Final Measurement of the

This Letter reports one of the most precise measurements to date of the antineutrino spectrum from a purely ^{235}U-fueled reactor, made with the final dataset from the PROSPECT-I detector at the High Flux Isotope Reactor. By extracting information from previously unused detector segments, this analysis effectively doubles the statistics of the previous PROSPECT measurement. The reconstructed energy spectrum is unfolded into antineutrino energy and compared with both the Huber-Mueller model and a spectrum from a commercial reactor burning multiple fuel isotopes. A local excess over the model is observed in the 5-7 MeV energy region. Comparison of the PROSPECT results with those from commercial reactors provides new constraints on the origin of this excess, disfavoring at 2.0 and 3.7 standard deviations the hypotheses that antineutrinos from ^{235}U are solely responsible and noncontributors to the excess observed at commercial reactors, respectively.

Experimental Search for Neutron to Mirror Neutron Oscillations as an Explanation of the Neutron Lifetime Anomaly.

An unexplained >4σ discrepancy persists between "beam" and "bottle" measurements of the neutron lifetime. A new model proposed that conversions of neutrons n into mirror neutrons n^{'}, part of a dark mirror sector, can increase the apparent neutron lifetime by 1% via a small mass splitting Δm between n and n^{'} inside the 4.6 T magnetic field of the National Institute of Standards and Technology Beam Lifetime experiment. A search for neutron conversions in a 6.6 T magnetic field was performed at the Spallation Neutron Source which excludes this explanation for the neutron lifetime discrepancy.

Joint Determination of Reactor Antineutrino Spectra from

A joint determination of the reactor antineutrino spectra resulting from the fission of ^{235}U and ^{239}Pu has been carried out by the Daya Bay and PROSPECT Collaborations. This Letter reports the level of consistency of ^{235}U spectrum measurements from the two experiments and presents new results from a joint analysis of both data sets. The measurements are found to be consistent. The combined analysis reduces the degeneracy between the dominant ^{235}U and ^{239}Pu isotopes and improves the uncertainty of the ^{235}U spectral shape to about 3%. The ^{235}U and ^{239}Pu antineutrino energy spectra are unfolded from the jointly deconvolved reactor spectra using the Wiener-SVD unfolding method, providing a data-based reference for other reactor antineutrino experiments and other applications. This is the first measurement of the ^{235}U and ^{239}Pu spectra based on the combination of experiments at low- and highly enriched uranium reactors.

Joint Measurement of the

The PROSPECT and STEREO collaborations present a combined measurement of the pure ^{235}U antineutrino spectrum, without site specific corrections or detector-dependent effects. The spectral measurements of the two highest precision experiments at research reactors are found to be compatible with χ^{2}/ndf=24.1/21, allowing a joint unfolding of the prompt energy measurements into antineutrino energy. This ν[over ¯]_{e} energy spectrum is provided to the community, and an excess of events relative to the Huber model is found in the 5-6 MeV region. When a Gaussian bump is fitted to the excess, the data-model χ^{2} value is improved, corresponding to a 2.4σ significance.

Nonfuel Antineutrino Contributions in the High Flux Isotope Reactor.

Reactor neutrino experiments have seen major improvements in precision in recent years. With the experimental uncertainties becoming lower than those from theory, carefully considering all sources of ν ¯ e is important when making theoretical predictions. One source of ν ¯ e that is often neglected arises from the irradiation of the nonfuel materials in reactors. The ν ¯ e rates and energies from these sources vary widely based on the reactor type, configuration, and sampling stage during the reactor cycle and have to be carefully considered for each experiment independently. In this article, we present a formalism for selecting the possible ν ¯ e sources arising from the neutron captures on reactor and target materials. We apply this formalism to the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory, the ν ¯ e source for the the Precision Reactor Oscillation and Spectrum Measurement (PROSPECT) experiment. Overall, we observe that the nonfuel ν ¯ e contributions from HFIR to PROSPECT amount to 1% above the inverse beta decay threshold with a maximum contribution of 9% in the 1.8-2.0 MeV range. Nonfuel contributions can be particularly high for research reactors like HFIR because of the choice of structural and reflector material in addition to the intentional irradiation of target material for isotope production. We show that typical commercial pressurized water reactors fueled with low-enriched uranium will have significantly smaller nonfuel ν ¯ e contribution.

Measurement of the Antineutrino Spectrum from

This Letter reports the first measurement of the ^{235}U ν[over ¯]_{e} energy spectrum by PROSPECT, the Precision Reactor Oscillation and Spectrum experiment, operating 7.9 m from the 85 MW_{th} highly enriched uranium (HEU) High Flux Isotope Reactor. With a surface-based, segmented detector, PROSPECT has observed 31678±304(stat) ν[over ¯]_{e}-induced inverse beta decays, the largest sample from HEU fission to date, 99% of which are attributed to ^{235}U. Despite broad agreement, comparison of the Huber ^{235}U model to the measured spectrum produces a χ^{2}/ndf=51.4/31, driven primarily by deviations in two localized energy regions. The measured ^{235}U spectrum shape is consistent with a deviation relative to prediction equal in size to that observed at low-enriched uranium power reactors in the ν[over ¯]_{e} energy region of 5-7 MeV.

First Search for Short-Baseline Neutrino Oscillations at HFIR with PROSPECT.

This Letter reports the first scientific results from the observation of antineutrinos emitted by fission products of ^{235}U at the High Flux Isotope Reactor. PROSPECT, the Precision Reactor Oscillation and Spectrum Experiment, consists of a segmented 4 ton ^{6}Li-doped liquid scintillator detector covering a baseline range of 7-9 m from the reactor and operating under less than 1 m water equivalent overburden. Data collected during 33 live days of reactor operation at a nominal power of 85 MW yield a detection of 25 461±283 (stat) inverse beta decays. Observation of reactor antineutrinos can be achieved in PROSPECT at 5σ statistical significance within 2 h of on-surface reactor-on data taking. A reactor model independent analysis of the inverse beta decay prompt energy spectrum as a function of baseline constrains significant portions of the previously allowed sterile neutrino oscillation parameter space at 95% confidence level and disfavors the best fit of the reactor antineutrino anomaly at 2.2σ confidence level.

Perceptual visual dysfunction, physical impairment and quality of life in Bangladeshi children with cerebral palsy.

BACKGROUND: Cerebral palsy (CP) is the most common cause of motor disability in children and is often accompanied by sensory and/or cognitive impairment. The aim of this study was to characterise visual acuity impairment, perceptual visual dysfunction (PVD) and physical disability in a community-based sample of Bangladeshi children with CP and to assess the impact of these factors on the quality of life of the children. METHODS: A key informant study was used to recruit children with CP from Sirajganj district. Gross Motor Function Classification System (GMFCS) levels and visual impairment were assessed by a physiotherapist and an optometrist, respectively. Assessments of visual perception were performed and standardised questionnaires were administered to each child's main carer to elicit indicators of PVD and parent-reported health-related quality of life. A generalised linear regression analysis was conducted to assess the determinants of the quality of life scores. RESULTS: 180 children were recruited. The median age was 8 years (IQR: 6-11 years); 112 (62%) were male; 57 (32%) had visual acuity impairment and 95 (53%) had some parent-reported PVD. In analyses adjusted for age, sex, GMFCS and acuity impairment, visual attention (p<0.001) and recognition/navigation (p<0.001) were associated with total health-related quality of life, and there were similar trends for total PVD score (p=0.006) and visual search (p=0.020). CONCLUSIONS: PVD is an important contributor in reducing quality of life in children with CP, independent of motor disability and acuity impairment. Better characterisation of PVD is important to help design interventions for affected children, which may improve their quality of life.

Ecological determinants of blindness in Nigeria: the Nigeria National Blindness and Visual Impairment Survey.

OBJECTIVE: To determine the prevalence and causes of visual loss in different ecological zones across Nigeria. METHODS: A population-based survey using multi-stage, stratified, cluster random sampling with probability proportional to size comprising a nationally representative sample of adults aged > or = 40 years from six ecological zones. OUTCOME MEASURES: Distance vision was measured using reduced logMAR charts. Clinical examination included basic eye examination for all respondents and a detailed examination including visual fields, gonioscopy and fundus photography for those who were visually impaired or blind (i.e. presenting vision < 20/40 in the better eye). A principal cause of visual loss was assigned to all respondents with presenting vision < 20/40 in the better eye. RESULTS: A total of 15 122 persons aged > or = 40 years were enumerated, 13 599 (89.9%) of whom were examined. The prevalence of blindness varied according to ecological zone, being highest in the Sahel region (6.6%; 95% confidence interval (CI) 4.2 - 10.4) and lowest in the rain forest region (3.23%; 95% CI 2.6 - 3.9). Age/ gender-adjusted analyses showed that risk of blindness was highest in Sahel (odds ratio (OR) 3.4; 95% CI 2.1 - 5.8). More than 80% of blindness in all ecological regions was avoidable. Trachoma was a significant cause only in the Sudan savannah belt. The prevalence of all major blinding conditions was highest in the Sahel. CONCLUSIONS: The findings of this national survey may be applicable to other countries in West and Central Africa that share similar ecological zones. Onchocerciasis and trachoma are not major causes of blindness in Nigeria, possibly reflecting successful control efforts for both these neglected tropical diseases.

Prophylactic laser peripheral iridotomy and cataract progression.

PURPOSE: To determine whether prophylactic laser peripheral iridotomy (LPI) for primary angle closure (PAC) is associated with cataract progression. METHODS: In 1999, Mongolian volunteers aged>or=50 years were invited to participate in a longitudinal study. Glaucoma was excluded in all participants and 712 of them were selected to undergo a full ophthalmic examination as part of the study protocol. Lenses were graded and PAC diagnosed using international classification systems. In 2005, all traced participants underwent a similar dilated examination. Diagnosis of cataract progression was based on the inter-observer variation +2 standard deviations. The association between LPI at baseline and cataract progression was assessed using chi2-test and logistic regression. RESULTS: Of 712 participants, 158 were diagnosed with occludable angles and treated with LPI. In 2005, 137 participants (19.2%) had died, 315 (315/575=54.8%) were traced, and dilated examination was performed on 276 (48%) of them. Progression of nuclear opacity (NO), cortical, and posterior subcapsular (PSC) opacities were evident in 40 (14.5%, 95% confidence interval (CI)=10.6-19.2%), 89 (32.2%, 95% CI=26.8-38.1%), and 11 participants (4.0%, 95% CI=2.0-7.0%), respectively. Although NO was more likely to progress in those with LPI in a crude analysis (odds ratio (OR)=2.02, 95% CI=1.00-4.11, P=0.05), no evidence of an independent association was detected in multivariate analysis adjusting for age, sex, and baseline Schaffer grading (adjusted OR=1.24, 0.41-3.75, P=0.7). There was no evidence of an association between LPI and progression of PSC or cortical opacities. CONCLUSIONS: There is no evidence that prophylactic LPI is independently associated with cataract progression in this study.

Incidence of occludable angles in a high-risk Mongolian population.

BACKGROUND: Primary angle closure glaucoma (PACG) accounts for nearly 50% of global glaucoma blindness. There are currently no public health strategies to deal with this problem. Screening and prophylactic treatment of primary angle closure suspects (PACS) with laser peripheral iridotomy (LPI) may form a feasible population-level intervention. However, more information about the natural history of PACS is required before such an approach could be considered. METHODS: Six hundred and forty-four participants aged 50 years with a central anterior chamber depth (cACD) of <2.53 mm underwent a full slit-lamp examination in 1999. Of these, 160 participants diagnosed as having occludable angles by gonioscopy (ISGEO classification) were excluded from all further analysis, leaving 484 for follow-up. Six years later, 95/484 (19.6%) had died. A total of 201 of 389 participants traced (51.7%) were re-examined. The potential risk factors for the development of an occludable angle were assessed using the chi squared test, t test and the Wilcoxon rank sum test. RESULTS: At follow-up, 41 participants (20.4%, 95% CI: 14.8 to 25.7) were diagnosed as having incident PACS. Narrower angles, identified by grading of limbal chamber depth and gonioscopy at baseline, were strongly associated with incident occludable angles (p = 0.01 and p<0.01, respectively). There was weak evidence of an association with change in cACD (p = 0.05), and no evidence of an association with age, gender, and baseline cACD for the development of occludable angles. CONCLUSIONS: Narrower angles as determined by limbal chamber depth grading and gonioscopy at baseline were the main risk factors identified for the development of occludable angles.

Cataract prevalence, cataract surgical coverage and barriers to uptake of cataract surgical services in Pakistan: the Pakistan National Blindness and Visual Impairment Survey.

AIM: To estimate the prevalence of visual impairment and blindness caused by cataract, the prevalence of aphakia/pseudophakia, cataract surgical coverage (CSC) and to identify barriers to the uptake of cataract services among adults aged >or=30 years in Pakistan. METHODS: Probability proportional-to-size procedures were used to select a nationally representative sample of adults. Each subject underwent interview, visual acuity measurement, autorefraction, biometry and ophthalmic examination. Those that saw <6/12 in either eye underwent a more intensive examination procedure including corrected visual acuity, slit lamp and dilated fundus examination. CSC was calculated for different levels of visual loss by person and by eye. Individuals with <6/60 in the better eye as a result of cataract were interviewed regarding barriers. RESULTS: 16 507 Adults were examined (95.5% response rate). The crude prevalence of blindness (presenting <3/60 in the better eye) caused by bilateral cataract was 1.75% (95% CI 1.55%, 1.96%). 1317 Participants (633 men; 684 women) had undergone cataract surgery in one or both eyes, giving a crude prevalence of 8.0% (95% CI 7.6%, 8.4%). The CSC (persons) at <3/60, <6/60 and <6/18 were 77.1%, 69.3% and 43.7%, respectively. The CSC (eyes) at <3/60, <6/60 and <6/18 were 61.4%, 52.2% and 40.7%, respectively. Cost of surgery (76.1%) was the main barrier to surgery. CONCLUSION: Approximately 570 000 adults are estimated to be blind (<3/60) as a result of cataract in Pakistan, and 3,560000 eyes have a visual acuity of <6/60 because of cataract. Overall, the national surgical coverage is good but underserved populations have been identified.

Causes of severe visual impairment and blindness in Bangladesh: a study of 1935 children.

OBJECTIVE: To identify the anatomical site and underlying aetiology of severe visual impairment and blindness (SVI/BL) in children in Bangladesh. DESIGN: A national case series. METHODS: Children were recruited from all 64 districts in Bangladesh through multiple sources. Causes were determined and categorised using standard World Health Organization methods. RESULTS: 1935 SVI/BL children were recruited. The median age was 132 months, and boys accounted for 63.1% of the sample. The main site of abnormality was lens (32.5%), mainly unoperated cataract, followed by corneal pathology (26.6%) and disorders of the whole eye (13.1%). Lens-related blindness was the leading cause in boys (37.0%) compared with corneal blindness in girls (29.8%). In 593 children, visual loss was due to childhood factors, over 75% being attributed to vitamin A deficiency. Overall 1338 children (69.2%) had avoidable causes. Only 2% of the country's estimated SVI/BL children have access to education and rehabilitation services. CONCLUSIONS: This is the first large-scale study of SVI/BL children in Bangladesh over two-thirds of whom had avoidable causes. Strategies for control are discussed.

Causes of blindness and visual impairment in Pakistan. The Pakistan national blindness and visual impairment survey.

OBJECTIVE: To determine the causes of blindness and visual impairment in adults (> or =30 years old) in Pakistan, and to explore socio-demographic variations in cause. METHODS: A multi-stage, stratified, cluster random sampling survey was used to select a nationally representative sample of adults. Each subject was interviewed, had their visual acuity measured and underwent autorefraction and fundus/optic disc examination. Those with a visual acuity of <6/12 in either eye underwent a more detailed ophthalmic examination. Causes of visual impairment were classified according to the accepted World Health Organization (WHO) methodology. An exploration of demographic variables was conducted using regression modeling. RESULTS: A sample of 16 507 adults (95.5% of those enumerated) was examined. Cataract was the most common cause of blindness (51.5%; defined as <3/60 in the better eye on presentation) followed by corneal opacity (11.8%), uncorrected aphakia (8.6%) and glaucoma (7.1%). Posterior capsular opacification accounted for 3.6% of blindness. Among the moderately visually impaired (<6/18 to > or =6/60), refractive error was the most common cause (43%), followed by cataract (42%). Refractive error as a cause of severe visual impairment/blindness was significantly higher in rural dwellers than in urban dwellers (odds ratio (OR) 3.5, 95% CI 1.1 to 11.7). Significant provincial differences were also identified. Overall we estimate that 85.5% of causes were avoidable and that 904 000 adults in Pakistan have cataract (<6/60) requiring surgical intervention. CONCLUSIONS: This comprehensive survey provides reliable estimates of the causes of blindness and visual impairment in Pakistan. Despite expanded surgical services, cataract still accounts for over half of the cases of blindness in Pakistan. One in eight blind adults has visual loss from sequelae of cataract surgery. Services for refractive errors need to be further expanded and integrated into eye care services, particularly those serving rural populations.

Causes and temporal trends of blindness and severe visual impairment in children in schools for the blind in North India.

AIMS: To describe the causes of severe visual impairment and blindness (SVI/BL) in children in schools for the blind in north India, and explore temporal trends in the major causes. METHODS: A total of 703 children were examined in 13 blind schools in Delhi. A modified WHO/PBL eye examination record for children with blindness and low vision which included sections on visual acuity, additional non-ocular disabilities, onset of visual loss, the most affected anatomical part of the eye concerning visual impairment, and the aetiological category of the child's disorder based on the timing of insult leading to visual loss was administered in all children. RESULTS: With best correction, 22 (3.1%) were severely visually impaired (visual acuity in the better eye of <6/60) and 628 (89.3%) children were blind (visual acuity in the better eye of <3/60). Anatomical sites of SVI/BL were whole globe in 27.4% children, cornea 21.7%, retina 15.1%, and lens 10.9%. The underlying cause of visual loss was undetermined in 56.5% children (mainly abnormality since birth 42.3% and cataract 8.3%), childhood disorders were responsible in 28.0% (mainly vitamin A deficiency/measles 20.5%), and hereditary factors were identified in 13.4%. Study of temporal trends of SVI/BL by comparing causes in children in three different age groups-5-8 years, 9-12 years, and 13-16 years-suggests that retinal disorders have become more important while childhood onset disorders (particularly vitamin A deficiency) have declined. CONCLUSIONS: Almost half of the children suffered from potentially preventable and/or treatable conditions, with vitamin A deficiency/measles and cataract the leading causes. Retinal disorders seem to be increasing in importance while childhood disorders have declined over a period of 10 years.

The familial contribution to non-syndromic ocular coloboma in south India.

AIMS: To identify the proportion of familial cases of isolated ocular colobomatous malformations in a case series from south India. METHODS: Children with ocular coloboma without systemic features were recruited from multiple sources in Andhra Pradesh, India. Their families were traced, pedigrees drawn, and family members examined. RESULTS: 56 probands, 25 females (44.6%) and 31 males (57.4%) with a colobomatous malformation were identified. In 12 cases (21.4%) another family member was affected. The risk to siblings was 3.8%. The parents were consanguineous in 25 cases (44.6%). CONCLUSIONS: 21.4% of cases of isolated ocular coloboma in this highly consanguineous population of south India were familial, with both autosomal dominant and autosomal recessive mechanisms likely in different families.

Prevalence and causes of severe visual impairment and blindness in children in Mongolia.

BACKGROUND: Reliable epidemiological data on the prevalence and causes of visual loss in children are difficult to obtain, but are essential for planning. No such data are available from Mongolia. AIM: To determine the prevalence and causes of severe visual impairment and blindness (SVI/BL) in children from a defined area of Mongolia, using several methods of identification. METHODS: Children with presenting visual acuities of <6/60 in the better eye who lived in 10 of the 18 provinces (Aimaks) were identified 1) by family doctors 2) in the school for the blind 3) by visiting eye departments in the capital. All eligible children were examined (or data extracted from hospital records) and the cause of visual loss determined using the WHO classification system. RESULTS: Sixty-four children with SVI/BL before refraction were identified who lived in the 10 study Aimaks. They were recruited by family doctors (52); by home visits (3); from hospital records (4); or from the school for the blind (5). The prevalence of SVI/BL before refraction was 0.19/1,000 children (95% CI 0.16-0.22), decreasing to 0.16/1,000 after refraction (95% CI 0.13-0.19) but there was considerable variation from Aimak to Aimak. The major causes of SVI/BL were lesions of the lens (34%), central nervous system disorders (19%), lesions of the whole globe (e.g. microphthalmos) (14%), and retinal conditions (12.5%). Hereditary factors were responsible for 27% of causes, and 17% of children were blind following acquired conditions of childhood. The underlying cause could not be determined in 48%. The causes of SVI/BL was analysed in a further 16 children who lived outside the study Aimaks to compare the causes in children in special education with those not in schooling, and by age. CONCLUSION: The prevalence estimate obtained was lower than anticipated, and possible reasons are discussed. The pattern of causes of SVI/BL is similar to that in children in schools for the blind in China, but is very different from other Asian countries. Meningococcal meningitis was the most common preventable cause of SVI/BL, and immunisation is being considered. Other preventable causes were rare, and the majority of children needing surgical intervention had already been identified and referred for treatment. The control of blindness in children could possibly be improved by better management of conditions requiring surgery, and by the provision of low vision devices.

Clinical findings, consanguinity, and pedigrees in children with anophthalmos in southern India.

This study aimed to describe clinical findings, pedigrees, and possible environmental risk factors in children with clinical anophthalmos and remnant microphthalmos in either eye in southern India. Twenty-four children (14 male, 10 female; mean age 10.3 years, age range 1.3 to 18 years,) were recruited from schools for the blind, hospitals, and community-based rehabilitation programmes in Andhra Pradesh, India, over 1 year. Family members were examined, and mothers interviewed. Fifteen children had anophthalmos and nine had remnant microphthalmos in one or both eyes. Twelve children had associated systemic findings, of which six were major and six were minor abnormalities. Information on consanguinity was available in 19 children, 12 of whom had consanguineous parents. Five children had a positive family history. Two mothers had a history of night blindness, and one had a history of pesticide exposure during pregnancy. High rates of consanguinity suggest a genetic recessive aetiology.

Genes and environment in refractive error: the twin eye study.

PURPOSE: A classical twin study was performed to examine the relative importance of genes and environment in refractive error. METHODS: Refractive error was examined in 226 monozygotic (MZ) and 280 dizygotic (DZ) twin pairs aged 49 to 79 years (mean age, 62.4 years). Using a Humphrey-670 automatic refractor, continuous measures of spherical equivalent, total astigmatism, and corneal astigmatism were recorded. Univariate and bivariate maximum likelihood model fitting was used to estimate genetic and environmental variance components using information from both eyes. RESULTS: For the continuous spectrum of myopia/hyperopia, a model specifying additive genetic and unique environmental factors showed the best fit to the data, yielding a heritability of 84% to 86% (95% confidence interval [CI], 81%-89%). If myopia and hyperopia (< or = -0.5 D and > or = 0.5 D, respectively) were treated as binary traits, the heritability was 90% (95% CI, 81%-95%) for myopia and 89% (95% CI, 81%-94%) for hyperopia. For total and corneal astigmatism, modeling showed dominant genetic effects are important; dominant genetic effects accounted for 47% to 49% of the variance of total astigmatism (95% CI, 37%-55%) and 42% to 61% of corneal astigmatism variance (95% CI, 8%-71%), with additive genetic factors accounting for 1% to 4% and 4% to 18%, respectively (95% CIs, 0%-13% and 0%-60%, respectively). CONCLUSIONS: Genetic effects are of major importance in myopia/hyperopia; astigmatism appears to be dominantly inherited.