Large scale coherent magnetohydrodynamic oscillations in a sunspot.

Although theoretically predicted, the simultaneous excitation of several resonant modes in sunspots has not been observed. Like any harmonic oscillator, a solar magnetic flux tube can support a variety of resonances, which constitute the natural response of the system to external forcing. Apart from a few single low order eigenmodes in small scale magnetic structures, several simultaneous resonant modes were not found in extremely large sunspots. Here we report the detection of the largest-scale coherent oscillations observed in a sunspot, with a spectrum significantly different from the Sun's global acoustic oscillations, incorporating a superposition of many resonant wave modes. Magnetohydrodynamic numerical modeling agrees with the observations. Our findings not only demonstrate the possible excitation of coherent oscillations over spatial scales as large as 30-40 Mm in extreme magnetic flux regions in the solar atmosphere, but also paves the way for their diagnostic applications in other astrophysical contexts.

Acoustic-gravity wave propagation characteristics in three-dimensional radiation hydrodynamic simulations of the solar atmosphere.

There has been tremendous progress in the degree of realism of three-dimensional radiation magneto-hydrodynamic simulations of the solar atmosphere in the past decades. Four of the most frequently used numerical codes are Bifrost, CO5BOLD, MANCHA3D and MURaM. Here we test and compare the wave propagation characteristics in model runs from these four codes by measuring the dispersion relation of acoustic-gravity waves at various heights. We find considerable differences between the various models. The height dependence of wave power, in particular of high-frequency waves, varies by up to two orders of magnitude between the models, and the phase difference spectra of several models show unexpected features, including ±180° phase jumps. This article is part of the Theo Murphy meeting issue 'High-resolution wave dynamics in the lower solar atmosphere'.

An overall view of temperature oscillations in the solar chromosphere with ALMA.

By direct measurements of the gas temperature, the Atacama Large Millimeter/submillimeter Array (ALMA) has yielded a new diagnostic tool to study the solar chromosphere. Here, we present an overview of the brightness-temperature fluctuations from several high-quality and high-temporal-resolution (i.e. 1 and 2 s cadence) time series of images obtained during the first 2 years of solar observations with ALMA, in Band 3 and Band 6, centred at around 3 mm (100 GHz) and 1.25 mm (239 GHz), respectively. The various datasets represent solar regions with different levels of magnetic flux. We perform fast Fourier and Lomb-Scargle transforms to measure both the spatial structuring of dominant frequencies and the average global frequency distributions of the oscillations (i.e. averaged over the entire field of view). We find that the observed frequencies significantly vary from one dataset to another, which is discussed in terms of the solar regions captured by the observations (i.e. linked to their underlying magnetic topology). While the presence of enhanced power within the frequency range 3-5 mHz is found for the most magnetically quiescent datasets, lower frequencies dominate when there is significant influence from strong underlying magnetic field concentrations (present inside and/or in the immediate vicinity of the observed field of view). We discuss here a number of reasons which could possibly contribute to the power suppression at around 5.5 mHz in the ALMA observations. However, it remains unclear how other chromospheric diagnostics (with an exception of Hα line-core intensity) are unaffected by similar effects, i.e. they show very pronounced 3-min oscillations dominating the dynamics of the chromosphere, whereas only a very small fraction of all the pixels in the 10 ALMA datasets analysed here show peak power near 5.5 mHz. This article is part of the Theo Murphy meeting issue 'High-resolution wave dynamics in the lower solar atmosphere'.

High-frequency oscillations in small chromospheric bright features observed with Atacama Large Millimetre/Submillimetre Array.

We report detection of oscillations in brightness temperature, size and horizontal velocity of three small bright features in the chromosphere of a plage/enhanced-network region. The observations, which were taken with high temporal resolution (i.e. 2 s cadence) with the Atacama large millimetre/ submillimetre array (ALMA) in Band 3 (centred at 3 mm; 100 GHz), exhibit three small-scale features with oscillatory behaviour with different, but overlapping, distributions of period on the order of, on average, 90 ± 22 s, 110 ± 12 s and 66 ± 23 s, respectively. We find anti-correlations between perturbations in brightness, temperature and size of the three features, which suggest the presence of fast sausage-mode waves in these small structures. In addition, the detection of transverse oscillations (although with a larger uncertainty) may also suggest the presence of Alfvénic oscillations which are likely representative of kink waves. This work demonstrates the diagnostic potential of high-cadence observations with ALMA for detecting high-frequency magnetohydrodynamic waves in the solar chromosphere. Such waves can potentially channel a vast amount of energy into the outer atmosphere of the Sun. This article is part of the Theo Murphy meeting issue 'High-resolution wave dynamics in the lower solar atmosphere'.

On the influence of magnetic topology on the propagation of internal gravity waves in the solar atmosphere.

The solar surface is a continuous source of internal gravity waves (IGWs). IGWs are believed to supply the bulk of the wave energy for the lower solar atmosphere, but their existence and role for the energy balance of the upper layers is still unclear, largely due to the lack of knowledge about the influence of the Sun's magnetic fields on their propagation. In this work, we look at naturally excited IGWs in realistic models of the solar atmosphere and study the effect of different magnetic field topographies on their propagation. We carry out radiation-magnetohydrodynamic simulations of a magnetic field free and two magnetic models-one with an initial, homogeneous, vertical field of 100 G magnetic flux density and one with an initial horizontal field of 100 G flux density. The propagation properties of IGWs are studied by examining the phase-difference and coherence spectra in the kh - ω diagnostic diagram. We find that IGWs in the upper solar atmosphere show upward propagation in the model with predominantly horizontal field similar to the model without magnetic field. In contrast to that the model with predominantly vertical fields show downward propagation. This crucial difference in the propagation direction is also revealed in the difference in energy transported by waves for heights below 0.8 Mm. Higher up, the propagation properties show a peculiar behaviour, which require further study. Our analysis suggests that IGWs may play a significant role in the heating of the chromospheric layers of the internetwork region where horizontal fields are thought to be prevalent. This article is part of the Theo Murphy meeting issue 'High-resolution wave dynamics in the lower solar atmosphere'.

An international comparison of retinopathy of prematurity grading performance within the Benefits of Oxygen Saturation Targeting II trials.

PurposeTo investigate whether the observed international differences in retinopathy of prematurity (ROP) treatment rates within the Benefits of Oxygen Saturation Targeting (BOOST) II trials might have been caused by international variation in ROP disease grading.MethodsGroups of BOOST II trial ophthalmologists in UK, Australia, and New Zealand (ANZ), and an international reference group (INT) used a web based system to grade a selection of RetCam images of ROP acquired during the BOOST II UK trial. Rates of decisions to treat, plus disease grading, ROP stage grading, ROP zone grading, inter-observer variation within groups and intra-observer variation within groups were measured.ResultsForty-two eye examinations were graded. UK ophthalmologists diagnosed treat-requiring ROP more frequently than ANZ ophthalmologists, 13.9 (3.49) compared to 9.4 (4.46) eye examinations, P=0.038. UK ophthalmologists diagnosed plus disease more frequently than ANZ ophthalmologists, 14.1 (6.23) compared to 8.5 (3.24) eye examinations, P=0.021. ANZ ophthalmologists diagnosed stage 2 ROP more frequently than UK ophthalmologists, 20.2 (5.8) compared to 12.7 (7.1) eye examinations, P=0.026. There were no other significant differences in the grading of ROP stage or zone. Inter-observer variation was higher within the UK group than within the ANZ group. Intra-observer variation was low in both groups.ConclusionsWe have found evidence of international variation in the diagnosis of treatment-requiring ROP. Improved standardisation of the diagnosis of treatment-requiring ROP is required. Measures might include improved training in the grading of ROP, using an international approach, and further development of ROP image analysis software.

The epidemiology, clinical characteristics, histopathology and management of juvenile- and adult-onset corneoscleral limbus xanthogranuloma.

PURPOSE: Adult-onset xanthogranuloma (AOX) of the corneoscleral limbus is a rare inflammatory condition of unknown aetiology. Similar to limbal juvenile xanthogranuloma (JXG), it presents as a growing mass at the corneoscleral junction. Limbal AOX and JXG can lead to sight-threatening complications if not managed in a timely manner. This systematic review summarises the main clinical and histopathological features of limbal AOX/JXG and discusses the management of this uncommon disease. METHODS: We performed a literature search in the MEDLINE database for all historical entries, using the search terms "limbus", "limbal" and "xanthogranuloma", and retrieved all articles reporting on limbal xanthogranuloma. After refining the search to articles relevant to limbal AOX, we were able to identify ten adult cases of limbal AOX and compare those with all reported cases of limbal JXG. RESULTS: Clinically, AOX usually presents as an isolated smooth, yellowish, dome-shaped nodule at the corneoscleral junction, similar to an ocular presentation of JXG, with which it also shares similar histopathological features. CONCLUSION: Limbal JXG and AOX may represent the same disease entity. Diagnosis relies on the clinical presentation, pathology and immunohistochemical profile. Spontaneous regression is unlikely, and thus prompt surgical intervention should be considered to prevent sight-threatening complications. Xanthogranuloma should be included in the differential diagnosis of corneoscleral limbal masses in patients of all age groups.

The effect of oxygen saturation targeting on retinal blood vessel growth using retinal image data from the BOOST-II UK Trial.

PURPOSE: Retinopathy of prematurity (ROP) is a disorder of developing retinal blood vessels in preterm infants. The purpose of this nested study was to investigate the effects of higher (91-95%) and lower (85-89%) oxygen saturation (SpO2) targeting on retinal blood vessel growth in preterm infants. METHODS: Retinal blood vessel growth in the higher (91-95%) and lower (85-89%) oxygen saturation (SpO2) targeting groups was compared. Suitable RetCam (Clarity, Pleasanton, CA, USA) images collected in the BOOST-II UK trial were used. The distances between the centre of the optic disc and the ROP ridge in the temporal and nasal retina were measured in pixel units. RESULTS: Images from 38 infants were studied, 20 from the higher SpO2 target group and 18 from the lower SpO2 target group. On average, temporal blood vessels extended further from the optic disc than nasal blood vessels, mean (standard deviation (SD)) 463.39 (55.05) pixels compared with 360.13 (44.47) pixels, respectively, P<0.0001. Temporal blood vessels extended less far from the optic disc in the higher SpO2 target group than in the lower SpO2 target group: mean (SD) 449.83 (56.16) pixels compared with 480.02 (49.94), respectively, P=0.055. Nasal retinal blood vessel measurements were broadly similar in the higher and lower SpO2 target groups; mean (SD) 353.96 (41.95) compared with 370.00 (48.82) pixels, respectively, P=0.38. CONCLUSIONS: Relatively high oxygen saturation targeting (91-95%) was associated with a trend (P=0.055) towards reduced retinal blood vessel growth in this study of preterm infants.

Surgical outcome and risk stratification for primary retinal detachment repair: results from the Scottish Retinal Detachment study.

OBJECTIVES: To report the early surgical outcome, risk of failure and predictive value of rhegmatogenous retinal detachment (RRD) classification based on all participants in the Scottish Retinal Detachment study. METHODS: Over 2 years, all incident cases of RRD in Scotland were approached for recruitment. Early postoperative success was defined as an attached retina following one procedure with a minimum follow-up of 6-8 weeks. Using a regression model, the influence of clinical factors on the failure risk was estimated and the sensitivity and specificity of the Royal College of Ophthalmologists (RCOphth) grading for RRD and the vitrectomy in retinal detachment stratification risk formula (VR-SRF) in predicting operative failure were assessed. RESULTS: Primary outcome data were available for 86.2% (975/1130) of patients. The overall primary success rate was 80.8% (95% CI 78.1 to 83.3%). The presence of preoperative proliferative vitreoretinopathy of any degree and each additional clock hour of detachment increased the risk of failure by an OR of 2.4 and 1.13 respectively (p<0.05). A specificity of >95% in predicting early surgical failure was noted for highly complex RRDs according to the VR-SRF formula and the RCOphth classification. CONCLUSIONS: Consistent with previous series, the overall early success rate of RRD repair was 80% after one operation. The type of surgical repair did not influence overall success rates. Significant predictors of failure are the presence of preoperative proliferative vitreoretinopathy of any grade and the extent of detachment. The analytical value of current classification systems in predicting failure is most useful in complex RRDs.

The fellow eye in retinal detachment: findings from the Scottish Retinal Detachment Study.

AIM: To characterise the predisposing pathology and clinical features in the fellow eyes of patients recruited as part of the Scottish Retinal Detachment Study. METHODS: The Scottish Retinal Detachment Study was a 2-year prospectively recruited population-based epidemiology study that sought to recruit all incident cases of primary rhegmatogenous retinal detachment (RRD) in Scotland. RESULTS: A total of 1202 incident cases of primary RRD were recruited in Scotland, over a 2-year period and in 94% (1130 cases) detailed data on the clinical features of fellow eyes with RRD were available. Full-thickness retinal breaks were found in 8.4% (95/1130) of fellow eyes on presentation. Lattice degeneration was present in 14.5% (164/1130) of fellow eyes. Thirteen per cent (148/1130) of affected fellow eyes had a best corrected visual acuity of 6/18 or worse with previous RRD, the second most common cause of poor vision. Overall, 7.3% (88/1202) of cases had RRD in both eyes; 60% of cases with consecutive bilateral RRD presented before the macula were affected. CONCLUSIONS: Rhegmatogenous pathology in the fellow eye represents an important threat to vision. Fellow-eye detachments are more common in pseudophakic individuals and those with a more myopic refractive error. Fellow-eye RRD has a greater likelihood of prompt presentation.

Early retinal blood vessel growth in normal and growth restricted rat pups raised in oxygen and room air.

BACKGROUND/AIMS: Premature infants are born with incompletely vascularised retinas and are at a risk of developing retinopathy of prematurity (ROP). Rate of prenatal and postnatal body growth is important in the pathogenesis of ROP. The aim of this study was to develop a physiology-based rat model in order to study the effect of growth restriction and oxygen on early retinal vascular development. METHODS: Rat mothers were fed either a normal (18% casein) or low (9% casein) protein diet (to cause pup growth restriction) from the last week of gestation. After birth, mother and pups were placed in either room air or a specialised oxygen chamber that delivered a rapidly fluctuating hyperoxic oxygen profile. The oxygen profile was based on that from a premature infant who developed severe ROP. On day 14, retinas were dissected, flat-mounted and stained using biotinylated lectin. Images were captured by confocal microscopy. The avascular areas of the retinas were measured and compared. RESULTS: Growth restricted rat pups had significantly larger retinal avascular areas than 'normally grown' rat pups (Mann-Whitney U test, p<0.001). Growth restricted rat pups raised in fluctuating oxygen had significantly larger retinal avascular areas than growth restricted rat pups raised in room air (Mann-Whitney U test, p=0.001). CONCLUSIONS: The authors have developed a novel model for ROP that involves inducing both intrauterine and postnatal growth restriction and also exposes neonatal rat pups to fluctuating oxygen. This physiology-based model can be used to study the effects of growth, nutrition and oxygen on early retinal vascular development.

SNP mistyping in genotyping arrays--an important cause of spurious association in case-control studies.

Using genome-wide association studies to identify genetic variants contributing to disease has been highly successful with many novel genetic predispositions identified and biological pathways revealed. Several pitfalls for spurious association or non-replication have been highlighted: from population structure, automated genotype scoring for cases and controls, to age-varying association. We describe an important yet unreported source of bias in case-control studies due to variations in chip technology between different commercial array releases. As cases are commonly genotyped with newer arrays and freely available control resources are frequently used for comparison, there exists an important potential for false associations which are robust to standard quality control and replication design.

Pain in neonates during screening for retinopathy of prematurity using binocular indirect ophthalmoscopy and wide-field digital retinal imaging: a randomised comparison.

OBJECTIVE: To compare the pain experienced by premature infants undergoing wide-field digital retinal imaging (WFDRI) and binocular indirect ophthalmoscopy (BIO) for retinopathy of prematurity (ROP) screening. METHODS: Infants were recruited at Edinburgh Royal Infirmary Neonatal Unit, Edinburgh, UK. Eyes were examined by WFDRI and BIO with eyelid speculum by two experienced paediatric ophthalmologists in random order. A pain score (Premature Infant Pain Profile (PIPP)) for WFDRI and BIO was generated. RESULTS: A total of 76 infants were recruited. The (mean, SD) PIPP score for WFDRI was 15.0, 2.1 and for BIO was 15.2, 2.4 (paired t test p=0.47). The authors observed that infants started crying with corresponding physiological changes as soon as the eyelid speculum was inserted and crying stopped on speculum removal. CONCLUSION: WFDRI and BIO with eyelid speculum are similarly painful for infants. The authors speculate that the eyelid speculum rather than the examination method may contribute most to the pain experienced.

Trajectory measurements of a wall jet impinging onto a forward facing step entering a cross-flow.

This study examines a horizontal wall jet impinging onto a forward facing step in a cross-flow. Planar laser induced fluorescence (PLIF) experiments in a water channel indicate that the wall-jet flow after impinging onto the step, becomes a vertical jet with an elliptical cross section. Experiments indicate that the jet trajectory scales with the perimeter of the elliptical jet issuing vertically into the cross-flow. The trajectory consists of three regions: the near-field region which is well described by a power law with an exponent of 1/2, the mid-field region where the jet is fully bent over which is described by a power law with an exponent of 1/3, and a far-field region where the jet is dominated by the cross-flow. This paper provides a prediction of the plume behaviour based on the geometric and initial conditions of the jet (diameter, step height, distance from jet to step, and velocity ratio) alone. The Briggs entrainment model for a round jet was also used to predict the trajectories of the jet in the cross-flow. It was found that the entrainment coefficients, alpha and beta, for the elliptical jet case had average values of 0.15 and 0.58 respectively.

The epidemiology of rhegmatogenous retinal detachment: geographical variation and clinical associations.

AIMS/BACKGROUND: Rhegmatogenous retinal detachment (RRD) is a potentially blinding condition. Obtaining an accurate estimate of RRD incidence in the population is essential in understanding the healthcare burden related to this disorder. METHODS: A systematic review of all population-based epidemiology studies of RRD published between January 1970 and January 2009 from Medline database searches was performed. RESULTS: RRD incidence demonstrates significant geographical variation and its incidence has been reported to be between 6.3 and 17.9 per 100,000 population. For studies with a sample size >300 the median annual incidence per 100,000 population was 10.5 (IQR 8.1-13.2) and the mean proportion of bilateral RRD was 7.26%. Overall, the mean prevalence of lattice degeneration was 45.7+/-20.3% and myopia was 47.28+/-12.59%. CONCLUSIONS: Estimates of RRD incidence have varied threefold, but inclusion criteria and other design features have differed across studies making direct comparisons difficult. The overall incidence of RRD is not yet well established: more incidence studies of adequate methodology are needed to explore temporal changes in incidence. RRD incidence varies with ethnicity and is strongly associated with increasing age, myopia and certain vitreo-retinal degenerations. Due to changes in cataract surgery trends, the proportion of pseudophakic RRD presenting to specialised centres appears to be increasing.

Wide-field digital retinal imaging versus binocular indirect ophthalmoscopy for retinopathy of prematurity screening: a two-observer prospective, randomised comparison.

AIM: To compare the diagnostic accuracy of wide-field digital retinal imaging (WFDRI) with the current "gold standard" of binocular indirect ophthalmoscopy (BIO) for retinopathy of prematurity (ROP) screening examinations. METHODS: A consecutive series of premature infants undergoing ROP screening at Edinburgh Royal Infirmary were eligible for recruitment into this prospective, randomised, comparative study. Infants were screened using both WFDRI (Retcam II with neonatal lens) and BIO by two paediatric ophthalmologists who were randomised to the examination technique. Both examiners documented their clinical findings and management plans in a masked fashion. WFDRI eye findings were compared with those of BIO. RESULTS: A total of 81 infants were recruited, and information from 245 eye examinations was analysed. The sensitivity of WFDRI in detecting any stage of ROP, stage 3 ROP and "plus" disease was 60%, 57% and 80%, respectively, and specificity 91%, 98% and 98%, respectively. The proportional agreement between WFDRI and BIO was 0.96 for detecting stage 3 disease and 0.97 for detecting "plus" disease. There was very good agreement on management decisions (kappa 0.85). CONCLUSION: When used in a routine ROP screening setting, a randomised comparison of WFDRI and BIO, WFDRI showed relatively poor sensitivity in detecting mild forms of ROP in the retinal periphery. This resulted in difficulty in making decisions to discharge infants from the screening programme. Sensitivity was better for more severe forms of ROP, but at present WFDRI should be regarded as an adjunct to, rather than a replacement for, BIO in routine ROP screening.

Retinopathy of prematurity in small-for-gestational age infants compared with those of appropriate size for gestational age.

AIM: To compare the incidence of retinopathy of prematurity (ROP) in small-for-gestational age (SGA) infants compared with appropriate-for-gestational age (AGA) infants undergoing eye screening in the Lothian region of south east Scotland 1990-2004. METHODS: All infants in Lothian born with birth weight <1500 g and/or gestational age <32 weeks underwent eye screening by two experienced paediatric ophthalmologists. The presence of any stage of ROP (1-5), severe (stage 3 or greater) ROP and treated ROP was compared between the SGA and AGA infants using chi(2) or Fisher exact tests. SGA was defined as birth weight below the 10th centile for gestational age. RESULTS: A total of 1413 babies with birth weights <1500 g and/or gestational age <32 weeks underwent eye screening; 329 (23%) were SGA. SGA infants born at gestational ages 26-31 weeks were more likely to develop any stage of ROP (p<0.01) than their AGA peers. SGA infants were also more likely to develop severe ROP (gestational age 26-27 weeks, p<0.01; 28-29 weeks, p = 0.01; 30-31 weeks, p = 0.01). CONCLUSIONS: SGA infants who underwent eye screening in the Lothian region of south east Scotland from 1990 to 2004 were significantly more likely to develop ROP and more severe disease than AGA infants.