average, the VDU workers suffered more than twice as many visual impairments as the controls. In those with correct vision, the near point of accommodation was measured at the beginning of the workday at the start of the week, and at the end of the workday, four days later. In the VDU group, the decrease in accommodation was uniformally distributed between zero and 1.0 diopter, whereas among the non-VDU workers, 77% of the decrease was between zero and 0.25 diopter. The dynamic range of accommodation in the VDU workers on the second examination was smaller than on the first. We conclude that some of the visual stress and visual fatigue that developed at work hindered visual activities after work.

Accommodation, Ocular↗

PubMed1992

Gaze and eye movement disorders.

Cortical areas were explored with regard to saccade control: the lateral intraparietal (LIP) area is involved in the spatial aspects of sensorimotor processing; the supplementary motor area in goal-directed gaze control; and from lesion studies; the posterior parietal cortex in triggering visually guided saccades. Different studies have suggested that the spatial-to-temporal transformation takes place in the superior colliculus (SC) and the cerebellum. When the vestibulo-ocular reflex (VOR) produces inadequate eye movements, other supplementary mechanisms (e.g. non-visual, saccade) may play a role in correcting gaze. A classification of central vestibular disorders of the brainstem and VOR has been proposed, as manifested in any one of the three major planes of action (yaw, pitch and role).

Cerebral Cortex↗

PubMed1991

Eye and head coupled and dissociated movements during orientation to a double step visual target displacement.

Tight coupling between eye and head movements has been observed in response to a single visual target offset. On this basis, when the visual stimulus consists of two successive steps in the same (horizontal) direction, either increasing in eccentricity (staircase) or decreasing in eccentricity (pulse-step) gaze should be due to concomitant eye and head angular displacement. That is, the eyes and head should aim at each target displacement so that their combined movement matches target offset. We have tested this hypothesis in five healthy subjects. The measured variables were head and gaze offset, the interval between two consecutive saccades from onset to onset (I) and the response delay between onset of the second step and onset of the first gaze saccade (D). With both staircase and pulse-step stimuli, the eye saccade preceded the head movement, and the gaze response either had the stimulus profile pattern or consisted of one gaze saccade to the final target offset. In response to staircase stimuli, I decreased concomitantly with an increase in D; with pulse-step stimuli, as D increased, I decreased slightly in three subjects and decreased markedly in two subjects. Dissociation between the eye and head movements could clearly be demonstrated with pulse-step stimuli: the first gaze saccade to the target pulse displacement was accompanied by a head movement to the target step offset. We also observed cases in which the gaze saccade to the target step displacement was made simultaneously with the head movement to the target pulse offset. Our study extends previous observations in head fixed condition and illustrates that in the majority of cases, when the head is free and a visual pulse step stimulus is presented, both the saccadic and head systems have the ability to modify or cancel the initial neural command to move to the first target displacement. When this modification takes place in only one system, eye and head movements are dissociated.

Electrooculography↗

PubMed1989

Target velocity based prediction in saccadic vector programming.

Two experiments have been designed to test whether the saccadic system takes target motion into consideration in computing saccade amplitude. In one experiment, while the subject fixated straight ahead, either a horizontal ramp-step-ramp or a horizontal step-ramp target moved from left to right. After the step, the subject had to make a saccade and follow the target. In the second set of experiments, the target, after an initial step, moved extrafoveally from up to down at fixed velocity; a tone, signaling the subject to make a saccade to the target and follow it, was delivered either after a variable delay (previewed condition) or simultaneously with the initial target step (non-previewed condition). In both experiments, eye position at saccade end was statistically different from target position 100 msec before saccade onset only when the target slow motion was presented before the step (i.e. in horizontal ramp-step-ramp and in previewed H-step V-ramp paradigms), suggesting that target motion could be used by the saccadic system to extrapolate the future target position, only if the subject is given enough time to observe the target ramp motion before the step.

Adult↗

PubMed1978

Ocular saccades in Duane's syndrome.

Since Hering's law might be affected when paradoxical innervation exists, 10 patients with Duane's syndrome were studied. Eye movements were measured by binocular recording of electro-oculogram. Our study shows clearly that the sound eye's motility is also affected. When adduction of the affected eye is present, Hering's law holds, whereas when adduction is limited this law cannot be demonstrated.

Adolescent↗

PubMed1978

Eye movements in brain damaged patients.

Saccades, smooth movements and vergence were recorded in 28 patients with brain lesions using an infrared scleral reflexion technique. Large impairment in eye movement responses under visual feedback were recorded from the majority of the patients. The implication of these deficiencies on the vocational rehabilitation of the patients is discussed.

Brain Damage, Chronic↗

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↗

PubMed1977

The cerebellum involvement in the generation of saccades.

It was assumed that the cerebellum is not essential for eye movements, playing only a modifying and influencing role. Recently it has been shown that the directions of the saccades can be related to a stimulated cerebellar site. This study was done on patients who underwent partial vermis and hemisphere ablations as a result of severe cranial or cerebellar tumors. The results further indicate that lack that lack of some cerebellar neural structure affects the nature of the saccade: it does not move the eyes in one saccade to acquire the new target and its amplitude duration relationship changes. It is suggested that cerebellar cortex generates a neural pulse based on teleceptive information about stimulus location with respect to an observer's head, corrects this information for initial eye position and sends out a signal to the saccadic pulse generators which move the eyes to acquire the new target.

Brain↗

PubMedDate not supplied

Contrast sensitivity and the near point of accommodation after work with a visual display unit.

After several hours of work with a visual display unit (VDU), operators become myopic for a short time. Such transient myopia may be evaluated by measuring contrast sensitivity to a modulated grating pattern. The aim of the present study was to determine whether there are any accumulative myopic effects after 1 day of VDU work. We examined grating contrast sensitivity in a group of 13 full-time workers and in 13 office employees who used VDUs only sporadically. The results, which were compared with the near point of accommodation, clearly illustrated that there is no decrease in contrast sensitivity. In the VDU group the decrease in the near point of accommodation was uniformly distributed between zero and 1.0 diopter, whereas among the non-VDU workers 77% of the decrease was between zero and 0.25 diopter. We conclude that the myopic changes in the refractive status of operators after VDU work are not evident in a decrease in contrast sensitivity. However, in VDU workers the dynamic range of accommodation was smaller, suggesting that the visual fatigue and visual stress that developed at work hindered visual activities after work.

Accommodation, Ocular↗

PubMedDate not supplied

Training in oculomotor tracking: occupational health aspects.

Smooth pursuit and optokinetic nystagmus were repeatedly examined in nine patients who sustained hemilateral brain injury. The follow-up period extended over several months of the in-hospital rehabilitation phase. Five of the patients were trained for 3-10 weeks to improve tracking responses using a biofeedback technique; the remaining four patients were not trained and served as a control group. In all patients in the first group gain responses improved and the recovery time constant increased at a rate higher than that in the untrained group. We suggest that our training procedure can be extended to other types of patients with impaired smooth pursuit tracking and may also benefit workers in need of good tracking performance.

Biofeedback, Psychology↗