723 research outputs found
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Effect of Stimulus Orientation on Visual Function in Children with Refractive Amblyopia.
Purpose: We investigated and characterized the patterns of meridional anisotropies in newly diagnosed refractive amblyopes using pattern onsetâoffset visual evoked potentials (POVEPs) and psychophysical grating acuity (GA).
Methods: Twenty-five refractive amblyopes were recruited and compared with non-amblyopic controls from our previous study. Monocular POVEPs were recorded in response to sinewave 4 cycles per degree (cpd) grating stimuli oriented along each individual participants' principal astigmatic meridians, which were approximately horizontal (meridian 1) and vertical (meridian 2). Binocular POVEPs in response to the same stimuli, but oriented at 45°, 90°, 135°, and 180°, were recorded. Psychophysical GAs were assessed along the same meridians using a two-alternative non-forced-choice technique. The C3 amplitudes and peak latencies of the POVEPs and GAs were compared across meridians for both groups (refractive amblyopes and controls) using linear mixed models (monocular) and ANOVA (binocular), and post hoc analysis was conducted to determine if meridional anisotropies in this cohort of amblyopes were related to low (â€1.50 diopters [D]), moderate (1.75â2.75 D) and high (â„3.00 D) astigmatism.
Results: In the newly diagnosed refractive amblyopes, there were no significant meridional anisotropies across all outcome measures, but the post hoc analysis demonstrated that C3 amplitude was significantly higher in those with low (P = 0.02) and moderate (P = 0.004) astigmatism compared to those with high astigmatism. Refractive amblyopes had poorer GA and C3 amplitudes compared to controls by approximately two lines on the logMAR chart (monocular: P = 0.013; binocular: P = 0.014) and approximately 6 ”V (monocular: P = 0.009; binocular: P = 0.027), respectively.
Conclusions: Deleterious effects of high astigmatism was evident in newly diagnosed refractive amblyopes, but the neural deficits do not seem to be orientation-specific for the stimulus parameters investigated
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Electrophysiological and Psychophysical Studies of Meridional Anisotropies in Children With and Without Astigmatism.
Purpose: We investigated the pattern of meridional anisotropies, if any, for pattern onset-offset visual evoked potential (POVEPs) responses and psychophysical grating acuity (GA) in children with normal letter visual acuity (20/20 or better).
Methods: A total of 29 children (aged 3-9 years), nine of whom were astigmatic (AS), were recruited. Orientation-specific monocular POVEPs were recorded in response to sinewave grating stimuli oriented along the subjects' principal AS meridians. Horizontal and vertical gratings were designated Meridians 1 and 2, respectively, for nonastigmatic patients (Non-AS). Binocular POVEPs in response to the same stimuli, but oriented at 45°, 90°, 135°, and 180°, were recorded. Psychophysical GAs were assessed monocularly and binocularly along the same meridians using the same stimuli by a 2-alternative-forced-choice staircase technique. The C3 amplitudes and peak latencies of the POVEP and GAs were compared across meridians using linear mixed models (monocular) and ANOVA (binocular).
Results: There were significant meridional anisotropies in monocular C3 amplitudes regardless of astigmatism status (P = 0.001): Meridian 2 (mean ± SE Non-AS, 30.13 ± 2.07 ΌV; AS, 26.53 ± 2.98 ΌV) was significantly higher than Meridian 1 (Non-AS, 26.14 ± 1.87 ΌV; AS, 21.68 ± 2.73 ΌV; P = 0.019), but no meridional anisotropies were found for GA or C3 latency. Binocular C3 amplitude in response to horizontally oriented stimuli (180°, 29.71 ± 3.06 ΌV) was significantly lower than the oblique (45°, 36.62 ± 3 .05 ΌV; P = 0.03 and 135°, 35.95 ± 2.92 ΌV; P = 0.04) and vertical (90°, 37.82 ± 3.65 ΌV; P = 0.02) meridians, and binocular C3 latency was significantly shorter in response to vertical than oblique gratings (P †0.001).
Conclusions: Meridional anisotropy was observed in children with normal vision. The findings suggest that horizontal gratings result in a small, but significantly lower POVEP amplitude than for vertical and oblique gratings
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Barriers to childhood cataract services across India. A mixed methods study using the Theoretical Domains Framework (TDF) of behaviour change
Purpose : Early identification and presentation for childhood cataract surgery remains a major challenge in developing countries. The main aim of this study was to identify potential barriers to childhood cataract services from the perspective of parentsâ and carersâ, as a critical step towards achieving the timely uptake of cataract services.
Methods : We used a mixed methods explanatory sequential study and interviewed 572 parents/carers attending tertiary hospitals in 8 states across India for their child's cataract surgery. We collected information on barriers to accessing services using a 12-item questionnaire and for each reported barrier, responses recorded on a 5 point scale ranging from âlow to high importanceâ. Based on the quantitative data, in-depth interview questions were prepared and 35 interviews were conducted with randomly selected parents/ carers. Majority of these interviews were conducted at the hospital and /at home for those who did not undergo the surgery. Quantitative questionnaires were completed by the trained interviewer and responses were recorded in a pre-designed format. In-depth interviews were audio taped and transcribed for analysis. Quantitative data were analysed using SPSS 22 while qualitative data were organised with NVivo 11 and a thematic analysis was conducted utilising TDF, an integrative framework of theories.
Results : From the 831 responses the 5 most important barriers were: economic (40%; n=222); child too young for surgery (17%; n=97); the problem was not felt as severe (16%; n=90); distance (14.5%; n=83) and no one to accompany to the hospital (9.5%; n=54). In addition, being advised by a local ophthalmologist to delay the surgery was also reported (n=16). Domains identified by the TDF included âKnowledgeâ, âBeliefs about consequencesâ, âIntentionsâ, âGoalsâ, âDecision processesâ, âEnvironmental context and resourcesâ, âSocial influences and emotionâ. This comprehensive TDF approach enabled us to understand the parents perceived barriers to access services for the children.
Conclusions : Barriers to accessing childhood cataract services include both practical concerns relating to the familyâs socio economic status as well as obstacles from the providers. Mapping out the barriers is necessary to design appropriate intervention for achieving positive behaviour change that can have potential social and economic impact
Isotopic and textural analysis of giant unmelted micrometeorites â identification of new material from intensely altered 16O-poor water-rich asteroids
Bulk oxygen isotope data has the potential to match extraterrestrial samples to parent body sources based on distinctive ÎŽ18O and Î17O ratios. We analysed 10 giant (>500 ÎŒm) micrometeorites using combined micro-Computer Tomography (ÎŒCT) and O-isotope analysis to pair internal textures to inferred parent body groups. We identify three ordinary chondrite particles (L and LL groups), four from CR chondrites and the first micrometeorite from the enstatite chondrite (EH4) group. In addition, two micrometeorites are from hydrated carbonaceous chondrite parent bodies with 16O-poor isotopic compositions and plot above the terrestrial fractionation line. They experienced intense aqueous alteration, contain pseudomorphic chondrules and are petrographically similar to the CM1/CR1 chondrites. These micrometeorites may be members of the newly established CY chondrites and/or derived from the enigmatic âGroup 4â micrometeorite population, previously identified by Yada et al., 2005 [GCA, 69:5789-5804], Suavet et al., 2010 [EPSL, 293:313-320] (and others). One of our 16O-poor micrometeorite plots on the same isotopic trendline as the CO, CM and CY chondrites â âthe CM mixing lineâ (with a slope of âŒ0.7 and a ÎŽ17O intercept of -4.23â°), this implies a close relationship and potentially a genetic link to these hydrated chondrites. If position along the CM mixing line reflects the amount of 16O-poor (heavy) water-ice accreted onto the parent body at formation, then the CY chondrites and these 16O-poor micrometeorites must have accreted at least as much water-ice as CM chondrites but potentially more. In addition, thermal metamorphism could have played a role in further raising the bulk O-isotope compositions through the preferential loss of isotopically light water during phyllosilicate dehydration. The study of micrometeorites provides insights into asteroid belt diversity through the discovery of material not currently sampled by larger meteorites, perhaps as a result of atmospheric entry biases preventing the survival of large blocks of friable hydrated material
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Refractive prescribing for pre-school children by optometrists in England
Purpose: Correction of refractive error in children is important for visual and educational development. The aim of this questionnaire-based study was to explore paediatric refractive correction by optometrists in England.
Methods: An online questionnaire was piloted and then distributed to optometrists in England. The questionnaire asked about respondentsâ characteristics (such as type of practice), management of refractive error in 1 and 3 year-old children, and sources of information used as a basis for decisions on prescribing refractive error in children.
Results: Two hundred and ninety-three questionnaires were returned, though only 139 (47%) of these were fully completed. In an average month, about half of respondents examined no children aged 0 to 2 years and about half examined no more than 5 children aged 3 to 4 years. A significant proportion indicated they would refer children aged 1 or 3 years with refractive error and no other signs or symptoms into the hospital eye service. Almost a quarter would prescribe in full or in part an isometropic refractive correction of +2D for a 3 year-old (within the normal range) with no other signs or symptoms, suggesting a degree of unnecessary prescribing. Almost none would take no action in cases of clinically significant refractive error. Respondents made similar use of their colleagues, undergraduate or postgraduate/continuing education, professional guidance and peer-reviewed research as sources of evidence on which to base decisions about prescribing for paediatric refractive errors. Most reported using Cochrane reviews âneverâ or ârarelyâ.
Conclusions: These results suggest optometrists often defer management of paediatric refractive error to the hospital eye service, with implications in terms of under-utilisation of community optometric expertise and burden on the National Health Service. In some cases, the results indicate a mismatch between respondentsâ reported management and existing guidance/guidelines on paediatric prescribing
Formation and Structure of a Current Sheet in Pulsed-Power Driven Magnetic Reconnection Experiments
We describe magnetic reconnection experiments using a new, pulsed-power
driven experimental platform in which the inflows are super-sonic but
sub-Alfv\'enic.The intrinsically magnetised plasma flows are long lasting,
producing a well-defined reconnection layer that persists over many
hydrodynamic time scales.The layer is diagnosed using a suite of high
resolution laser based diagnostics which provide measurements of the electron
density, reconnecting magnetic field, inflow and outflow velocities and the
electron and ion temperatures.Using these measurements we observe a balance
between the power flow into and out of the layer, and we find that the heating
rates for the electrons and ions are significantly in excess of the classical
predictions. The formation of plasmoids is observed in laser interferometry and
optical self-emission, and the magnetic O-point structure of these plasmoids is
confirmed using magnetic probes.Comment: 14 pages, 12 figures. Accepted for publication in Physics of Plasma
An Experimental Platform for Pulsed-Power Driven Magnetic Reconnection
We describe a versatile pulsed-power driven platform for magnetic
reconnection experiments, based on exploding wire arrays driven in parallel
[Suttle, L. G. et al. PRL, 116, 225001]. This platform produces inherently
magnetised plasma flows for the duration of the generator current pulse (250
ns), resulting in a long-lasting reconnection layer. The layer exists for long
enough to allow evolution of complex processes such as plasmoid formation and
movement to be diagnosed by a suite of high spatial and temporal resolution
laser-based diagnostics. We can access a wide range of magnetic reconnection
regimes by changing the wire material or moving the electrodes inside the wire
arrays. We present results with aluminium and carbon wires, in which the
parameters of the inflows and the layer which forms are significantly
different. By moving the electrodes inside the wire arrays, we change how
strongly the inflows are driven. This enables us to study both symmetric
reconnection in a range of different regimes, and asymmetric reconnection.Comment: 14 pages, 9 figures. Version revised to include referee's comments.
Submitted to Physics of Plasma
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The EU as a Good Global Actor
This paper outlines an exploratory workshop at City Law School, City, University of London funded by HEIF/ âEUTIPâ Marie SkĆodowska-Curie Innovative Training Network (ITN) on understanding of the EU as a Good Global Actor.1 The EU has as its mission to be a good global governance actor yet is continuously challenged in the world. As a global actor, the EU is both a weak and strong actor in a divergent range of global governance areas. It is not comparable to study the EU as a global trade actor for example to its efforts in human rights, data, cyber or the environment. EU international relations constitutes arguably a booming field of law where the EU appears often to be a victim of its own success. The range of the subjects and objects of EU law continues to expand and the EU is arguably increasingly a victim of its own success, increasingly taking decisions with impacts on third countries or parties, subjecting more entities to sanctions regimes, being bound to consult more entities and have more third countries, parties and entities such as lobbyists interested in the directions of EU law. The assessment of the EU as a global actor includes broad checks on normative action ex ante and ex post facto- yet it is no less harsh. Ex ante metrics of EU global action include court-centred ones such as an opinion from the CJEU on legality of an international agreement, often precluded in most constitutional systems on account of its conflict with pacta sunt servanda. The contours of the principle of the autonomy of EU law have the capacity to put more stringent parameters on EU institutionalised evolutions as to international engagement. How can we assess the EU as a global actor given these realities? The aim of the event was to explore informally the nexus between trade and security, trade and economics and trade and human rights as a future research agenda with input from a variety of scholars It reflected upon four major themes: 1) The EUâs Contribution to the Democratisation of Global Governance 2) Deeper Trade Agreements and New Normative Foundations 3) The EU as a Global Actor in Trade and Fundamental Rights 4) EUâs Trade in the Era of Global Data Flows
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