PubMed Health⌕ Search

Biomedical subjects

L A Abel

Publications and source records attributed to L A Abel.

At least 19 recordsLinked to original sources
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↗
PubMed1988

Frequency and velocity of rotational head perturbations during locomotion.

We used the magnetic search coil technique to record horizontal (yaw) and vertical (pitch) head rotations of 20 normal subjects during (1) walking in place, (2) running in place, (3) vigorous, voluntary, horizontal head rotation and (4) vigorous, voluntary, vertical head rotation. During walking or running, the predominant frequency of pitch rotations was at least twice that of yaw rotations. During running, the median, predominant pitch frequency from all subjects was 3.2 Hz, but significant harmonics were present up to 15-20 Hz in several subjects. Group median maximal head velocity during walking or running did not exceed 90 degrees/second. During vigorous, voluntary head rotations median frequency for yaw and pitch was similar and did not exceed 2.6 Hz. However, group median maximal head velocity during vigorous voluntary yaw rotation was 780 degrees/second. Thus, (1) during locomotion, the head is stabilized in space incompletely but adequately so that the vestibulo-ocular reflex (VOR) is not saturated, (2) during vigorous, voluntary head rotations, the maximum head velocity exceeds the range where the VOR can stabilize gaze, (3) the frequencies of head rotations that occur during locomotion greatly exceed frequencies conventionally used in the laboratory for testing the VOR.

Adult↗
PubMed1988

Smooth pursuit eye movements in schizophrenics--what constitutes quantitative assessment?

Although a voluminous literature exists on the eye movements of schizophrenic and affective disorder patients, many of the assessments made of smooth pursuit have been qualitative in nature. Most of them have not differentiated between abnormal functioning of the smooth pursuit system and intrusion of inappropriate saccades during a smooth tracking task. Specific identification of the pursuit or saccadic defect is necessary if the origins of the abnormalities are to be understood and related to psychopathology. Analytical techniques, such as the ln(S/N) ratio, although numerical in nature, are still unable to discriminate among pursuit and saccadic defects, as shown by our analysis of simulated tracking. Thus, to understand the effects of psychiatric disorders on the ocular motor system, specific defects must be identified and quantified.

Attention↗
PubMed1987

Spasmus nutans. A quantitative prospective study.

Spasmus nutans includes ocular oscillations, head nodding, and anomalous head positions. No quantitative longitudinal study verifying the natural history of this self-limited condition has appeared in the literature. Using infrared oculography, we prospectively examined the eye movements of otherwise neurologically normal infants in whom a diagnosis of spasmus nutans had been made. At this writing the ocular oscillations and head movements in two of the children were clinically absent, thereby confirming the diagnosis. The ocular movements are characterized by a phase difference between the oscillations of each eye that varies both during one recording session and during development. The dissociated, pendular nystagmus consists of high-frequency oscillations that may be disconjugate, conjugate, or purely uniocular.

Electrooculography↗
PubMed1987

Hyperactive vestibulo-ocular reflex in cerebellar degeneration: pathogenesis and treatment.

We studied a patient with a cerebellar degeneration and hyperactive vestibulo-ocular reflex (VOR). He complained of oscillopsia and blurred vision with head movement. A twofold increase in VOR gain (peak eye velocity/peak head velocity) at high frequencies was associated with a VOR time constant of 6 seconds (low normal). Visual cancellation ("suppression") of the VOR and smooth pursuit were also abnormal. We hypothesized that his high VOR gain was due to dysfunction of olivocerebellar projections. Physostigmine reduced his VOR gain, consistent with the hypothesis that these projections are cholinergic.

Atrophy↗
PubMed1987

Latent/manifest latent nystagmus reversal using an ocular prosthesis. Implications for vision and ocular dominance.

Latent/manifest latent nystagmus (LMLN) is a jerk nystagmus with a decreasing-velocity or linear slow phase whose fast phase is in the direction of the fixating eye. Change of the fixating eye by alternating tropias or cover will cause reversal of the LMLN to preserve this relationship. In the dark, where no fixation is possible, the fast phases of LMLN are in the direction of the intended fixating eye; actual visual input will override this effect of intention. A patient with persistent hyperplastic primary vitreous of the right eye, which was enucleated at age 9 due to glaucoma, had LMLN with fast phases to the left. His congenitally blind right eye was replaced with an ocular prosthesis whose movements were conjugate with his seeing eye. In the dark, we found that his LMLN spontaneously reversed as the normally fixating left eye became esotropic. Furthermore, as is the case with LMLN patients who have sight in both eyes, he was able to willfully reverse his LMLN in the dark by alternating his "fixating" eye. We conclude from these observations that the direction of LMLN is determined at a cortical level, is intimately related to the intended fixating eye and that eye "dominance" is predetermined and not altered by visual abnormalities, including blindness.

Adolescent↗
PubMed1979

Saccades in extremes of lateral gaze.

Saccades (between targets at 30 degrees and 40 degrees) were recorded with DC electro-oculography in 10 normal subjects. Velocity-amplitude relationships were examined on the basis of abduction vs. adduction and centering vs. eccentric movement. In these small peripheral saccades the former pairing showed no consistent differences in peak velocity, whereas centering saccades were consistently faster than both eccentric movements and those made around primary position.

Adult↗
PubMed1979

Saccadic velocity characteristics: intrinsic variability and fatigue.

Saccadic eye movements exhibit a characteristic peak velocity vs. amplitude relationship. As with all quantifications of biological function, there exists and associated intra- and intersubject variability of this relationship. This paper documents this variability and demonstrates both the absence of a predictable short-term "muscle fatigue" effect and the presence of a generalized "mental fatigue" (i.e. tiredness) effect.

Adolescent↗
PubMed1978

Saccadic system plasticity in humans.

A subject with a medial rectus paresis secondary to a partial third nerve palsy was forced to use the affected eye for six days while the good eye was constantly patched. Saccadic eye movements were carefully measured each day; the grain increased, with a time constant of 0.85 day. The patch was then switched to the paretic eye and the gain decreased, with a time constant of 0.85 day. The patch was then switched to the paretic eye and the gain decreased, with a time constant of 1.54 days. This demonstrated central nervous system plasticity of the pulse and step of neural activity responsible for the generation of saccades in the adult human. In addition to gain changes, postsaccadic drift velocity and saccadic velocity/amplitude relationship alterations during the patching are reported. A major conclusion that can be drawn from analysis fo these data is that the gain changing is accomplished by pulse width changes rather than pulse height (firing frequency), which was not markedly altered.

Eye Movements↗