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Biomedical subjects

M Flanders

Publications and source records attributed to M Flanders.

36 records · Page 2Linked to original sources
PubMed1990

Superior oblique palsy: diagnosis and treatment.

To pinpoint the diagnostic dilemmas and to look for differentiating preoperative features in cases of masked bilateral superior oblique palsy, the authors reviewed the charts of 50 patients (26 males and 24 females with an average age at presentation of 25.6 years) with an established diagnosis of superior oblique palsy seen between 1980 and 1987. Most patients had a history of symptoms from childhood or following trauma. Typically, patients complained of torticollis and diplopia and manifested inferior oblique overaction and superior oblique underaction of the paretic eye. Twenty-two of the patients underwent a total of 28 operations; surgery resulted in elimination of symptoms and neutralization of the hyperdeviation in 77%. On the basis of this experience the authors discuss the presenting features and the differential diagnosis of superior oblique palsy and present a rational approach to surgical intervention.

Adolescent↗
PubMed1990

Parcellation of sensorimotor transformations for arm movements.

Pointing to a visual target in 3-dimensional space requires a neural transformation from a visually derived representation of target location to an appropriate pattern of activity in arm muscles. Previous results suggested that 1 step in this process involves a transformation from a representation of target location to a representation of intended arm orientation, and that the neural implementation of this transformation involves a linear approximation to the mathematically exact, nonlinear solution. These results led to the hypothesis that the transformation is parceled into 2 separate channels. In 1 channel a representation of target azimuth is transformed into a representation of arm yaw angles, while in the other channel representations of target distance and target elevation are transformed into a representation of arm elevation angles. The present experiments tested this hypothesis by measuring the errors made by human subjects as they pointed to various parameters of the remembered location of a target in space. The results show that subjects can use the 2 hypothesized channels separately. For example, subjects can accurately point to the target's azimuth while ignoring the target's elevation and distance. The results also show that subjects are unable to point to the target's elevation while ignoring the target's distance, consistent with the hypothesis that information about target elevation and target distance is tied together in the same channel. The parcellation demonstrated in this study is compared to reports of parceled sensorimotor transformation in other vertebrate species.

Arm↗
PubMed1989

Sensory control of target acquisition.

Recent research has expanded our understanding of how the nervous system uses visual and kinesthetic input to move the arm to a target. In this review, we present data to show how the nervous system can rapidly use sensory input to control impending or ongoing motor activity. We contrast visual control with kinesthetic control to show how these two sources of sensory input are used to control parameters of motor command such as amplitude and direction, to trigger the motor commands, and then to correct errors in trajectory. Despite many differences in the organization of the visual and the kinesthetic sensory systems, the nervous system appears to process these two types of sensory input similarly.

Afferent Pathways↗
PubMed1989

Sensorimotor representations for pointing to targets in three-dimensional space.

1. The accuracy with which subjects pointed to targets in extrapersonal space was assessed under a variety of experimental conditions. 2. When subjects pointed in the dark to remembered target locations, they made substantial errors. Errors in distance, measured from the shoulder to the target, were sometimes as much as 15 cm. Errors in direction, also measured from the shoulder, were smaller. 3. An analysis of the information transmitted by the location of the subject's finger about the location of the target showed that the information about the target's distance was consistently lower than the information about its direction. 4. The errors in distance persisted when subjects had their arm in view and pointed in the light to remembered target locations. 5. The errors were much smaller when subjects used a pointer to point to the target or when they were asked to reproduce the position of their finger after it had been passively moved to the target. 6. From these findings we conclude that subjects have a reasonably accurate visual representation of target location and are able to effectively use kinesthetically derived information about target location. We therefore suggest that errors in pointing result from errors in the sensorimotor transformation from the visual representation of the target location to the kinematic representation of the arm movement.

Darkness↗
PubMed1989

Errors in pointing are due to approximations in sensorimotor transformations.

1. We define an extrinsic frame of reference to represent the location of a point in extrapersonal space relative to a human subject's shoulder, and we define an intrinsic frame of reference to represent the orientation of the arm and forearm. 2. We examined the relations between coordinates in the extrinsic and intrinsic frames of reference under two experimental conditions: when subjects made inaccurate movements by pointing to virtual targets in the dark and when they made accurate movements by pointing to actual targets in the light. 3. When subjects made inaccurate movements, there was a close-to-linear relationship between the orientation angles of the arm (intrinsic coordinates) at its final position and the extrinsic coordinates of the target. When they made accurate movements, these relationships were more nonlinear. 4. Specifically, arm and forearm elevations depended principally on target distance and elevation, whereas the two yaw angles depended mainly on the target's azimuth. 5. We propose that errors in pointing occur because subjects implement a linear approximation to the transformation from extrinsic to intrinsic coordinates and that this transformation is one step in the process of transforming a visually derived representation of target location into an appropriate pattern of muscle activity.

Darkness↗
PubMed1989

Bilateral congenital third cranial nerve palsy.

We describe a patient in whom bilateral congenital third cranial nerve palsy was diagnosed at 2 weeks of age. The ptosis was treated at 3 weeks with bilateral eyelid suspension surgery, and surgical repair of the exotropia was done at 4 months. To our knowledge this is the fourth reported case of this condition. It was probably caused by a single lesion involving the oculomotor and possibly the trochlear nuclei in the brain stem. Magnetic resonance imaging scans supported this hypothesis and suggested other central nervous system anomalies.

Child, Preschool↗
PubMed1989

Kinesthetic and visual control of a bimanual task: specification of direction and amplitude.

Kinesthetic information about a perturbation can quickly modify motor activity by producing reflexive compensation. The purpose of the present study was to determine how quickly kinesthetic information about target movement can modify motor activity. Visual information about target movement is known to guide motor activity both quickly and accurately. Therefore, we compared the speed and accuracy of responses to kinesthetically and visually presented targets. Human subjects produced changes in elbow torque as quickly and accurately as possible after the random presentation of 1 of 8 target torques. Information about the direction and amplitude of the target torque was provided either kinesthetically or visually. Responses to kinesthetic targets started at an average latency of 150 msec, and after an additional 159 msec, these responses became accurately graded according to target amplitude. Responses to visual targets started at an average latency of 250 msec, and after an additional 208 msec, these responses became accurately graded according to target amplitude. The accuracy of responses to kinesthetic targets was very similar to the accuracy of responses to visual targets. We conclude that the neural processing of kinesthetic information about target movement is sufficiently fast and accurate to guide typical motor activities.

Adult↗
PubMed1988

Head movement co-ordination in the African chameleon.

Chameleon head movement was studied to learn how information from more than one sensory system can be co-ordinated to produce a single motor behavior. In this study, the co-ordination of visual, vestibular, and kinesthetic senses was examined by: (1) moving a cricket back and forth in front of a hungry chamelon, (2) moving the body of an alert chameleon or the body of an anesthetized chameleon, and (3) moving both a cricket and the body of an alert chameleon. During cricket movement, the chameleon locked both eyes straight forward in their orbits and followed the cricket movement with a visually guided head movement. During movement of the body of an alert chameleon, the vestibulo-collic reflex kept the chameleon's head relatively stationary in space. During movement of the body of an anesthetized chameleon, there was no measurable movement of the head relative to the body. Thus, during the body movements used in this study, passively induced kinesthetic stimulation was negligible. It was hypothesized that during movement of both a cricket and the body of an alert chameleon, the visually guided head movement and the vestibulo-collic reflex were additive. This hypothesis was supported by demonstrating that in this situation, the vestibulo-collic reflex was not suppressed. It is suggested that the vestibulo-collic reflex compensated for the passive head movement produced by body movement without canceling active, visually guided head movement. This may have been accomplished by the use of an efference copy system associated with the motor commands that produce visually guided head movement.

Afferent Pathways↗
PubMed1987

Quantification of peripherally induced reciprocal activation during voluntary muscle contraction.

A new method was developed to compare patterns of coactivation and reciprocal activation of antagonistic muscles during different experimental conditions. Pure coactivation was defined as a muscle activity pattern where there was never a difference between the slope of the agonist EMG record and the slope of the antagonist EMG record. The degree of reciprocal activation was defined as being proportional to the average absolute value of the difference between these two slope values. Use of this method for the comparison of muscle activity patterns during isometric contractions and unexpected movements showed that peripheral input related to agonist unloading and antagonist stretch significantly increased reciprocal activity.

Adult↗
PubMed1987

Injection of type A botulinum toxin into extraocular muscles for correction of strabismus.

Between July 1984 and March 1985, 51 injections of type A botulinum toxin were given to 39 patients aged 11 to 81 years with various types of strabismus, including paralytic strabismus, sensory exotropia, consecutive and residual postsurgical deviations and partially accommodative esotropia. All deviations were documented by orthoptic assessment and photography. After treatment the patients were followed for up to 3 years. The beneficial effects of a single injection were modest, and a second injection was often necessary to achieve satisfactory ocular alignment. Thirteen of the 26 patients (50%) with nonparalytic strabismus and 10 of the 13 patients (77%) with paralytic strabismus had a good outcome (final deviation 12 prism dioptres or less). Adverse side effects included transient ptosis and diplopia and inadvertent vertical deviation. Twenty-one consecutive cases of nonparalytic horizontal strabismus treated with adjustable sutures were also reviewed. The results in these patients were more predictable and longer lasting than those in the patients who received botulinum toxin.

Adolescent↗
PubMed1987

Nonhealing corneal defects due to herpes simplex in children.

Two young children with unilateral photophobia, redness, blepharospasm and corneal epithelial defects unresponsive to conservative therapy were seen between December 1982 and June 1983. Herpes simplex virus was established as the causal agent in both cases, only after the children had been examined under general anesthesia and appropriate cultures obtained. The difficulties in diagnosing herpetic keratitis in children and the treatment and long-term prognosis are discussed.

Child, Preschool↗
PubMed1987

Treatment of blepharospasm with medication, surgery and type A botulinum toxin.

A total of 39 patients with essential blepharospasm and 2 patients with hemifacial spasm were treated with one or more forms of therapy. All patients underwent neurologic and ophthalmic assessment to rule out ocular causes of blepharospasm. Thirty-six patients were given a trial of various medications. Only one patient was successfully treated: her condition was markedly improved with pimozide after benztropine mesylate, clonazepam and amantadine hydrochloride had failed to help. Patients who did not respond to drug therapy were offered the option of undergoing eyebrow-eyelid muscle stripping surgery. The six patients who underwent surgery showed considerable improvement; however, side effects such as frontal anesthesia, exposure keratitis, lagophthalmus, scarring and eyelid malposition occurred, and three of the six had residual spasm. At this point type A botulinum toxin became available. A total of 27 patients (26 who did not respond to drug therapy, including the 3 with residual spasm after surgery, and 1 previously untreated patient) received type A botulinum toxin injections. Most experienced rapid relief from their spasms. The beneficial effects lasted weeks to months, and there were no major side effects. Treatment with type A botulinum toxin appears to be a safe and effective means of temporarily relieving blepharospasm. The long-term results with repeated injections are yet to be determined.

Baclofen↗
PubMed1985

Visually guided head movement in the African chameleon.

Visually guided head movement was studied in the African chameleon. Within certain ranges of frequencies and amplitudes, the chameleons followed horizontal, sinusoidal cricket (bait) movement with sinusoidal head movement and no apparent eye movement. Although head movement lagged behind bait movement, the chameleons used head amplitudes that minimized the motion of the bait relative to the head.

Animals↗
PubMed1984

Keratoconus and Leber's congenital amaurosis: a clinicopathological correlation.

A 42-year-old man with Leber's congenital amaurosis, cataracts and keratoconus died following abdominal surgery. Postmortem pathological examination of the globes disclosed cone-shaped corneas with unusual central subepithelial scars and a retinopathy consistent with retinitis pigmentosa. A review of the family history revealed two siblings with congenital blindness.

Adult↗
PubMed1983

Atypical sensory nystagmus and its surgical management.

Two patients with oculocutaneous albinism who had presumed sensory-defect nystagmus also showed the features of congenital motor-defect nystagmus. Both patients used an abnormal head posture to block the nystagmus, and each had coexisting strabismus. Modern surgical techniques simultaneously shifted the null point of the nystagmus to the primary position and corrected the strabismus.

Adult↗
PubMed1982

Adjustable sutures in strabismus surgery.

The results of conventional strabismus surgery are always somewhat uncertain, despite the most careful preoperative assessment. Yet it is important to achieve good alignment in patients with fusion potential who have intermittent exotropia, extraocular muscle paresis or a restrictive syndrome. Planning surgery for patients with thyroid myopathy and planning reoperations is particularly difficult. In 30 patients with various strabismus disorders the use of adjustable sutures proved safe and of value; the results were unacceptable in only 5 of the 28 patients with horizontal deviations. The inconvenience for the surgeon and the extra discomfort for the patient seemed outweighed by the predictability of the surgical result.

Adult↗