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Biomedical subjects

R F Lewis

Publications and source records attributed to R F Lewis.

At least 37 records · Page 2Linked to original sources
PubMed1997

Influence of advanced recipient and donor age on the outcome of corneal transplantation. Australian Corneal Graft Registry.

AIMS: The aims of this study were to examine the influence of advanced recipient and donor age on the long term outcome of corneal transplantation. METHODS: Records of 1036 penetrating corneal grafts in recipients aged > or = 80 years at surgery (defined as the elderly subset) and 8092 donor corneas used for transplantation were obtained from the Australian Corneal Graft Register database, Kaplan-Meier graft survival plots were compared using log rank statistics. RESULTS: Elderly recipients constituted 15% of the recipient pool. The major indication for corneal transplantation in the elderly was bullous keratopathy. Graft survival fell with increasing recipient age (p < 0.00001); the major cause of graft failure was rejection (33%). The desired outcome in 51% of cases was to improve vision and in 42% of cases to relieve pain; 23% of elderly recipients achieved a Snellen acuity of 6/18 or better in the grafted eye and 66% recorded improved acuity after transplantation. Elderly recipients suffered more complications and comorbidities in the grafted eye than did younger recipients. Donor age (stratified in 10 year intervals) did not influence corneal graft survival significantly (p = 0.10). CONCLUSIONS: Elderly graft recipients fared less well after corneal transplantation than did younger recipients, but outcomes in terms of long term graft survival and visual rehabilitation were still good. Donor age did not affect graft survival.

Age Factors↗
PubMed1996

Vertigo: some uncommon causes of a common problem.

Vertigo, an extremely common symptom, may be caused by numerous disorders affecting the central or peripheral vestibular systems. Patients can usually be categorized into four groups based on the clinical presentation: monophasic, prolonged episodes of vertigo due to acute unilateral vestibular hypofunction; recurrent episodes of vertigo, due to transient vestibular dysfunction; vertigo provoked by changes in head position with respect to gravity (positional vertigo); and bilateral vestibulopathies, which present with imbalance and oscillopsia. Although each clinical syndrome is usually caused by a limited number of disorders, many less common entities must be considered in the differential diagnosis. This article reviews the clinical presentation of the less common causes of vestibular syndromes and discusses their medical and nonmedical management.

Adult↗
PubMed1996

Dynamic susceptibility contrast MRI of regional cerebral blood volume in Alzheimer's disease.

OBJECTIVE: The purpose of this study was to investigate the potential effectiveness of dynamic susceptibility contrast magnetic resonance imaging (MRI) to discriminate elderly patients with Alzheimer's disease from normal matched comparison subjects. METHOD: Images of regional cerebral blood volume (CBV) were generated from echo-planar MRI with the dynamic susceptibility contrast method in 13 Alzheimer's disease patients and 13 comparison subjects group-matched on age and gender. RESULTS: Temporoparietal cerebral blood volume, expressed as a percentage of the cerebellum value, was reduced 17% bilaterally in the patients with Alzheimer's disease. Blood volume in sensorimotor regions was reduced only 8.5% in the patients. Discriminant function analysis based on left and right temporoparietal measures correctly classified 88.5% of the subjects as patients or comparison subjects. Temporoparietal CBV was reduced even in mildly affected Alzheimer's disease patients (Mini-Mental State scores > 24). CONCLUSIONS: Dynamic susceptibility contrast MRI of regional CBV is promising as a nonradioactive, potentially lower-cost alternative to other functional neuroimaging methods for evaluating Alzheimer's disease.

Aged↗
PubMed1996

The Digit Vigilance Test: reliability, validity, and sensitivity to diazepam.

The Digit Vigilance Test (DVT), a measure of sustained attention and psychomotor speed, was evaluated in terms of test-retest and alternate-form reliability as well as sensitivity to a single dose of diazepam (10 mg). A one-page version was compared to the standard two-page format. Forty undergraduates, randomly assigned in a double-blind manner to either drug or placebo condition, were tested three times in two sessions (1 week apart). Both Page 1 and Total Time scores were found to be highly reliable across time and forms. Repeated measures ANOVAs revealed the Total Time score, but not the Page 1 score, to be significant in discriminating diazepam from placebo across time, supporting the use of the complete DVT for measuring drug effects. Findings based on convergent measures also help to validate the DVT as a measure of sustained attention.

Journal Article↗
PubMed1995

Regulation of static and dynamic ocular alignment in patients with trochlear nerve pareses.

Ocular alignment and saccades were studied in seven patients with trochlear nerve pareses, before and after strabismus surgery. Prior to surgery, a position-dependent vertical ocular misalignment was present, and downward saccades were hypometric in the paretic eye. Strabismus surgery reduced the magnitude and position-dependence of the static misalignment. Saccade conjugacy improved in the patients with congenital pareses, and in the patient with a gradual-onset acquired paresis, but less improvement occurred in subjects with traumatic pareses. The post-operative change in saccade conjugacy relative to the change in static alignment correlated with pre-operative vertical vergence, suggesting that changes in saccade yoking depend on an interaction between saccades and vertical vergence.

Adaptation, Ocular↗
PubMed1995

How successful is corneal transplantation? A report from the Australian Corneal Graft Register.

Corneal graft outcome was assessed within a large, prospectively collected database of 4499 records. Penetrating corneal graft survival was 91% at 1 year, 72% at 5 years and 69% at 7 years. The three most common indications for graft were keratoconus (30%), bullous keratopathy (25%) and failed previous graft (18%); the three most common causes of graft failure were rejection (34%), infection (18%) and glaucoma (9%). The vast majority of grafts were performed for improved visual acuity. About four-fifths of recipients achieved at least one line of better acuity on the Snellen chart post-operatively; of the remainder with unchanged or worse acuity, only 21% had failed grafts. Overall, 43% of recipients achieved a best corrected Snellen acuity of 6/12 or better, 52% achieved 6/18 or better, and 20% had acuitities of less than 6/60. Reasons for poor post-operative acuity (recorded as less than 6/60) included graft failure (41%) and comorbidities in the grafted eye (43%). A number of risk factors for graft failure were examined: in most instances, there was little room for decision-making or expert intervention.

Astigmatism↗
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

The Gravitational Plant Physiology Facility--description of equipment developed for biological research in Spacelab.

In January 1992, the NASA Shuttle mission STS 42 carried a facility designed to perform experiments on plant gravi- and photo-tropic responses. This equipment, the Gravitational Plant Physiology Facility (GPPF) was made up of a number of interconnected units mounted within a Spacelab double rack. The details of these units and the plant growth containers designed for use in GPPF are described. The equipment functioned well during the mission and returned a substantial body of time-lapse video data on plant responses to tropistic stimuli under conditions of orbital microgravity. GPPF is maintained by NASA Ames Research Center, and is flight qualifiable for future Spacelab missions.

Avena↗
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↗
PubMed1992

Evaluating the effects of drugs on behavior and quality of life: an alternative strategy for clinical trials.

Conventional clinical trials involve tests of hypotheses with statistics computed from values of dependent variables alone. An alternative is to test hypotheses with statistics computed from benefit/harm scores that measure longitudinal associations between dose and values of the dependent variables. The proposed standardized measure of benefit/harm quantifies the strength of evidence that a patient did either better or worse while on treatment. A benefit/harm score, particularly when obtained from a randomized, N-of-1 trial, indicates a beneficial or harmful treatment effect for the individual. Benefit/harm scores from samples of patients are evaluated with standard statistical tests, with or without group comparisons, to make inferences about populations. The proposed alternative strategy can yield within-patient indicators of treatment effect that are more reliable, valid, comprehensive, and detailed. This, in turn, could help make many population-based clinical trials more informative, cost-effective, and clinically useful for participants.

Administration, Oral↗
PubMed1990

Circumnutations of sunflower hypocotyls in satellite orbit.

The principal objective of the research reported here was to determine whether a plant's periodic growth oscillations, called circumnutations, would persist in the absence of a significant gravitational or inertial force. The definitive experiment was made possible by access to the condition of protracted near weightlessness in an earth satellite. The experiment, performed during the first flight of Spacelab on the National Aeronautics and Space Administration shuttle, Columbia, in November and December, 1983, tested a biophysical model, proposed in 1967, that might account for circumnutation as a gravity-dependent growth response. However, circumnutations were observed in microgravity. They continued for many hours without stimulation by a significant g-force. Therefore, neither a gravitational nor an inertial g-force was an absolute requirement for initiation [correction of initation] or continuation of circumnutation. On average, circumnutation was significantly more vigorous in satellite orbit than on earth-based clinostats. Therefore, at least for sunflower (Helianthus annuus L.) circumnutation, clinostatting is not the functional equivalent of weightlessness.

Acceleration↗