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PubMed1981

[Pigment formation in photocoagulation lesions of the retina--biomicroscopic observations (author's transl)].

Retinal changes following photocoagulation (argon laser, xenon coagulator) were documented biomicroscopically in 31 patients who were studied prospectively for 90 days following treatment. Older photocoagulation scars were examined retrospectively in another 15 patients. The purpose of the study was to evaluate a possible new formation of pigment in the pigment epithelial layer. In most patients new pigment first appeared in the lesions two to three weeks after coagulation. The amount of pigment increased more and more slowly with time, but did not stop until the end of the observation period. Different forms of scar formation were observed, such as severe pigmentation, pigmentation outside the coagulated area, scars with glial components, but also extraretinal effects and effects on the retinal surface far from the coagulated area.

Cicatrix↗
PubMed1997

Measurement of Absolute Coagulation Rate Constants for Colloidal Particles: Comparison of Single and Multiparticle Light Scattering Techniques

The absolute coagulation rate constants of monodisperse spherical colloids in aqueous suspension were measured at the early stage of the coagulation processes by using two different techniques: single particle light scattering (SPLS) and simultaneous static and dynamic light scattering (SLS + DLS). Single particle light scattering determines the cluster-size distribution directly by counting the number of different clusters during the coagulation process and therefore can be used to test the kinetic growth model used for obtaining the coagulation rate constants. The simultaneous static and dynamic light-scattering method is an in-situ experiment, where the average cluster size is estimated by simultaneous static and dynamic light-scattering measurements at different angles on a multiangle fiber-optics-based setup. A combined evaluation of the static and dynamic light-scattering data permits the determination of the absolute rate constants without the explicit use of light scattering form factors and hydrodynamic properties for dimers. In this paper, we compare results obtained with both techniques. Good agreement was found for the absolute coagulation rate constants of two different latex particle suspensions. Furthermore, we show that the two techniques complement one another and the limitations of the first are overcome by the second and vice versa. Copyright 1997Academic Press

Journal Article↗
PubMed1995

Binding of blood coagulation factor VIII and its light chain to phosphatidylserine/phosphatidylcholine bilayers as measured by ellipsometry.

Factor VIII is a plasma protein which plays an essential role in the coagulation system. When assembled with the enzyme Factor IXa on a phospholipid membrane, it functions as a cofactor in the enzyme complex that cleaves the zymogen Factor X to Factor Xa. We studied the binding of both Factor VIII and the Factor VIII light chain to planar phospholipid bilayers consisting of 25% dioleoylphosphatidylserine and 75% dioleoylphosphatidylcholine (PSPC) by ellipsometry. Equilibrium-binding studies revealed that both Factor VIII and its light chain bind with high affinity to PSPC bilayers. The binding affinity of Factor VIII, with a dissociation constant Kd of 0.24 nM, was comparable with that of the Factor VIII light chain (Kd 0.49 nM). Maximal binding was 2.3 mmol of protein per mol of PSPC for Factor VIII and 7.1 mmol of protein per mol of PSPC for the Factor VIII light chain. Adsorption kinetics of both Factor VIII and its light chain conformed to the classical Langmuir adsorption model yielding dissociation constants calculated from the rates of adsorption that were similar to those obtained by equilibrium-binding studies. In contrast, measurements of rates of desorption revealed a deviation from those expected for a single class of binding sites. The desorption rate of Factor VIII increased with increasing residence time on the lipid membrane. This indicates transition of Factor VIII to a configuration with a lower binding affinity. As this time-dependent change in affinity could affect the validity of the measurement of binding parameters, in particular equilibrium-binding determinations carried out on a long timescale, binding affinity was also estimated from adsorption kinetics at half-maximal surface coverage, a relatively rapid procedure for the determination of the affinity. A Kd of 0.087 nM was obtained under these conditions. Measurement of equilibrium binding to small PSPC vesicles, a system in which equilibrium is rapidly attained, resulted in similar binding parameters (Kd = 0.13 nM and a maximal binding of 2.8 mmol of protein per mol of PSPC). These data confirm the results of equilibrium binding to planar bilayers. Taken together, our results indicate that Factor VIII, by means of its 80 kDa light chain, binds to PSPC bilayers with a dissociation constant below the concentration of Factor VIII in plasma and therefore may readily bind to exposed phospholipid membranes under physiological conditions.

Adsorption↗
PubMed1976

Fluorescein angioscopy: techniques of partial fluorescence, permanent drawing record and photocoagulation.

Fluorescein angioscopy with the indirect ophthalmoscope might be the preferred technique for evaluating and treating certain lesions, particularly those in the retinal periphery. Three techniques which are helpful in extending the advantages of angioscopy are described. (1) Partial fluorescence is achieved with careful adjustment of the cobalt blue filter which relates the fluorescence to retinal landmarks, ie, color angioscopy. (2) A permanent record of angioscopy in different phases can be made with tracing paper over the retinal drawing. (3) Correct localization of lesions to be coagulated is achieved with blue filters over the coagulator beam following fluorescein injection. The filter is removed during coagulation.

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