Correlación entre el resultado refractivo post-catarata con la predicción biométrica pre-operatoria

La cirugía de cataratas por Facoemulsificación es tal vez uno de los procedimientos más realizados en la práctica de oftalmología general, sin embargo el resultado refractivo de esta cirugía no siempre llena las expectativas del oftalmólogo y del paciente, es por esto que es de gran importancia observar los resultados post quirúrgicos obtenidos y las distintas variables que pudieron influir en dicho resultado. Objetivo: determinar la capacidad predictiva de la formula biométrica empleada en el preoperatorio con el resultado refractivo post operatorio expresada en porcentajes. Materiales y métodos: se realizó un estudio de correlación basándose en la refracción prevista por la biometría y la refracción encontrada en el post operatorio. Se analizó los diferentes grupos de pacientes miopes, hipermétropes y emétropes en de los rangos de 0,50D, 0,75 D y 1,00D. Resultados: el porcentaje de pacientes que presento 0,50D de diferencia con el previsto fue de 57,7% para el total, 100% para hipermétropes, 53,1% para emétropes, 56,3% para miopes. En el rango de 0,75D 71,2% para el total, 62,5% para emétropes y 81,3% para miopes. En el rango de 1,00D 82,7% para el total, 75% para emétropes y 93,8% para miopes. Conclusiones: la formula SRK/T presento un buen desempeño en todos los grupos encontrándose resultados concordantes con los descritos en la literatura.

Comparación de grosor macular y grado de miopía en grupo de pacientes de la Fundación Oftalmológica Nacional

OBJETIVOS: Comparar las medidas de grosor macular, medido por HD-OCT Cirrus®, en pacientes de la Fundación Oftalmológica Nacional con miopía baja y alta. MÉTODOS: Estudio transversal analítico, en el que se incluyeron pacientes con miopía alta, definida como defecto esférico mayor a – 6.0 dioptrías (D), y pacientes con miopía baja, definida como defecto esférico entre -1.00 D y -6.00 D; a los que se le realizó mapa de grosores maculares con el HD-OCT Cirrus®, y se compararon las medias de los grosores (1, 3 y 6 mm). RESULTADOS: Un total de 128 ojos de pacientes entre 12 y 80 años fueron incluidos; 64 ojos en grupo de miopes bajos y 64 ojos en grupo de miopes altos. La media de edad fue: 37.3 y 38.4 años, y el defecto esférico promedio fue de 2.2 D y 11.5 D, respectivamente. El promedio de grosores en mácula interna (319.9 vs. 307.87 micras, P=0.002), y mácula externa (276.08 vs. 270.23 micras, P=0.047) fue significativamente mayor en el grupo de miopía baja que en el de miopía alta. Sin embargo la media del grosor macular central (1 mm) no tuvo diferencia (261.25 vs. 262 micras P=0.891). CONCLUSIÓN: Este estudio muestra que el grosor macular de 3 y 6 mm centrales es más delgado en miopes altos, pero en 1 mm central es similar que en miopes bajos. En los pacientes estudiados no se encontró diferencia en grosores maculares según género o subgrupos de edad.

Capacidad de respuesta hospitalaria distrital en Bogotá ante un evento con múltiples victimas

Los hospitales son el pilar fundamental para la atención de las víctimas de situaciones de emergencia o desastre. Las instituciones de salud son consideradas indispensables para la población, por lo que deben estar preparadas para funcionar no solo en condiciones normales sino en situaciones de alerta, como suele suceder en desastres de origen natural como los sismos. La relevancia de la problemática, radica en que de acuerdo con la amenaza sísmica de Colombia, Bogotá se encuentra en una zona de amenaza sísmica intermedia, los actuales eventos naturales como el terremoto de Haití con un saldo de 300.000 muertos y más de 700.000 mil heridos, y el de Chile, nos hace pensar en la importancia de la preparación hospitalaria ante un evento con múltiples víctimas como lo es un sismo. El Objetivo general del estudio es identificar la capacidad de respuesta hospitalaria distrital en Bogotá ante un evento con múltiples víctimas (terremoto). Además se identificaran las oportunidades de mejora para optimizar la respuesta hospitalaria de acuerdo a su nivel de atención. La Investigación se realizó por medio de un estudio de corte transversal, en donde se tomó una muestra de la red hospitalaria Distrital por conveniencia, bajo la aplicación de una encuesta dirigida. Los resultados fueron recopilados en una base de datos de Excel 2013, y fueron analizados bajo un software estadístico, STATA 12.0, donde se evaluaron variables, categóricas, nominales y cuantitativas. Como resultados se encontraron un porcentaje de ocupación de más del 100% en el 25% de los hospitales. Los 16 hospitales encuestados cuentan con comité hospitalario de emergencias, así como también con la elaboración de planes de emergencia y la revisión e implementación de estos. El 50% de los hospitales contemplan dentro su estructura de plan de emergencias, el sistema comando de incidentes; Sólo el 18.8% de los hospitales cuentan con reforzamiento estructural, y el 81,2% de los hospitales refieren tener una cooperación con organizaciones locales o externas. Solo 4 de los 16 hospitales cuentan con protocolos de diagnóstico y tratamiento médico en desastres. El plan de contingencia para un Sismo, es el plan bandera de todos los hospitales dado el esfuerzo por parte de la secretaria de salud y de FOPAE en información y capacitación en todo el Distrito, es por eso que el 93,85 de todos los hospitales cuentan con este plan. Al realizar el análisis general, la red hospitalaria no está en capacidad de una adecuada respuesta en caso de un evento con múltiples víctimas, en el escenario de un sismo de gran magnitud, teniendo en cuenta el porcentaje de ocupación actual donde el 25% de la red hospitalaria distrital cuenta con sobrecupo y el 50% se encuentra a tope de su capacidad instalada. En cuanto a la capacidad de respuesta, no se cuenta con protocolos de atención; Haciendo una evaluación según los niveles de atención, solo los hospitales de III nivel estarían medianamente preparados y con capacidad de respuesta ante un evento con víctimas en masa.

Plotino y Grosseteste: El neoplatonismo en la cosmología medieval

En este trabajo se estudia el caso de la cosmología del filósofo y científico Robert Grosseteste como un ejemplo de la notable influencia del neoplatonismo en la ciencia medieval. Uno de los propósitos de la cosmología de Grosseteste consistió en explicar la secuencia efectiva de la creación del cosmos. Sostengo que la explicación que ofrece Grosseteste acerca de la creación es una expresión renovada de algunas ideas de Plotino a propósito de cómo el Uno engendra lo múltiple. Me interesa resaltar tres aspectos de la estrecha relación entre el sistema cosmológico de Grosseteste y el sistema metafísico de Plotino: (1) Unidad de principio, (2) Mecanismos de generación y (3) Unidad del sistema.

Velocities of compressional and shear waves in limestones

Carbonate rocks are important hydrocarbon reservoir rocks with complex textures and petrophysical properties (porosity and permeability) mainly resulting from various diagenetic processes (compaction, dissolution, precipitation, cementation, etc.). These complexities make prediction of reservoir characteristics (e.g. porosity and permeability) from their seismic properties very difficult. To explore the relationship between the seismic, petrophysical and geological properties, ultrasonic compressional- and shear-wave velocity measurements were made under a simulated in situ condition of pressure (50 MPa hydrostatic effective pressure) at frequencies of approximately 0.85 MHz and 0.7 MHz, respectively, using a pulse-echo method. The measurements were made both in vacuum-dry and fully saturated conditions in oolitic limestones of the Great Oolite Formation of southern England. Some of the rocks were fully saturated with oil. The acoustic measurements were supplemented by porosity and permeability measurements, petrological and pore geometry studies of resin-impregnated polished thin sections, X-ray diffraction analyses and scanning electron microscope studies to investigate submicroscopic textures and micropores. It is shown that the compressional- and shear-wave velocities (V-p and V-s, respectively) decrease with increasing porosity and that V-p decreases approximately twice as fast as V-s. The systematic differences in pore structures (e.g. the aspect ratio) of the limestones produce large residuals in the velocity versus porosity relationship. It is demonstrated that the velocity versus porosity relationship can be improved by removing the pore-structure-dependent variations from the residuals. The introduction of water into the pore space decreases the shear moduli of the rocks by about 2 GPa, suggesting that there exists a fluid/matrix interaction at grain contacts, which reduces the rigidity. The predicted Biot-Gassmann velocity values are greater than the measured velocity values due to the rock-fluid interaction. This is not accounted for in the Biot-Gassmann velocity models and velocity dispersion due to a local flow mechanism. The velocities predicted by the Raymer and time-average relationships overestimated the measured velocities even more than the Biot model.

Acoustic and petrophysical relationships in low-shale sandstone reservoir rocks

This paper describes the measurements of the acoustic and petrophysical properties of two suites of low-shale sandstone samples from North Sea hydrocarbon reservoirs, under simulated reservoir conditions. The acoustic velocities and quality factors of the samples, saturated with different pore fluids (brine, dead oil and kerosene), were measured at a frequency of about 0.8 MHz and over a range of pressures from 5 MPa to 40 MPa. The compressional-wave velocity is strongly correlated with the shear-wave velocity in this suite of rocks. The ratio V-P/V-S varies significantly with change of both pore-fluid type and differential pressure, confirming the usefulness of this parameter for seismic monitoring of producing reservoirs. The results of quality factor measurements were compared with predictions from Biot-flow and squirt-flow loss mechanisms. The results suggested that the dominating loss in these samples is due to squirt-flow of fluid between the pores of various geometries. The contribution of the Biot-flow loss mechanism to the total loss is negligible. The compressional-wave quality factor was shown to be inversely correlated with rock permeability, suggesting the possibility of using attenuation as a permeability indicator tool in low-shale, high-porosity sandstone reservoirs.

Sonic to ultrasonic Q of sandstones and limestones: Laboratory measurements at in situ pressures

Laboratory measurements of the attenuation and velocity dispersion of compressional and shear waves at appropriate frequencies, pressures, and temperatures can aid interpretation of seismic and well-log surveys as well as indicate absorption mechanisms in rocks. Construction and calibration of resonant-bar equipment was used to measure velocities and attenuations of standing shear and extensional waves in copper-jacketed right cylinders of rocks (30 cm in length, 2.54 cm in diameter) in the sonic frequency range and at differential pressures up to 65 MPa. We also measured ultrasonic velocities and attenuations of compressional and shear waves in 50-mm-diameter samples of the rocks at identical pressures. Extensional-mode velocities determined from the resonant bar are systematically too low, yielding unreliable Poisson's ratios. Poisson's ratios determined from the ultrasonic data are frequency corrected and used to calculate the sonic-frequency compressional-wave velocities and attenuations from the shear- and extensional-mode data. We calculate the bulk-modulus loss. The accuracies of attenuation data (expressed as 1000/Q, where Q is the quality factor) are +/- 1 for compressional and shear waves at ultrasonic frequency, +/- 1 for shear waves, and +/- 3 for compressional waves at sonic frequency. Example sonic-frequency data show that the energy absorption in a limestone is small (Q(P) greater than 200 and stress independent) and is primarily due to poroelasticity, whereas that in the two sandstones is variable in magnitude (Q(P) ranges from less than 50 to greater than 300, at reservoir pressures) and arises from a combination of poroelasticity and viscoelasticity. A graph of compressional-wave attenuation versus compressional-wave velocity at reservoir pressures differentiates high-permeability (> 100 mD, 9.87 X 10(-14) m(2)) brine-saturated sandstones from low-permeability (< 100 mD, 9.87 X 10 (14) m(2)) sandstones and shales.

The role of eddies in driving the tropospheric response to stratospheric heating perturbations

A simplified general circulation model has been used to investigate the chain of causality whereby changes in tropospheric circulation and temperature are produced in response to stratospheric heating perturbations. Spinup ensemble experiments have been performed to examine the evolution of the tropospheric circulation in response to such perturbations. The primary aim of these experiments is to investigate the possible mechanisms whereby a tropospheric response to changing solar activity over the 11-yr solar cycle could be produced in response to heating of the equatorial lower stratosphere. This study therefore focuses on a stratospheric heating perturbation in which the heating is largest in the tropics. For comparison, experiments are also performed in which the stratosphere is heated uniformly at all latitudes and in which it is heated preferentially in the polar region. Thus, the mechanisms discussed have a wider relevance for the impact of stratospheric perturbations on the troposphere. The results demonstrate the importance of changing eddy momentum fluxes in driving the tropospheric response. This is confirmed by the lack of a similar response in a zonally symmetric model with fixed eddy forcing. Furthermore, it is apparent that feedback between the tropospheric eddy fluxes and tropospheric circulation changes is required to produce the full model response. The quasigeostrophic index of refraction is used to diagnose the cause of the changes in eddy behavior. It is demonstrated that the latitudinal extent of stratospheric heating is important in determining the direction of displacement of the tropospheric jet and storm track.

Atmospheric electricity coupling between earthquake regions and the ionosphere

We propose a mechanism to explain suggested links between seismic activity and ionospheric changes detected overhead. Specifically, we explain changes in the natural extremely low-frequency (ELF) radio noise recently observed in the topside ionosphere aboard the DEMETER satellite at night, before major earthquakes. Our mechanism utilises increased electrical conductivity of surface layer air before a major earthquake, which reduces the surface-ionosphere electrical resistance. This increases the vertical fair weather current, and (to maintain continuity of electron flow) lowers the ionosphere. Magnitudes of crucial parameters are estimated and found to be consistent with observations. Natural variability in ionospheric and atmospheric electrical properties is evaluated, and may be overcome using a hybrid detection approach. Suggested experiments to investigate the mechanism involve measuring the cut-off frequency of ELF “tweeks”, the amplitude and phase of very low frequency radio waves in the Earth–ionosphere waveguide, or medium frequency radar, incoherent scatter or rocket studies of the lower ionospheric electron density.

Modelling the lava dome extruded at Soufrière Hills Volcano, Montserrat, August 2005–May 2006. Part II: Rockfall activity and talus deformation

During many lava dome-forming eruptions, persistent rockfalls and the concurrent development of a substantial talus apron around the foot of the dome are important aspects of the observed activity. An improved understanding of internal dome structure, including the shape and internal boundaries of the talus apron, is critical for determining when a lava dome is poised for a major collapse and how this collapse might ensue. We consider a period of lava dome growth at the Soufrière Hills Volcano, Montserrat, from August 2005 to May 2006, during which a 100 × 106 m3 lava dome developed that culminated in a major dome-collapse event on 20 May 2006. We use an axi-symmetrical Finite Element Method model to simulate the growth and evolution of the lava dome, including the development of the talus apron. We first test the generic behaviour of this continuum model, which has core lava and carapace/talus components. Our model describes the generation rate of talus, including its spatial and temporal variation, as well as its post-generation deformation, which is important for an improved understanding of the internal configuration and structure of the dome. We then use our model to simulate the 2005 to 2006 Soufrière Hills dome growth using measured dome volumes and extrusion rates to drive the model and generate the evolving configuration of the dome core and carapace/talus domains. The evolution of the model is compared with the observed rockfall seismicity using event counts and seismic energy parameters, which are used here as a measure of rockfall intensity and hence a first-order proxy for volumes. The range of model-derived volume increments of talus aggraded to the talus slope per recorded rockfall event, approximately 3 × 103–13 × 103 m3 per rockfall, is high with respect to estimates based on observed events. From this, it is inferred that some of the volumetric growth of the talus apron (perhaps up to 60–70%) might have occurred in the form of aseismic deformation of the talus, forced by an internal, laterally spreading core. Talus apron growth by this mechanism has not previously been identified, and this suggests that the core, hosting hot gas-rich lava, could have a greater lateral extent than previously considered.

Hypo-accommodation responses in hypermetropic infants and children

Aims: Accommodation to overcome hypermetropia is implicated in emmetropisation. This study recorded accommodation responses in a wide range of emmetropising infants and older children with clinically significant hypermetropia to assess common characteristics and differences. Methods: A PlusoptiXSO4 photorefractor in a laboratory setting was used to collect binocular accommodation data from participants viewing a detailed picture target moving between 33cm and 2m. 38 typically developing infants were studied between 6-26 weeks of age and were compared with cross-sectional data from children 5-9 years of age with clinically significant hypermetropia (n=15), corrected fully accommodative strabismus (n=14) and 27 age-matched controls. Results: Hypermetropes of all ages under-accommodated compared to controls at all distances, whether corrected or not (p<0.00001) and lag related to manifest refraction. Emmetropising infants under-accommodated most in the distance, while the hypermetropic patient groups underaccommodated most for near. Conclusions: Better accommodation for near than distance is demonstrated in those hypermetropic children who go on to emmetropise. This supports the approach of avoiding refractive correction in such children. In contrast, hypermetropic children referred for treatment for reduced distance visual acuity are not likely to habitually accommodate to overcome residual hypermetropia left by an under-correction.

The NAO troposphere–stratosphere connection

Using monthly mean data, daily data, and theoretical arguments, relationships between surface pressure variations associated with the North Atlantic Oscillation (NAO), tropopause height, and the strength of the stratospheric vortex are established. An increase in the NAO index leads to a stronger stratospheric vortex, about 4 days later, as a result of increased equatorward refraction of upward-propagating Rossby waves. At tropopause level the effects of the enhanced NAO index and stratospheric polar vortex are opposite, resulting in a lower tropopause over Iceland and a higher tropopause over the Arctic. The raising of the Arctic tropopause leads to a stretching and spinup of the tropospheric column and is therefore associated with a lowering of the surface pressure near the North Pole. For monthly mean data it is found that a standard deviation increase in the NAO index is associated with a 10% increase in the strength of the stratospheric vortex, as measured by potential vorticity at 500 K. A simple theoretical model predicts that this is associated with about 300-m elevation of the Arctic tropopause, as is observed, and a 5-hPa lowering of the surface pressure at the North Pole. The effects of the spinup of the tropospheric column may project on the NAO pattern so that the stratosphere acts as an integrator of the NAO index.

Receding and disparity cues aid relaxation of accommodation

Purpose. Accommodation can mask hyperopia and reduce the accuracy of non-cycloplegic refraction. It is, therefore, important to minimize accommodation to obtain a measure of hyperopia as accurate as possible. To characterize the parameters required to measure the maximally hyperopic error using photorefraction, we used different target types and distances to determine which target was most likely to maximally relax accommodation and thus more accurately detect hyperopia in an individual. Methods. A PlusoptiX SO4 infra-red photorefractor was mounted in a remote haploscope which presented the targets. All participants were tested with targets at four fixation distances between 0.3 and 2 m containing all combinations of blur, disparity, and proximity/looming cues. Thirty-eight infants (6 to 44 weeks) were studied longitudinally, and 104 children [4 to 15 years (mean 6.4)] and 85 adults, with a range of refractive errors and binocular vision status, were tested once. Cycloplegic refraction data were available for a sub-set of 59 participants spread across the age range. Results. The maximally hyperopic refraction (MHR) found at any time in the session was most frequently found when fixating the most distant targets and those containing disparity and dynamic proximity/looming cues. Presence or absence of blur was less significant, and targets in which only single cues to depth were present were also less likely to produce MHR. MHR correlated closely with cycloplegic refraction (r = 0.93, mean difference 0.07 D, p = n.s., 95% confidence interval +/-<0.25 D) after correction by a calibration factor. Conclusions. Maximum relaxation of accommodation occurred for binocular targets receding into the distance. Proximal and disparity cues aid relaxation of accommodation to a greater extent than blur, and thus non-cycloplegic refraction targets should incorporate these cues. This is especially important in screening contexts with a brief opportunity to test for significant hyperopia. MHR in our laboratory was found to be a reliable estimation of cycloplegic refraction. (Optom Vis Sci 2009;86:1276-1286)

The temperature-dependent spectral properties of filter substrate materials in the far-infrared (6-40 mu m)

This paper presents the experimental results on the low temperature absorption and dispersion properties for a variety of frequently used infrared filter substrate materials. Index of refraction (n) and transmission spectra are presented for a range of temperatures 300-50 K for the Group IV materials silicon (Si) and germanium (Ge), and Group II-VI materials zinc selenide (ZnSe), zinc sulphide (ZnS) and cadmium telluride (CdTe). (C) 2003 Elsevier B.V. All rights reserved.