PubMed Health⌕ Search

Biomedical subjects

L Tychsen

Publications and source records attributed to L Tychsen.

At least 37 records · Page 2Linked to original sources
PubMed1992

Comparative effects of laryngeal mask airway and endotracheal tube insertion on intraocular pressure in children.

Intraocular pressure (IOP) measurements in children are frequently performed under halothane-nitrous oxide anesthesia; however, anesthesia face masks may limit access to the eyes, and tracheal intubation is associated with transient increases in IOP. Use of the laryngeal mask airway (LMA) permits the maintenance of a patent airway without the need for laryngoscopy and tracheal intubation. In a randomized study of 41 children, we compared the IOP, hemoglobin oxygen saturation, and hemodynamic responses to the insertion of an LMA or tracheal tube during a standardized steady-state anesthetic technique consisting of 1 MAC halothane and 66% nitrous oxide. Baseline measurements of IOP, hemoglobin oxygen saturation, heart rate, and arterial blood pressure were recorded and repeated within 15-30 s after insertion of the airway device and at 1-min intervals for 5 min. Insertion of the LMA required significantly less time (26 +/- 16 vs 39 +/- 17 s [mean +/- SD]) and was associated with higher hemoglobin oxygen saturation values compared with the tracheal intubation. The LMA did not increase IOP, heart rate, or arterial blood pressure above baseline values. In contrast, tracheal intubation was associated with significant increases of IOP, heart rate, and arterial blood pressure. We concluded that the laryngeal mask offers advantages over tracheal intubation and the face mask for airway management in patients undergoing IOP measurements.

Anesthesia↗
PubMed1990

Periodic saccadic oscillations and tinnitus.

A man with essential hypertension developed stereotyped cycles of oscillopsia and bilateral "sparking" tinnitus. Eye movement recordings showed cycles of disconjugate opsoclonus, square-wave jerks, and saccadic dynamic overshoot disrupting stable fixation. Neuroimaging studies were normal. We postulate a lesion episodically disturbing saccade-related neurons and central auditory neurons in the pons.

Eye Movements↗
PubMed1989

Catecholamine depletion produces irrepressible saccadic eye movements in normal humans.

To determine the effect of catecholamine depletion on ocular motor pathways in humans, we studied the eye movements of 3 normal subjects who received the drug metyrosine (alpha-methylparatyrosine). This drug temporarily depleted dopamine and norepinephrine, as measured by a reduction in the metabolite, 3-methoxy-4-hydroxy-phenylethyleneglycol (MHPG). Saccadic, pursuit, and vestibulo-ocular eye movements were recorded using infrared oculography with subjects both on placebo and on metyrosine. The most consistent effect observed with metyrosine was an increase in the amplitude and frequency of saccadic intrusions during fixation and pursuit. Two of the 3 subjects also had shortened time constants for the vestibulo-ocular reflex, attributable in part to the sedative effect of catecholamine depletion. The increase in saccadic intrusions implies that catecholamines modulate the activity of a subpopulation of suppressor motor neurons in the human brainstem.

Administration, Oral↗
PubMed1989

Recovery of pupillomotor function after cataract surgery.

To determine the effect of cataract surgery upon pupillomotor function, we studied the pupillary response to light in four subjects who had extracapsular cataract extraction with implantation of an intraocular lens. A video infrared pupillometer was used to record pupillary responses 6-20 weeks after surgery. Non-operated eyes were compared to operated eyes in each subject. Amplitudes and peak velocities of constriction for operated versus non-operated eyes differed over a small range (2-14%). No evidence of dilation lag or segmental palsy was found in the operated eyes. The latency of constriction was not prolonged. We conclude that pupillomotor function can be expected to recover in aviators who require routine cataract surgery, and that visual disability due to a poorly dilating or constricting pupil should not be an overriding concern.

Aged↗
PubMed1989

Touching the cornea enhances pharmacologic dilation of the pupil, mainly in the dark iris.

Adequate pupillary dilation is often difficult to achieve in darkly pigmented persons when using standard dilating drops. To quantify the degree to which mild corneal disruption could enhance this dilation, we touched the cornea of one eye and then placed dilating drops in both eyes of darkly pigmented and lightly pigmented subjects. The touch was either standard Gold-mann applanation tonometry or corneal reflex testing using a cotton-tipped applicator. Pupil diameter was measured using a video infrared pupillometer. The mean difference in pupil diameter between the touched and the control eye at 30 min was six-fold greater in darkly pigmented, compared to lightly pigmented, subjects. Touching the cornea by the method described herein appears to be a safe, useful technique for routinely enhancing pharmacologic dilation of the pupil in persons who have dark irises.

Adult↗
PubMed1987

Visual motion processing and sensory-motor integration for smooth pursuit eye movements.

The function of smooth pursuit is to keep the fovea pointed at a small visual target that moves smoothly across a patterned background. Chemical lesions, single cell recordings, and behavioral measures have shown that the cortical motion processing pathways form the afferent limb for pursuit. Important areas include at least the striate cortex and the middle temporal visual area, and probably the medial superior temporal visual area and the posterior parietal cortex. We argue that the visual inputs are transmitted through a simple sensory motor interface in the pons, to the efferent limb in the brain stem and cerebellum. The efferent limb uses neural velocity memory to maintain pursuit automatically. We present evidence that the velocity memory is provided, at least in part, by eye velocity positive feedback between the flocculus of the cerebellum and the brain stem. Finally, we use a computer model to show how the maintenance of pursuit can be simulated on a millisecond time scale. The structure and internal elements of the model are based on the biological experiments reviewed in our paper. In the past five years, progress on the neural basis of pursuit eye movements has been rapid. Several areas of research have made substantial contributions, by using combinations of new and conventional methods. Many of the pathways that contribute to pursuit have been identified, and their physiological activity and functions are becoming understood. Continuing progress promises to yield an understanding of one specific form of visually guided movement, at the level of neuronal circuits and behavior, in the primate.

Animals↗
PubMed1986

Bilateral congenital restriction of upward eye movement.

Neurologic evaluation of a child with a severe headache revealed a bilateral inability to move the eyes above the horizontal plane. Computed tomographic and magnetic resonance scans of the brain obtained for a suspected midbrain lesion were normal. Photographs from early childhood confirmed that the deficit was congenital.

Child↗
PubMed1986

Resolution of saccadic palsy after treatment of brain-stem metastasis.

A 65-year-old man was unable to generate normal horizontal saccadic eye movements. Smooth pursuit of sinusoidal target motion was normal. The saccadic palsy resolved rapidly, twice, after treatment with intravenous corticosteroids. Computed tomography showed a lesion in the pons, and seven months later he was found to have metastatic adenocarcinoma.

Adenocarcinoma↗
PubMed1986

Visual motion processing for the initiation of smooth-pursuit eye movements in humans.

We have used the initiation of pursuit eye movements as a tool to reveal properties of motion processing in the neural pathways that provide inputs to the human pursuit system. Horizontal and vertical eye position were recorded with a magnetic search coil in six normal adults. Stimuli were provided by individual trials of ramp target motion. Analysis was restricted to the first 100 ms of eye movement, which precedes the onset of corrective feedback. By recording the transient response to target motion at speeds the pursuit motor system can achieve, we investigated the visual properties of images that initiate pursuit. We have found effects of varying the retinal location, the direction, the velocity, the intensity, and the size of the stimulus. Eye acceleration in the first 100 ms of pursuit depended on both the direction of target motion and the initial position of the moving target. For horizontal target motion, eye acceleration was highest if the stimulus was close to the center of the visual field and moved toward the vertical meridian. For vertical target motion, eye acceleration was highest when the stimulus moved upward or downward within the lower visual field. The shape of the relationship between eye acceleration and initial target position was similar for target velocities ranging from 1.0 to 45 degrees/s. The initiation of pursuit showed two components that had different visual properties and were expressed early and late in the first 100 ms of pursuit. In the first 20 ms, instantaneous eye acceleration was in the direction of target motion but did not depend on other visual properties of the stimulus. At later times (e.g., 80-100 ms after pursuit initiation), instantaneous eye acceleration was strongly dependent on each property we tested. Targets that started close to and moved toward the position of fixation evoked the highest eye accelerations. For high-intensity targets, eye acceleration increased steadily as target velocity increased. For low-intensity targets, eye acceleration was selective for target velocities of 30-45 degrees/s. The properties of pursuit initiation in humans, including the differences between the early and late components, are remarkably similar to those reported by Lisberger and Westbrook (12) in monkeys. Our data provide evidence that the cell populations responsible for motion processing are similar in humans and monkeys and imply that the functional organization of the visual cortex is similar in the two species.

Adult↗
PubMed1986

Maldevelopment of visual motion processing in humans who had strabismus with onset in infancy.

Binocular experience in infancy is necessary for the normal development of the visual cortex. However, it is not known whether binocular experience also affects the processing of specific kinds of visual information such as motion. We now report deficits in visual motion processing in 7 adult humans who lacked binocularity in infancy because of strabismus. As probes for assessing visual motion processing, we used the initiation of smooth pursuit eye movements and the judgment of target velocity independent of eye movement. Monocular viewing was essential to reveal the deficits. For horizontal pursuit, strabismic subjects showed nasal-temporal asymmetries, such that nasally directed target motion evoked more vigorous pursuit. For vertical pursuit, strabismics showed up-down asymmetries, such that upward target motion evoked more vigorous pursuit. In addition, strabismics had abnormalities in the relative effectiveness of different parts of the visual field for initiating both horizontal and vertical pursuit. Psychophysical judgements of horizontal target velocity revealed deficits analogous motion was perceived as faster than temporally directed motion, even when the 2 directions of motion were actually presented at the same speed. The magnitude of the motion processing deficits in each subject was correlated with the severity of the clinical signs of the strabismus. Our results suggest 2 possible interpretations. Maldevelopments of visual motion processing may cause strabismus in infancy, or alternatively, strabismus in the critical period for visual development may cause a maldevelopment of visual motion processing.

Adult↗
PubMed1985

Pursuit is impaired but the vestibulo-ocular reflex is normal in infantile strabismus.

To determine if infantile (congenital) strabismus is associated with a defect of ocular pursuit or vestibulo-ocular reflexes, eye movements were recorded in 14 subjects. Subjects with infantile strabismus had an impairment of temporally directed pursuit when monocularly viewing a moving target. They were unable to normally enhance or cancel the vestibulo-ocular reflex using visual tracking. Vestibulo-ocular reflexes were normal during rotation at 0.3 Hz in the dark. The pursuit defect was not found in subjects with noninfantile strabismus. We suggest that patients with infantile strabismus have a defect of cerebral pursuit control.

Child, Preschool↗
PubMed1984

Trochleitis with superior oblique myositis.

Thirteen patients complained of recent fluctuating aching of one orbit, punctuated by stabbing pains. All had exquisite point tenderness over the trochlea and in half of the patients the pain was aggravated by eye movement. Standardized A-scan echography demonstrated swelling of the peritrochlear tissue and thickening of the superior oblique muscle with low internal acoustic reflectivity, typical of myositis. CT scan showed a soft tissue density in the region of the trochlea. Biopsy, performed on two patients, revealed peri-trochlear inflammation. In all patients the symptoms resolved within a period of weeks or months: indomethacin or naproxen were not effective, but oral or locally injected corticosteroids shortened the course compared to no treatment. None of the patients had ptosis, proptosis, Brown's syndrome, or a click, nor did they have echographic or radiographic signs of sinusitis or inflammation away from the trochlea. This probably represents a highly localized subtype of idiopathic orbital inflammation ("pseudotumor").

Adult↗
PubMed1980

Fundal abnormalities of Gaucher's disease.

The evidence for cherry-red maculas in Gaucher's disease is questionable, but in occasional patients, scattered white spots in and on the retina appear to be characteristic. These white spots consist of clusters of swollen histiocytes (Gaucher cells).

Adolescent↗