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Biomedical subjects

L A Abel

Publications and source records attributed to L A Abel.

At least 19 recordsLinked to original sources
PubMed2000

Eye movements in Parkinson's disease: before and after pallidotomy.

PURPOSE: To evaluate the effects of unilateral, stereotactic, posteroventral pallidotomy on saccadic eye movements in patients with Parkinson disease (PD). METHODS: Eye movements of 31 patients with moderate to advanced PD were recorded with an infrared system 1 month before and 3 months after pallidotomy. Two kinds of saccade tasks were used: saccade tasks for eliciting visually guided saccades and saccade tasks for eliciting internally mediated saccades (memory-guided, predictive, and anti-saccades). Latency, accuracy, peak velocity, and other parameters of saccades were evaluated. RESULTS: Internally mediated saccades were more impaired in patients with advanced PD compared with those with moderate PD. Pallidotomy did not affect visually guided saccades. After pallidotomy, the peak saccadic velocity of internally mediated saccades decreased. CONCLUSIONS: Hence, although pallidotomy has led to improvements in other motor functions, none were observed in saccadic responses. Rather, several modest decrements, below the level of clinical significance and all in internally mediated saccades, were observed.

Aged↗
PubMed1999

Bedside tests of saccades after head injury.

OBJECTIVES: To compare the techniques of bedside and infrared oculographic tests of saccades and to compare the results of both tests in control subjects and in patients with traumatic brain injuries (TBI). MATERIALS AND METHODS: The authors elicited single memory-guided saccades, antisaccades, and self-paced saccades in 19 TBI subjects and 26 age-matched control subjects at the bedside. Taped instructions were used to ensure that the timing and sequence of each stimulus (index finger flexion) were the same in all subjects and as close as possible to those used in both the current and previous laboratory studies. RESULTS: Self-paced saccade rate was significantly decreased in patients with TBI. The increased error rate in single memory-guided saccades and antisaccades was not statistically significant. CONCLUSION: The authors concluded that the bedside saccade tests have limited value in patients with TBI because of the range of results and large overlap of the distributions of these two groups. The number of parameters that can be measured is limited. Bedside saccade tests are easier than infrared oculographic tests because the target remains visible.

Adolescent↗
PubMed1998

Effects of acupuncture on foveation characteristics in congenital nystagmus.

AIMS/BACKGROUND: To examine the effects of acupuncture at the sternocleidomastoid muscles on foveation characteristics in congenital nystagmus. METHODS: Six patients with congenital nystagmus (CN) received a series of treatments consisting of two needles inserted into each sternocleidomastoid, stimulated by tapping gently every 5 minutes, for 20 minutes per session. Their eye movements were recorded using scleral search coils and changes in their CN waveforms analysed at each point in the treatment. Changes in the stability and duration of foveation periods were examined. RESULTS: Four of the six patients showed improved foveation at the commencement of treatment; three maintained this response throughout the treatment period and after the needles were removed. In two, the CN waveform itself was modified. CONCLUSION: This study and others involving afferent stimulation to the neck and face suggest that projections from these areas to the reticular formation and vestibular nucleus may alter the behaviour of the pathophysiological mechanism underlying congenital nystagmus.

Acupuncture Therapy↗
PubMed1998

Influences of chorion type on saccadic eye movements in twins.

PURPOSE: The influence of genetic and prenatal environmental factors on characteristics of saccadic performance were evaluated in young monozygotic (MZ) twins (8-19 years old) of known chorion type. METHODS: Saccadic eye movements were recorded using an infrared system. Saccadic latency, accuracy, and parameters of amplitude-peak velocity exponential equation (main sequence) were quantified. RESULTS: Intraclass correlations of saccadic parameters differed significantly from zero for monochorionic and dichorionic MZ twins. The within-pair mean squares were significantly less, and intraclass correlations were significantly higher in monochorionic than in dichorionic twins for latency and were similar for other saccadic parameters (accuracy, slope of main sequence, and peak velocity for 15 degrees saccades). CONCLUSIONS: These findings confirmed previous reports that saccadic parameters of MZ twins are significantly correlated and indicated that similarity of these parameters seen in MZ twins may be driven both by genetic and by prenatal environmental factors.

Adolescent↗
PubMed1997

Smooth pursuit in twins before and after alcohol ingestion.

PURPOSE: The influence of genetic factors on characteristics of smooth pursuit were evaluated in young adult monozygotic (MZ) and dizygotic (DZ) twins before and after the administration of a single dose of ethanol. METHODS: Sinusoidal pursuit was recorded using a scleral search coil at frequencies of 0.25 and 0.5 Hz before and after alcohol consumption. Pursuit gain, interval between saccades, saccadic accuracy, and saccadic amplitude were quantified. RESULTS: Alcohol consumption reduced pursuit gain and saccadic accuracy and increased the rate and amplitude of saccades. Before and after alcohol consumption, the intraclass correlations for MZ twins (rMZ) were highly significant for pursuit gain, interval between saccades, and saccade amplitude. Corresponding correlations for DZ twins (rDZ) were not significant. Heritability values were similar before and after alcohol ingestion. CONCLUSIONS: The disparity between rMZ and rDZ suggests either multiple gene interactions or common environmental influences for MZ twins, greater than those for DZ twins.

Adult↗
PubMed1996

Saccadic characteristics of monozygotic and dizygotic twins before and after alcohol administration.

PURPOSE: To evaluate the degree of heritability in the latency, accuracy, and peak velocity of reflexive saccades in young adult monozygotic (MZ) and dizygotic (DZ) twins before and after the administration of a single dose of ethanol. METHODS: Saccades were recorded using a scleral search coil before and after alcohol consumption, and data were analyzed offline. Estimates of heritability based in intraclass correlations (ICCs) and using a maximum likelihood estimates of genetic variance were calculated for the saccadic measures made before and after alcohol, as well as for the changes in latency, accuracy, and velocity. RESULTS: Intraclass correlations for MZ twins (rMZ) were highly significant; those for DZ twins (rDZ) were not significantly different from zero. This disparity between rMZ and rDZ suggests either multiple gene interactions or in utero environmental differences in the MZ twins. Alcohol significantly prolonged latency, reduced accuracy, and lowered peak velocity. Although the changes after alcohol were not significant, heritability values increased in all three measures after alcohol administration. CONCLUSIONS: Latency, accuracy, and peak velocity appear to be controlled by multiple genes or to depend on prenatal environmental factors. Even a single low dose of alcohol appeared to enhance heritability measures. Differences seen between ICCs for latency, accuracy, and velocity after alcohol administration suggest that developmental control of the neural mechanisms underlying each measure may vary.

Adult↗
PubMed1995

Effects of stimulus velocity and acceleration on smooth pursuit in motor neuron disease.

Sinusoidal smooth pursuit eye movements were evaluated in 11 normals, five moderately and four severely affected motor neuron disease (MND) patients, using two target amplitudes and a range of frequencies. This enabled us to examine separately the effects of peak target velocity and acceleration on pursuit gain. Moderately affected patients showed an acceleration, but not a velocity saturation; severely impaired patients' performance declined with increased velocity. Smooth pursuit eye movements are thus impaired in MND, but the nature of this pursuit deficit is complex and changes with the progression of the disease.

Aged↗
PubMed1994

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.

Adult↗
PubMed1994

Voluntary saccadic oscillations, resembling ocular flutter and opsoclonus.

Two human subjects, who had no signs of other neurologic disorders, produced large amplitude, to-and-fro saccadic oscillations. One subject generated these oscillations intentionally. Eye movement recordings by DC electro-oculography and/or magnetic scleral search coil showed that the movements were bursts of conjugate saccades in opposing directions with no intersaccadic intervals. They were multidirectional (horizontal, vertical, or oblique), had amplitudes up to 40 degrees and had linear or curvilinear trajectories. These characteristics are similar to those of ocular flutter and opsoclonus in patients with brainstem and/or cerebellar disorders. Our observations show that fixation instabilities resembling ocular flutter and opsoclonus can be produced voluntarily.

Electrooculography↗
PubMed1993

Hereditary congenital nystagmus and gaze-holding failure: the role of the neural integrator.

Congenital nystagmus (CN) may be due to an instability of the neural integrator responsible for gaze holding. This longitudinal study tests that hypothesis, investigates the saccadic instabilities of relatives, and assesses the effects of afferent stimulation on both the CN and the coexisting gaze-holding failure. We recorded four siblings who had CN and gaze-holding failure while fixating in primary position and lateral gaze. In lateral gaze, the CN waveforms were superimposed on the centripetal drift caused by the gaze-holding failure; the drift time constants ranged from 300 to 1,450 msec. CN waveforms lacked extended foveation periods. Saccadic instabilities were present in the father and two clinically unaffected siblings; the mother's eye movements were normal. We conclude that CN in the subjects of this study, and in others with idiopathic CN, is not due to gaze-holding abnormalities, and we speculate that development of the fixation reflexes that produce CN foveation periods requires some minimal foveation interval during which the target image is in the foveal area with low retinal slip velocity and acceleration.

Child↗
PubMed1992

Saccadic intrusions into smooth pursuit in patients with schizophrenia or affective disorder and normal controls.

Two types of saccadic intrusions into smooth pursuit eye tracking, anticipatory saccades (AS), and square wave jerks (SWJ), were measured in 23 patients with schizophrenia, 16 patients with affective disorder, and 21 normal controls. Constant velocity (5 degrees and 20 degrees/sec) predictable targets were employed. High resolution infrared oculography was employed to record eye movements. Although most subjects had at least one SWJ, there were no significant group differences, and the highest individual rates of SWJ were seen in the normal control group. On the other hand, AS were never seen in normals, but were present in 25%-44% of patients with either schizophrenia or affective disorder. Both patient groups had significantly more AS than controls, but the two patient groups were not significantly different.

Adult↗
PubMed1992

Abnormalities of smooth pursuit and saccadic control in schizophrenia and affective disorders.

Smooth pursuit abnormalities have been reported in patients with schizophrenia and their first-degree relatives, suggesting that abnormal tracking may serve as a biological marker for schizophrenia. Recent studies in schizophrenic patients have found reduced pursuit gain, low initial acceleration and abnormal gain-corrective saccade interactions. Impaired saccadic initiation has been noted in anti-saccade tasks and in predictive saccade generation, as has saccadic hypometria. While abnormalities have been found in affective disorder patients, studies of their first-degree relatives suggest that abnormalities during pursuit are more closely associated with schizophrenia. Identification of specific defects allows informed speculation about their neural substrates and suggests possible relationships between the ocular motor defects and other cognitive and perceptual abnormalities associated with the major psychiatric disorders.

Humans↗
PubMed1992

Catch-up saccade amplitude is related to square wave jerk rate.

Mean catch-up saccade (CUS) amplitude and square wave jerk (SWJ) rate during pursuit were recorded in 20 normal controls, 23 patients with schizophrenia, and 15 patients with affective disorder, using infrared oculography. Target speed during pursuit was 5 degrees/sec. An especially robust correlation was noted in normal controls between SWJ rate during pursuit and mean CUS amplitude (Spearman's rs = 0.87, P less than 0.0001). This correlation also was present in the psychiatric patients (rs = 0.53, P = 0.0006), although it was significantly weaker than in normal controls (P less than 0.02). There were no significant differences between the patient groups regarding the strength of the relationship. Furthermore, similar strong correlations between SWJ rate during fixation and mean CUS amplitude also were found for normals (rs = 0.73, P = .0002) and both patient groups combined (rs = 0.52, P = 0.0009). The results suggest that saccadic intrusions during tracking tax the saccade correcting system, delaying correction for the position error that accumulates when gain is less than 1.0.

Adult↗
PubMed1991

Quantitative assessment of smooth pursuit gain and catch-up saccades in schizophrenia and affective disorders.

The smooth pursuit responses to 5 degrees and 20 degrees/sec constant-velocity stimuli were recorded from 23 patients with schizophrenia, 16 affective disorder patients, and 21 normals using low-noise infrared oculography. Pursuit gain, catch-up saccade (CUS) rate and amplitude, and their interrelationships were examined. Gain in the schizophrenic patients was reduced only at 20 degrees/sec, but for both patient groups, CUS rate at 5 degrees/sec was significantly lower than in normals. Using CUS rate at 20 degrees/sec, the patient groups could be distinguished from each other (the rate for schizophrenic patients being highest, and the rate for affectives the lowest) but neither differed significantly from normals. The diagnostic groups did not differ significantly in mean CUS amplitude, although there was a trend for patients to have larger saccades. Gain-CUS rate correlation was strong in normals but reduced or absent in both patient groups. These results indicate that the ocular motor systems of patients with schizophrenia and affective disorders process eye position error abnormally.

Adult↗
PubMed1991

Intermittent oscillopsia in a case of congenital nystagmus. Dependence upon waveform.

Spontaneous reports of oscillopsia are rare in cases of congenital nystagmus (CN). We examined the relationship between nystagmus waveform characteristics and oscillopsia in one such case. To reduce the patient's nystagmus, she was fitted with contact lenses. We examined the effects of tactile feedback by applying local anesthetic while she wore the lenses. When she was without lenses, we provided tactile feedback by applying gentle finger pressure to one eyelid. She was also asked to look at a peripheral afterimage. Nystagmus was analyzed for frequency, amplitude, foveation duration, and drift velocity, if foveation was not perfectly stable. Perceived target stability was recorded. The patient noted oscillopsia during the initial baseline recording and with lid pressure. The image was stable with contact lenses with and without anesthesia and during the second session baseline; at these times, drift velocity was less than 4 degrees/sec and foveation duration was greater than 100 msec. No oscillopsia of the afterimage in dark was noted; she perceived it moving with her gaze as she attempted to look at it. It appears that in some CN patients, the suppression of oscillopsia operates only within fixed limits of foveation stability and duration. When, because of internal or external factors, their nystagmus exceeds these, oscillopsia results.

Adolescent↗