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Biomedical subjects

P A Davison

Publications and source records attributed to P A Davison.

8 recordsLinked to original sources
PubMed1995

Clinical comparison of three techniques for evaluating visual function behind cataract.

The aim of the study was to compare the ability of displacement threshold hyperacuity to identify reduced retinal/neural function in cataract patients with that of the potential acuity meter (PAM) and laser interferometer. Fifty-two patients (mean age 72.0 +/- 10.8 years) admitted for extracapsular cataract extraction were randomly selected for inclusion in the study. Patients underwent routine refraction and logMAR acuity measurement on the eve of cataract surgery. Following pupillary dilation and in random order, the oscillatory displacement threshold (ODT; defined as the smallest detectable displacement of an object) was determined, and predictions of the post-operative acuity were obtained using the PAM and Rodenstock Retinometer (RR). Patients were re-examined approximately 7 weeks post-operatively when logMAR acuities and ODTs were remeasured. On the basis of the results of an independent fundus examination, patients were assigned to either a normal or a pathology group. Increasing cataract density adversely affected the predictions provided by the PAM (p = 0.0001) and ODT (p = 0.0001) techniques, but not the RR (p = 0.137). One-factor ANOVA revealed that pre-operative ODT (p = 0.0001), PAM (p = 0.0001) and RR (p = 0.0004) measures successfully distinguished patients with retinal/neural pathology from normals. Pre-operative cut-off levels to distinguish normal from pathology cases were retrospectively determined for each technique. The cut-off values for the PAM and ODT techniques yielded higher sensitivity and specificity values than was the case for the RR. The results suggest that the predictive abilities of the PAM and ODT techniques are similar, and superior to that of the RR. Further work involving larger numbers of patients with posterior segment pathology is necessary to reveal which technique provides the best means of assessing retinal/neural function in the presence of ocular media opacities.

Aged↗
PubMed1994

Assessing retinal/neural function in patients with cataract using oscillatory displacement thresholds.

Oscillatory displacement threshold (ODT) measurement has been proposed as a useful means of assessing retinal/neural function behind cataract. In order to examine the qualitative predictive ability of this technique, the influence of age, simulated cataract, and various posterior segment disorders upon ODT's were investigated. In a separate investigation, thresholds were measured in 30 cataract patients on the eve of surgery, and again 6 to 8 weeks postoperatively. ODT's were found to increase with age (p < 0.001) and were highly resistant to the effects of image degradation as produced by simulated cataract. In addition, thresholds were sensitive to the presence of retinal/neural disorders (p << 0.001). Although not completely independent of the presence of cataract, higher ODT's were measured in cataract patients with coexistent retinal/neural dysfunction than was the case for patients with normal posterior segments (p < 0.001). Preoperative ODT measurement may offer a means of distinguishing between the optical and retinal/neural components of visual impairment in patients with cataract.

Adolescent↗
PubMed1994

Effects of posterior segment disorders on oscillatory displacement thresholds, and on acuities as measured using the potential acuity meter and laser interferometer.

Oscillatory displacement thresholds (ODTs) were measured in 67 subjects with clear ocular media, but known posterior segment disorders. The ability of these thresholds to assess reduced visual function, as quantified by visual acuity deficits, was compared with that of the Potential Acuity Meter (PAM) and the Rodenstock Retinometer (RR). ODTs were found to be sensitive to acuity deficits which were retinal/neural in origin. Despite the fact that interferometric acuities are, unlike ODTs, a measure of resolution, the RR proved no more accurate in assessing the level of letter acuity which existed than did ODT measurement. As would be expected, the PAM provided for the most accurate means of assessing non-optical visual acuity deficits. However, the PAM proved to be less useful in eyes with: very poor levels of acuity, and certain anomalous conditions. The results have implications for the relative ability of each of the three tests to identify reduced visual function behind cataract.

Adolescent↗
PubMed1991

Three-dimensional imaging of the musculoskeletal system: an overview.

The clinical applications of three-dimensional computed tomography (3-D CT) reconstruction continue to expand rapidly. Recently, the field of three-dimensional magnetic resonance (3-D MR) reconstruction has also been developing. Three dimensional imaging offers a new approach to the analysis of complex anatomic relationships. The spatial configuration of an object can be directly displayed without observers requiring mental integration of a series of two-dimensional images. The easily interpretable images of 3-D CT have proven to be useful for surgical planning. Three-dimensional CT displays have used widely in the preoperative planning of craniofacial surgery, dysplastic hips in children, and complex fractures of skeletal systems. However, 3-D MR displays are technically more difficult than those of CT scans, and 3-D MR displays of the musculaskeletal system are still in a developing stage. Recently, we explored the feasibility of 3-D MR displays. This article provides an overview of those areas of the musculoskeletal system where the use of 3-D MR has proven valuable. The current techniques and ongoing applications are also presented. We believe that this exciting development will expand our ability to visualize pathologic anatomy in the near future.

Algorithms↗
PubMed1988

Effect of ileal infusion of lipid on jejunal motor patterns after a nutrient and nonnutrient meal.

To investigate how ileal lipid delays small bowel transit, pressure activity was recorded at multiple sites in the human small intestine during ileal infusion of either lipid or saline. Initial studies showed that ileal lipid reduced the contraction rate in the jejunum but not in the duodenum or ileum. The effect of ileal lipid was further investigated by recording pressures at seven sites in the jejunum after ingestion of either a nutrient or a nonnutrient meal. The nutrient meal induced an irregular motility pattern; ileal lipid significantly reduced the contraction rate, the percentage of contractions involved in propagated events, the mean length of propagation, and the propagation index. The nonnutrient meal induced a pattern containing discrete clusters of contractions. Ileal lipid significantly reduced the occurrence of contraction clusters and the mean length of propagation. Thus, although the delay in small bowel transit observed during ileal infusion of lipid can be explained by reductions in the rate and the degree of propagation of jejunal contractions, the mechanism varies according to the type of meal.

Adult↗
PubMed1987

Anorectal sensitivity and responses to rectal distention in patients with ulcerative colitis.

Anorectal function in ulcerative colitis was assessed by measuring pressures at multiple sites in the anus and rectum under basal conditions and during balloon distention of the rectum in 29 patients with ulcerative colitis (12 active, 11 quiescent, and 6 during both phases) and in 12 normal controls. Resting and squeeze sphincter pressures were similar in the three groups. The lowest rectal volume that could be perceived, the volume required to induce a desire to defecate, and the maximum tolerable rectal volume were all lower in patients with active colitis than in patients with quiescent colitis (p less than 0.001) and controls (p less than 0.001). The rectal volume required to cause a sustained anal relaxation was lower in patients with active colitis (p less than 0.05) than in controls. Both peak and steady state rectal pressures in response to rectal distention were significantly higher in patients with active colitis than in patients with quiescent colitis (p less than 0.05) and controls (p less than 0.02). Paired studies showed that during remission of disease there was a decrease in rectal sensitivity (p less than 0.05) and an increase in rectal compliance (p less than 0.05). These results suggest that the frequent and urgent defecation, i.e., the predominant feature of active colitis, is related to a hypersensitive and poorly compliant rectum, which, upon distention, is more reactive and is more likely to induce prolonged sphincter relaxation.

Adult↗
PubMed1985

Inter-relationships between British drivers' visual abilities, age and road accident histories.

Statistical analysis is described of data on 1000 British drivers' accident histories and their performance on a vision screening instrument. Significant positive associations are evident between various accident variables and tests of hyperphoria, right eye visual acuity, left eye acuity and binocular acuity. The clustering of associations is strongest for older drivers. The significance of hyperphoria has received little attention previously. The age-related associations with accidents parallel the decline with age of other visual abilities. Statutory re-testing of drivers' vision at about the age of 50 is recommended.

Accidents, Traffic↗