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At least 667 records · Page 37Linked to original sources
PubMed1978

Biometric analysis of intraocular lens power required to produce emmetropia: results of 450 implants.

We analyzed 450 consecutive cases of intraocular lens implantation (omitting only two inadvertent implantations in patients with high myopia) to determine the dioptric lens power in each case required to produce emmetropia. The mean was 18.3 D with a standard deviation of 2.6 D. The data did not conform to a normal or Gaussian distribution because of an abnormally high number of cases that required greater than 25 D to achieve emmetropia and clustering between 17 to 19 D. The deviation from a normal distribution may be explained by our considering patients with high hyperopia and high myopia (which are for the most part excluded from intraocular lens data) to be separate populations. The data are valuable to the intraocular lens surgeons, in that they demonstrate the range and frequency of intraocular lens powers needed to achieve emmetropia in a large population sample.

Aphakia↗
PubMed1983

A slide rule for calculating the power of an intraocular lens.

We have designed a slide rule to calculate the emmetropizing and iseikonizing power of an intraocular lens (IOL). Like the dial biometer currently used for these calculations, the slide rule is inexpensive, easy to use, simple, and a compact pocket size. It can, however, also be used to calculate postoperative refractive error, corneal power when various keratometers are used, and conversion of refractive correction at the spectacle frame to that at the cornea, or vice versa. All the calculated data are within the accuracy suitable for clinical work.

Eyeglasses↗
PubMed1988

Long-term healing of the central cornea after photorefractive keratectomy using an excimer laser.

Using an excimer laser at 193 nm, 3-mm diameter discs were ablated from the optical zone of monkey corneas at a variety of depths up to 130 micron. Tissue was examined by light and electron microscopy 4 and 5 weeks and 6 and 8 months postoperatively. With the exception of the deepest ablation, all corneas were clear immediately postoperatively. At 1 month, ablations of 40 micron remained clear, whereas all others showed some degree of haze. By 3 months, discs at 60 micron depth were clear, and there was less haze in others. Haze was progressively lost over 6 months, but in the deepest discs it could still be discerned on slit-lamp examination. Microscopic observation showed that reepithelialization had occurred within 24 to 48 hours. Over subsequent months, a normal morphology was maintained in this layer with the exception that basal cells were slightly more elevated particularly at the disc margins where the epithelium contained more cell layers. Stromal reorganization was accompanied by an initial phase of vacuolation and invasion by keratocytes, but by 6 months postoperatively almost all vacuolation had disappeared and keratocyte numbers had almost returned to normal. By 8 months, the morphology was near normal with the exception that Bowman's membrane was absent and there was still a degree of disorder in the immediate subepithelial stromal fibers. The basement membrane of epithelial cells was reestablished but slightly more undulant than in nonirradiated areas. This undulation was retained in the 8-month postoperative specimens and at this time a normal thickness of 60 nm was displayed.

Animals↗
PubMed2003

Size-exclusion chromatography of enzymatically treated cellulose and related polysaccharides: a review.

Size-exclusion chromatography (SEC) of wood pulp polysaccharides (cellulose and hemicelluloses) has become widely used for the analysis of these polymers, including monitoring of transformations occurring under various chemical and biological processes. The present review provides information on the different procedures and methodologies developed for the characterization of molecular mass distribution (MMD) and chemical composition of cellulose and hemicelluloses by SEC. This paper also includes the significant results obtained in the characterization of enzymatically treated wood polysaccharides. Conventional SEC with double detection (refractometric and UV), "hyphenated" with a fractional dissolution, was demonstrated to be an efficient method for simultaneous determination of MMD and chemical heterogeneity.

Cellulose↗
PubMed2003

Problems connected with band-broadening in size-exclusion chromatography with dual detection.

The sources of band-broadening (axial dispersion) in size-exclusion chromatography (SEC) of polymers and its influence on data obtained using dual detection of concentration and molecular weight are reviewed. Special attention is paid to the combination of a multiangle light-scattering photometer and a differential refractometer as detectors. The local polydispersity is discussed in the relation to the band-broadening as well as to heterogeneity of the polymer with respect to molecular weight and hydrodynamic volume.

Chromatography, Gel↗
PubMed2000

Light scattering in brain slices measured with a photon counting fiber optic system.

Measurements of intrinsic optical signals (IOSs) from neural tissue, commonly with a reflection-type or transmittance-type set-up, have been used increasingly to study physiological events. Even for the same event, however, such as spreading depression (SD) or osmotic challenge, signals of opposite polarities (increase or decrease) have been obtained by different investigators using similar set-ups under similar conditions. The origin of the inconsistencies is still unknown. It is suggested here that the inconsistencies may be caused by artifacts associated with tissue surface scattering. The main goal of this paper was to present a photon counting fiber optic (PCFO) system designed to exclude surface artifacts and predominantly measure the light scattering (LS) within the tissue. Experiments on rat neocortical slices under osmotic challenges demonstrated the consistency of the PCFO data: hypertonic challenge always increased LS signal while hypotonic challenge decreased it, as long as the challenge did not induce SD. Under strong osmotic challenge (-100 mOsm), the signal suddenly reversed the polarity at the onset of SD induced by the challenge and continued to increase until the challenge was removed. When SD was blocked by high [Mg(2+)](o), the LS signal remained decreased during the -100 mOsm challenge. A spectroscopic study with the PCFO system showed that the spectrum of tissue scattering was almost a flat function in most of the visible range (650-470 nm) with a maximum at 500 nm and a rapid drop at 450 nm.

Animals↗
PubMed1998

Acetonitrile-protein interactions: amino acid solubility and preferential solvation.

The solubility of amino acids and the preferential solvent interaction of hen-egg lysozyme in acetonitrile (AN)-water mixtures (<60 w/v% AN) were investigated by means of densimetric and refractometric methods at 25 degreesC. The free energy of transfer from water to aqueous AN was negative for most nonpolar side-chains of amino acids and positive for the peptide group, the extent being comparable to those for methanol and ethanol systems. Addition of AN to an aqueous solvent was thus suggested to weaken the hydrophobic interaction and to enhance the peptide-peptide hydrogen bond therein leading to the denaturation of proteins. A parallel examination by circular dichroism confirmed that the conformation of lysozyme (pH 3) remains native in aqueous AN up to 40% but changes to the helix-rich form at higher AN concentrations. At all solvent compositions up to 50% AN (pH 3), however, lysozyme was preferentially hydrated probably due to a local salting-out of the AN molecules from the charges on the protein surface, indicating the increase of the chemical potential of the protein. These results are discussed in relation to the role of AN as an eluting organic solvent in reverse-phase chromatography.

Acetonitriles↗
PubMed2001

Quantification of biofilm accumulation by an optical approach.

Methods for non-invasive, in situ, measurements of biofilm optical density and biofilm optical thickness were evaluated based on Pseudomonas aeruginosa experiments. Biofilm optical density, measured as intensity reduction of a light beam transmitted through the biofilm, correlates with biofilm mass, measured as total carbon and as cell mass. The method is more sensitive and less labor intensive than other commonly used methods for determining extent of biofilm mass accumulation. Biofilm optical thickness, measured by light microscopy, is translated into physical thickness based on biofilm refraction measurements. Biofilm refractive index was found to be close to the refractive index of water. The P. aeruginosa biofilms studied reached a pseudo steady state in less than a week, with stable liquid phase substrate, cell and TOC concentrations and average biofilm thickness. True steady state was, however, not reached as both biofilm density and roughness were still increasing after 3 weeks.

Biofilms↗
PubMed2006

[Advantages of the autorefractometer and the Orbscan for measuring pupil diameter].

PURPOSE: We compared pupil size measurements obtained with the Orbscan and autorefractometer to the Colvard Infrared pupillometer in order to determine their respective clinical advantages. MATERIAL AND METHODS: We prospectively measured the pupil diameter in 94 eyes of 47 normal patients using the Colvard device, the Nikon NKR 8000 autorefractometer, and the Orbscan device. For each device, two successive measurements were taken to determine its reproducibility. We also studied the relationship with the contralateral eye (i.e., difference and correlation). The measurements obtained with the different devices in different light intensities were compared and studied using regression analysis. RESULTS: Pupil diameter measured using the Orbscan had the highest reproducibility (mean difference between the two successive measurements: 3.8% or 0.15mm) and showed the smallest difference between the two eyes (5.0% or 0.19mm) and the strongest correlation with the contralateral eye (r=0.93; p<0.001). Scotopic Colvard measurements and autorefractometer measurements with low light settings were not significantly different (5.86mm versus 5.86mm; p=0.48). Autorefractometer measurements with low light settings showed the strongest correlation with the scotopic Colvard measurements (r=0.84; p<0.001). The Orbscan measurements were less correlated with the scotopic or photopic Colvard measurements (r=0.73; p<0.001 and r=0.51; p=0.003, respectively). For the Colvard pupillometer, the correlation between photopic measurements and scotopic measurements was also poor (r=0.51; p<0.001). CONCLUSION: Pupil size measurements with the autorefractometer may be advantageous before refractive surgery. Measuring pupil size in photopic conditions, as with the Orbscan, cannot screen people with large pupils in mesopic conditions.

Adolescent↗
PubMed1989

Clinical chemistry. In-clinic analysis, quality control, reference values, and system selection.

The clinician never has had a better selection of user friendly analytical systems for in-clinic use. Selection of a system should be made only after several questions have been answered, including: What is the technical knowledge and experience of the persons who will use the system? Who will initiate and supervise a quality assurance program? Which analysis and what volume of samples are anticipated now and in the future? The estimated cost per test should include the total cost of instrumentation and maintenance, calibrators, controls, reagents, and technical and supervisory time. Have the methods been validated for the animal species involved and are adequate reference values available? Read the package inserts completely for each analyte. Do not rely on the advice of salespeople for guidance in answering many of these questions, but do question them carefully about statements made, especially regarding warranties and technical service. For those clinicians willing to accept the responsibilities associated with in-clinic testing, an increased awareness of laboratory medicine and a resulting increased interest and ability to provide quality medical care can be expected.

Animals↗
PubMedDate not supplied

Study of the behavior of biological molecules in a thin gap by refractive index and force measurements with an automatic surface force apparatus.

The automation of the mica surface displacement of a surface force apparatus (SFA) increases the accuracy of the intermolecular force measurements that is obtained without the presence of the experimenter. The automatic device cancels any thermal drift and the stability of the mica surfaces is optimum. The distance between the mica surfaces is measured by Tolansky multiple-beam interferometry (FECO method) which offers a sensitivity of 0.1 nm in the direction perpendicular to the plane of contact area. The mean refractive index of the medium between the mica plates is computed from simultaneous measurements of the wavelengths of two successive fringes of equal chromatic order (FECO). A conversion of an isotropic molecule to another anisotropic molecule can be identified from the variations of the refractive index. In good conditions, we can compute the local concentration of the molecules in the gap of the device, and estimate the Young's modulus of a protein.

Animals↗
PubMed1998

Kinetics of the "black hole" phenomenon in ultrasound backscattering measurements with red blood cell aggregation.

The observation of a hypoechoic zone around the center of large tubes (the "black hole" phenomenon) in ultrasound backscattering measurements with red blood cell (RBC) aggregation was reported for the first time in 1989. Since then, a very limited number of studies tried to explain its complex mechanisms. In this study, blood models characterized by different RBC aggregation levels were prepared by diluting horse blood plasma with a saline solution in different proportions. A laser reflectometry technique was used to characterize the RBC aggregation kinetics and cohesion forces between RBCs for each blood sample. The blood was circulated in a 12.7 mm diameter vertical tube. For each experimental flow condition tested, 25 or 15 power Doppler ultrasound measurements were performed across the tube with a 10-MHz system and insonation angles varying between 40 degrees to 70 degrees. For flow rates varying between 100 and 1250 mL/min, the "black hole" was observed in most measurements performed with different aggregating RBC models. The "black hole" was more pronounced for RBCs with a high kinetics of aggregation and measurements with increasing Doppler angles. Previous studies suggested that this phenomenon is due to tube entrance effects, and the reduction of RBC aggregation at very low shear rates around the center of the tube. In the present study, the "black hole" was observed for shear rates up to 25 s(-1). It is suggested that the structural organization and orientation of RBC rouleaux may participate in the mechanism leading to the "black hole" phenomenon. A schematic representation of the rheological behavior of horse RBCs in a large tube under steady flow is presented.

Animals↗
PubMed1999

Nematode burdens and cellular responses in the abomasal mucosa and blood of Florida Native, Rambouillet and crossbreed lambs.

This experiment was carried out to compare the worm burden and cellular responses in the abomasal mucosa and blood of Florida Native and Rambouillet lambs and also in animals produced by crosses of these two breeds (generations F1 and F2). Animals were exposed to infection by gastrointestinal nematodes on three different occasions. The first infection was natural, occurring while they were suckling lambs. After weaning, they were kept indoors for 53 days and then were allowed to graze a contaminated pasture for 50 days for a second natural infection. The third infection was an artificial challenge with 6000 Haemonchus contortus infective larvae. The highest mean fecal egg counts (FEC) values were found in Rambouillet lambs followed in decreasing order by F1, F2 and Florida Native lambs. Throughout the trial, most of the high mean packed cell volumes and plasma protein levels were recorded in the F2 lambs; in contrast, most of the low values were found in the Rambouillet lambs. During the natural infection period, the highest percentages of larvae in the fecal cultures of the lambs were Haemonchus. However, high percentages of Trichostrongylus larvae were found particularly in Florida Native lambs. The mean number of blood eosinophils increased after the artificial challenge, reached a peak 21 days after infection and then declined. The highest and lowest blood eosinophil means were recorded in F2 and Florida Native lambs, respectively. The H. contortus burden was significantly higher in Rambouillet and in F1 lambs than in Florida Native and F2 lambs (p < 0.05), while no significant differences were recorded among eosinophil, mast cell and globule leucocyte counts in the abomasal mucosa (p > 0.05). The highest correlation coefficient recorded at the end of this study was between FEC and worm burden (r = 0.7). These two parameters showed a moderate negative correlation with PCV, plasma protein and mast cell counts in the abomasal mucosa. The results obtained in this study indicate that crossbreeding Florida Native and Rambouillet sheep can be a rapid way to combine and improve the characteristics of these two breeds. The parasitological results were promising, however, more studies will be necessary to verify the impact of crossbreeding in other traits.

Abomasum↗
PubMed1999

Combined silver-ion and reversed-phase high-performance liquid chromatography for the separation and identification of C20 metabolites of conjugated linoleic acid isomers in rat liver lipids.

Reversed-phase high-performance liquid chromatography (RP-HPLC) and silver-ion high-performance liquid chromatography (Ag-HPLC) were successively combined for the separation of the longer-chain metabolites of conjugated linoleic acids (CLAs). Commercial silver nitrate-impregnated columns were used with an eluting solvent composed of a mixture of hexane-acetonitrile. Fatty acid methyl esters (FAMEs) from liver lipids of rats fed CLA were analysed. This method allowed separation both of the non-conjugated FAME, as C16:1, C18:2, C18:3, C20:4 and C22:5, but also the conjugated fatty acids like CLA, 8,12,14-20:3, 5,8,12,14-20:4 and 5,8,11,13-20:4. The presence of 8,11,13-20:3 is reported for the first time. This method is of interest for the isolation and identification of the C20 conjugated metabolites that cannot be resolved by gas chromatography. Furthermore, it allows the isolation of FAME for further characterisation by GC-mass spectrometry (MS).

Animals↗