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Biomedical subjects

B J Evans

Publications and source records attributed to B J Evans.

At least 19 recordsLinked to original sources
PubMed2001

Hybridization and population genetics of two macaque species in Sulawesi, Indonesia.

This study investigates hybridization and population genetics of two species of macaque monkey in Sulawesi, Indonesia, using molecular markers from mitochondrial, autosomal, and Y-chromosome DNA. Hybridization is the interbreeding of individuals from different parental taxa that are distinguishable by one or more heritable characteristics. Because hybridization can affect population structure of the parental taxa, it is an important consideration for conservation management. On the Indonesian island of Sulawesi an explosive diversification of macaques has occurred; seven of 19 species in the genus Macaca live on this island. The contact zone of the subjects of this study, M. maura and M. tonkeana, is located at the base of the southwestern peninsula of Sulawesi. Land conversion in Sulawesi is occurring at an alarming pace; currently two species of Sulawesi macaque, one of which is M. maura, are classified as endangered species. Results of this study indicate that hybridization among M. maura and M. tonkeana has led to different distributions of molecular variation in mitochondrial DNA and nuclear DNA in the contact zone; mitochondrial DNA shows a sharp transition from M. maura to M. tonkeana haplotypes, but nuclear DNA from the parental taxa is homogenized in a narrow hybrid zone. Similarly, within M. maura divergent mitochondrial DNA haplotypes are geographically structured but population subdivision in the nuclear genome is low or absent. In M. tonkeana, mitochondrial DNA haplotypes are geographically structured and a high level of nuclear DNA population subdivision is present in this species. These results are largely consistent with a macaque behavioral paradigm of female philopatry and obligate male dispersal, suggest that introgression between M. maura and M. tonkeana is restricted to the hybrid zone, and delineate one conservation management unit in M. maura and at least two in M. tonkeana.

Animals↗
PubMed1999

A review of the management of 323 consecutive patients seen in a specific learning difficulties clinic.

Visual correlates of specific learning difficulties (SpLD) include: binocular instability, low amplitude of accommodation, and Meares-Irlen Syndrome. Meares-Irlen Syndrome describes asthenopia and perceptual distortions which are alleviated by using individually prescribed coloured filters. Data from 323 consecutive patients seen over a 15 month period in an optometric clinic specialising in SpLD are reviewed. Visual symptoms and headaches were common. 48% of patients were given a conventional optometric intervention (spectacles, orthoptic exercises) and 50% were issued with coloured filters, usually for a trial period. 40% of those who were given orthoptic exercises were later issued with coloured overlays. 32% of those who were issued with coloured overlays were ultimately prescribed Precision Tinted lenses. Approximately half the sample were telephoned more than a year after the last clinical appointment. More than 70% of those who were prescribed Precision Tints were still wearing them daily, and results for this intervention compared favourably with data for non-tinted spectacles. The data suggest that many people with SpLD need optometric care and that the optometrist needs to be skilled in orthoptic techniques and cognisant of recent research on coloured filters.

Accommodation, Ocular↗
PubMed1998

Randomised double-masked placebo-controlled trial of a treatment for congenital nystagmus.

Several therapies have been developed for congenital nystagmus (CN) but without placebo-controlled trials. We investigated a treatment which combined two therapies that had been advocated by several authors and were reported to improve visual acuity (VA). A placebo treatment was designed to mimic the time, attention, 'high tech' apparatus, and the explanation used in the experimental treatment. To each group, 38 subjects with CN were randomly allocated. Their VA and contrast sensitivity (CS) were assessed three times before undergoing treatment for 6 weeks and then once more. An improvement in VA occurred, however, this was not significantly different in the two groups. The improvement in CS was greater in the experimental than in the control group, but the difference failed to reach significance in most statistical tests. We conclude that putative therapies for CN should be assumed to be placebos until proven otherwise with randomized controlled trials.

Biofeedback, Psychology↗
PubMed1998

The underachieving child.

Visual factors in specific learning difficulties (SpLD) are reviewed. People with SpLD fail to achieve at a level that is commensurate with their intelligence. The commonest SpLD is dyslexia, which usually results from phonological processing/decoding deficits. Additionally, there are several optometric correlates of SpLD which may, in some cases, contribute to the learning difficulty. These correlates include binocular instability and a low amplitude of accommodation. Some people with reading difficulties and perceptual distortions/eyestrain can be helped by individually prescribed coloured filters. A visual processing anomaly is also often present in the form of a deficit of the transient visual system. The role of the optometrist is discussed.

Accommodation, Ocular↗
PubMed1997

Comparative molecular phylogeography of two Xenopus species, X. gilli and X. laevis, in the south-western Cape Province, South Africa.

Xenopus gilli is a vulnerable anuran with a patchy distribution along the south-western coast of the Cape Province, South Africa. This species is sympatric with Xenopus laevis laevis, a widespread relative found over much of southern Africa. We examined the molecular phylogeography and population structure of the contact zone between these species to obtain information about historical biogeography and conservation management of this region. Analyses of the distribution, frequency, and cladistic and phenetic relationships among mitochondrial DNA haplotypes indicate that population subdivision is present in both taxa but that long-term isolation of sets of populations has occurred in X. gilli only. Haplotype and nucleotide diversity are also considerably higher within and among X. gilli ponds than X. l. laevis ponds in this region. We attribute the genetic segregation of X. gilli populations to ancient habitat fragmentation by ocean transgression into X. gilli habitat and to continued habitat alteration by human activity. The lower level of genetic diversity in X. L. laevis in this region is likely a result of a recent arrival of this taxon to the south-western Cape region relative to X. gilli. Population structure in X. l. laevis may be a result of isolation by distance. Clear evidence exists for at least two management units within X. gilli and strongly supports the establishment of protective measures east of False Bay in order to conserve a substantial portion of this species' extant genetic diversity.

Animals↗
PubMed1996

Coronary operations in patients with spinal cord injury.

BACKGROUND: The risk of heart disease in patients with spinal cord injury is similar to that in the general population. The physiologic derangements raise special problems in patients with SCI having coronary operations. METHODS: From January 1980 to May 1995, we performed coronary artery bypass procedures on 20 patients with SCI; 4 were tetraplegic and the remainder were paraplegic. The indication for operation was angina: unstable (13), exertional (4), or postinfarctional (3). Bowel and bladder care was given immediately before operation; operating room tables were double padded and a pelvic wrap was used to protect the back. Electric wheelchairs were used for early mobilization. RESULTS: Vasomotor instability from cardiopulmonary bypass was not present in patients with SCI. Pharmacologic support was required in the operating room by 4 patients for low vascular resistance, but in only one case in the intensive care unit. One patient required ventilation support for more than 24 hours. All patients were able to cough effectively. No thoracic wound complications occurred. There were three operative deaths, all in patients with multiple risk factors. The acute hospital stay averaged 9.3 days; patients were then transferred to an SCI unit for rehabilitation, were upper-extremity weight bearing was restricted for 2 to 4 weeks. CONCLUSIONS: Patients should not be denied coronary artery bypass procedures because of an SCI, but their special needs must be managed properly.

Adult↗
PubMed1996

New technique for studying incision depth in experimental radial keratotomy.

Older techniques of analyzing incision depth in incisional keratotomy consist of serial transverse sections taken at various points along the incision. Information as to shape and depth of the incision are reconstructed from these sections. We describe a new method for studying the incision depth and profile along the entire incision length.

Cadaver↗
PubMed1996

A preliminary investigation into the aetiology of Meares-Irlen syndrome.

A recent double-masked placebo-controlled trial has confirmed that some children experience a reduction in symptoms of eyestrain and headache when they read through individually prescribed coloured filters and has shown that this benefit cannot be solely attributed to a placebo effect. People who are helped by coloured filters in this way have been described as having "Meares-Irlen syndrome'. We investigated the mechanism of this benefit by studying the optometric and visual perceptual characteristics of the children in the double-masked study. This population had normal refractive errors and heterophorias (none of the subjects had strabismus). They demonstrated slightly, but significantly, reduced amplitudes of accommodation and vergence and poor stereo-acuity. However, these factors seemed to be correlates of Meares-Irlen syndrome rather than the underlying cause. Pattern glare, a sensitivity to striped patterns (e.g. lines of text), was prevalent in our sample and was significantly associated with the subjects' symptoms. The spatial contrast sensitivity function was normal.

Adolescent↗
PubMed1996

Consulting skills training and medical students' interviewing efficiency.

In more traditional medical education, medical students took a patient's medical history by asking a series of sequenced, routine questions, covering presenting medical problem(s); medical history; social and personal history; systems review; and physical examination. Following this process, the student then attempted to derive the patient's medical problems. This inductive problem-solving paradigm may not assist students to prepare for their future interviewing needs, given doctors use a hypothetico-deductive, problem-solving approach when interviewing patients and numerous researchers have developed specialized communication skills training programmes designed to enhance students' interviewing skills. Students given specific consulting skills training have tended to show significantly greater interpersonal effectiveness and improved interview behaviours compared with students who experience traditional patient clerking training. These improvements in interviewing tend to persist over the period of students' medical training. The aim of the present study was to determine whether specialized communication skills training helped students elicit greater quantity and quality of information from patients and if so, whether such information assisted students in improving their diagnostic skills. Videotaped history-taking interviews conducted by students trained in communication skills and untrained (control) students were rated for their interview efficiency. A comparison of ratings given by experimentally naive, independent observers revealed that trained students were more efficient, but took no longer than their control group counterparts to elicit fuller, more relevant information. However, the student groups did not differ in the accuracy or scope of their medical diagnoses. It is argued that students' lack of medical knowledge in this early phase of their clinical training militated against their being able to use their interviewing competence to derive more potentially accurate medical diagnoses.

Adult↗
PubMed1996

Monoclonal antibody assay for free urinary pyridinium cross-links.

The pyridinium cross-links of collagen, pyridinoline (Pyd) and deoxypyridinoline (Dpd), provide structural integrity and rigidity to collagen fibrils in bone. During bone degradation (resorption), the cross-links are released into the circulation and eventually excreted in urine. Pyridinium cross-link measurements in urine have been shown to be sensitive and specific indicators of resorption by both established HPLC and newer enzyme immunoassay (EIA) techniques. We have developed a monoclonal antibody that preferentially binds to the non-peptide-bound free forms of Pyd & Dpd. We have incorporated the antibody conjugated to alkaline phosphatase in a competitive EIA by using Pyd-coated microtiter strip wells. After a 3-h incubation of sample and antibody-enzyme conjugate, color is developed for 1 h with p-nitrophenyl phosphate as the substrate. The intraassay (n = 52) CVs were 3.0-7.6%, and interassay (n = 8) CVs were 6.1-7.4%. Comparisons of the assay (y) with HPLC (x) and a polyclonal antibody-based EIA (x') gave regression equations of y = 0.46x + 4, r = 0.96, and y = 0.56x' + 8, r = 0.96. The EIA detected increased Pyd & Dpd concentrations in urine from postmenopausal women and patients with osteoporosis, hyperthyroidism, hyperparathyroidism, and Paget disease of bone. EIA concentrations also reflected the reduction in Pyd&Dpd excretion resulting from estrogen replacement in surgically menopausal women. Measurement of pyridinium cross-links with this simple EIA appears to provide an accurate index of the rate of resorption and may be useful for metabolic bone disease assessment and monitoring the effects of antiresorptive therapy.

Adult↗
PubMed1996

Dyslexia: the link with visual deficits.

Some research reports suggest that visual anomalies may have a causative role in dyslexia, and on this basis certain forms of therapy have been proposed. Recently, we have published the initial results of a matched group study which found dyslexia to be associated with binocular instability, reduced amplitude of accommodation, and reduced contrast sensitivity for both low spatial frequencies and uniform field flicker. The binocular instability was best identified by measuring the vergence amplitude: a modified Dunlop test failed to differentiate reliably between the two groups. Here, we report a significant correlation between flicker threshold and binocular instability, thus linking sensory and motor visual correlates of dyslexia. We also present further new analyses on the interaction between optometric variables and the psychometric measurement of coding skills. The results of these analyses disagree with a recent claim that binocular vision anomalies might cause poor performance at coding tasks. Our studies indicate that visual characteristics are not the major aetiological factors in specific reading difficulty.

Adolescent↗
PubMed1996

Standardization of pyridinium crosslinks, pyridinoline and deoxypyridinoline, for use as biochemical markers of collagen degradation.

The collagen crosslinks, pyridinoline and deoxypyridinoline, have been developed as urinary markers of bone resorption but, despite wide clinical application of the technique, comparatively little attention has been paid to the standardization of these compounds. In this study, pyridinoline and deoxypyridinoline have been purified from bone and converted completely to monochloride trihydrochloride salts. In addition to mass spectrometry and NMR spectroscopy, the purity of the isolated materials was assessed by microelemental analysis including the chloride counterions. These purified compounds were used to establish individual molar absorptivity values as primary standardization criteria for the two crosslinks. For pyridinoline in 0.1 mol/L HCl, epsilon at 295 nm was 5490 L mol(-1) cm(-1); in 50 mmol/L sodium phosphate, pH 7.5, epsilon at 325 nm was 5785. The corresponding values for deoxypyridinoline at acid and neutral pH were 5160 and 5290 L mol(-1) cm(-1). The availability of standardization criteria for the crosslinks will allow more meaningful comparisons of clinical data between different laboratories.

Amino Acids↗
PubMed1995

Optometric correlates of Meares-Irlen syndrome: a matched group study.

People who report visual perceptual distortions, typically when reading, that are alleviated by using coloured filters are described as suffering from 'Meares-Irlen Syndrome'. A recent double-masked placebo-controlled trial showed that this condition cannot be solely explained as a placebo effect and that the beneficial filter is idiosyncratic and sometimes needs to be highly specific. Several mechanisms have been suggested for Meares-Irlen Syndrome including ocular motor (binocular and accommodative) anomalies, a sensitivity to patterned stimuli (pattern glare), and a deficit of the transient visual sub-system. We investigated these hypotheses by comparing 16 children, who reported the symptoms described above and who showed a sustained benefit from coloured filters, with 25 control children who came from the same school and were matched for age, reading performance and intelligence. The 'Meares-Irlen Syndrome' group had slightly, but significantly, reduced vergence and accommodative amplitudes and stereo-acuity; they also demonstrated significantly more pattern glare. The two groups did not differ significantly in their visual acuities, refractive error, dissociated or associated heterophoria, AC/A ratio, or ability to perceive 20 Hz flicker. It appears that certain ocular motor factors are correlates of Meares-Irlen Syndrome, rather than the primary underlying cause of the symptoms. The results support the hypothesis that pattern glare may be involved in the mechanism of Meares-Irlen Syndrome.

Accommodation, Ocular↗
PubMed1995

A new protocol for the optometric management of patients with reading difficulties.

Research by Evans et al. (Ophthal. Physiol. Opt. 15, 481-487, 1995) has demonstrated a correlation between visual processing and ocular motor factors in people with specific reading difficulties (dyslexia). In addition, research by Wilkins et al. (Ophthal. Physiol. Opt. 14, 365-370, 1994) has shown that some people with dyslexia will benefit from a reduction of perceptual symptoms of discomfort and distortion if they use individually prescribed coloured filters. Three examples of the dyslexic patients who attend at the Institute of Optometry clearly demonstrate the importance of full investigation of ocular function, including the assessment of the effect of colour on visual perception. All three patients presented with similar symptoms of asthenopia when reading. Symptoms were alleviated for the first patient by use of orthoptic treatment of an exotropia with intermittent suppression. With the second patient, ocular motor functions were found to be within acceptable limits and relief of symptoms was obtained by the prescribing of lenses of a specific chromaticity. For the third patient, both orthoptic intervention and the use of specifically tinted lenses were necessary to relieve the visual difficulties that were being experienced. By taking advantage of recent research and developments in optometric instrumentation, it is possible for some of those with dyslexia to receive considerable benefit from optometric intervention.

Adolescent↗