PubMed Health⌕ Search

Biomedical subjects

M H Edwards

Publications and source records attributed to M H Edwards.

At least 19 recordsLinked to original sources
PubMed2006

Opacity measurements of a hot iron plasma using an x-ray laser.

The temporal evolution of the opacity of an iron plasma at high temperature (30-350 eV) and high density (0.001-0.2 g cm-3) has been measured using a nickel-like silver x-ray laser at 13.9 nm. The hot dense iron plasma was created in a thin (50 nm) iron layer buried 80 nm below the surface in a plastic target that was heated using a separate 80 ps pulse of 6-9 J, focused to a 100 microm diameter spot. The experimental opacities are compared with opacities evaluated from plasma conditions predicted using a fluid and atomic physics code.

Journal Article↗
PubMed2004

Effectiveness of intermediate care in nursing-led in-patient units.

BACKGROUND: The Nursing led inpatient Unit (NLU) is one of a range of services that have been considered in order to manage more successfully the transition between hospital and home for patients with extended recovery times. OBJECTIVES: To determine whether nursing-led inpatient units are effective in preparing patients for discharge from hospital compared to usual inpatient care. SEARCH STRATEGY: We searched The Cochrane Library, the Specialized Register of the Cochrane Effective Practice and Organisation of Care (EPOC) group, MEDLINE, CINAHL, EMBASE, BNI and HMIC databases. Citation searches were undertaken on the science and social science citation indices. Authors were contacted to identify additional data. SELECTION CRITERIA: Controlled trials and interrupted time series designs that compared the NLU to usual inpatient care managed by doctors. Patients over 18 years of age following an acute hospital admission for a physical health condition. DATA COLLECTION AND ANALYSIS: Two reviewers independently extracted data and assessed study quality. MAIN RESULTS: Ten random or quasi-random controlled trials reported on a total of 1896 patients. There was no statistically significant effect on inpatient mortality ( OR 1.10, 95% CI 0.56 to 2.16) or mortality to longest follow up (OR 0.92, 95% CI 0.65 to 1.29) but higher qaulity studies showed a larger non-significant increase in inpatient mortality (OR 1.52, 95% CI 0.86 to 2.68). Discharge to institutional care was reduced for the NLU (OR 0.44 95% CI 0.22 to 0.89) and functional status at discharge increased (SMD 0.37, 95% CI 0.20 to 0.54) but there was a near significant increase in inpatient stay (WMD 5.13 days 95% CI -0.5 days to 10.76 days). Early readmissions were reduced (OR 0.52 95% CI 0.34 to 0.80). One study compared a NLU for the chronically critically ill with ICU care. Mortality (OR 0.62 95% CI 0.35 to 1.10) and length of inpatient stay differ did not differ (WMD 2 days, 95% CI 10.96 to -6.96 days). Early readmissions were reduced (OR 0.33 95% CI 0.12 to 0.94). Costs of care on the NLU were higher for UK studies but lower for US based studies. REVIEWERS' CONCLUSIONS: There is some evidence that patients discharged from a NLU are better prepared for discharge but it is unclear if this is simply a product of an increased length of inpatient stay. No statistically significant adverse effects were noted but the possibility of increased early mortality cannot be discounted. More research is needed.

Health Care Costs↗
PubMed2004

The epidemiology of myopia in Hong Kong.

INTRODUCTION: The prevalence of myopia amongst the Chinese has escalated in recent decades. While this refractive error was previously a little more than an inconvenience and a source of unwanted expense to the affected individuals, it is now sufficiently prevalent to warrant national concern. Myopia is also a major cause of low vision. This review aims to provide information on the prevalence of myopia in the Chinese community in Hong Kong. MATERIALS AND METHODS: Based on a number of studies carried out mainly at the Centre for Myopia Research in The Hong Kong Polytechnic University, myopia in the Chinese community in Hong Kong is described. RESULTS: Infants in Hong Kong appear to have refractive errors similar to infants of European descent; however, by the age of 7 years myopia is already prevalent. The annual incidence of myopia thereafter averages 11% to 12%; by the age of 17 years more than 70% are myopic, and this prevalence is greater than in people of European descent. In Hong Kong, myopia is much less prevalent in the older generation. CONCLUSION: The increase in prevalence of myopia over a short period of time is postulated to be due to environmental factors. Children of Chinese descent have a susceptibility to environmental factors which cause myopia.

Astigmatism↗
PubMed2001

Ice shelves in the Pleistocene Arctic Ocean inferred from glaciogenic deep-sea bedforms.

It has been proposed that during Pleistocene glaciations, an ice cap of 1 kilometre or greater thickness covered the Arctic Ocean. This notion contrasts with the prevailing view that the Arctic Ocean was covered only by perennial sea ice with scattered icebergs. Detailed mapping of the ocean floor is the best means to resolve this issue. Although sea-floor imagery has been used to reconstruct the glacial history of the Antarctic shelf, little data have been collected in the Arctic Ocean because of operational constraints. The use of a geophysical mapping system during the submarine SCICEX expedition in 1999 provided the opportunity to perform such an investigation over a large portion of the Arctic Ocean. Here we analyse backscatter images and sub-bottom profiler records obtained during this expedition from depths as great as 1 kilometre. These records show multiple bedforms indicative of glacial scouring and moulding of sea floor, combined with large-scale erosion of submarine ridge crests. These distinct glaciogenic features demonstrate that immense, Antarctic-type ice shelves up to 1 kilometre thick and hundreds of kilometres long existed in the Arctic Ocean during Pleistocene glaciations.

Journal Article↗
PubMed2001

Evidence of recent volcanic activity on the ultraslow-spreading Gakkel ridge.

Seafloor spreading is accommodated by volcanic and tectonic processes along the global mid-ocean ridge system. As spreading rate decreases the influence of volcanism also decreases, and it is unknown whether significant volcanism occurs at all at ultraslow spreading rates (<1.5 cm yr(-1)). Here we present three-dimensional sonar maps of the Gakkel ridge, Earth's slowest-spreading mid-ocean ridge, located in the Arctic basin under the Arctic Ocean ice canopy. We acquired this data using hull-mounted sonars attached to a nuclear-powered submarine, the USS Hawkbill. Sidescan data for the ultraslow-spreading (approximately 1.0 cm yr(-1)) eastern Gakkel ridge depict two young volcanoes covering approximately 720 km2 of an otherwise heavily sedimented axial valley. The western volcano coincides with the average location of epicentres for more than 250 teleseismic events detected in 1999, suggesting that an axial eruption was imaged shortly after its occurrence. These findings demonstrate that eruptions along the ultraslow-spreading Gakkel ridge are focused at discrete locations and appear to be more voluminous and occur more frequently than was previously thought.

Journal Article↗
PubMed2001

Clinical evaluation of the Shin-Nippon SRW-5000 autorefractor in children.

The Canon Autoref R-1 is an 'open-field' autorefractor which has been widely used for research purposes for the past 20 years, but is no longer manufactured. A new autorefractor, the Shin-Nippon SRW-5000, is now available, and if measures using this instrument are shown to be equally accurate and reliable, is likely to replace the R-1. Here we report on the accuracy and reliability (repeatability and reproducibility) of refraction measures in a paediatric population (from 4 to 8 years of age). Subject numbers were 44 for cycloplegic measures and 53 for non-cycloplegic measures. As would be expected, agreement with cycloplegic refraction and reliability were better when SRW-5000 measures were taken using cycloplegia. Repeatability results from the SRW-5000 autorefractor, both with and without cycloplegia were similar to those reported for the Canon R-1.

Accommodation, Ocular↗
PubMed2001

Variation in vernier evoked cortical potential with age.

PURPOSE: To investigate the effects of age on transient vernier visual evoked potential (VEP) and vernier acuity estimated by extrapolation. METHODS: Transient vernier VEPs were examined in normal subjects aged 20 to 75 years. Vernier offsets were presented for the first 350 msec of the stimulus period, and the segments were then realigned in the following 400 msec. The six vernier offsets used were 20, 40, 60, 80, 100, and 140 seconds of arc. Averaging for each offset setting produced vernier VEP waveforms, for which amplitude and latency of visual evoked response and background electroencephalographic (EEG) noise level were determined. Extrapolation of the function relating signal-to-noise ratio and log vernier offset to a ratio of 1.0 resulted in an estimate of vernier acuity. RESULTS: Amplitude of vernier VEP waveforms was significantly reduced in subjects more than 60 years of age, and the latency to the first negative peak was progressively prolonged with increasing age. There was no statistically significant change in electroencephalographic (EEG) noise with advancing age. VEP vernier acuity was significantly degraded in the 61- to 75-year age group. These results are parallel to recent psychophysical findings that alignment performance is worse in older persons than in younger ones. CONCLUSIONS: The present findings provide the first electrophysiological evidence of age-related cortical degeneration associated with vernier processing. Reduced neural activity probably contributes to the loss of vernier acuity with advancing age. Also provided are the first normative data for subjects of different ages for vernier VEP and VEP vernier acuity. Moreover, the present study has demonstrated that vernier VEP is sensitive to neural changes and therefore may be applied in clinical situations to evaluate the integrity of the visual system.

Adult↗
PubMed2000

Variation in vernier acuity with age.

Many visual functions deteriorate with increasing age, vernier acuity apparently being an exception. We used an improved experimental protocol to investigate vernier thresholds in subjects in four age groups. Vernier threshold was found to increase with increasing age, and the difference in this, compared with previous findings is probably due to the smaller inter-pixel angle used. Vernier acuities in young subjects in other studies seem to have been underestimated. As vernier acuity did not vary with retinal illuminance and the sensitivity loss does not seem to be a learning effect, neural rather than optical changes are likely to account for the deterioration. Measurement of vernier acuity may have clinical application in the determination of visual function behind cataract, and it will be necessary to consider the effect of age on vernier acuity.

Adult↗
PubMed2000

Contact lenses in myopia reduction - from orthofocus to accelerated orthokeratology.

Orthokeratology has been used to provide temporary reduction of myopia since the 1950s and in recent years the development of new lens designs, materials and advanced instrumentation for corneal modelling has resulted in a resurgence in interest in this procedure. In particular, the reverse geometry design has allowed greater myopia reduction. Materials with high oxygen permeability have improved the corneal response to rigid lenses and in orthokeratology they allow overnight retainer lens wear. Corneal modelling systems allow the orthokeratology changes to be monitored and measured, and have increased our understanding of the technique. This paper summarises previous published work in this area and identifies the uncertainties which still remain.

Journal Article↗
PubMed2000

Orthokeratology in low myopia. Part 1: efficacy and predictability.

AIMS: Modern orthokeratology (ortho-k) using reverse geometry lens designs is being widely used for myopia reduction world-wide although there has been no well-controlled clinical trial of this procedure. This paper reports on the efficacy and predictability of an ortho-k procedure using the OK-74 lens design (now known as OK-704). METHODS: We carried out a 100-day, controlled, randomised clinical trial in which 14 subjects underwent ortho-k and a further 14 were fitted with aligned rigid contact lenses. RESULTS: The mean reduction in myopia was 1.50 (SD 0.45) D in the ortho-k group and 0.01 (SD 0.20) D in the control group. Unaided vision improved by -0.64 (SD 0.22) logMAR units in the ortho-k group, compared with -0.09 (SD 0.11) units in the control group. Variables which correlated with refractive change were corneal thickness, p-value of the nasal semi-meridian and the difference between central and peripheral corneal powers. A multiple factors model can account for 72% of the refractive change. CONCLUSIONS: Ortho-k using the OK-74 lens design achieved an average myopia reduction of 1.50 D. The model developed can provide an estimate of the refractive change likely to occur in ortho-k, a matter of importance to both clinician and patient.

Journal Article↗
PubMed2000

Orthokeratology in low myopia. Part 2: corneal topographic changes and safety over 100 days.

AIMS: Modern orthokeratology (ortho-k), using reverse geometry lens designs, is being widely used for myopia reduction world-wide but there has been no well-controlled clinical trial of this procedure. This study reports on the associated corneal changes and short-term safety of an orthokeratology procedure using the OK-74 lens design (known as OK704 in the UK). METHODS: We carried out a 100-day, controlled, randomised clinical trial in which 14 subjects underwent ortho-k and a further 14 were fitted with alignment fit contact lenses. RESULTS: Central corneal flattening and peripheral corneal steepening occurred and myopia reduction was explained by the flattening of the central 2 mm of the cornea. The overall ocular health effects were similar in conventional and OK-74 lens wear. CONCLUSIONS: Corneal sphericalisation occurred. Daily wear of OK-74 lens and the conventionally-designed lens were equally safe over the 100-day period investigated. Further work is needed to evaluate the long term safety of ortho-k.

Journal Article↗
PubMed2000

Intraocular pressure in anisometropic children.

BACKGROUND: There is evidence that intraocular pressure (IOP) is higher in myopes than in hyperopes or emmetropes, and it has been suggested that myopia may be the result of a high IOP. We studied IOP in the two eyes of anisometropes, thus controlling for nuisance variables affecting IOP measurement. METHODS: Sixty-seven Chinese children, aged between 8 and 14 years, with anisometropia not <2 D were studied. A Topcon CT-60 noncontact tonometer was used for IOP measurement. Cycloplegia was achieved using two drops of tropicamide 1%, and retinoscopy was performed after residual accommodation had decreased to <2 D. A-scan ultrasonography was carried out using a Storz Alpha II Biometric Ruler. RESULTS: There were no statistically significant differences in IOP between the less myopic and more myopic eyes. CONCLUSIONS: Refractive error and axial length differences in anisometropic children are not related to differences in IOP and seem more likely to be due to genetically determined discrepancies in scleral structure, as previously proposed.

Adolescent↗
PubMed1999

The development of myopia in Hong Kong children between the ages of 7 and 12 years: a five-year longitudinal study.

The purpose of this work was to characterize the development of refractive error in Hong Kong children between the ages of 7 and 12 years. A non self-selected sample of 7-year old children was recruited and followed for 5 years, non-cycloplegic refractions being carried out annually. A life-table was used to determine myopia incidence and prevalence. The mean annual change in the spherical equivalent refraction (SER) was -0.32 D; 75 out of 83 subjects followed for 5 years became less hyperopic or more myopic, the maximum progression occurring between 9 and 11 years of age. The mean change in SER over the 5 years in children who were myopic at age 12 years was significantly greater than that in children who remained non-myopic. The incidence of myopia at age 7-8 years was 9% and at age 11-12 years was 18-20%. At age 7 years the prevalence of progressive myopia was 1.6% and 2.5% of subjects had anisometropia. Any treatment to prevent myopia should start by the age of 6 years and treatment to retard development should commence before age 9 years.

Aging↗
PubMed1999

Is refraction in early infancy a predictor of myopia at the age of 7 to 8 years? The relationship between cycloplegic refraction at 11 weeks and the manifest refraction at age 7 to 8 years in Chinese children.

Thirty-two children who had been refracted in early infancy were re-refracted at the age of 7 to 8 years. Refraction comprised cycloplegic retinoscopy at the mean age of 11 weeks and noncycloplegic retinoscopy and subjective examination at the mean age of 94 months. The change in spherical equivalent refraction (SER) was highly negatively correlated with the initial refraction (-0.863), demonstrating emmetropization; however, the correlation between the refractive error at age 7 to 8 years and the refractive error in infancy was much weaker (+0.225). The SER was significantly less and the astigmatism was greater in infancy in children who were myopic at age 7 to 8 years. There was, however, extensive overlap in range between the SER for the two groups and the initial SER was not a good predictor of myopia at 7 to 8 years, although it may help to identify children who are unlikely to become myopic. One hyperopic child with bilateral ptosis failed to emmetropize.

Aging↗
PubMed1999

The effect of having myopic parents: an analysis of myopia in three generations.

PURPOSE: The etiology of myopia has been attributed to both genetic and environmental factors. The purpose of this paper is to attempt to distinguish between genetic and environmental factors in three generations of subjects from three locations. METHODS: Noncycloplegic autorefraction and distance visual acuity were measured in 3131 Chinese children 7 to 17 years old from Hong Kong, Tianjin, and Ban Chau. Data on the refractive status of the parents and grandparents were collected using questionnaires. Myopia was defined operationally as spherical equivalent refractive error (SER) of at least -1.00 D and uncorrected vision worse than logMAR 0.18 (6/9). RESULTS: The odds of having myopia for the grandparents', parents', and children's generations were 0.06, 0.26, and 0.35, respectively. Having myopic parents increased the odds ratio for having myopia (odds ratio 1.85 for children's generation and 6.71 for parents' generation), showing a genetic influence. However, the odds of having myopia also increased in offspring of nonmyopic parents between generation 2 and 3, suggesting an environmental influence. Results of prevalence and odds ratios from the three locations also demonstrated an environmental effect on development of myopia. CONCLUSION: We propose that myopic development in Chinese follows a multifactorial and polygenic model in which the genetic input has remained constant while the environmental influence has increased over the last three generations.

Adolescent↗