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Biomedical subjects

M J Morrow

Publications and source records attributed to M J Morrow.

At least 19 recordsLinked to original sources
PubMed1998

Epidural anaesthesia for caesarean section in an achondroplastic dwarf.

We describe the anaesthetic management of a parturient with achondroplasia presenting for Caesarean section under epidural anaesthesia. A block extending from T4 to S4 was established over 25 min using a total of 12 ml of 2.0% lidocaine (lignocaine) with epinephrine (adrenaline) 1:200,000 and fentanyl 37.5 micrograms. Apart from mild discomfort during peritoneal incision, her perioperative course was uneventful. Achondroplasia is reviewed and the anaesthetic implications of the condition are discussed.

Achondroplasia↗
PubMed1998

Function and dysfunction of supranuclear and internuclear eye movement pathways.

Recent investigations in ocular motility have shed light on the anatomical and physiological mechanisms that govern smooth pursuit, saccades, and the vestibulo-ocular reflex in normal humans and patients with neurological disorders. Functional neuroimaging and transcranial magnetic stimulation have been used in normal human subjects to draw parallels with basic investigations in animals. Quantitative studies of eye movement disorders in patients with focal brain dysfunction have added to our understanding of human pathophysiology. Finally, some of the most practical of recent work has been aimed at developing therapies to alleviate the functional limitations caused by abnormal eye movements.

Animals↗
PubMed1997

Deficits of gaze stability in multiple axes following unilateral vestibular lesions.

Abnormalities in the vestibulo-ocular reflex (VOR) after unilateral vestibular injury may cause symptomatic gaze instability. We compared five subjects who had unilateral vestibular lesions with normal control subjects. Gaze stability and VOR gain were measured in three axes using scleral magnetic search coils, in light and darkness, testing different planes of rotation (yaw and pitch), types of stimulus (sinusoids from 0.8 to 2.4 Hz, and transient accelerations) and methods of rotation (active and passive). Eye velocity during horizontal tests reached saturation during high-velocity/acceleration ipsilesional rotation. Rapid vertical head movements triggered anomalous torsional rotation of the eyes. Gaze instability was present even during active rotation in the light, resulting in oscillopsia. These abnormal VOR responses are a consequence of saturating nonlinearities, which limit the usefulness of frequency-domain analysis of rotational test data in describing these lesions.

Adaptation, Physiological↗
PubMed1997

Effects of eye and head position on horizontal and vertical smooth pursuit.

PURPOSE: To identify and explain the effects of eye and head position on smooth pursuit eye movements in normal humans. METHODS: Horizontal and vertical smooth pursuit were measured in different eye-in-orbit positions in normal subjects, using a magnetic search coil technique with sinusoidal and step-ramp stimuli. Pursuit also was tested in different horizontal head-on-trunk positions. RESULTS: Pursuit gain to sinusoidal targets averaged approximately 15% less with the eyes centered 30 degrees horizontally or vertically from the primary position than with the eyes near the orbital midline. In contrast, initial pursuit responses to step-ramp stimuli were similar regardless of eye position. For sinusoidal and step-ramp responses in eccentric eye positions, no significant differences were found between pursuit movements directed toward the orbital midposition and pursuit movements directed away from it. Changes in head position had no effect on smooth pursuit. CONCLUSIONS: Sinusoidal smooth pursuit function decreases modestly for horizontal and vertical motion in eccentric eye positions. This effect is not caused by reductions in gain for centrifugal movements compared to centripetal movements, implying that the pursuit nonlinearities expected to arise from orbital mechanics are largely eliminated by central processing. Eye position-related differences in retinal or eye motion feedback or in predictive input may explain the influence of eye position on smooth pursuit maintenance. Changes in target position with respect to a trunk-centered frame of reference did not produce the orbital eccentricity effects that were documented because sinusoidal pursuit gain did not vary with head rotation.

Adult↗
PubMed1996

Effects of fixation target timing on smooth-pursuit initiation.

We measured smooth pursuit and anticipatory smooth eye movements in four normal subjects, using step-ramp stimuli. Between trials, subjects fixated a motionless central target which disappeared before, after, or at the same time as the ramp stimulus appeared. We found that gaps or overlaps in the relative timing of fixation target offset and ramp onset neither expedited nor delayed the initiation of smooth pursuit. In contrast, anticipatory and smooth pursuit eye accelerations were influenced by the presence of a stationary foveal target; both were significantly higher when the fixation stimulus disappeared before ramp onset than when it disappeared after ramp onset.

Adult↗
PubMed1996

Bilateral ocular neuromyotonia: oculographic correlations.

We observed bilateral ocular neuromyotonia in a 45-year-old woman previously treated for a pituitary adenoma. She experienced episodic diplopia attributable to dysfunction of muscles innervated by both oculomotor nerves. Oculography demonstrated episodes of tonic adduction with slowing and restriction of saccades in all directions, but no oscillatory component. A combination of impaired phasic firing in agonist muscles and tonic contraction of antagonist muscles explains the paroxysms of eye movement limitation in this disorder.

Female↗
PubMed1996

Craniotopic defects of smooth pursuit and saccadic eye movement.

I recorded smooth pursuit and saccadic eye movements in six patients with unilateral cerebral infarction. By comparing responses within the hemiranges of eye position to the right and left of the orbital midline and in rightward and leftward directions, I quantified craniotopic and directional ocular motor deficits. Two patients had ipsiversive gaze deviation and severe craniotopic defects in which they could not generate smooth pursuit or saccadic eye movement into the contralateral orbital hemirange. Three patients without gaze deviation generated worse smooth pursuit in the contralateral hemirange than in the ipsilateral hemirange, but each had symmetric saccades according to eye position. All patients with craniotopic pursuit defects also had directional smooth tracking asymmetries in which eye velocities were lower for targets moving ipsilaterally than for targets moving contralaterally. Craniotopic and directional defects were associated with damage in the frontal eye field region. Orbital position is taken into account by cerebral circuits that govern smooth pursuit and saccades.

Adult↗
PubMed1995

Deficits of smooth-pursuit eye movement after unilateral frontal lobe lesions.

We recorded horizontal smooth-pursuit responses to sinusoidal and step-ramp stimuli in 7 patients with unilateral frontal lobe lesions. Five patients had directional smooth-pursuit deficits, all with impairment toward the side of cerebral damage. Ipsidirectional pursuit defects involved pursuit maintenance to sinusoidal targets, pursuit initiation to step-ramp targets, or both. No patient had asymmetry of smooth pursuit according to the retinal hemifield of target appearance. Smooth-pursuit velocities were subnormal in both horizontal directions in 4 patients. The human frontal lobes participate in the initiation and maintenance of smooth pursuit in both directions, with a greater ipsilateral contribution. Of 5 patients with ipsilateral pursuit impairment, 3 had cerebral lesions in the area of the frontal eye field (FEF). These 3 patients also made inaccurate saccades to targets moving away from the side of the lesion, implying that the FEF transmits motion information to the saccadic system. Two patients with ipsidirectional smooth-pursuit defects had cerebral damage that spared the FEF, indicating that other frontal regions also contribute to smooth pursuit.

Adult↗
PubMed1994

The relationship of anticipatory smooth eye movement to smooth pursuit initiation.

We measured anticipatory smooth eye movements and smooth pursuit initiation with predictable and unpredictable step-ramp stimuli in normal subjects. Subjects generated anticipatory eye motion before targets moved and during intervals when targets suddenly disappeared. Expectations of target trajectory modified pursuit acceleration and latency, demonstrating that pursuit initiation is not governed by visual inputs alone. Anticipatory smooth eye movements and predictive contributions to smooth pursuit had similar accelerations and velocities. Anticipation and pursuit initiation varied in parallel between subjects; anticipation was stronger in subjects who generated faster smooth pursuit. These findings imply that anticipatory and smooth pursuit eye movements are governed by a common mechanism.

Adult↗
PubMed1993

The effects of head and trunk position on torsional vestibular and optokinetic eye movements in humans.

We measured torsional vestibular and optokinetic eye movements in human subjects with the head and trunk erect, with the head supine and the trunk erect, and with the head and trunk supine, in order to quantify the effects of otolithic and proprioceptive modulation. During active head movements, the torsional vestibulo-ocular reflex (VOR) had significantly higher gain with the head upright than with the head supine, indicating that dynamic otolithic inputs can supplement the semicircular canal-ocular reflex. During passive earth-vertical axis rotation, torsional VOR gain was similar with the head and trunk supine and with the head supine and the trunk erect. This finding implies that static proprioceptive information from the neck and trunk has little effect upon the torsional VOR. VOR gain with the head supine was not increased by active, self-generated head movement compared with passive, whole body rotation, indicating that the torsional VOR is not augmented by dynamic proprioceptive inputs or by an efference copy of a command for head movement. Viewing earth-fixed surroundings enhanced the torsional VOR, while fixating a chair-fixed target suppressed the VOR, especially at low frequencies. Torsional optokinetic nystagmus (OKN) evoked by a full-field stimulus had a mean slow-phase gain of 0.22 for 10 degrees/s drum rotation, but gain fell to 0.06 for 80 degrees/s stimuli. Despite this fall in gain, mean OKN slow-phase velocities increased with drum speed, reaching maxima of 2.5 degrees/s-8.0 degrees/s in our subjects. Optokinetic after nystagmus (OKAN) was typically absent.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Smooth pursuit initiation in young and elderly subjects.

Smooth pursuit initiation to step-ramp stimuli was investigated in normal subjects, young and elderly. Older subjects had significant reductions in initial pursuit acceleration before saccades, and in post-saccadic and peak pursuit velocities. Aging impairs the open-loop performance of the pursuit system, possibly by decreasing sensitivity to retinal image motion or by limiting the conversion of visual motion signals into commands for smooth pursuit. Lower open-loop pursuit gain degrades steady-state, closed-loop smooth pursuit in senescence. Our elderly subjects also made less accurate saccades to moving targets, implying defective use of visual motion information by the saccadic system.

Adult↗
PubMed1993

Oblique misdirection and slowing of vertical saccades after unilateral lesions of the pontine tegmentum.

Three patients with unilateral lesions of the pontine tegmentum, identified by CT and MRI, had abnormal vertical saccades and slowed ipsilateral horizontal saccades. Attempted vertical saccades were misdirected obliquely, away from the side of the lesion, and their vertical components were prolonged. Oblique saccades had curved trajectories and prolonged durations of their vertical components. Unilateral damage to excitatory burst neurons and pause cells in the medial part of the caudal paramedian pontine reticular formation may cause these abnormal vertical and oblique saccades. Misdirection and slowing of vertical saccades can accompany the paralysis or slowing of ipsilateral horizontal saccades caused by pontine damage.

Electrooculography↗
PubMed1993

Retinotopic and directional deficits of smooth pursuit initiation after posterior cerebral hemispheric lesions.

We investigated the initiation of ocular smooth pursuit with horizontal ramp targets in 16 patients with unilateral posterior cerebral lesions. Four of the 16 patients had directional pursuit asymmetry, in which smooth eye movement velocities were reduced toward the lesion, independent of target location on the retina. Of seven patients with normal visual fields for the target, two had a retinotopic eye movement deficit consisting of impaired smooth pursuit of targets moving in both horizontal directions in the hemifield contralateral to their lesion. Patients with retinotopic deficits and normal visual fields, and those with directional deficits, had impairment of smooth pursuit similar to that caused by unilateral lesions of cortical areas MT (middle temporal) and MST (medial superior temporal) in monkeys. All but one patient with either of these defects had a lesion near the junction of Brodmann's areas 19, 37, and 39, providing evidence that this region includes the human homologues of monkey areas MT and MST. One patient with a retinotopic pursuit defect and normal visual fields had a lesion of the rostral superior temporal sulcus, which may have included the homologue of the superior temporal polysensory area of monkeys.

Adult↗