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At least 1,783 records · Page 99Linked to original sources
PubMed2000

Optical coherence tomography in the study of the Goldmann-Favre syndrome.

PURPOSE: To report a case of Goldmann-Favre syndrome with special emphasis on the optical coherence tomography findings. METHODS: In a 23-year-old white man with an 8-year history of visual impairment in both eyes and night blindness, vertical and horizontal optical coherence tomography images were obtained through the macula and through the retinoschisis located at the temporal side of the macula. RESULTS: Optical coherence tomography showed in the left eye a clear loss of the inner retinal layer at the fovea and the formation of inner and outer retinal layer holes in the temporally located retinoschisis. The outer retinal layer hole had rolled edges. CONCLUSION: In Goldmann-Favre syndrome, optical coherence tomography demonstrated confluent macular cystoid changes and retinoschisis in both eyes. In the left eye, a lamellar macular hole and retinoschisis with inner retinal layer and outer retinal layer holes were observed. The outer retinal layer hole had rolled edges.

Adult↗
PubMed2001

Direct measurements of multiple adhesive alignments and unbinding trajectories between cadherin extracellular domains.

Direct measurements of the interactions between antiparallel, oriented monolayers of the complete extracellular region of C-cadherin demonstrate that, rather than binding in a single unique orientation, the cadherins adhere in three distinct alignments. The strongest adhesion is observed when the opposing extracellular fragments are completely interdigitated. A second adhesive alignment forms when the interdigitated proteins separate by 70 +/- 10 A. A third complex forms at a bilayer separation commensurate with the approximate overlap of cadherin extracellular domains 1 and 2 (CEC1-2). The locations of the energy minima are independent of both the surface density of bound cadherin and the stiffness of the force transducer. Using surface element integration, we show that two flat surfaces that interact through an oscillatory potential will exhibit discrete minima at the same locations in the force profile measured between hemicylinders covered with identical materials. The measured interaction profiles, therefore, reflect the relative separations at which the antiparallel proteins adhere, and are unaffected by the curvature of the underlying substrate. The successive formation and rupture of multiple protein contacts during detachment can explain the observed sluggish unbinding of cadherin monolayers. Velocity-distance profiles, obtained by quantitative video analysis of the unbinding trajectory, exhibit three velocity regimes, the transitions between which coincide with the positions of the adhesive minima. These findings suggest that cadherins undergo multiple stage unbinding, which may function to impede adhesive failure under force.

Animals↗
PubMed2002

Unzipping DNA with optical tweezers: high sequence sensitivity and force flips.

Force measurements are performed on single DNA molecules with an optical trapping interferometer that combines subpiconewton force resolution and millisecond time resolution. A molecular construction is prepared for mechanically unzipping several thousand-basepair DNA sequences in an in vitro configuration. The force signals corresponding to opening and closing the double helix at low velocity are studied experimentally and are compared to calculations assuming thermal equilibrium. We address the effect of the stiffness on the basepair sensitivity and consider fluctuations in the force signal. With respect to earlier work performed with soft microneedles, we obtain a very significant increase in basepair sensitivity: presently, sequence features appearing at a scale of 10 basepairs are observed. When measured with the optical trap the unzipping force exhibits characteristic flips between different values at specific positions that are determined by the base sequence. This behavior is attributed to bistabilities in the position of the opening fork; the force flips directly reflect transitions between different states involved in the time-averaging of the molecular system.

Calibration↗
PubMed2003

Sound velocity and elasticity of tetragonal lysozyme crystals by Brillouin spectroscopy.

Quasilongitudinal sound velocities and the second-order elastic moduli of tetragonal hen egg-white lysozyme crystals were determined as a function of relative humidity (RH) by Brillouin scattering. In hydrated crystals the measured sound velocities in the [110] plane vary between 2.12 +/- 0.03 km/s along the [001] direction and 2.31 +/- 0.08 km/s along the [110] direction. Dehydration from 98% to 67% RH increases the sound velocities and decreases the velocity anisotropy in (110) from 8.2% to 2.0%. A discontinuity in velocity and an inversion of the anisotropy is observed with increasing dehydration providing support for the existence of a structural transition below 88% RH. Brillouin linewidths can be described by a mechanical model in which the phonon is coupled to a relaxation mode of hydration water with a single relaxation time of 55 +/- 5 ps. At equilibrium hydration (98% RH) the longitudinal moduli C(11) + C(12) + 2C(66) = 12.81 +/- 0.08 GPa, C(11) = 5.49 +/- 0.03 GPa, and C(33) = 5.48 +/- 0.05 GPa were directly determined. Inversion of the measured sound velocities in the [110] plane constrains the combination C(44) + (1/2)C(13) to 2.99 +/- 0.05 GPa. Further constraints on the elastic tensor are obtained by combining the Brillouin quasilongitudinal results with axial compressibilities determined from high-pressure x-ray diffraction. We constrain the adiabatic bulk modulus to the range 2.7-5.3 GPa.

Acoustics↗
PubMed1994

Vectorially oriented membrane protein monolayers: profile structures via x-ray interferometry/holography.

X-ray interferometry/holography was applied to meridional x-ray diffraction data to determine uniquely the profile structures of a single monolayer of an integral membrane protein and a peripheral membrane protein, each tethered to the surface of a solid inorganic substrate. Bifunctional, organic self-assembled monolayers (SAMs) were utilized to tether the proteins to the surface of Ge/Si multilayer substrates, fabricated by molecular beam epitaxy, to facilitate the interferometric/holographic x-ray structure determination. The peripheral membrane protein yeast cytochrome c was covalently tethered to the surface of a sulfhydryl-terminated 11-siloxyundecanethiol SAM via a disulfide linkage with residue 102. The detergent-solubilized, photosynthetic reaction center integral membrane protein was electrostatically tethered to the surface of an analogous amine-terminated SAM. Optical absorption measurements performed on these two tethered protein monolayer systems were consistent with the x-ray diffraction results indicating the reversible formation of densely packed single monolayers of each fully functional membrane protein on the surface of the respective SAM. The importance of utilizing the organic self-assembled monolayers (as opposed to Langmuir-Blodgett) lies in their ability to tether specifically both soluble peripheral membrane proteins and detergent-solubilized integral membrane proteins. The vectorial orientations of the cytochrome c and the reaction center molecules were readily distinguishable in the profile structure of each monolayer at a spatial resolution of 7 A.

Amines↗
PubMed1997

Stretching DNA with optical tweezers.

Force-extension (F-x) relationships were measured for single molecules of DNA under a variety of buffer conditions, using an optical trapping interferometer modified to incorporate feedback control. One end of a single DNA molecule was fixed to a coverglass surface by means of a stalled RNA polymerase complex. The other end was linked to a microscopic bead, which was captured and held in an optical trap. The DNA was subsequently stretched by moving the coverglass with respect to the trap using a piezo-driven stage, while the position of the bead was recorded at nanometer-scale resolution. An electronic feedback circuit was activated to prevent bead movement beyond a preset clamping point by modulating the light intensity, altering the trap stiffness dynamically. This arrangement permits rapid determination of the F-x relationship for individual DNA molecules as short as -1 micron with unprecedented accuracy, subjected to both low (approximately 0.1 pN) and high (approximately 50 pN) loads: complete data sets are acquired in under a minute. Experimental F-x relationships were fit over much of their range by entropic elasticity theories based on worm-like chain models. Fits yielded a persistence length, Lp, of approximately 47 nm in a buffer containing 10 mM Na1. Multivalent cations, such as Mg2+ or spermidine 3+, reduced Lp to approximately 40 nm. Although multivalent ions shield most of the negative charges on the DNA backbone, they did not further reduce Lp significantly, suggesting that the intrinsic persistence length remains close to 40 nm. An elasticity theory incorporating both enthalpic and entropic contributions to stiffness fit the experimental results extremely well throughout the full range of extensions and returned an elastic modulus of approximately 1100 pN.

DNA↗
PubMed1997

Atomic force microscope measurements of long-range forces near lipid-coated surfaces in electrolytes.

The interaction of DMPC (L-alpha-dimyristoyl-1,2-diterradecanoyl-sn-glycero-3-phosphoch oli ne, C36H72NO8P) lipid-coated Si3N4 surfaces immersed in an electrolyte was investigated with an atomic force microscope. A long-range interaction was observed, even when the Si3N4 surfaces were covered with nominally neutral lipid layers. The interaction was attributed to Coulomb interactions of charges located at the lipid surface. The experimental force curves were compared with solutions for the linearized as well as with exact solutions of the Poisson-Boltzmann equation. The comparison suggested that in 0.5 mM KCl electrolyte the DMPC lipids carried about one unit of charge per 100 lipid molecules. The presence of this surface charge made it impossible to observe an effective charge density recently predicted for dipole layers near a dielectric when immersed in an electrolyte. A discrepancy between the theoretical results and the data at short separations was interpreted in terms of a decrease in the surface charge with separation distance.

Dimyristoylphosphatidylcholine↗
PubMed1998

Energy of adhesion of human T cells to adsorption layers of monoclonal antibodies measured by a film trapping technique.

A novel method for studying the interaction of biological cells with interfaces (e.g., adsorption monolayers of antibodies) is developed. The method is called the film trapping technique because the cell is trapped within an aqueous film of equilibrium thickness smaller than the cell diameter. A liquid film of uneven thickness is formed around the trapped cell. When observed in reflected monochromatic light, this film exhibits an interference pattern of concentric bright and dark fringes. From the radii of the fringes one can restore the shape of interfaces and the cell. Furthermore, one can calculate the adhesive energy between the cell membrane and the aqueous film surface (which is covered by a layer of adsorbed proteins and/or specific ligands), as well as the disjoining pressure, representing the force of interaction per unit area of the latter film. The method is applied to two human T cell lines: Jurkat and its T cell receptor negative (TCR-) derivative. The interaction of these cells with monolayers of three different monoclonal antibodies adsorbed at a water-air interface is studied. The results show that the adhesive energy is considerable (above 0.5 mJ/m2) when the adsorption monolayer contains antibodies acting as specific ligands for the receptors expressed on the cell surface. In contrast, the adhesive energy is close to zero in the absence of such a specific ligand-receptor interaction. In principle, the method can be applied to the study of the interaction of a variety of biological cells (B cells, natural killer cells, red blood cells, etc.) with adsorption monolayers of various biologically active molecules. In particular, film trapping provides a tool for the gentle micromanipulation of cells and for monitoring of processes (say the activation of a T lymphocyte) occurring at the single-cell level.

Adsorption↗
PubMed1999

Stoichiometry of dipalmitoylphosphatidylcholine-DNA interaction in the presence of Ca2+: a temperature-scanning ultrasonic study.

DNA-DPPC complexes can be prepared by means of a single step procedure of mixing DNA solution and aqueous lipid dispersion in the presence of calcium ions. Interaction between DPPC and DNA brings about a biphasic shape of melting curves corresponding to the free lipid and the strongly bound one. The amount of the strongly bound lipid is 5 molecules per nucleotide which is close to the size of the first lipid monolayer around DNA molecule.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2004

Differential strain measurement using multiplexed fiber Bragg grating sensors.

We investigate differential measurement of strain using fiber Bragg gratings and spatial demultiplexing methods. Differential measurement is shown to improve strain resolution in the presence of noise by an average of 34% compared to absolute measurements of the Bragg wavelengths. Spatial demultiplexing of the gratings provides potentially high-resolution sensing without calculating the sensor wavelengths. The differential method is still temperature dependent. We apply the differential technique to the problem of oil-water boundary detection in production columns, with promising preliminary results.

Algorithms↗
PubMed2006

Active vibration suppression in a suspended Fabry-Pérot cavity.

This paper is concerned with active vibration suppression in a suspended Fabry-Pérot cavity, employed as the sensor in an innovative thrust-stand, called Nanobalance. The Nanobalance aims to exploit the sensitivity of in-vacuum Fabry-Pérot interferometers to sub-nanometric displacements in order to measure thrust (<1 mN) and noise of space microthrusters with micronewton accuracy. The instrument has been conceived around an in-vacuum optical Fabry-Pérot cavity embraced by two pendulums (the active and the passive) suspended to an athermic spacer. The thruster under test is mounted on the active pendulum and an equal dummy thruster is mounted on the passive one for balancing. The objective of the paper is to suppress the beat motion centered on the mean pendulum natural frequency (10-14 Hz depending on the thruster under test) without affecting the measurement bandwidth (2 Hz) where thrust has to be measured. Beat motion arises because of small pendulum imbalances excited by ground noise. Relevant digital control strategies and experimental results will be presented and discussed.

Artifacts↗
PubMedDate not supplied

Comparative study of experimental choroidal neovascularization by optical coherence tomography and histopathology.

PURPOSE: To study the development, progression, and regression of experimental choroidal neovascularization (CNV) by correlating the cross-sectional images from sequential optical coherence tomography (OCT) with histopathologic sections of the same retinal regions. METHODS: Laser photocoagulation was performed in the posterior pole of the eye of 4 rhesus monkeys to induce CNV. Funduscopy, fluorescein angiography (FAG), and OCT were performed on day 1 and weekly for 13 weeks. Histological serial sections of CNV tissue were compared to corresponding OCT images. RESULTS: In the developmental stage of CNV, the CNV was observed by OCT as a nodular high reflex area continuing from the highly reflective retinal pigment epithelium (RPE). Histopathological studies showed that the CNV was composed of tightly packed proliferated RPE and immature vascular endothelial cells. In the active stage, OCT revealed a thick multi-layered high reflex area under the sensory retina. This high reflex area corresponded with the CNV membrane that consisted of newly formed blood vessels with wide vascular lumens and proliferated spindle-shaped RPE cells. In the regressive stage, OCT revealed a dome-like, white-colored highly reflective layer continuing from the RPE layer with moderate reflection beneath the layer. Histopathologically, the neovascular tissue was enveloped by mono-layered, cuboidal-shaped RPE cells with melanin granules. CONCLUSION: Optical coherence tomography images clearly demonstrated the positional relationship between the CNV and the RPE. Optical coherence tomography imaging provides information on the CNV which complements conventional examinations by funduscopy and FAG.

Animals↗
PubMedDate not supplied

Adult-onset foveomacular vitelliform dystrophy with retinal folds.

BACKGROUND: Adult-onset foveomacular vitelliform dystrophy is characterized by a solitary, oval, slightly elevated, yellowish subretinal lesion of the fovea. We examined a patient with adult-onset foveomacular vitelliform dystrophy with stellate retinal folds by optical coherence tomography and scanning laser ophthalomoscopy. CASE: A 58-year-old Japanese woman with a complaint of decreased vision in her right eye was diagnosed as having adult-onset foveomacular vitelliform dystrophy. OBSERVATIONS: Ophthalmoscopic examination revealed a yellowish lesion of one-third disc diameter in size at the fovea in the right eye. Fluorescein angiography demonstrated an irregular block of choroidal fluorescence corresponding to the yellowish lesion, which was surrounded by stellate retinal folds. Optical coherence tomography images showed a steep elevation of the retinal pigment epithelium (RPE) as a focally protruded reflective band over an optically clear space. Scanning laser ophthalmoscopy provided morphologic enhancement in the specifically affected layers of the macula. Using an argon green laser, band-shaped bright reflexes were seen in the right fovea. The helium-neon laser revealed a bright patch corresponding to the yellowish lesion over the fovea, which was surrounded by stellate retinal folds. The diode laser revealed a bright patch corresponding to the yellowish lesion. CONCLUSION: The stellate retinal folds of this patient were considered to be caused by the steep elevation of the RPE with an extracellular accumulation of the vitelliform deposits.

Electroretinography↗
PubMedDate not supplied

Comparison of optic disc topography measured by Retinal Thickness Analyzer with measurement by Heidelberg Retina Tomograph II.

PURPOSE: To compare the optic disc topography measurements from a digitized laser slit-lamp and a confocal scanning laser ophthalmoscope (SLO). METHODS: Ten normal subjects (10 eyes) were recruited. Topographic measurements of the optic disc were performed three times in all eyes using the Retinal Thickness Analyzer (RTA) and the Heidelberg Retina Tomograph II (HRT II), and the mean values determined. The mean values of 11 optic disc parameters were compared between the two instruments by the Wilcoxon signed rank test. To test the reproducibility of the topographic measurements, the coefficients of variation (CV) of the topographic parameters among the three measurements from each of the two instruments were compared using the Wilcoxon signed rank test. RESULTS: The mean cup depth, mean retinal nerve fiber layer (RNFL) thickness, and RNFL cross-sectional area were significantly smaller when measured by RTA compared with HRT II (P =.0067, P =.0364, P =.0467, respectively). The mean CVs from the RTA were larger than those from the HRT II for all parameters; however, the differences in all parameters did not reach significance. CONCLUSION: The RTA measured smaller z-axis values compared with the HRT II. The reproducibility of the topographic data was not significantly different between the instruments.

Adult↗
PubMed2003

Performance characteristics of a pressure microsensor.

A new fiber optic microsensor has been developed for pressure measurement. The pressure microsensor is extremely small (360 micro m). Performance characteristics of the microsensor were evaluated over a pressure range from 0 to 250mmHg. Five sensors were compared to a National Institute of Standards and Technology traceable reference pressure. The microsensor had an accuracy, repeatability, and linearity better than 2% full-scale output (FSO) and a hysteresis of 4.5% FSO.

Calibration↗
PubMed1981

Moiré phototopography in the evaluation of anterior chest wall deformities.

One of the major remaining problems in the management of children with anterior chest wall deformities is the lack of a widely accepted objective method of evaluating the severity of the deformity. This deficiency has made it difficult to evaluate indications for operation or the results of operative repair. Moiré phototopography is a new method of accurately measuring human body contours utilizing recent developments in applied optics and has been used successfully in scoliosis screening programs. This technique has been applied to the evaluation of anterior chest wall deformities and the initial results of this study are presented. Moiré phototopography has proven to be a sensitive, reproducible, and easy to perform method of quantitating pectus deformities. While further evaluation is required, this early experience suggests this technique may provide a means of accurately and objectively measuring chest wall deformities so that their physiologic significance can be precisely investigated and the results of therapy critically reviewed.

Adolescent↗
PubMed1987

Surgical correction of pectus carinatum.

Pectus carinatum is an infrequent but eminently correctable chest wall deformity. It is encountered much less frequently than pectus excavatum. In 12 years, from 1973 to 1985, 152 pectus carinatum (16.7%) and 758 pectus excavatum deformities (83.3%) were corrected. It occurs more frequently in boys (119 patients) than girls (33 patients). The majority, 89 cases, were symmetric, while 49 were asymmetric, and 14 were mixed deformities (ipsilateral carinatum, contralateral excavatum). In almost half the patients the deformity was not identified until after the 11th birthday. A family history of chest wall deformities was present in 26%, and of scoliosis in 12%. Associated musculoskeletal abnormalities were identified in 34 patients (scoliosis 23, Poland's syndrome 4, neurofibromatosis 2, Morquio's disease 2, vertebral anomalies 1, hyperlordosis 1, and kyphosis 1). Surgical correction required bilateral resection of the third through seventh costal cartilages in 143 patients, and unilateral resection in nine patients with an isolated abnormality. A single osteotomy was used in 88 patients and a double osteotomy in 53 patients. In 11 cases no osteotomy was required. Mixed deformity with posterior angulation of the sternum was managed by osteotomy and anterior displacement. The remaining cases had sternal osteotomy and fracture of the posterior cortex to correct anterior angulation. The operation was completed with a low complication rate 3.9% (pneumothorax 4, wound infection 1, atelectasis 1, and local tissue necrosis 1). Three patients required revision with additional unilateral lower cartilage resection for persistent malformation of the costal arch. All patients ultimately had a satisfactory result.

Adolescent↗
PubMed1988

Surgical correction of chondromanubrial deformity (Currarino Silverman syndrome).

Chondromanubrial (arcuate) pectus carinatum is the rarest protrusion deformity of the chest. Its surgical correction was first described by Ravitch in 1952. We have recently encountered five patients with this deformity who have provided additional insight into the anatomy and optimal repair of this condition. It is notable for a short nonsegmented sternum with marked posterior angulation at the site of the normal chondromanubrial junction. It is optimally corrected by subperichondrial resection of the second to the seventh costal cartilages with a broad wedge-shaped osteotomy through the anterior cortex of the sternum at the point of maximal angulation. Anterior displacement of the sternum is achieved by closing the osteotomy with heavy silk sutures while the costal cartilages are regenerating.

Adolescent↗