702 research outputs found
Predictability of refraction following immediate sequential bilateral cataract surgery (ISBCS) performed under general anesthesia
Abstract
Background: To evaluate the predictability of refraction following immediate sequential bilateral cataract surgery
(ISBCS) performed under general anaesthesia.
Methods: This is a retrospective review of all ISBCS performed at Kantonsspital Winterthur, Switzerland, between
April 2000 and September 2013. The case notes of 250 patients were reviewed. Patients having full refraction
reported (110 patients/220 eyes) were included. 210 (95 %) eyes had a straight forward phacoemulsification with
posterior chamber intraocular lens implantation, seven eyes had a planned extracapsular cataract extraction (ECCE);
three eyes had an intracapsular cataract extraction.
Results: Both eyes of 110 patients (64 women, 46 men) with a mean age of 79.0 years, standard deviation (SD) ±11.4
(range 26 to 97 years) were included. Median preoperative best corrected visual acuity (BCVA) was 0.5 LogMAR in the
first eye, the interquartile range (IQR) was [0.4, 1.2]; 0.7 LogMAR in the second eye with IQR [0.4, 1.8]. At one month, the
median BCVA was 0.2 LogMAR, IQR [0.1, 0.3] in the first eye, median BCVA was 0.1 LogMAR and IQR [0.0, 0.5] in the
second eye. There were 3 eyes (3 %) that lost 3 lines or more in BCVA at one month (control vs. pre-operatively). In all
three cases, poor visual acuity had been recorded pre-operatively (>1 LogMAR). Achieved refraction was within ±1.0 D
of the target in 83 % of eyes. There were only 5 % (n = 6) of cases where if delayed sequential bilateral extraction had
been performed could potentially intraocular lens (IOL) choice have been adjusted, in four of these cases, target
refraction was within ±1.0 D in the second eye.
Conclusions: ISBCS performed under general anaesthesia achieves target refraction in 83 % of eyes after consideration
of complications, ocular co-morbidities and systemic restrictions. In the majority of cases where IOL power calculation
could be considered, the achieved refraction of the second surgical eye was within ±1.0 D of intended refraction. This
undermines the utility of IOL power adjustments in the second surgical eye.
Keywords: Cataract, Cataract surgery, Immediate sequential bilateral cataract surger
Predictability of refraction following immediate sequential bilateral cataract surgery (ISBCS) performed under general anaesthesia.
BACKGROUND: To evaluate the predictability of refraction following immediate sequential bilateral cataract surgery (ISBCS) performed under general anaesthesia.
METHODS: This is a retrospective review of all ISBCS performed at Kantonsspital Winterthur, Switzerland, between April 2000 and September 2013. The case notes of 250 patients were reviewed. Patients having full refraction reported (110 patients/220 eyes) were included. 210 (95 %) eyes had a straight forward phacoemulsification with posterior chamber intraocular lens implantation, seven eyes had a planned extracapsular cataract extraction (ECCE); three eyes had an intracapsular cataract extraction.
RESULTS: Both eyes of 110 patients (64 women, 46 men) with a mean age of 79.0 years, standard deviation (SD) ±11.4 (range 26 to 97 years) were included. Median preoperative best corrected visual acuity (BCVA) was 0.5 LogMAR in the first eye, the interquartile range (IQR) was [0.4, 1.2]; 0.7 LogMAR in the second eye with IQR [0.4, 1.8]. At one month, the median BCVA was 0.2 LogMAR, IQR [0.1, 0.3] in the first eye, median BCVA was 0.1 LogMAR and IQR [0.0, 0.5] in the second eye. There were 3 eyes (3 %) that lost 3 lines or more in BCVA at one month (control vs. pre-operatively). In all three cases, poor visual acuity had been recorded pre-operatively (>1 LogMAR). Achieved refraction was within ±1.0 D of the target in 83 % of eyes. There were only 5 % (n = 6) of cases where if delayed sequential bilateral extraction had been performed could potentially intraocular lens (IOL) choice have been adjusted, in four of these cases, target refraction was within ±1.0 D in the second eye.
CONCLUSIONS: ISBCS performed under general anaesthesia achieves target refraction in 83 % of eyes after consideration of complications, ocular co-morbidities and systemic restrictions. In the majority of cases where IOL power calculation could be considered, the achieved refraction of the second surgical eye was within ±1.0 D of intended refraction. This undermines the utility of IOL power adjustments in the second surgical eye
The ancient heritage of water ice in the solar system
Identifying the source of Earth's water is central to understanding the
origins of life-fostering environments and to assessing the prevalence of such
environments in space. Water throughout the solar system exhibits
deuterium-to-hydrogen enrichments, a fossil relic of low-temperature,
ion-derived chemistry within either (i) the parent molecular cloud or (ii) the
solar nebula protoplanetary disk. Utilizing a comprehensive treatment of disk
ionization, we find that ion-driven deuterium pathways are inefficient,
curtailing the disk's deuterated water formation and its viability as the sole
source for the solar system's water. This finding implies that if the solar
system's formation was typical, abundant interstellar ices are available to all
nascent planetary systems.Comment: 33 pages, 7 figures including main text and supplementary materials.
Published in Scienc
Unlocking CO Depletion in Protoplanetary Disks II. Primordial C/H Predictions Inside the CO Snowline
CO is thought to be the main reservoir of volatile carbon in protoplanetary
disks, and thus the primary initial source of carbon in the atmospheres of
forming giant planets. However, recent observations of protoplanetary disks
point towards low volatile carbon abundances in many systems, including at
radii interior to the CO snowline. One potential explanation is that gas phase
carbon is chemically reprocessed into less volatile species, which are frozen
on dust grain surfaces as ice. This mechanism has the potential to change the
primordial C/H ratio in the gas. However, current observations primarily probe
the upper layers of the disk. It is not clear if the low volatile carbon
abundances extend to the midplane, where planets form. We have run a grid of
198 chemical models, exploring how the chemical reprocessing of CO depends on
disk mass, dust grain size distribution, temperature, cosmic ray and X-ray
ionization rate, and initial water abundance. Building on our previous work
focusing on the warm molecular layer, here we analyze the results for our grid
of models in the disk midplane at 12 au. We find that either an ISM level
cosmic ray ionization rate or the presence of UV photons due to a low dust
surface density are needed to chemically reduce the midplane CO gas abundance
by at least an order of magnitude within 1 Myr. In the majority of our models
CO does not undergo substantial reprocessing by in situ chemistry and there is
little change in the gas phase C/H and C/O ratios over the lifetime of the
typical disk. However, in the small sub-set of disks where the disk midplane is
subject to a source of ionization or photolysis, the gas phase C/O ratio
increases by up to nearly 9 orders of magnitude due to conversion of CO into
volatile hydrocarbons.Comment: Accepted for publication in ApJ, 15 pages, 10 figures, 3 table
Exploring the Origins of Deuterium Enrichments in Solar Nebular Organics
Deuterium-to-hydrogen (D/H) enrichments in molecular species provide clues
about their original formation environment. The organic materials in primitive
solar system bodies have generally higher D/H ratios and show greater D/H
variation when compared to D/H in solar system water. We propose this
difference arises at least in part due to 1) the availability of additional
chemical fractionation pathways for organics beyond that for water, and 2) the
higher volatility of key carbon reservoirs compared to oxygen. We test this
hypothesis using detailed disk models, including a sophisticated, new disk
ionization treatment with a low cosmic ray ionization rate, and find that disk
chemistry leads to higher deuterium enrichment in organics compared to water,
helped especially by fractionation via the precursors CHD/CH. We
also find that the D/H ratio in individual species varies significantly
depending on their particular formation pathways. For example, from
AU, CH can reach , while D/H in CHOH
remains locally unaltered. Finally, while the global organic D/H in our models
can reproduce intermediately elevated D/H in the bulk hydrocarbon reservoir,
our models are unable to reproduce the most deuterium-enriched organic
materials in the solar system, and thus our model requires some inheritance
from the cold interstellar medium from which the Sun formed.Comment: 11 pages, 7 figures, accepted for publication in Ap
Chemical differentiation in regions of high mass star formation II. Molecular multiline and dust continuum studies of selected objects
The aim of this study is to investigate systematic chemical differentiation
of molecules in regions of high mass star formation. We observed five prominent
sites of high mass star formation in HCN, HNC, HCO+, their isotopes, C18O, C34S
and some other molecular lines, for some sources both at 3 and 1.3 mm and in
continuum at 1.3 mm. Taking into account earlier obtained data for N2H+ we
derive molecular abundances and physical parameters of the sources (mass,
density, ionization fraction, etc.). The kinetic temperature is estimated from
CH3C2H observations. Then we analyze correlations between molecular abundances
and physical parameters and discuss chemical models applicable to these
species. The typical physical parameters for the sources in our sample are the
following: kinetic temperature in the range ~ 30-50 K (it is systematically
higher than that obtained from ammonia observations and is rather close to dust
temperature), masses from tens to hundreds solar masses, gas densities ~ 10^5
cm^{-3}, ionization fraction ~ 10^{-7}. In most cases the ionization fraction
slightly (a few times) increases towards the embedded YSOs. The observed clumps
are close to gravitational equilibrium. There are systematic differences in
distributions of various molecules. The abundances of CO, CS and HCN are more
or less constant. There is no sign of CO and/or CS depletion as in cold cores.
At the same time the abundances of HCO+, HNC and especially N2H+ strongly vary
in these objects. They anti-correlate with the ionization fraction and as a
result decrease towards the embedded YSOs. For N2H+ this can be explained by
dissociative recombination to be the dominant destroying process. N2H+, HCO+,
and HNC are valuable indicators of massive protostars.Comment: 15 pages, 8 figure
Chemical differentiation in regions of high-mass star formation I. CS, dust and N2H^+ in southern sources
Aims. Our goals are to compare the CS, N2H+ and dust distributions in a
representative sample of high-mass star forming dense cores and to determine
the physical and chemical properties of these cores. Methods. We compare the
results of CS(5-4) and 1.2 mm continuum mapping of twelve dense cores from the
southern hemisphere presented in this work, in combination with our previous
N2H+(1-0) and CS(2-1) data. We use numerical modeling of molecular excitation
to estimate physical parameters of the cores. Results. Most of the maps have
several emission peaks (clumps). We derive basic physical parameters of the
clumps and estimate CS and N2H+ abundances. Masses calculated from LVG
densities are higher than CS virial masses and masses derived from continuum
data, implying small-scale clumpiness of the cores. For most of the objects,
the CS and continuum peaks are close to the IRAS point source positions. The
CS(5-4) intensities correlate with continuum fluxes per beam in all cases, but
only in five cases with the N2H+(1-0) intensities. The study of spatial
variations of molecular integrated intensity ratios to continuum fluxes reveals
that I(N2H+)/F{1.2} ratios drop towards the CS peaks for most of the sources,
which can be due to a N2H+ abundance decrease. For CS(5-4), the I(CS)/F{1.2}
ratios show no clear trends with distance from the CS peaks, while for CS(2-1)
such ratios drop towards these peaks. Possible explanations of these results
are considered. The analysis of normalized velocity differences between CS and
N2H+ lines has not revealed indications of systematic motions towards CS peaks.Comment: 13 pages, 5 figures, accepted by Astronomy and Astrophysic
Programming: Predicting student success early in CS1. A re-validation and replication study
This paper describes a large, multi-institutional revalidation study conducted in the academic year 2015-16. Six hundred and ninetytwo students participated in this study, from 11 institutions (ten institutions in Ireland and one in Denmark). The primary goal was to validate and further develop an existing computational prediction model called Predict Student Success (PreSS). In doing so, this study addressed a call from the 2015 ITiCSE working group (the second Grand Challenge ), to systematically analyse and verify previous studies using data from multiple contexts to tease out tacit factors that contribute to previously observed outcomes . PreSS was developed and validated in a longitudinal study conducted over a three year period (twelve years previous from 2004- 06). PreSS could predict with near 80% accuracy, how a student would likely perform on an introductory programming module. Notably this could be achieved at a very early stage in the module. This paper describes a revalidation of the original PreSS model on a significantly larger multi-institutional data set twelve years after its initial development and looks at recent research on additional factors that may improve the model. The work involved the development of a fully automated end-to-end tool, which can predict student success early in CS1, with an accuracy of 71%. This paper describes, in detail the PreSS model, recent research, pilot studies and the re-validation and replication study of the PreSS model
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