In quantum magnets, magnetic moments fluctuate heavily and are strongly entangled with each other, a fundamental distinction from classical magnetism. Here, with inelastic neutron scattering ...measurements, we probe the spin correlations of the honeycomb lattice quantum magnet YbCl
. A linear spin wave theory with a single Heisenberg interaction on the honeycomb lattice, including both transverse and longitudinal channels of the neutron response, reproduces all of the key features in the spectrum. In particular, we identify a Van Hove singularity, a clearly observable sharp feature within a continuum response. The demonstration of such a Van Hove singularity in a two-magnon continuum is important as a confirmation of broadly held notions of continua in quantum magnetism and additionally because analogous features in two-spinon continua could be used to distinguish quantum spin liquids from merely disordered systems. These results establish YbCl
as a benchmark material for quantum magnetism on the honeycomb lattice.
To assess the prevalence of refractive error and visual impairment in school-age children in Gombak District, a suburban area near Kuala Lumpur city.
Population-based, cross-sectional survey.
Four ...thousand six hundred thirty-four children 7 to 15 years of age living in 3004 households.
Random selection of geographically defined clusters was used to identify the study sample. Children in 34 clusters were enumerated through a door-to-door survey and examined in 140 schools between March and July 2003. The examination included visual acuity measurements; ocular motility evaluation; retinoscopy and autorefraction under cycloplegia; and examination of the external eye, anterior segment, media, and fundus.
Distance visual acuity and cycloplegic refraction.
The examined population was 70.3% Malay, 16.5% Chinese, 8.9% Indian, and 4.3% of other ethnicity. The prevalence of uncorrected (unaided), presenting, and best-corrected visual impairment (visual acuity < or =20/40 in the better eye) was 17.1%, 10.1%, and 1.4%, respectively. More than half of those in need of corrective spectacles were without them. In eyes with reduced vision, refractive error was the cause in 87.0%, amblyopia in 2.0%, other causes in 0.6%, and unexplained causes in 10.4%, mainly suspected amblyopia. Myopia (spherical equivalent of at least -0.50 diopter D in either eye) measured with retinoscopy was present in 9.8% of children 7 years of age, increasing to 34.4% in 15-year-olds; and in 10.0% and 32.5%, respectively, with autorefraction. Myopia was associated with older age, female gender, higher parental education, and Chinese ethnicity. Hyperopia (> or =2.00 D) with retinoscopy varied from 3.8% in 7-year-olds, 5.0% with autorefraction, to less than 1% by age 15, with either measurement method. Hyperopia was associated with younger age and "other" ethnicity. Astigmatism (> or =0.75 D) was present in 15.7% of children with retinoscopy and in 21.3% with autorefraction.
Visual impairment in school-age children in urban Gombak District is overwhelmingly caused by myopia, with a particularly high prevalence among children of Chinese ethnicity. Eye health education and screening may help address the unmet need for refractive correction.
PURPOSE For the past 25 years, the WHO Programme for the Prevention of Blindness and Deafness has maintained a Global Data Bank on visual impairment with the purpose of storing the available ...epidemiological data on blindness and low vision. The Data Bank has now been updated to include studies conducted since the last update in 1994. METHODS An extensive literature search was conducted in international and national scientific and medical journals to identify epidemiological studies that fulfilled basic criteria for inclusion in the Data Bank, namely a clearly stated definition of blindness and low vision, and prevalence rates derived from population-based surveys. Sources such as National Prevention of Blindness Programmes, academic institutions or WHO country or regional reports were also investigated. RESULTS Two-hundred-and-eight population-based studies on visual impairment for 68 countries are reported in detail, providing an up-to-date, comprehensive compilation of the available information on visual impairment and its causes globally.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
PURPOSE:
To assess the prevalence of refractive error and vision impairment in school age children in the terai area of the Mechi zone in Eastern Nepal.
METHODS:
Random selection of village-based ...clusters was used to identify a sample of children 5 to 15 years of age. Children in the 25 selected clusters were enumerated through a door-to-door household survey and invited to village sites for examination. Visual acuity measurements, cycloplegic retinoscopy, cycloplegic autorefraction, ocular motility evaluation, and anterior segment, media, and fundus examinations were done from May 1998 through July 1998. Independent replicate examinations for quality assurance monitoring took place in all children with reduced vision and in a sample of those with normal vision in seven villages.
RESULTS:
A total of 5,526 children from 3,724 households were enumerated, and 5,067 children (91.7%) were examined. The prevalence of uncorrected, presenting, and best visual acuity 0.5 (20/40) or worse in at least one eye was 2.9%, 2.8%, and 1.4%, respectively; 0.4% had best visual acuity 0.5 or worse in both eyes. Refractive error was the cause in 56% of the 200 eyes with reduced uncorrected vision, amblyopia in 9%, other causes in 19%, with unexplained causes in the remaining 16%. Myopia −0.5 diopter or less in either eye or hyperopia 2 diopters or greater was observed in less than 3% of children. Hyperopia risk was associated with female gender and myopia risk with older age.
CONCLUSIONS:
The prevalence of reduced vision is very low in school-age children in Nepal, most of it because of correctable refractive error. Further studies are needed to determine whether the prevalence of myopia will be higher for more recent birth cohorts.
Purpose: To establish normative data on morphological characteristics and quantitative parameters of Foveal Avascular Zone (FAZ) as well as their systemic and ocular associations using OCT ...angiography (OCT-A) in healthy Nepalese subjects. Patients and Methods: A prospective, cross-sectional, population-based study recruiting 210 healthy samples (420 eyes) aged 10 to 70 years was conducted. All the samples underwent detailed comprehensive eye examination followed by Optical Coherence Tomography Angiography (OCTA) and Enhanced Depth Imaging performed in each eye using Spectral Domain Optical Coherence Tomography. Foveal avascular zone area and vessel density in superficial and deep retinal plexus and Sub foveal Choroidal Thickness (SFCT) were evaluated. Ocular and systemic associations of these parameters were also studied in a multivariate analysis utilizing linear regression. Results: The mean superficial and deep FAZ area was 459.96 + or - 124.75 gm (95% confidence interval CI, 443.08-476.83) and 589.0 + or - 141.39 gm (95% CL, 570.77-609.02), respectively. The vessel density in superficial capillary plexus was 54.03 + or - 9.34% (95% CL, 53.98-54.11) while the vessel density in deep capillary plexus was 25.91 + or - 38% (95% CL, 25.85-25.96). The mean SFCT in this study was 308.89 + or - 68.87gm (95% CL, 299.64-318.14 gm). There was no statistically significant inter-eye difference in the FAZ parameters. Myopic eyes had smaller FAZ, lesser vessel density and thinner SFCT. Association was observed between superficial FAZ area and systolic blood pressure, and deep FAZ area and diastolic blood pressure. Conclusion: This study reports the normative data on FAZ parameters in healthy Nepalese subjects which can serve as references for interpreting these parameters in different retinal-choroidal diseases. Keywords: choroidal thickness, EDI-OCT, foveal avascular zone, healthy eyes, OCT-angiography
Purpose: To evaluate the accuracy of Eclipse electron Monte Carlo (eMC) dose calculation algorithm in inhomogeneous medium. Methods: The PTW inhomogeneity phantom consisting of base plate and inserts ...of different inhomogeneous materials (bone, tissue and lung) was used in this study. The base plate can be placed on a slab with a hole drilled for PTW diode (TN600017). With the combination of these inhomogeneous inserts, solid water slabs and bolus, a number of inhomogeneous geometries were created and CT scanned with the diode in place. The image set was then imported to Eclipse TPS (version 11.1) workstation. Several treatment plans were created for the cone size of 10×10 with the prescription dose of 200cGy at the center of the diode. All of the eMC dose calculations were performed at grid size of 2 mm and accuracy level of 2%. Measurements with diode were then carried out in Varian TrueBeam machine. The bone inhomogeneity measurements were only carried out for 15, 18 and 22Mev electron energies. Results: The measured doses agreed well within 2% with eMC calculated doses for 9, 18 and 22Mev for all the inhomogeneities considered. For 6Mev, measured dose for tissue only was 4.28% higher whereas 4.02% lower for lung inhomogeneity. In case of 12Mev, measured doses were 2.83% and 4.61% lower compared to calculated doses for tissue only and lung inhomogeneity. In case of 15Mev, measured doses were 1.47%, 4.61% and 10.5% lower compared to eMC for tissue only, lung and bone inhomogeneity. Conclusion: This work indicates that eMC algorithm in Eclipse provides acceptable agreement with measured data for most of the clinical cases involving inhomogeneities. However, variation as high as 10.5%, was observed for 15Mev in bone inhomogeneity case. So, care must be taken if eMC is used to calculate dose for15Mev involving bone inhomogeneity.
PURPOSE:
The Refractive Error Study in Children was designed to assess the prevalence of refractive error and vision impairment in children of different ethnic origins and cultural settings.
METHODS:
...Population-based cross-sectional samples of children 5 to 15 years of age were obtained through cluster sampling. Presenting, uncorrected, and best-corrected visual acuity, along with refractive error under cycloplegia, were the main outcome measures. Amblyopia and other causes of uncorrectable vision impairment were determined.
RESULTS:
Study design and sample size calculations, survey enumeration and ophthalmic examination methods, quality assurance monitoring, and data analyses and statistical methods are described.
CONCLUSIONS:
The study design, sample size, and measurement methods ensure that the prevalence of age-specific and sex-specific refractive error can be estimated with reasonable accuracy in the target populations. With commonality of methods, a comparison of findings between studies in different ethic origins and cultural settings is possible.
The physical properties of the spinel LiGaCr4S8 have been studied with neutron diffraction, x-ray diffraction, magnetic susceptibility, and heat capacity measurements. The neutron diffraction and ...synchrotron x-ray diffraction data reveal negative thermal expansion (NTE) below 111(4) K. The magnetic susceptibility deviates from Curie-Weiss behavior with the onset of NTE. At low temperature a broad peak in the magnetic susceptibility at 10.3(3) K is accompanied by the return of normal thermal expansion. First-principles calculations find a strong coupling between the lattice and the simulated magnetic ground state. These results indicate strong magnetoelastic coupling in LiGaCr4S8.
Background/aim: Himalaya Eye Hospital (HEH), established in 1993, is rendering eye care services in the Gandaki and Dhaulagiri zones. The hospital has extensive community outreach activities along ...with services for outpatients, emergencies, and subspecialties such as vitreoretinal, paediatric, and low vision. The operation theatre is well equipped to match the surgical needs including phaco surgery for cataract. The hospital has performed more than 14 000 cataract surgeries and 250 000 treatment services during this period. The aim of this study was to estimate the prevalence of blindness, visual impairment, and cataract surgical coverage among the older adult population of three districts of Gandaki Zone, where 80% of the hospital’s service recipients reside. Methods: People aged 45 years and older were enrolled in the study using a stratified cluster design. Subjects in 25 randomly selected clusters from the listed 806 were recruited through door to door visits. Each recruited subject had visual acuity (VA) and clinical examination conducted by an ophthalmologist. The survey was preceded by pre-pilot and pilot studies to refine the operational method. To assess quality assurance the interobserver variation in VA measurement was also carried out in five different clusters. Results: Out of 5863 selected subjects 85.3% were examined. Blindness defined as presenting VA <6/60 in both eyes was found in 2.6% (95% confidence interval (CI): 2.2 to 3.9), whereas 16.8% individuals examined had vision <6/19 in one or both eyes. Cataract was the principal cause of blindness in 60.5%, and refractive error was the dominant cause of vision impairment (<6/19) 83.3%. Cataract surgical coverage was 59.5% among the cataract blind and associated with younger age, literacy, and male sex. Conclusion: The finding suggests a positive impact of the HEH programme on the prevalence of blindness and cataract surgical services in the survey area. Strategies to further improve access and utilisation of facilities and increase cataract surgical coverage need to be developed.
BACKGROUND Visual acuity and vision related quality of life outcomes in cataract surgery were evaluated in a population based survey in two geographic zones in Nepal. METHODS Case finding was based ...on random sampling using a stratified cluster design with door to door enumeration of people aged ⩾45 years followed by eye examinations at village sites. All aphakics/pseudophakics, those with visual acuity less than 6/60 in either eye, and a sample of those with normal visual acuity were administered visual functioning (VF) and quality of life (QOL) questionnaires. RESULTS 15% of the 159 cataract operated cases had presenting visual acuity ⩾6/18 in both eyes, 38% with best corrected visual acuity. 21% were still blind with presenting visual acuity <6/60 in both eyes, 7% with best correction. On a 0–100 scale, mean VF and QOL scores were 87.2 and 93.9 respectively in normally sighted unoperated individuals, dropping to 15.6 and 29.5 for those severely blind (<3/60). Among the cataract operated, mean VF and QOL scores were 47.5 and 55.4, respectively. VF and QOL scores correlated with vision status at statistically significant levels (p <0.0001) CONCLUSION Cataract surgery outcomes, whether measured by traditional visual acuity or by patient reported VF/QOL, are at levels many would consider unacceptably low. It is apparent that in the quest to reduce cataract blindness much more attention must be given to improving surgery outcomes.
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