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Biomedical subjects

D S Zee

Publications and source records attributed to D S Zee.

At least 91 records · Page 5Linked to original sources
PubMed1994

Extraocular muscle proprioception functions in the control of ocular alignment and eye movement conjugacy.

1. The function of extraocular muscle proprioception in the control of eye movements is uncertain. We tested the hypothesis that proprioception contributes to the long-term regulation of ocular alignment and eye movement conjugacy. 2. Eye movements were recorded in monkeys with unilateral extraocular muscle palsies, before and after proprioceptive deafferentation of the paretic eye. Following deafferentation, ocular alignment and saccade conjugacy gradually worsened over several weeks. In contrast, disconjugate adaptation induced by habitual binocular viewing with a prism (disparity-mediated adaptation) occurred normally after deafferentation. 3. These results provide the first evidence that proprioception functions in the control of eye movements in primates, and indicate that proprioception contributes to the long-term adaptive mechanisms that regulate ocular alignment during fixation and saccades. The error signal used in this process may be derived from a mismatch between the efference copy and proprioceptive afference.

Afferent Pathways↗
PubMed1994

Localizing value of optokinetic afternystagmus.

Previous reports have indicated that optokinetic afternystagmus (OKAN) becomes asymmetric after the occurrence of unilateral peripheral vestibular lesions, and suggested that OKAN may be used for localizing the side of the lesion. These studies did not take into account spontaneous nystagmus. We compared OKAN in 12 subjects with unilateral vestibular loss after resection of acoustic neuroma to OKAN in 30 normal subjects. After offsetting the data for spontaneous nystagmus, we calculated the initial amplitude, the time constant, and the slow-phase cumulative eye position (SCEP) parameters of OKAN. The directional asymmetry of parameters to rightward and leftward stimulation were also calculated. The mean SCEP, initial amplitude, and time constant parameters were reduced significantly in the patients, and each also showed a directional asymmetry, such that they were greater for stimulation toward the side of the lesion. The directional preponderance of the SCEP parameter had the highest sensitivity for the side of the lesion, being abnormally elevated in 58.3% of patients with unilateral loss. We conclude that OKAN might be useful in combination with other subtests of a battery, but that by itself OKAN is only moderately sensitive to unilateral peripheral vestibular loss.

Adult↗
PubMed1994

Head position dependent adjustment of the three-dimensional human vestibuloocular reflex.

We studied the influence of static head position relative to the rotation axis on the three-dimensional (3-D) vestibuloocular reflex (VOR). By means of a 3-D rotating chair and a 3-D magnetic search-coil system, eye movements were recorded in 6 normal human subjects during sinusoidal rotation about an earth-vertical axis (yaw) with the head positioned at different pitch angles and about an earth-horizontal axis (pitch) with the head positioned at different yaw angles. We confirmed that torsional VOR gain is about 2/3 of horizontal and vertical VOR gain leading to non-collinear axes of eye and head rotation whenever torsional head movement components were present with eye movement axes tilting away from the torsional direction. Despite this non-collinearity of stimulus and eye movement rotation axes there was close to perfect adjustment of the different VOR components depending on the angle between gaze direction and stimulation axis, indicating a vectorial summation of gains obtained for rotations in the major body axes (roll, pitch and yaw). The horizontal and vertical eye movement components followed a cosine function of the angle between the plane of rotation and gaze direction. The torsional component followed a sine function.

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↗
PubMed1994

Characteristics of postural stability in patients with aminoglycoside toxicity.

Postural stability in patients with bilateral vestibular deficits from aminoglycoside toxicity was characterized by examining their ability to use different sensory cues to maintain balance and by recording their automatic postural responses to sudden translational and rotational (pitch) perturbations of the support surface. We found our patients had increased sway on sensory tests in which either visual or somatosensory cues were altered and were unable to maintain their balance when both visual and somatosensory cues were altered compared to age-matched normal subjects. The amount of vestibular loss, as inferred from the VOR Tc, accounted for a significant amount of A-P sway on test 4 in which somatosensory cues were altered. The frequency response of anterior-posterior sway in the BVL group suggests that they use more hip movements than do normal subjects to maintain postural stability. The responses of BVL patients to sudden translations of the support surface did not differ from those of normal subjects. More BVL patients lost their balance, however, on the initial trial of the toes-up rotational perturbation of the support surface than did normal subjects.

Adult↗
PubMed1993

Single treatment approaches to benign paroxysmal positional vertigo.

OBJECTIVE: To determine the effectiveness of two different physical therapy approaches for benign paroxysmal positional vertigo. DESIGN: Randomized study. SETTING: Outpatient clinic. PATIENTS: Consecutive sample of 60 patients with benign paroxysmal positional vertigo. INTERVENTION: Patients received either a single treatment based on the hypothesis that the vertigo and nystagmus of benign paroxysmal positional vertigo are due to debris adhering to the cupula of the posterior semicircular canal (cupulolithiasis) or a single treatment based on the hypothesis that the debris is free floating in the long arm of the posterior canal (canalithiasis). Patients were reevaluated 1 to 2 weeks after the treatment and again 4 to 6 months later. OUTCOME: Treatment outcome was classified as either asymptomatic, more than 70% improved as rated by the patient, or no change. RESULTS: The treatment designed for cupulolithaisis resulted in remission of vertigo and nystagmus in 70% of the patients and in improvement of the symptoms in another 20%. The treatment designed for canalithiasis resulted in remission of vertigo and nystagmus in 57% of the patients and in improvement in another 33%. There was no statistically significant difference between treatments. CONCLUSIONS: These single-treatment approaches are equally effective treatments for benign paroxysmal positional vertigo. Further studies are needed to look at the long-term effectiveness of these treatments.

Adult↗
PubMed1993

Abnormal spatial localization with trigeminal-oculomotor synkinesis. Evidence for a proprioceptive effect.

We examined spatial localization, using open-loop pointing to visual targets, in a patient with a congenital trigeminal-oculomotor synkinesis. This patient demonstrated abnormal co-activation of the left medial rectus muscle when the left lateral pterygoid contracted. Because one eye could be deviated in the absence of a normal oculomotor innervational command, the efference copy (derived from monitoring of central oculomotor commands) could be dissociated from the proprioceptive afferent signal (determined by the mechanical state of the extraocular muscles). Under conditions of monocular viewing with the normal right eye, when the covered left eye was adducted by the aberrant trigeminal innervation, the patient pointed to the left of the actual position of the target. This finding indicates that proprioceptive afference from the adducted, covered left eye was used in the process of spatial localization. While synkinetic adduction produced a shift in pointing in the opposite direction of rotation of the non-viewing eye, previous studies using passive deviation of the non-viewing eye in normal subjects reported a shift in pointing in the same direction as eye rotation (Gauthier et al., 1990; Bridgeman and Stark, 1991). We propose that this discrepancy is due to the different effects of passive eye rotation and active muscle contraction on the tendon organs of the extraocular muscles. On this basis, we hypothesize that the tendon organs, rather than the muscle spindles, are primarily responsible for the transduction of proprioceptive information about eye position in the orbit.

Adolescent↗
PubMed1993

Ocular motor disorders associated with cerebellar lesions: pathophysiology and topical localization.

A number of ocular motor abnormalities can be correlated with damage in specific parts of the cerebellum, especially the vestibulo-cerebellum (flocculus, paraflocculus, nodulus, uvula), and the dorsal vermis and the underlying (posterior) fastigial nuclei. These abnormalities of eye movements reflect both immediate, on-line and long-term adaptive functions of the cerebellum. Various types of image-stabilizing reflexes are in the province of the flocculus (and probably paraflocculus) including pursuit, vestibulo-ocular reflex (VOR) cancellation, and holding the eye steady for fixation, both immediately after saccades and in eccentric positions of gaze. The nodulus (and ventral uvula) modulates "low-frequency" aspects of vestibular responses and hence controls the duration (time constant) of the VOR. The dorsal vermis and underlying (posterior) fastigial nuclei participate in the control of the size of the saccadic pulse of innervation and hence saccadic accuracy. Here we review the eye signs that reflect abnormalities of these clearly defined cerebellar functions. We will also discuss less well localized but presumed cerebellar eye signs and consider a potential role for the cerebellum in the control of both dynamic and static ocular alignment.

Cerebellar Diseases↗
PubMed1993

Adaptation of the vestibulo-ocular reflex with the head in different orientations and positions relative to the axis of body rotation.

We investigated the influence of static head orientation and position, relative to the axis of body rotation, upon vestibular adaptation. With the head centered, displaced anterior to the axis of body rotation, or tilted 40 degrees to 45 degrees in roll or pitch, the gain of the vestibulo-ocular reflex (VOR) was trained (to go either up or down) for one hour using artificial manipulation of the visual surround to produce a visual-vestibular mismatch. Before and after each training session, the VOR was measured in darkness with the head in the training as well as in several non-training positions. We found that transfer of VOR adaptation to non-training positions was almost complete when comparing head eccentric versus head-centered rotations. For tilts, however, transfer of VOR learning was far less complete suggesting that static otolith signals provide a strong contextual cue that gates the expression of an adaptive VOR response. Finally, following training to increase the VOR, gain was greater for centripetally than centrifugally directed slow phases. Centripetally directed postsaccadic drift also developed. These findings imply that the gain increase paradigm also leads to abnormal function of the velocity-to-position neural integrator, which holds eccentric positions of gaze.

Adaptation, Physiological↗
PubMed1993

Latent nystagmus. Release and suppression at will.

PURPOSE: The authors report the cases two unusual patients with infantile convergent strabismus and latent nystagmus. METHODS: Electronystagmography was used. RESULTS: The two patients were able to release and suppress their nystagmus at will. With voluntary effort, the nystagmus became as strong as it was when brought out by occlusion of the squinting eye and, in one of the patients, even stronger. The nystagmus beat toward the fixing eye, and the slow phases had slightly decreasing velocity or were linear. Both patients were able to evoke and to stop the nystagmus in front of visual contours and, one of them, also in the dark. CONCLUSIONS: This phenomenon could be the result of voluntary control of the visual input contributed by the amblyopic eye and/or a direct influence of will on the slow eye movement and fixation systems. A mechanism related to vergence eye movements is less likely. The ability to release and suppress a latent nystagmus at will is unusual and, to the authors' knowledge, has not been described before.

Adult↗
PubMed1992

Velocity storage in labyrinthine disorders.

We studied 13 patients with unilateral peripheral vestibular lesions following removal of acoustic neurinomas. The time constant of the VOR after surgery was 6.4 +/- 2.6 seconds (normal is 18.5 +/- 7.7 seconds). The time constant of OKAN after surgery was 7.2 +/- 1.8 seconds (normal is 11.3 +/- 3.2 seconds). The mean initial velocity of OKAN after surgery was 9.7 +/- 2.4 deg/second (normal is 11.7 +/- 5.9 deg/second). These data suggest that unilateral peripheral vestibular loss is associated with a complete loss of velocity storage for canal input but only a partial loss of velocity storage for visual input. These results can be accounted for by current mathematical models of the velocity storage mechanism.

Humans↗
PubMed1992

Disconjugate ocular motor adaptation in rhesus monkey.

We report a model for inducing disconjugate, orbital-position dependent, ocular motor adaptation in the rhesus monkey. Animals wore a combination of laterally-displacing prisms placed in front of one eye calling for a discrete change in ocular alignment when the eyes reached particular orbital positions. After wearing the prism combination the animals developed adaptive changes both in static alignment during fixation and in dynamic alignment during eye movements. These changes persisted with only one eye viewing and so became independent of the immediate presence of disparity cues. There were, however, imperfections in the adaptive responses; the changes in the innervation were gradual across the prism edge, not abrupt as required. This finding may reflect inherent limitations in the capability for disconjugate adaptation.

Adaptation, Ocular↗
PubMed1992

Abnormalities of predictive saccades in hemi-Parkinson's disease.

We studied reflexive and predictive saccades by direct current electro-oculography in nine patients with mild hemi-Parkinson's disease (hemi-PD) and in 16 age-matched controls. In five patients, the neurological syndrome was predominant on the right side of the body (RPD) and in four patients, on the left side (LPD). Reflexive saccades were elicited in response to the random appearance (timing and location) of a light-emitting diode (LED). Predictive saccades were elicited by alternatively illuminating LEDs at 10 degrees right and left, at various fixed frequencies (0.25-1 Hz). In the reflexive task, latency and amplitude of the saccades were normal in both PD groups. In the predictive task, mean saccade latency was not significantly different between patients and normals but there were two significant abnormalities in timing: first, but only in LPD, a directional asymmetry in latency (left greater than right, e.g. at 0.25 Hz, mean difference of 90 ms); secondly, especially in RPD, an abnormal tracking pattern, reflected by more variability of the mean value (for each group of patients) of saccade latency at each point in time, throughout a period of tracking at a given frequency. Predictive saccades were also strongly hypometric in both PD groups but especially in LPD (e.g. for rightwards saccades: controls = 19 degrees, SD = 1.6; LPD = 14 degrees, SD = 2.7; RPD = 15.7 degrees, SD = 2.3). These defects in saccadic timing and amplitude during predictive tracking were most salient at low frequencies. While these defects were largely bilateral, our findings suggest slightly different contributions of the right and left cerebral hemispheres to the spatial and timing components, respectively, that comprise optimal predictive saccadic behaviour.

Adult↗
PubMed1992

Saccade-vergence interactions in humans.

1. We recorded eye movements in four normal human subjects during refixations between targets calling for various combinations of saccades and vergence. We confirmed and extended prior observations of 1) transient changes in horizontal ocular alignment during both pure horizontal saccades (relative divergence followed by relative convergence) and pure vertical saccades (usually divergence for upward and convergence for downward saccades); 2) occasional, high-frequency (20-25 Hz), conjugate oscillations along the axis orthogonal to the main saccade; and 3) the speeding up of horizontal vergence by both horizontal and vertical saccades. 2. To interpret these findings, we developed a hypothesis for the generation of vergence to step changes in target depth, both with and without associated saccades. The essential features of this hypothesis are 1) the transient changes in horizontal ocular alignment during pure horizontal saccades reflect asymmetries in the mechanical properties of the lateral and medial rectus muscles causing adduction to lag abduction; 2) pure vergence movements in response to step changes in target depth are generated by a neural network that uses a desired change in vergence position as its input command and instantaneous vergence motor error (the difference between the desired change and the actual change in vergence) to drive vergence premoter neurons; and 3) the facilitation of horizontal vergence by saccades arises from nonlinear interactions in central premotor circuits. 3. The hypothetical network for generating pure vergence to step changes in target depth is analogous in structure to the local feedback model for the generation of saccades and has the same conceptual appeal. With the assumption of a single nonlinearity describing the relationship between a vergence motor error signal and the output of the neurons that generate promoter vergence velocity commands, this model generates pure vergence movements with peak velocity-amplitude relationships and trajectories that closely match those of experimental data. 4. Several types of models are proposed for the central, nonlinear interaction that occurs when saccades and vergence are combined. Common to all models is the idea that omnidirectional pause neurons (OPN), which are thought to gate activity for saccade burst neurons, also gate activity for saccade-related vergence. In one model we hypothesize the existence of a separate class of saccade-related vergence burst neurons, which generate premotor horizontal vergence commands but only during saccades. In a second model we hypothesize separate right eye and left eye saccadic burst neurons that receive not only conjugate, but also equal but oppositely directed vergence error signals.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1992

Postural stability in patients with Huntington's disease.

We characterized postural stability in patients with Huntington's disease (HD) by examining their ability to use different sensory cues to maintain balance and by recording their automatic postural responses to externally applied perturbations. Our HD patients, like normal subjects, depended more on proprioceptive than on visual cues to maintain balance. HD patients, however, developed more sway than normal subjects when proprioceptive cues, or when proprioceptive cues and vision, were altered. Thus, HD patients showed a defect in using vestibular information alone to maintain normal postural stability. The onset of compensatory motor responses in the lower extremities following sudden translations of the support surface was delayed by 30 to 60 msec in HD patients as compared with normal subjects. HD patients also had more sway and falls during unexpected rotations of the support surface, although they could appropriately reduce their motor responses on the next trial.

Adult↗
PubMed1992

Internuclear ophthalmoplegia: pathophysiology and diagnosis.

The main findings in unilateral INO are paresis of adduction in the eye on the side of the lesion (for conjugate but not vergence eye movements) and abduction nystagmus in the eye on the side opposite to the lesion. A skew deviation (eye usually higher on the side of the lesion) or a dissociated, mixed vertical-torsional nystagmus, with the eye beating down on the side of the lesion, may also occur. The main findings in bilateral INO are paresis of adduction in both eyes, bilateral abduction nystagmus and, in the vertical plane, impaired gaze-holding, vestibular responses and smooth tracking. Abduction nystagmus in INO may have a number of causes; probably most common are a gaze-evoked nystagmus superimposed on adduction weakness and adaptation to adduction weakness. Most of the findings in INO can be explained by interruption of projections from abducens internuclear neurones, mediating adduction, and from the vestibular nuclei, mediating both canal- and otolith-induced reflexes as well as vertical gaze holding and pursuit. Extension of the lesion to structures near but outside the MLF, or involvement of cell bodies intermixed with MLF fibres, may also be important in the pathogenesis of the abduction nystagmus and the occasional slowing of abducting saccades.

Eye Movements↗
PubMed1992

Clinical implications of otolith-ocular reflexes.

While difficult to test clinically, otolith-induced vestibular responses play an important role in both vestibulo-ocular and vestibulo-spinal reflexes, and are likely a source of symptoms in patients with vestibular disorders. Here we review basic aspects of otolith-induced vestibulo-ocular reflexes and consider some clinical implications of disordered otolith function. Emphasis is placed on ocular responses to translation and to tilt and the influence of gravity on vestibulo-ocular responses induced during head rotation.

Adaptation, Physiological↗