Van Hove singularity in the magnon spectrum of the antiferromagnetic quantum honeycomb lattice.

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 YbCl3. 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 YbCl3 as a benchmark material for quantum magnetism on the honeycomb lattice.

Prevalence and correction of near vision impairment at Kaski, Nepal.

INTRODUCTION: Presbyopia is an important cause of avoidable visual disability. OBJECTIVE: To estimate the prevalence of near vision impairment and spectacle coverage among middle and older-aged adults in rural Nepal. MATERIALS AND METHODS: The surveys was carried out among the people of age 35 and over in randomly-selected cluster samples in rural settings of Kaski district of western Nepal, Near visual acuity, with and without presenting near correction, was measured at 40 cm using a LogMAR near vision tumbling E chart under ambient indoor lighting. Subjects with uncorrected binocular distance vision of 20/40 or worse were refracted and those with near vision of 20/40 or worse tested with plus sphere to obtain the best-corrected binocular near visual acuity. RESULTS: A total of 2,360 persons aged 35 years and over were enumerated and 2,156 (91.3%) were examined. The age- and gender-standardized prevalence of uncorrected near visual impairment (vision of 20/40 or worse) in study population was found to be 66.1 %. Near vision could not be corrected (>20/40) even after distance and near vision correction in 6.4 % . Using the multiple logistic regression models, uncorrected visual impairment was associated with an older age (odds ratio [OR] = 1.13, P less than 0.001) and a lower educational level (OR = 1.11, P = 0.01) was less associated with female gender (OR = 0.72, P = 0.038). Over 90 % of people with near visual impairment did not have spectacles. CONCLUSION: The prevalence of presbyopia appears to be higher with an earlier onset and over 90 % of people in need of near correction do not have spectacles in this setting.

Prevalence of blindness and cataract surgery in Gandaki Zone, Nepal.

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.

2002 global update of available data on visual impairment: a compilation of population-based prevalence studies.

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.

Barriers to up take cataract surgery in Gandaki Zone, Nepal.

OBJECTIVE: Cataract though avoidable remains as leading cause of blindness in Nepal. Though, Himalaya Eye Hospital rendering high quality surgical service through its base hospital and out reach service in Gandaki Zone having cataract surgical rate is below 1500 per million. Therefore, it is mater of interest to investigate the reason and the finding would be helpful to plan the future cataract programme to CSR to desirable level, if we know the reason(s) that forced them living as blind in community and not seeking available surgical services. METHOD: All person with cataract affecting their visual acuity to <6/60 (corrected) in either eye found in stratified cluster design sampling were enrolled in the study. They were interviewed with structured questionnaire investigating their knowledge and attitude of their visual impairment and barriers for not seeking cataract surgical service to date. RESULTS: A total of 303 eligible subjects were enrolled in the study. Out of them 57.8% of people knew about the cataract and they also think their vision impairment is due to cataract. But 56.11% of people were not aware their vision will improve. Surgical camp attendant or operated patients were found to be effective media to spread the message that the cataract is curable. Among the barriers: fear for surgery 31.1%, lack of attendant and geographical distance 32.8%, financial 24.1% and other clinical reason were found to be 12% as a reason for not seeking available surgical service. CONCLUSION: The cataract service marketing, eye health education disseminating the information on cataract and its curability is not found to be adequate. Therefore, the future cataract programme should give more concentration on creating awareness on cataract and subsidizing the available surgical service and service need to be brought to more proximity for the needy poor people.

Refractive Error Study in Children: sampling and measurement methods for a multi-country survey.

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 da ta 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 ethnic origins and cultural settings is possible.

Refractive Error Study in Children: results from Mechi Zone, Nepal.

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.

Prevalence of blindness and cataract surgery in Nepal.

BACKGROUND: A national eye care programme was launched in Nepal in the early 1980s. The impact of this programme on blindness and cataract surgery prevalence was evaluated in two geographic zones. METHODS: People aged 45 years and older were sampled using a stratified cluster design. Within randomly selected clusters, door to door enumeration was followed by visual acuity measurement and eye examinations at conveniently located sites. The full survey was preceded by a pilot study where operational methods were refined and quality assurance measures carried out. RESULTS: Of the 5112 enumerated individuals 90% were examined. Blindness, defined as presenting visual acuity less than 6/60 in both eyes, was found in 5.3% (95% CI 3.6, 6.8) of individuals examined, with cataract being the principal cause in at least one eye in 78% of cases. Considering both cataract operated and unoperated cataract blind cases, surgical coverage was approximately 42%. CONCLUSION: The findings suggest that blindness prevalence may have decreased slightly from that estimated in a 1981 national survey, both overall and cataract related. Similarly, cataract surgical coverage may have increased somewhat. None of these changes, however, are at statistically significant levels. Accordingly, the blindness problem remains challengingly high.

Visual functioning and quality of life outcomes among cataract operated and unoperated blind populations in Nepal.

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 > or = 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 > or = 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.

Nutrition education and mega-dose vitamin A supplementation in Nepal.

Two approaches to improve vitamin A nutriture are compared: nutrition education and mega-dose capsule distribution. The impact of these programmes on vitamin A deficiency (VAD), wasting malnutrition, and excessive childhood mortality are compared for approximately 40,000 children who were assigned to either intervention cohorts or a control group from 75 sites within seven districts in two ecological settings (Terai, or lowland, and hills) of Nepal. Twenty-four months after the implementation of the project, the reduction of risk of xerophthalmia was greater among children of mothers who were able to identify vitamin A-rich foods [relative risk (RR) = 0.25; 95% CI = 0.10-0.62] than among children who received mega-dose capsules (RR = 0.59; 95% CI = 0.41-0.84). The risk of mortality at two years was reduced for both the nutrition education cohort (RR = 0.64; 95% CI = 0.48-0.86) and capsule distribution cohort (RR = 0.57; 95% CI = 0.42-0.77). The nutrition education program, however, was more expensive to deliver than the capsule distribution programme. High rates of participation in the supplementation programme were achieved within a short period. The nutrition education message spread rapidly throughout the study population, although practice was slower to change. Where maternal literacy was low and channels of communication were limited, the capsule programme appeared to be more cost-effective. However, economies of scale for nationwide programmes exist for nutrition education programmes that do not exist for capsule distribution programmes. A comprehensive national programme requires both dietary supplementation and nutrition education.

Impact of nutrition education and mega-dose vitamin A supplementation on the health of children in Nepal.

The impact on vitamin A deficiency (VAD), wasting malnutrition, and excessive childhood mortality of two alternative approaches-nutrition education and mega-dose capsule distribution (6-12-month-olds: 100,000 IU; 1-5-year-olds: 200,000 IU)-in communities in Nepal are compared. Approximately 40,000 children from 75 locations in seven districts in two ecological settings (lowland and hills) took part in the study and were randomly allocated to intervention cohorts or a control group. At 24 months after the implementation of the project the reduction of risk for xerophthalmia was greater among children whose mothers were able to identify vitamin-A-rich foods (relative risk (RR) = 0.25; 95% confidence interval (CI) = 0.10-0.62) than among the children who received mega-dose capsules (RR = 0.59; 95% CI = 0.41-0.84). The risk of mortality at 2 years was reduced for both the nutrition education (RR = 0.64; 95% Cl = 0.48-0.86) and capsule distribution (RR = 0.57; 95% CI = 0.42-0.77) cohorts. The nutrition education programme was, however, more expensive to deliver than the capsule distribution programme. High rates of participation for children in the supplementation programme were achieved quickly. The nutrition education messages also spread rapidly throughout the study population (regardless of intervention cohort assignment). Practices, however, were slower to change. In communities where maternal literacy was low and channels of communication were limited the capsule distribution programme appeared to be more economical. However, there are economies of scale for nationwide education programmes that do not exist for capsule distribution programmes. Although nutrition education provides economies of scale and the promise of long-term sustainability, a comprehensive national programme requires both dietary supplementation and nutrition education components.

PIP: The effectiveness of two approaches to vitamin A deficiency prevention--nutrition education and mega-dose capsule distribution--was compared in a 3-year study involving almost 40,000 children 6 months to 10 years of age from seven ecologically diverse districts in Nepal. The nutrition education program promoted increased intake of vitamin A-rich foods during the dry season, serving wild greens, and primary health care service utilization. At baseline, 44.9% of the study villages did not have any cases of Bitot's spots; by the third year, 65.5% were free of this sign of vitamin A deficiency. 85% of community risk variation was explained by agricultural patterns, market food availability, household income, maternal literacy, sanitation, and the village's average nutritional status. At 12 months, capsule distribution had reduced the risk of new Bitot's spots by 55% (relative risk (RR), 0.45; 95% confidence interval (CI), 0.33-0.60); however, its impact had declined by 24 months and was non-significant at 36 months. At 24 months, the reduction of risk for xerophthalmia was greatest among children whose mothers were able to identify vitamin A-rich foods (RR, 0.25; 95% CI, 0.10-0.62) and were literate (RR, 0.06; 95% CI, 0.01-0.42). By 24 months, child mortality risk had declined in both the nutrition education (RR, 0.64; 95% CI, 0.48-0.86) and capsule distribution (RR, 0.57; 95% CI, 0.42-0.77) groups. Although the effects of both programs were similar, the capsule program achieved higher coverage rates at a lower cost while the educational intervention provided economies of scale and potential for long-term sustainability. Most feasible would be a comprehensive national program that included both these components as well as maternal literacy training.