Changes In Relative Thickness Research Articles

Thermal protection of roads in the permafrost zone

The problem of choosing a method of construction of thermal protection layer of the road pavement in permafrost zone was solved. Simple engineering formulas to justify the choice of the specific type of thermal insulation structure were obtained. It was determined that a structure composed of two layers (separate layers insulant and of sand) is always more efficient than a thermal insulation mixture (combined insulant and sand) applied in one layer for the purposes of maximizing thermal resistance. At the same time, a quantitative assessment demonstrated that in many practical cases, the difference in thermal resistance of the two kinds of structures is slight and is within the margins of permissible precision of engineering calculations. For this reason, it is expedient to also consider the technological demands of application of one or the other type of thermal insulation layer in addition to the thermal resistance considerations. Formulas to find the area of rational use of thermal insulation mixtures instead of merely sand bedding were devised. It was determined that the thickness of bedding in one or the other case is significantly dependent on the ratio of thermal conductivity coefficients of sand and the insulant. In addition, the change in relative thickness of the layer can have both negative and positive values.

Lifespan trajectories of relative corpus callosum thickness: Regional differences and cognitive relevance

The cerebral hemispheres are specialized for different cognitive functions and receive divergent information from the sensory organs, so that the interaction between the hemispheres is a crucial aspect of perception and cognition. At the same time, the major fiber tract responsible for this interaction, the corpus callosum, shows a structural development across the lifespan which is over-proportional. That is, compared to changes in overall forebrain volume, the corpus callosum shows an accentuated growth during childhood, adolescence, and early adulthood, as well as pronounced decline in older age. However, this over-proportionality of growth and decline along with potential consequences for cognition, have been largely overlooked in empirical research. In the present study we systematically address the proportionality of callosal development in a large mixed cross-sectional and longitudinal sample (1867 datasets from 1014 unique participants), covering the human lifespan (age range 4–93 years), and examine the cognitive consequences of the observed changes. Relative corpus callosum thickness was measured at 60 segments along the midsagittal surface, and lifespan trajectories were clustered to identify callosal subsections of comparable lifespan development. While confirming the expected inverted u-shaped lifespan trajectories, we also found substantial regional variation. Compared with anterior clusters, the most posterior sections exhibited an accentuated growth during development which extends well into the third decade of life, and a protracted decline in older age which is delayed by about 10 years (starting mid to late 50s). We further showed that the observed longitudinal changes in relative thickness of the mid splenium significantly mediates age-related changes in tests assessing verbal knowledge and non-verbal visual-spatial abilities across the lifespan. In summary, we demonstrate that analyzing the proportionality of callosal growth and decline offers valuable insight into lifespan development of structural connectivity between the hemispheres, and suggests consequences for the cognitive development of perception and cognition.

Fast Optical Humidity Sensor Based on Hydrogel Thin Film Expansion for Harsh Environment.

With the application of a recently developed deposition method called initiated chemical vapor deposition (iCVD), responsive hydrogel thin films in the order of a few hundred nanometers were created. When in contact with humid air, the hydrogel layer increases its thickness considerably. The measurement of the thickness change was realized interferometrically with a laser and a broadband light source in two different implementations. The relative change in thickness with respect to humidity can be described with the Flory–Huggins theory. The required Flory–Huggins interaction parameter was determined for the actual hydrogel composition. The setup was designed without electric components in the vicinity of the active sensor layer and is therefore applicable in harsh environments such as explosive or corrosive ones. The implemented sensor prototype delivered reproducible relative humidity () values and the achieved response time for an abrupt change of the humidity s was about three times faster compared to one of the fastest commercially available sensors on the market.

EFFECT OF GEOMETRICAL PARAMETERS ON THE DEFORMATIONS OF THE HUMAN OPTIC NERVE HEAD BASED ON INDIVIDUAL-SPECIFIC MODELS

The elevated intraocular pressure (IOP) is one of the important risk factors of glaucomatous optic nerve damage. The deformations of glaucomatous optic nerve head (ONH) due to the elevated IOP might lead to further damage to the optic nerve. The ONH deformations due to the elevated IOP depend on their geometry. Therefore, it is meaningful to investigate the relationship between geometrical parameters and the deformation of ONH. Firstly, the geometrical parameters of ONH were obtained by in vivo using spectral domain optical coherence tomography. Then, individual-specific three-dimensional (3D) models of ONH for glaucoma and normal subjects were established and the deformations of ONH were acquired by using finite element method. Furthermore, the thickness changes of retina and lamina cribrosa were calculated under different IOPs. Finally, correlations between geometrical parameters and the relative deformations of the human ONH were researched by using Spearman correlation. It was found that the relative thickness change of patient’s retina was larger than that of normal subjects under the same condition. The correlation of several parameters, including cup area, and lamina cribrosa depth, with relative deformations of ONH had statistical significance.

Difference between subjects in early chronic phase of low back pain with and without neuropathic component: observational cross-sectional study

Neuropathic pain in early chronic low back pain is insufficiently recognized and treated. The aim of this study was to establish if there is a difference among chronic low back pain subjects with and without neuropathic pain and healthy subjects, in clinical characteristic and the level of trunk muscle activation. Cross sectional observational study. Rehabilitation clinic, inpatient and outpatient. Thirty-three subjects in early chronic phase of low back pain and 26 healthy subjects were included in this research. Clinical characteristics and relative thickness change of lumbar multifidus and transversal abdominal muscle, measured by ultrasound, in neuropathic, non-neuropathic chronic low back pain and healthy subjects were analyzed. Chronic low back pain subjects with neuropathic pain reported higher level of pain on Visual Analog Scale (VAS) (back pain P=0.016, leg pain P=0.006), had higher Oswestry Disability Score (P=0.029), had lower motor (P=0.001) and sensory leg scores (P=0.000), and decreased level of activation of transversal abdominal muscle (P=0.000) comparing to chronic low back pain group without neuropathic pain. Low back pain subjects with leg pain ≥5 on VAS were 11.2 times more prone to develop neuropathic pain. Motor leg score ≤47 increases this chance 35 times. Sensory leg score ≤25 increases this chance 14 times. Reduced activation of transversal abdominal muscle for 40-50% increases this chance 7-24 times. Chronic low back pain subjects with neuropathic pain were more painful and disabled, had lower motor and sensory scores, and lower relative thickness change of transversal abdominal muscle comparing to the low back pain group without neuropathic pain. Self -reported leg pain intensity of 5 or more on VAS, motor score of 47 and less, sensory scores of 25 and less and diminished activation of transversal abdominal muscle significantly increase the chance that chronic low back pain subject has neuropathic component of pain. Neuropathic pain in early chronic low back pain subjects might be more readily recognized if patients with radiculopathy and diminished activation of transversal abdominal muscle were regularly screened for neuropathic pain.

Calculating Membrane Area Compressibility from MD Simulations: a Novel Computational Framework

Like thin elastic sheets, lipid bilayers can bend and stretch, and are characterized by mechanical constants such as bending rigidity (Kc) and area compressibility (Ka), which define the free energy of bilayer deformation and thus have direct implications in quantifying the energetics of protein-membrane interactions. Limited experimental data for Kc and Ka of different lipid mixtures makes such calculations challenging. Existing computational methods for calculating Ka from MD simulations exhibit strong dependence on bilayer size, or require multiple simulations with constraints on the area, or tension. We present a novel computational framework that is independent of system size and requires analysis only of a single sufficiently converged simulation trajectory. The method is based on Helfrich's theory of elasticity by relating relative changes in area to relative changes in thickness. The distribution of local fluctuations in the thickness of each bilayer leaflet is used to construct a potential of mean force and recover the bilayer Ka from a quadratic fit. The rapid calculation utilizes freely available software packages. We present results for a variety of single and multicomponent bilayers of phosphatidylcholine, phosphatidylethanolamine and sphingomyelin, utilizing simulation results at different temperatures and bilayer sizes. The calculated compressibility moduli range from 170 to 320 mN/m and agree for the majority of tested cases with values reported from experiments and other computational methods. We further validate our method in a comparison with an existing polymer brush model and confirm the linear relationship between thickness and (Kc/Ka) ˆ (1/2), all calculated from the simulation trajectories.

Modeling of bending characteristics of symmetric tri-layer laminated Sheet materials

Bending of sheet materials is widely applied to shaping many automotive, aerospace and other industrial components. Tailored laminate sheet materials are desirable in bending applications where monolithic sheets do not meet the design requirements or manufacturing demands. An accurate analytical model can be effectively utilized for rapid design of components for laminated sheet materials for a given application. Many analytical models based on advanced theory of bending have been proposed in the literature to predict plane strain bending characteristics of monolithic sheet materials. However, there are very few such models for laminated sheet materials. In this study, an analytical model for tri-layer laminated sheet material is developed based on advanced theory of bending. The model considers Mises yielding and Ludwik non-linear plastic hardening with Bauschinger effect for various laminate thickness ratios. Also, a 3D FE model based on Marciniak-Kuczynski (MK) bend test design is developed to assess pure bending characteristics of a symmetric tri-layer aluminum sheet laminate with softer and thinner clad layers on both surfaces and a harder thicker core in the middle. The through-thickness tangential stresses from the analytical model are compared with those from FE model for different clad to matrix thickness ratios. The tangential stresses decrease in magnitude with increasing aluminum clad thickness ratios in the analytical model. This behavior is in good general agreement with the results from the mid-width section for the FE model. The analytical and FE models also yield similar order trend in relative thickness change with increasing clad thickness ratios and with increasing specimen radius of curvature. The 3D FE model exhibited anticlastic curvature at the edges as a result of strain inhomogeneity across the width. Unlike the tangential stress distribution, the tangential strain is maximum at the specimen edges than at the mid-width. The inhomogeneity in stress and strain across the bend line shows that plane strain condition is not consistent across the width of the sheet.

The effect of impurity on temperature variations in the refractive indices and thickness of TGS crystals

Temperature dependences of optical path difference δΔі and the relative changes in thickness δlі/l of TGS crystals doped with L-valine are studied. Temperature dependences of the relative changes in refractive indices δnі/(n–1) are calculated. The anisotropy coefficients of refractive indices Аn–1(Т) and linear expansion Аα(Т) are calculated, and a characteristic minimum of these dependences is found near the phase transition temperature.

Modeling and Experimental Assessment of Bending Characteristics of Laminated Bilayer Sheet Materials

Many mathematical models based on the advanced theory of bending to predict bending characteristics for monolithic sheet materials are available in the literature. In this work, a similar approach is utilized to develop bending models for a bilayer laminated sheet material. The principal stresses and strains through the thickness and change in relative thickness, at specified bend curvatures, are obtained as a function of increasing curvature during bending. Additionally, three-dimensional (3D) finite element (FE) based models for bilayer laminate bending are developed to overcome simplifications of the analytical models. In order to experimentally validate the two models, a new experimental bend test-jig is developed and experiments are performed on bilayer steel–aluminum laminate for different clad to matrix thickness ratios. These experiments have enabled continuous measurements of strain along the width at the bend line and through the laminate thickness at one of the specimen edges using an online strain mapping system based on digital image correlation (DIC) method. Analytical model results indicate how the through-thickness strain distribution and relative thickness of the specimen in bending are influenced by the location and thickness of the soft clad material. The FE model and experimental results exhibit similar trends in the relative thickness change for different geometric arrangements of steel–aluminum layers. The tangential and radial stresses decrease in magnitude with increasing aluminum clad thickness ratios. The 3D FE model of laminate bending provided strain predictions across the specimen width at the bend line on the tension and compression sides that increased with increasing clad thickness ratios. Also, relative thickness data from the 3D FE model showed uniaxial and plane strain stress states at the edge and midwidth sections of the test specimen. The results from analytical and FE models and from DIC and microscopic thickness measurements indicate that thickness at the bend line increases with increasing clad thickness for the case of clad layer on the compressive side of the laminate (i.e., C-C case) and vice versa for clad layer on the tensile side (C-T).

Relationship Between Electromyographic Signal Amplitude and Thickness Change of the Trunk Muscles in Patients With and Without Low Back Pain.

To compare the relative thickness change of the transversal abdominal (TrA) and lumbar multifidus (LM) muscles during activation in individuals with and without low back pain (LBP), and to establish a relationship between surface electromyography (sEMG) signal amplitude and the relative thickness change of the corresponding muscle during clinically relevant activity, with preferential activation of TrA/LM. Thirty-seven pain-free participants and 36 LBP patients were assessed by ultrasound for thickness changes of TrA and LM and by sEMG for changes of electrical activity of the same muscles. sEMG is done with wireless LUMBIA system. The position of the sEMG sensors and activation maneuvers were chosen carefully. Significant group effect was found for relative thickness change of TrA (F1,142=60.69, P<0.0001) and LM (F1,142=36.01, P<0.0001). We found significant correlations between relative thickness change of TrA and sEMG signal amplitude on both sides for LBP (r=0.46 to 0.63, P<0.05) and pain-free patients (r=0.43-0.47, P<0.05). The correlation between LM thickness change and sEMG was significant in pain-free participants for both sides (r=0.36 to 0.38 P<0.05), and right LM in LBP participants (r=0.43, P<0.05), but not for LM in LBP group (r=0.16, P=0.351). US and sEMG measurements can be used for objective TrA/LM assessment. Correlation results suggest that the relative change of the muscle thickness could be used as the indicator of the muscle activity. Insight into the activity of TrA/LM in pain-free individuals and LBP patients during and after painful episodes may clarify the role of functional abnormalities of these muscles in LBP.

Interrater and intrarater reliability of transverse abdominal and lumbar multifidus muscle thickness in subjects with and without low back pain.

Two-group, repeated-measures reliability study. To determine interrater and intrarater reliability of ultrasound measurements of transverse abdominal (TrA) and lumbar multifidus (LM) muscle thickness, during rest and contraction, in subjects with low back pain (LBP) and healthy subjects over 3 consecutive days, performed by an experienced and a novice rater. Previous reliability studies of TrA or LM thickness did not simultaneously account for muscle state, rater experience, and multiday assessment in large subject samples. The 2 raters measured TrA and LM thickness on 3 consecutive days in 42 healthy subjects and 56 subjects with LBP, during rest and contraction, and calculated the percent thickness change from rest to contraction. Intraclass correlation coefficients (ICC(2,k)) and 95% minimal detectable change in thickness were derived for a single measure (day 1) and an average measure (days 1-3). The interrater ICC(2,1) values for single-measure thickness (LBP group, 0.71-0.87; healthy group, 0.94-1.00) were similar to those for average-measure thickness (LBP group, 0.73-0.84; healthy group, 0.93-1.00). Both interrater ICC(2,1) and ICC(2,3) were lower for the relative thickness change (0.61-0.96). Intrarater ICC(2,1) values across 3 consecutive days were high for both raters across the 2 groups (LBP group, 0.95-1.00; healthy group, 0.93-1.00), albeit lower for the relative thickness change (0.79-0.99). The 95% minimal detectable changes were < 0.3 mm for the TrA and < 2 mm for the LM (but, in most cases, less than 10% of average thickness). Both experienced and trained novice raters provided reliable measurements of TrA and LM thickness in participants with LBP and healthy participants, during rest and contraction. One-time measurements were similar to averaged measurements. Small absolute errors were observed. Public trial registry: Australian New Zealand Clinical Trials Registry ACTRN12613001077752.

Unconventional-Asset-Development Work Flow in the Eagle Ford Shale

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 168973, ’Unconventional-Asset-Development Work Flow in the Eagle Ford Shale,’ by David Cook, Kirsty Downing, Sebastian Bayer, Hunter Watkins, Vanon Sun Chee Fore, Marcus Stansberry, Saurabh Saksena, and Doug Peck, BHP Billiton Petroleum, prepared for the 2014 SPE Unconventional Resources Conference - USA, The Woodlands, Texas, USA, 1-3 April. The paper has not been peer reviewed. Development of the Eagle Ford shale typically consists of horizontal wells stimulated with multiple hydraulic-fracture stages. This paper presents a pragmatic integrated work flow used to optimize development and guide critical development decisions in the Black Hawk field. Geoscientists and reservoir and completion engineers worked collaboratively to identify optimal completion designs and well spacings for development focus areas. Multiple simplistic simulation models were history matched to existing production wells. Introduction In 2008, the operator drilled several successful wells in the Hawkville field of what would become the Eagle Ford shale play. Early results led to substantial land acquisition. The Eagle Ford, while continuous over wide sections, varies substantially in terms of fluid and rock properties. Fig. 1 shows a cross section for an arbitrary line through Black Hawk and Hawkville to the Maverick basin, showing the relative changes in thickness and Young’s modulus. An understanding of the characterization of shale systems for simulation has evolved rapidly. Flow contributions from natural fractures, induced fractures, and matrix rock along with the nature of the hydrocarbon deposit itself should be considered. Perhaps even more important is regional variation. In the world of conventional assets, property estimation needs to be reliable only for a small geographical area, often within one sandstone structure of a few square miles at most. This can be compared with the scale of the play in Fig. 1. For conventional reservoirs, standardized laboratory methods and years of research and trial and error have educated our approaches to well-defined best practices. In shale plays, these have not yet been fully worked through and adopted by consensus, often leaving the owner of the asset as the arbiter of methodology.

Bioinspired Hygromorphic Actuator Exhibiting Controlled Locomotion.

We report a bioinspired hygromorphic double-layered actuator (HDA), of which the movement is controlled by cyclical changes in relative humidity (RH). The basic principle of the HDA lies in the rapid swelling and deswelling of highly hygroscopic layer-by-layer (LbL) assembled films deposited on a moisture-resistant and flexible polytetrafluoroethylene (PTFE) ribbon. We engineer the geometry of the HDA to induce locomotion on a ratchet track. By controlling the exposure time and RH, the HDA is remotely controlled to move a precise number of steps on the ratchet track during one cycle of RH changes. We demonstrate that the step length of the HDA depends on the relative thickness change of the LbL film. We also provide theoretical considerations based on a plate theory and the Flory-Huggins theory to describe the actuation of the HDA. Our work provides fundamental insights into the fabrication and design of hygromorphic actuators driven by RH changes.

Electromechanical Strain Responses of SEBS/CB and SEBS/SWCNT Composites

Electromechanical strain responses of poly (styrene-b-ethylbutylene-b-styrene) (SEBS) /carbon black (CB) composites and SEBS/single wall carbon nanotube (SWCNT) composites were investigated. The electric field induced thickness strains sz of the composites increased with the conductive filler content at the low filler concentration region and then showed the maximum. sz represents relative thickness change relative to the initial thickness of the composite film. A further increase of the filler concentration caused a decrease in the actuation strain. The SEBS/SWCNT showed a larger sz than SEBS/CB at the same filler content.

Abdominal and Lumbar Multifidus Muscle Size and Symmetry at Rest and During Contracted States

The purpose of this study was to establish reference values for abdominal and lumbar multifidus muscles at rest and while contracted in a sample of active healthy adults. Three hundred forty participants (mean age ± SD, 21.8 ± 3.9 years; 96 females and 244 males) completed the study. Ultrasound imaging was used to assess the thickness of the transversus abdominis, internal and external oblique, rectus abdominis, and lumbar multifidus muscles. Additionally, the cross-sectional area of the rectus abdominis was assessed. Although males had significantly thicker muscles than females (P < .05), the relative change in thickness during specified tasks was equivalent. Overall, relative muscle thickness and symmetry were similar to previous studies using smaller sample sizes. These findings provide a robust data set of muscle thickness values measured by ultrasound imaging and can be used for comparison to those with pain, abnormal function, and pathologic conditions.

Effects of mechanical indentation on diffuse reflectance spectra, light transmission, and intrinsic optical properties in ex vivo porcine skin

Mechanical indentation has been shown to increase light transmission through turbid tissue. In this study, we investigated the effects of localized indentation on the optical properties of ex vivo porcine skin specimens by dynamically monitoring diffuse reflectance spectra, light transmission, and applied load while controlling tissue thickness. A custom-built diffuse reflectance spectroscopy (DRS) system was used to capture diffuse reflectance spectra from tissue specimens undergoing indentation. The DRS probe was designed to perform both optical sensing and tissue indentation. A mechanical load frame was used to dynamically control probe displacement and resultant specimen thickness change while recording applied load. Diffuse reflectance spectra, as well as light transmission at 630 nm, were recorded during stress relaxation tests where tissue specimens were displaced to and held at a final thickness. Tissue optical properties were extracted from reflectance spectra using a previously established look-up table (LUT) approach. Indentation increased light transmission through tissue during linear displacement, and continued to increase transmission during subsequent stress relaxation at constant tissue thickness. The magnitude of relative transmission increases was shown to be a function of bulk tissue compressive strain (relative thickness change). Reduced scattering coefficients calculated from the LUT at 630 nm decreased during stress relaxation, with the relative decrease in scattering also depending strongly on tissue compressive strain. Reduced scattering coefficients decreased by 12.0 ± 4.7% at 0.44 ± 0.022 compressive strain, and reduced by 35.6 ± 1.3% at 0.71 ± 0.01 compressive strain. DRS can be used to capture transient changes in intrinsic tissue optical properties during mechanical loading. Mechanical indentation modifies tissue optical properties and may be harnessed as a minimally-invasive optical clearing technique to improve optical diagnostics and therapeutics.

Geologic significance of anomalous instantaneous frequency

Anomalous frequency spikes derived from complex-trace analysis have long been considered more as a flaw of algorithms than a valuable seismic attribute. However, synthetic models and field data show that instantaneous frequency spikes are clearly linked to physical models that could help geologic interpretations of seismic data. Frequency spikes are related to relative amplitude minima along a seismic trace that occur either at the merging point of the top and base reflections of a wedge (type I) or at the tip of the wedge (type II). A type II spike is indicative of a seismically thin bed (average [Formula: see text] or thinner in this study; [Formula: see text] denotes wavelength), although the bed thickness tends to decrease with the data frequency and bed spacing in a multibed acoustic-impedance profile (in the range of [Formula: see text] to [Formula: see text] in this study). Interpretive values of instantaneous frequency include recognizing thin reservoirs that are otherwise difficult to detect, mapping relative thickness changes of lithofacies, detecting lithofacies boundaries and faults, and locating a stratal discontinuity or flow barrier. Uncertainties caused by type I spikes, noise-derived fake spikes, and the lack of lithologic and time-stratigraphic information can be reduced by integrating well data, local geologic models, lithology-indicative seismic attributes (e.g., 90°-phase data), and facies-oriented seismic displays (e.g., stratal slices).

Changes in Abdominal Muscle Thickness Measured by Ultrasound Are Not Associated With Recovery in Athletes With Longstanding Groin Pain Associated With Resisted Hip Adduction

Longitudinal single-cohort study. Athletes with longstanding groin pain associated with resisted hip adduction have been shown to have abnormal activation of the transversus abdominis (TA). Therefore, exercises targeting the TA to help stabilize the lumbopelvic area are generally used in the rehabilitation of these athletes. To investigate if (1) changes in abdominal muscle resting thickness and changes in relative thickness during lower extremity tasks after 14 weeks of intervention are related to changes in clinical status and (2) the changes in abdominal muscle resting/relative thickness are significant postintervention. In 21 athletes with longstanding groin pain associated with resisted hip adduction, ultrasound imaging of the abdominal musculature on the right side was performed at rest, during the active straight-leg raise (left and right), and during bilateral isometric hip adduction. Athletes then followed a 14-week rehabilitation protocol. Clinical outcome measured by self-reported sports restriction and change in abdominal muscle resting and relative thickness during lower extremity tasks were evaluated. There was an overall significant decrease in self-reported sports restriction after intervention for this group of athletes. Apart from a significant negative correlation for changes in TA resting thickness, no significant association between changes in abdominal muscle thickness and change in self-reported sports restriction were found. Postintervention, TA resting thickness was significantly increased but relative thickness during the lower extremity tasks was found not to be statistically different for all muscles, except for a decreased relative thickness of obliquus externus abdominus (OE) during the active straight-leg raise for the left lower extremity. There was no association between changes in abdominal muscle resting thickness and relative thickness during lower extremity tasks, and change in self-reported sports restriction after a period of physical therapy in athletes with longstanding groin pain associated with resisted hip adduction. Although this study was designed as a single-cohort longitudinal study, the data suggest that the intervention described can change TA resting thickness. The intervention did not influence abdominal muscle relative thickness during lower extremity tasks.

Formation of stromal collagen fibrils and proteoglycans in the developing zebrafish cornea

Collagen fibrils and proteoglycans are the main components of the corneal extracellular matrix and corneal transparency depends crucially on their proper arrangement. In the present study, we investigated the formation of collagen fibrils and proteoglycans in the developing cornea of the zebrafish, a model organism used to study vertebrate embryonic development and genetic disease. We employed thin-section electron microscopy to investigate the ultrastructure of the zebrafish cornea at different developmental stages. The layering of the zebrafish cornea into an epithelium, a Bowman's layer, stroma and endothelium was observed starting at 72 hr post-fertilization. At this stage, the stroma contained orthogonally arranged collagen fibrils and small proteoglycans. The density of proteoglycans increased gradually throughout subsequent development of the cornea. In the stroma of 2-week-old larvae, the collagen fibrils were organized into thin lamellae and were separated by very large, randomly distributed proteoglycans. At 4 weeks, a regular arrangement of proteoglycans in relation to the collagen fibrils was observed for the first time and the lamellae were also thickened. The present study, for the first time, provides ultrastructural details of collagen fibril and proteoglycan development in the zebrafish cornea. Furthermore, it directly correlates the collagen fibril and proteoglycan composition of the zebrafish cornea with that of the human cornea. The similarities between the two species suggest that the zebrafish could serve as a model for investigating the genetics of human corneal development and diseases.

Optical Coherence Tomography Measurements and Analysis Methods in Optical Coherence Tomography Studies of Diabetic Macular Edema

To evaluate optical coherence tomography (OCT) measurements and methods of analysis of OCT data in studies of diabetic macular edema (DME). Associations of pairs of OCT variables and results of 3 analysis methods using data from 2 studies of DME. Two hundred sixty-three subjects from a study of modified Early Treatment of Diabetic Retinopathy Study (mETDRS) versus modified macular grid (MMG) photocoagulation for DME and 96 subjects from a study of diurnal variation of DME. Correlations were calculated for pairs of OCT variables at baseline and for changes in the variables over time. Distribution of OCT measurement changes, predictive factors for OCT measurement changes, and treatment group outcomes were compared when 3 measures of change in macular thickness were analyzed: absolute change in retinal thickness, relative change in retinal thickness, and relative change in retinal thickening. Concordance of results using different OCT variables and analysis methods. Center point thickness correlated highly with central subfield mean thickness (CSMT) at baseline (0.98-0.99). The distributions of changes in CSMT were approximately normally distributed for absolute change in retinal thickness and relative change in retinal thickness, but not for relative change in retinal thickening. Macular thinning in the mETDRS group was significantly greater than in the MMG group when absolute change in retinal thickness was used, but not when relative change in thickness and relative change in thickening were used. Relative change in macular thickening provides unstable data in eyes with mild degrees of baseline thickening, unlike the situation with absolute or relative change in retinal thickness. Central subfield mean thickness is the preferred OCT measurement for the central macula because of its higher reproducibility and correlation with other measurements of the central macula. Total macular volume may be preferred when the central macula is less important. Absolute change in retinal thickness is the preferred analysis method in studies involving eyes with mild macular thickening. Relative change in thickening may be preferable when retinal thickening is more severe.