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The kinetics of form change (flattening) of Chinese hamster fibroblast cell surface facing the glass has been studied during attachment of fibroblasts to the glass using the effect of frustrated total reflection. Two stages of the process were shown to exist. The first one is characterized by a rapid (5 min) partial flattening and requires no serum in the medium. The second stage occurs only in the presence of serum in the medium, it lasts no longer than one hour and ends in a complete flattening. After the second stage is completed, spreaded cells appear.
Measurements of the back central optical radius in the course of 336 hours of hydration of lathe cut corneal lenses disclosed changes in curvature which were more rapid and of greater magnitude than those previously reported for poly (methyl methacrylate) lenses.
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A simple method is proposed to calculate bilayer lipid membrane (BLM) thickness using measurements of BLM reflectivity. BLM is considered to be nonhomogenous with the refractive index n = n(z)--a function of coordinate z normal to the membrane plane. The membrane thickness obtained with this method is 4 divided by 6% less than that obtained with the standard method.
Eight lenses with nuclear cataracts have been classified. The light-scattering properties of the eight lenses were obtained with thin sections cut perpendicularly to the posterior-anterior axis. Analysis of the light scattering envelop in the I and I+ models yielded eight structural parameters that describe the density and orientation fluctuations. The variation of these parameters within each less corresponded well to the clinical description obtained from the stereoscopic photos.
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The light scattering pattern from absorbing cylinders has been shown to be adequately described by Fraunhofer diffraction for cylinders with diameters as small as 4 micrometers for light of wavelength 632.8 nm. A simple inversion procedure based on a Fourier transform of the scattering pattern may be used to obtain the size distribution of fibre widths. For fibres of diameter less than 4 micrometers the same inversion procedure may be used when an electron micrograph of the fibres becomes the scattering object. The size distribution for aligned and unaligned fibres may be obtained directly, and no initial calibration is required.
The problem of the mean of refractive errors is solved using the theorems applied to the curvature of a surface. A numerical illustration of he method and a statistical sample ae included amongst the appendices.
The Pharmacopoeia of the GDR provides no direct method for the determination of the fat base content in ointments. The indirect determination which is due to in calculating the difference between 100% and the percentages of all the other constituents is tedious and inexact. For this reason, it was tried to find a direct method which was to be reliable, rapid and easy. In principle, the refractometric method divised by Rudischer [2--5, 9] for the determination of fat in meat and meat products, which has been compulsory since 1965, is suitable for this purpose. Consequently, this method was adapted to the requirements of ointment analysis and subjected to modifications which resulted in the variant A for non-ionic ointments, and the variant B for ointments containing ionic fatty alcohol sulphates. The results obtained with the refractometric method from all kinds of ointments tested were in full agreement with the actual fat contents. Parallel determinations differed by 0.5% at the most.
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BACKGROUND: Studies of corneal power changes resulting from photorefractive keratectomy generally rely on keratometer or videokeratograph measurements. These instruments convert corneal radius of curvatures values to optical powers by means of the single refracting surface formula, which incorporates an index of refraction value of 1.3375. This index approximates that of the tears but not the 1.376 index of the corneal epithelium or stroma. A hypothetical optical model was used to determine the most appropriate index to be chosen with respect to corneal power calculations relative to photorefractive keratectomy. METHODS: The contribution of each refractive element in the tear lens-corneal surface to the total power of the eye was calculated in order to identify which index of refraction was most appropriate for the corneal power calculation. RESULTS: The outer tear surface has significant optical power but the tear layer as a whole has nearly zero power due to the offsetting negative power of the posterior test surface. There is no significant difference in the effective power of light leaving the corneal anterior surface when considered with or without the tear layer. Photorefractive keratectomy changes the epithelium and anterior surface of the corneal stroma, but does not affect the posterior stroma or other ocular media. Hence the refractive index for the corneal epithelium or stroma of 1.376 should be used in converting radius to optical power values. The error in assuming a corneal index of 1.3375 is a constant proportion equal to 11.4% of the corneal power reading. CONCLUSIONS: Photorefractive keratectomy presents a situation in which the actual corneal refractive index of 1.376 should be used for correct corneal radius to power conversions. This may be accomplished by changing the index value in the instrument algorithm for keratometry and videokeratography to 1.376 or by adding a correction factor of either 11.4% of the regular reading to its value or multiplying by the factor 1.114. In other applications of keratometry or videokeratography, the index 1.3375 may be more appropriate.