Saccadic Measures Research Articles

3-D eye movement measurements on four Comex's divers using video CCD cameras, during high pressure diving.

Previous studies have shown the vulnerability of the vestibular system regarding barotraumatism (1) and deep diving may induce immediate neurological changes (2). These extreme conditions (high pressure, limited examination time, restricted space, hydrogen-oxygen mixture, communication difficulties etc.) require adapted technology and associated fast experimental procedure. We were able to solve these problems by developing a new system of 3-D ocular movements on line analysis by means of a video camera. This analyser uses image processing and forms recognition software which allows non-invasive video frequency calculation of eye movements including torsional component. As this system is immediately ready for use, we were able to realize the subsequent examinations in a maximum time of 8 min for each diver: oculomotor tests including saccadic, slow and optokinetic traditional automatic measurements; vestibular tests regarding spontaneous and positional nystagmus, and reactional nystagmus to the pendular test. For pendular induced nystagmus we used appropriate head positions to stimulate separately the lateral and the posterior semicircular canal, and we measured the gain by operating successively in visible light and complete darkness. Recordings were done during a simulated onshore dive to an ambient pressure corresponding to a depth of 350 m. The above examinations were completed on the first and last days by caloric tests with the same video system analyser. The results of the investigations demonstrated perfect tolerance of the oculomotor and vestibular systems of these 4 divers thus fulfilling the preventive conditions defined by Comex Co. We were able to overcome the limitations due to low cost PC computer operation and cameras (necessity of adaptation to pressure, focus difficulties and direct light exposure eye reflexions). We still have on line accurate measurements even on the torsional component of the eye movement. Due to this technological efficiency we also present some mathematical aspects of the software.

Concordance of smooth pursuit and saccadic measures in normal monozygotic twin pairs

Although the range of normal ocular motor performance is broad, little is known about the sources of variability. Genetic transmission of eye movement deficits has been described but such possible control of normal function has been little investigated. Characteristics of smooth pursuit and saccades can be examined for the degree of concordance in related individuals. In this pilot study, we studied saccades and pursuit in eight monozygotic (MZ) twin pairs. The statistical analysis of the data used the intraclass correlation of MZ twins (rMZ) to estimate what fraction the covariance of the twin pairs was of the population variance. All saccadic measures showed significant MZ correlations ( p < 0.05). Smooth pursuit gains were even more highly correlated ( p < 0.001). These results indicate considerable similarity within pairs of twins, particularly for horizontal smooth pursuit, and suggest that larger studies on monozygotic and dizygotic twins would be desirable, to help separate out the relative contributions of environmental and genetic factors.

Eye movement impairment and schizotypal psychopathology

Eye movement dysfunction in relation to a smooth pursuit task has been documented in schizophrenic patients and in patients with the related personality disorder, schizotypal personality disorder. To investigate which quantitative measures are associated with the eye movement dysfunction and whether the dysfunction is more related to the psychotic-like or the deficit-like symptoms of schizotypal personality disorder, ratings of eye movements in several groups of subjects were compared. The study groups consisted of 26 patients with schizotypal personality disorder, 42 patients with other personality disorders (22 who also had two or more schizotypal personality traits and 20 who had fewer than two), and 37 normal comparison subjects. Smooth pursuit eye tracking of sinusoidal and constant velocity targets was recorded by an infrared eye tracking system. Two raters evaluated pursuit gain and large and small saccades in the direction of the target and in the direction opposite to that of the target (quantitative ratings) and constant velocity (qualitative rating). Patients with schizotypal personality disorder and patients with other personality disorders and two or more schizotypal traits, but not those with fewer than two schizotypal traits, had significantly poorer qualitative ratings of tracking than the normal comparison subjects. Neither gain nor any of the saccadic measures significantly differed between groups. The number of large saccades in the direction of the target was the only quantitative variable that predicted low qualitative ratings. Qualitatively poor tracking was associated with the deficit-like, but not the psychotic-like, symptoms of schizotypal personality disorder. Patients with schizotypal personality disorder demonstrate qualitatively poorer tracking than comparison groups, and the impaired tracking is associated with deficit-like symptoms.

Saccadic eye movement parameters in normal subjects

The present study obtained saccadic eye movements from 122 normal subjects to establish normative values and test-retest reliability data, using a recently developed electrooculographic recording and analysis system. Factors that might affect saccade values, such as age, sex, and time of day when testing, were also assessed. Mean (± S.D.) peak velocity values over saccade angles of 15°, 25° and 35° were in agreement with those previously reported. Repeat testing in 11 subjects on 4 separate occasions showed that saccade measurements were consistent across tests. Several saccade parameters were significantly negatively associated with age for 35° saccades. The association between age and peak velocity was examined in greater detail over a range of saccade angles, and the greatest effect was observed for saccades of ⩾ 35°. Diurnal changes in performance were observed, with a tendency for slightly slower values in the early afternoon. There were no significant differences between males and females.

Reflex horizontal saccades in multiple sclerosis

The authors used infrared oculography to measure reflex horizontal saccades in 50 normal subjects and 65 patients with multiple sclerosis. MS patients were divided into three groups on the basis of a current or past history of ocularmotor disorder or neither. Saccadic duration and peak velocity characteristics were modelled using simple mathematical functions. Data were segregated by eye and direction and anatomical interpretations made on the basis of abnormalities found. The authors were able to show that duration more so than velocity data, using small angles, was sensitive to clinical and presumed ‘subclinical’ abnormalities. Saccadic latency did not correlate with visual pathway problems, and dysmetria frequently occurred in patients with a previous history of ocular palsy. In contrast to previous studies the authors have demonstrated that careful measurement of small saccades provides clinically robust and useful information, and suggest that this approach could be extended to aid in the evaluation ...

Oculomotor and skeletal motor systems share one map of visual space

Previous research has shown that cognitive and motor visual systems have separate maps of visual space because spatial values in them can be manipulated independently. Here we ask whether the motor map in turn can be divided into separate representations of space. Forty large saccadic eye movements in darkness resulted in significant ocular undershoot of a remembered eccentric target location, and a comparable amount of undershoot with manual pointing to the same remembered target. Saccadic and manual measures were also highly correlated within sessions as well as between sessions. Because pointing could be changed by manipulating only saccades, we conclude that the two systems share a single map of space.

The role of attention in the preparation of visually guided eye movements in monkey and man.

Neurophysiological data from single cells in the monkey's visual association cortex as well as saccadic reaction time measurements in monkey and man are reported. When a monkey directs his attention to a peripheral light stimulus the visual activation of cortical cells responsive to that stimulus is increased. If visual attention is directed to a particular part of the visual field the saccadic reaction time is long (around 200 ms in monkey and above 200 ms in man). In contrast, if attention is disengaged from any location to which it might have been engaged before, monkeys and men can execute express saccades, that is, saccades after extremely short and stable reaction times (around 75 ms in monkey and 100 ms in man). The results are interpreted in the context of a hypothesis according to which the initiation of voluntary, visually guided saccades includes three premotor mechanisms: the computation of the target location, the decision to make a saccade, and the disengagement of attention.

Saccadic velocity studies in superior oblique palsy.

Eighteen patients (21 eyes) with superior oblique palsy had vertical saccadic velocity measurements in primary gaze, adduction, and abduction. No noticeable difference was found when upward saccades were compared with downward saccades in all fields of gaze. Thus, saccadic velocity studies would not be helpful in the diagnosis of superior oblique palsy.

Saccadic latency measurements in dementia.

We measured saccadic latencies in patients with Alzheimer's dementia (AD) and other types of dementia. The saccadic latencies for both groups were considerably longer than those for age-matched controls. The prolongation was as extensive in patients with other types of dementia as it was in those with AD. There was no correlation between latency and the severity of the dementia.

Spike artefact associated with fast eye movements in electronystagmography and its importance in the automatic analysis of saccades.

A negative spike of 10–20 ms duration can be recorded at the onset of a saccade in the electronystagmogram (ENG) of most patients if the electrode locations are suitably selected. Probably it originates in the muscles of the face. If care is not taken to minimize this artefact in ENG recording, it can prevent the accurate measurement of saccades from the ENG.

Saccades With Limited Downward Gaze

Fourteen patients with monocular limitation of downward gaze had vertical saccadic velocity measurements. Patients with orbital floor fracture and endocrine ophthalmopathy were excluded from the group. In four cases (29%), the difference between upward downward saccadic velocities was 20% or less. These patients were not thought to have any evidence of inferior rectus muscle paresis. In ten cases (71%), the difference between upward and downward saccades varied between 46% to 275% (average, 115%), upward saccades being more rapid in each case. These cases were all believed to have moderate to great inferior rectus muscle palsy. In one subject with a lidocaine hydrochloride-induced inferior rectus muscle palsy, upward saccades were 135% faster than downward saccades. These findings were compared with those in patients with monocular limitation of elevation, and the surgical management was reviewed.

Quantitative eye tracking tests in lead workers

A microcomputer system for on-lone analysis of saccadic and smooth-pursuit tracking eye movements is described. Results from a longitudinal study of lead workers and matched controls reveal a consistent decrease in saccade accuracy in the lead workers compared to the controls. Saccade peak velocity and latency and smooth pursuit were not significantly different in the two groups. The abnormal saccade accuracy measurements may indicate a subclinical effect of increased lead absorption, but because of the large scatter in normal values, saccade accuracy measurements are not a reliable indicator of early lead toxicity in a single lead worker.

Saccadic Velocity Measurements in Internuclear Ophthalmoplegia

Five patients with internuclear ophthalmoplegia had horizontal saccades measured by electro-oculography. In all patients, abduction saccadic velocities were normal while adduction saccades were slowed either binocularly or monocularly. In one patient, adduction saccades were reduced in velocity, even though full adduction was present. Saccadic velocity measurements may be helpful in diagnosing internuclear ophthalmoplegia, especially in the early or subclinical case. As bilateral internuclear ophthalmoplegia frequently suggests multiple sclerosis, prolonged examination with more sophisticated and difficult diagnostic tests is avoided.

Forced Duction, Active Force Generation, and Saccadic Velocity Tests

The forced duction test reveals information about mechanical limitations to full ocular rotation. When voluntary ocular rotation is limited, and the forced duction test is completely free, paresis of an extraocular muscle is suggested. The active force generation test and saccadic velocity measurements both provide information about the active forces available to move the globe. Active force can be felt with the forceps in the force generation test. These forces can be measured quantitatively with the calibrated Scott forceps. The saccadic velocity test measures the work an extraocular muscle performs (the eye movement) but does not measure active force directly. The force available is inferred by comparing saccadic velocity measurements to normal control values. This test is especially useful in infants and children, in whom the force duction test cannot be done without general anesthesia, and whose cooperation is insufficient to allow force generation measurements to be performed. It is likely that future improvements in instrumentation and further knowledge of basic oculomotor mechanisms will increase the value of these techniques in clinical strabismus.

Human eye movements following horizontal rectus muscle disinsertion.

Patient with long-standing exotropia had strabismus surgery performed using only topical anesthesia. During the surgical procedure, horizontal saccades were measured by electro-oculography. It was found that horizontal saccades were slowed from 240°/sec, preoperatively to 100°/sec following muscle disinsertion. Further saccadic slowing was noted when the disinserted muscle was held taut and was prevented from contracting. This decrease is attributed to limitation of the effective action of the disinserted muscle through posterior attachments to intermuscular membrane and fascia bulbi. Findings following disinsertion may resemble the ocular rotations and saccades noted after release of a suture in early postoperative period after strabismus surgery. Saccadic velocity measurements may be clinically useful in the diagnosis of this problem.