268 research outputs found
Differences in optic nerve structure between individuals of predominantly African and European ancestry: Implications for disease detection and pathogenesis
Glaucoma disproportionately affects individual of African ancestry. Additionally, racial differences in the optic nerve head have been well described that may alter the vulnerability to intraocular pressure related injury and, in addition, alter the clinical ability to detect the presence of early optic nerve injury. This paper will review the literature describing racial differences in the optic nerve head between individuals of African and European ancestry with regards to the potential effects of these differences on the ability to detect glaucoma in different racial groups and to potential differences in the pathogenesis of glaucomatous injury
Spectral index selection method for remote moisture sensing under challenging illumination conditions
Remote sensing using passive solar illumination in the Short-Wave Infrared spectrum is exposed to strong intensity variation in the spectral bands due to atmospheric changing conditions and spectral absorption. More robust spectral analysis methods, insensitive to these effects, are increasingly required to improve the accuracy of the data analysis in the field and extend the use of the system to ānon idealā illumination condition. A computational hyperspectral image analysis method (named HIAM) for deriving optimal reflectance indices for use in remote sensing of soil moisture content is detailed and demonstrated. Using histogram analysis of hyperspectral images of wet and dry soil, contrast ratios and wavelength pairings were tested to find a suitable spectral index to recover soil moisture content. Measurements of local soil samples under laboratory and field conditions have been used to demonstrate the robustness of the index to varying lighting conditions, while publicly available databases have been used to test across a selection of soil classes. In both cases, the moisture was recovered with RMS error better than 5%. As the method is independent of material type, this method has the potential to also be applied across a variety of biological and man-made samples
Integrated fiber optic spectrally resolved downwelling irradiance sensor for pushbroom spectrometers
We present an integrated fiber optic spectrally resolved downwelling irradiance sensor for pushbroom hyperspectral imagers. The system comprises of a cosine corrector and custom fiber patch cables, collecting the ambient light in a large solid angle and feeding it directly to the entrance slit of the spectrometer. The system enables simultaneous measurement of downwelling and upwelling irradiance using the main hyperspectral camera sensor. As a demonstration, the spectral reflectance of a soil sample was measured with a RMSE of 8.4%, a significant improvement on the RMSE of 54% found without correction. At a weight of approximately 10 grams, this system provides a substantial weight saving over standalone incident light sensing instruments
Structural Change Can Be Detected in Advanced-Glaucoma Eyes.
PurposeTo compare spectral-domain optical coherence tomography (SD-OCT) standard structural measures and a new three-dimensional (3D) volume optic nerve head (ONH) change detection method for detecting change over time in severely advanced-glaucoma (open-angle glaucoma [OAG]) patients.MethodsThirty-five eyes of 35 patients with very advanced glaucoma (defined as a visual field mean deviation < -21 dB) and 46 eyes of 30 healthy subjects to estimate aging changes were included. Circumpapillary retinal fiber layer thickness (cpRNFL), minimum rim width (MRW), and macular retinal ganglion cell-inner plexiform layer (GCIPL) thicknesses were measured using the San Diego Automated Layer Segmentation Algorithm (SALSA). Progression was defined as structural loss faster than 95th percentile of healthy eyes. Three-dimensional volume ONH change was estimated using the Bayesian-kernel detection scheme (BKDS), which does not require extensive retinal layer segmentation.ResultsThe number of progressing glaucoma eyes identified was highest for 3D volume BKDS (13, 37%), followed by GCPIL (11, 31%), cpRNFL (4, 11%), and MRW (2, 6%). In advanced-OAG eyes, only the mean rate of GCIPL change reached statistical significance, -0.18 Ī¼m/y (P = 0.02); the mean rates of cpRNFL and MRW change were not statistically different from zero. In healthy eyes, the mean rates of cpRNFL, MRW, and GCIPL change were significantly different from zero. (all P < 0.001).ConclusionsGanglion cell-inner plexiform layer and 3D volume BKDS show promise for identifying change in severely advanced glaucoma. These results suggest that structural change can be detected in very advanced disease. Longer follow-up is needed to determine whether changes identified are false positives or true progression
Glaucomatous Patterns in Frequency Doubling Technology (FDT) Perimetry Data Identified by Unsupervised Machine Learning Classifiers
Purpose: The variational Bayesian independent component analysis-mixture model (VIM), an unsupervised machine-learning classifier, was used to automatically separate Matrix Frequency Doubling Technology (FDT) perimetry data into clusters of healthy and glaucomatous eyes, and to identify axes representing statistically independent patterns of defect in the glaucoma clusters.
Methods: FDT measurements were obtained from 1,190 eyes with normal FDT results and 786 eyes with abnormal FDT results from the UCSD-based Diagnostic Innovations in Glaucoma Study (DIGS) and African Descent and Glaucoma Evaluation Study (ADAGES). For all eyes, VIM input was 52 threshold test points from the 24-2 test pattern, plus age.
Results: FDT mean deviation was -1.00 dB (S.D. = 2.80 dB) and -5.57 dB (S.D. = 5.09 dB) in FDT-normal eyes and FDT-abnormal eyes, respectively (p<0.001). VIM identified meaningful clusters of FDT data and positioned a set of statistically independent axes through the mean of each cluster. The optimal VIM model separated the FDT fields into 3 clusters. Cluster N contained primarily normal fields (1109/1190, specificity 93.1%) and clusters G(1) and G(2) combined, contained primarily abnormal fields (651/786, sensitivity 82.8%). For clusters G(1) and G(2) the optimal number of axes were 2 and 5, respectively. Patterns automatically generated along axes within the glaucoma clusters were similar to those known to be indicative of glaucoma. Fields located farther from the normal mean on each glaucoma axis showed increasing field defect severity.
Conclusions: VIM successfully separated FDT fields from healthy and glaucoma eyes without a priori information about class membership, and identified familiar glaucomatous patterns of loss.open0
Pressure-dependent regulation of Ca2+ signaling in the vascular endothelium
The endothelium is an interconnected network upon which hemodynamic mechanical forces act to control vascular tone and remodeling in disease. Ca2+ signaling is central to the endothelium's mechanotransduction and networked activity. However, challenges in imaging Ca2+ in large numbers of endothelial cells under conditions that preserve the intact physical configuration of pressurized arteries have limited progress in understanding how pressure-dependent mechanical forces alter networked Ca2+ signaling. We developed a miniature wide-field, gradient-index (GRIN) optical probe designed to fit inside an intact pressurized artery which permitted Ca2+ signals to be imaged with subcellular resolution in a large number (ā¼200) of naturally-connected endothelial cells at various pressures. Chemical (acetylcholine) activation triggered spatiotemporally-complex, propagating IP3-mediated Ca2+ waves that originated in clusters of cells and progressed from there across the endothelium. Mechanical stimulation of the artery, by increased intraluminal pressure, flattened the endothelial cells and suppressed IP3-mediated Ca2+ signals in all activated cells. By computationally modeling Ca2+ release, endothelial shape changes were shown to alter the geometry of the Ca2+ diffusive environment near IP3 receptor microdomains to limit IP3-mediated Ca2+ signals as pressure increased. Changes in cell shape produce a geometric, microdomain-regulation of IP3-mediated Ca2+ signaling to explain macroscopic pressure-dependent, endothelial-mechanosensing without the need for a conventional mechanoreceptor. The suppression of IP3-mediated Ca2+ signaling may explain the decrease in endothelial activity as pressure increases. GRIN imaging provides a convenient method that provides access to hundreds of endothelial cells in intact arteries in physiological configuration
Flicker-assisted localization microscopy reveals altered mitochondrial architecture in hypertension
Mitochondrial morphology is central to normal physiology and disease development. However, in many live cells and tissues, complex mitochondrial structures exist and morphology has been difficult to quantify. We have measured the shape of electrically-discrete mitochondria, imaging them individually to restore detail hidden in clusters and demarcate functional boundaries. Stochastic āflickersā of mitochondrial membrane potential were visualized with a rapidly-partitioning fluorophore and the pixel-by-pixel covariance of spatio-temporal fluorescence changes analyzed. This Flicker-assisted Localization Microscopy (FaLM) requires only an epifluorescence microscope and sensitive camera. In vascular myocytes, the apparent variation in mitochondrial size was partly explained by densely-packed small mitochondria. In normotensive animals, mitochondria were small spheres or rods. In hypertension, mitochondria were larger, occupied more of the cell volume and were more densely clustered. FaLM provides a convenient tool for increased discrimination of mitochondrial architecture and has revealed mitochondrial alterations that may contribute to hypertension
Chapter 9 Mitochondria Structure and Position in the Local Control of Calcium Signals in Smooth Muscle Cells
Features of Ca2+ signals including the amplitude, duration, frequency and location
are encoded by various physiological stimuli. These features of the signals
are decoded by cells to selectively activate smooth muscle functions that include
contraction and proliferation [1ā3]. Central, therefore, to an appreciation of how
smooth muscle is controlled is an understanding of the regulation of Ca2+
Use of fiber optic technology to measure the effects of anesthesia on luciferase reaction kinetics
In vivo bioluminescent imaging (BLI) is a sensitive and reliable technique for studying gene expression, although experiments must be controlled tightly to obtain reproducible and quantitative measurements. The luciferase reaction depends on the availability of the reaction substrate, oxygen, and ATP, the distribution of which can vary markedly in different tissues. Here we used in vivo fiber optic technology, combined with stereotaxis-assisted surgery, to assess luciferase reaction kinetics in response to 2 anesthetic regimens, isoflurane and ketamineāxylazine. Transgenic rats that expressed luciferase under the control of the human prolactin promoter were used as a model organism. Anesthesia had a marked effect on luciferase reaction kinetics. The rise time to peak emission differed by 20 min between isoflurane and ketamineāxylazine. Optical imaging using a charge-coupledādevice camera confirmed this delay. These results demonstrate that different anesthetics can have substantial effects on luciferase reaction kinetics and suggest that the timing of image acquisition after substrate injection should be optimized in regard to experimental conditions and the tissues of interest
Root oxygen mitigates methane fluxes in tropical peatlands
Tropical peatlands are a globally important source of methane, a potent greenhouse gas. Vegetation is critical in regulating fluxes, providing a conduit for emissions and regular carbon inputs. However, plant roots also release oxygen, which might mitigate methane efflux through oxidation prior to emission from the peat surface. Here we show, using in situ mesocosms, that root exclusion can reduce methane fluxes by a maximum of 92% depending on species, likely driven by the significant decrease in root inputs of oxygen and changes in the balance of methane transport pathways. Methanotroph abundance decreased with reduced oxygen input, demonstrating a likely mechanism for the observed response. These first methane oxidation estimates for a tropical peatland demonstrate that although plants provide an important pathway for methane loss, this can be balanced by the influence of root oxygen inputs that mitigate peat surface methane emissions
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