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PubMed1982

Chromatic dispersion of the ocular media.

Measurements of chromatic dispersion of aqueous and vitreous humors, cornea and lens of the eye are sparse and incomplete. The wavelength variation in refractive index of the ocular media of cow, pig, frog (Rana pipiens), chicken, rock bass (Ambloplites rupestris), albino rat and cat as well as human lenses was determined by means of Abbe and Pulfrich refractometry. While the humors are somewhat less dispersive than water, the cornea is more dispersive at short wavelengths. In general, the lens is significantly more dispersive than water with dispersion increasing asymptotically at the blue end of the spectrum. The exaggerated dispersion taking place at short wavelengths should be taken into account in calculations of chromatic aberration.

Adolescent↗

PubMed1983

Longitudinal chromatic aberration of the vertebrate eye.

A recent study involving Abbe and Pulfrich refractometry analyses the dispersion of the human lens and the ocular media of a number of vertebrates. In general, the lens and, to a lesser extent, the cornea, are more dispersive than expected at wavelengths below 500 nm. The dispersion findings of this study were used in conjunction with reduced eye parameters of a number of vertebrates to calculate the longitudinal chromatic aberration of rock bass, frog, chicken, rat, cat, pig, cow, and human eyes. The calculated chromatic aberration of the human eye is greater than values reported earlier, because of the exaggerated dispersion of the lens at short wavelengths. While the values calculated for the additional species studies may be larger in some instances than expected, presumably due to lens dispersion as well, chromatic aberration is not large enough to account for the hyperopia found by retinoscopic study of small eyes.

Animals↗

PubMed1985

A schematic eye for the mouse, and comparisons with the rat.

The thicknesses and spheric and aspheric curvatures of the optic components were measured from cross-sections of frozen eyes of C57B1/6J mice. The equivalent refractive index of the crystalline lens was obtained from its back-vertex power in albumin. Refractive indices of the cornea, aqueous and vitreous humors were obtained by refractometry or interferometry at four wavelengths across the visible spectrum. The measurements parallel earlier ones on the hooded rat. The eyes of the mouse and rat differ mainly in size, by a linear scale factor of 1.9-2.0, and only slightly in refractive index. Thus refraction, chromatic aberration, and retinal illumination are easily compared in the two species. An analysis of the contribution of each optical surface to refraction may facilitate extrapolation to other strains of mice. Chromatic aberration is discussed with respect to depth of field and the retinoscopy artefact.

Animals↗

PubMed1985

The magnitude of longitudinal chromatic aberration of the human eye between 458 and 633 nm.

The longitudinal chromatic aberration (LCA) of the human eye was determined between wavelengths 458 and 633 nm for ten observers by incorporating Argon and Helium-Neon Lasers into a Badal optometer system such that tonic (or "dark focus") resting positions of accommodation could be measured under darkroom conditions. A mean chromatic range of 1.87 D was found between 488 and 633 nm. The range increased slightly to 1.91 D when the experiment was repeated under cycloplegia on a subset of three subjects. Additional wavelengths (458 and 476 nm) for a further subset (four subjects) increased the range to 2.65 D. This magnitude of LCA would support recent predictions based on Abbe and Pulfrich refractometry analyses of the dispersion of the human crystalline lens and ocular media.

Accommodation, Ocular↗

PubMed1981

Solution characterization of starch nicotinates with different degrees of esterification.

A series of starch-nicotinic acid copolymers with a degree of esterification ranging from about 15% to about 90% was prepared, and the stability in solution of two representative samples of the series was tested. The variation of some physico-chemical characteristics in the series was examined by solubility tests, viscometry and refractometry, and found to be not simply correlatable to the nicotinylation degree.

Esters↗

PubMed1982

Estimation of molecular weights of membrane proteins in the presence of SDS by low-angle laser light scattering combined with high-performance porous silica gel chromatography. Confirmation of the trimer structure of porin of the E. coli outer membrane.

An assessment study was carried out to evaluate the performance of the low-angle laser light-scattering technique combined with high-performance porous silica gel chromatography in the presence of sodium dodecyl sulfate and precision differential refractometry. It was found that the combined technique is highly promising as a reliable method for determining the molecular weight of a membrane protein solubilized by the surfactant. As a test, molecular weights of porin forming the permeability channel of the outer membrane of E. coli B in an oligomeric form were measured before and after heat treatment, which is known to cause dissociation. The results obtained indicate that the porin oligomer is a trimer with stoichiometric composition.

Chromatography, High Pressure Liquid↗

PubMed1983

Determination of molecular weight of membrane proteins by the use of low-angle laser light scattering combined with high-performance gel chromatography in the presence of a non-ionic surfactant.

An assessment study was carried out to evaluate the performance of the low-angle laser light scattering technique combined with high-performance gel chromatography in the presence of a nonionic surfactant, octaethyleneglycol n-dodecyl ether, precision differential refractometry and ultraviolet photometry. It was found that the combined technique is highly promising as a method for the determination of the molecular weight of a membrane protein solubilized by the surfactant. For trial, molecular weights of the following membrane proteins of Escherichia coli, both solubilized in oligomeric forms, were measured; porin that forms the transmembrane diffusion pore in the outer membrane, and lambda-receptor protein that facilitates the diffusion of maltose-maltodextrins across the outer membrane. The result obtained indicates that both porin and lambda-receptor protein exist as trimers in the surfactant solution.

Bacterial Outer Membrane Proteins↗

PubMed1986

A comparison of three methods for determining the concentration of rat urine.

The concentrations of 78 rat urines were compared using osmometry, refractometry and test strips for specific gravity. Test strip specific gravity values are a guide to urine concentration; where small changes of urine concentration are expected, the test strips should not be a replacement for more accurate methods such as osmometry.

Animals↗

PubMed1989

A field lab method to determine urine concentration in small mammals.

1. The concentrations of 136 urine samples from four species of small mammals were compared using osmometry, refractometry and a colorimetric test for urea concentration. 2. To obtain a wide range of concentrations (430-3950 mOsm/kg), urine samples were collected under normal and dehydration conditions. 3. Regression analyses of paired values indicate that measurements of total solids concentration (refractometric method) permit evaluations of urine osmolality and estimations of the concentration of urea with a high degree of confidence.

Animals↗

PubMed1981

Dilatometric, refractometric and viscometric study of lysozyme-cation interaction.

The interaction between hen egg-white lysozyme and Cu(II) or Co(II) cations has been studied by dilatometry, equilibrium dialysis-differential refractometry and viscometry at different metal cation concentrations. Delta V isotherms in copper and cobalt solutions have been obtained from dilatometry. Preferential adsorption parameters and specific viscosity have been determined from refractometric and viscosimetric measurements. It has been observed that this interaction produces structural alterations in lysozyme. The magnitude of these conformational changes depends on the metal ion and protein concentration. The results obtained using the three techniques are in good agreement.

Animals↗

PubMed1990

Water-soluble proteins do not bind octyl glucoside as judged by molecular sieve chromatographic techniques.

It is well known that the non-ionic detergent octyl glucoside (1-O-n-octyl-beta-D-glucopyranoside) solubilizes biological membrane components. It forms complexes with membrane-spanning proteins by hydrophobic interactions and it forms mixed micelles with membrane lipids. In contrast, non-ionic detergents usually do not bind to water-soluble proteins. According to a recent report, substantial and cooperative binding of octyl glucoside to several water-soluble proteins does occur near the critical micelle concentration. However, data have been obtained that contradict this report. No decrease was found in the elution volumes of five water-soluble proteins on molecular sieve chromatography on two Superose columns in tandem when 35 mM octyl glucoside was included in the eluent. No binding of the detergent to these proteins was observed at 20 or 22.5 mM octyl glucoside on molecular sieve chromatography on a TSK SW guard column as determined by differential refractometry and UV spectrophotometry of the proteins in the absence or presence of octyl glucoside. The experiments were done with the same buffer system and with six of the proteins used in the reported study. It is concluded that, as expected, there is no binding of octyl glucoside to water-soluble proteins above the detection limit (0.1 g detergent/g protein) of the refractometric method. The binding of, on average, 1.3 +/- 0.2 g of detergent per gram of water-soluble protein that was observed at 20 mM octyl glucoside in the reported study is not consistent with the present results.

Chromatography, Gel↗

PubMed1984

Macroscale high-performance liquid chromatographic separation and instrumental identification of components of diethylaminoethyl murine epidermal growth factor.

Murine epidermal growth factor (m-EGF), a polypeptide produced as a chromatographically homogeneous peak on diethylaminoethyl (DEAE) cellulose by the method of Savage and co-workers, and characterised as a single compound, has been shown by ourselves and several other groups to be a mixture. The present contribution extends our previously reported work and discusses the separation of this material, termed DEAE-m-EGF, into its components by preparative ion-pair reversed-phase high-performance liquid chromatography (RP-HPLC) on C18 mu Bondapak in quantities up to 50 mg per run. Isocratic elution was used and the mobile phase was acetonitrile-water (26:74, v/v, 0.04 M in triethylamine acetate); pH was 5.6, temperature 40 degrees C, and detection was by ultraviolet absorption at 254 nm, and (for some runs) by differential refractometry. Seven significant peaks, four major, three minor, were detected. Of the major peaks, two designated alpha- and beta-EGF, constituted 70% of the total mass and were the most important to our work. Each of the eluted peaks was recovered by lyophilisation, and this product checked for homogeneity by ion-pair RP-HPLC on a C18 mu Bondapak analytical column, with ultraviolet detection as before. All recovered peaks were found to be homogeneous by this criterion. These chromatographically homogeneous compounds were investigated by modern physicochemical instrumentation to determine their structure. The molecular weight of each of the species was determined by fast atom bombardment mass spectrometry. High-field proton magnetic resonance at 270 MHz provided structural and conformational information. Polarimetry and ultraviolet absorption were also used to characterise the compound. alpha-EGF, for example, had a molecular weight of 6040 corresponding to the 53 amino acid residue peptide previously designated EGF; beta-EGF had a molecular weight of 5930. This molecular weight differential of 110 suggested the hypothesis that beta-EGF was a 52 residue peptide corresponding to alpha-EGF minus the terminal asparagine at position 1. Proton magnetic resonance difference spectroscopy (beta spectrum subtracted from alpha) provided powerful confirmatory evidence for this hypothesis. All materials recovered from RP-HPLC were tested in the sheep and found to retain their biological activity.

Animals↗

PubMed1978

Interaction of ribonuclease A with aqueous 2-methyl-2,4-pentanediol at pH 5.8.

The interactions between ribonuclease A and solvent components in aqueous 2-methyl-2,4-pentanediol (MPD) have been investigated by differential refractometry and light scattering at pH 5.8, i.e., conditions similar to those used to crystallize the protein from this solvent system. Application of multicomponent thermodynamic theory shows that, at all solvent compositions up to 50% (v/v) MPD, the protein is preferentially hydrated; i.e., addition of ribonuclease to the mixed solvent leads to an increase in the chemical potential of MPD. This unfavorable thermodynamic interaction leads to phase separation, probably caused by local salting out of the MPD by the charges on the surface of the protein molecule. A parallel examination by circular dichroism (CD) has shown that the CD spectrum of ribonuclease in 50% MPD is indistinguishable from that in dilute buffer.

Animals↗

PubMed1976

Proton-dependent dissociation equilibrium of hemoglobin. 1. A 700-nanometer light-scattering study on horse methemoglobin in the pH range 4.8 to 7.2.

The effect of proton concentration upon the subunit dissociation of horse methemoglobin has been investigated at two ionic strengths by light scattering photometry at 700 nm. Differential refractometry revealed a slight but systematic decrease of the specific refractive index increment with decreasing protein concentration for solutions in dialytic equilibrium with the solvent. In the pH range 4.8-7.2 the dissociation can be described by a simple equilibrium between tetramers and dimers. The dissociation constant Kd of the met derivative is found to be very similar to those of the O2- and CO-ligated states. From the slope of a plot of log Kd vs. pH, the number of protons bound is n = 1.3 +/- 0.1 resulting from an increase in the pK values of two groups upon dissociation. These two groups must be identical because the dissociation is symmetrical.

Animals↗

PubMed1995

[Sensitivity of refraction measurement with the infrared videorefractometer VRB 200].

AIM OF THE STUDY: This study investigates the sensitivity of a computerised videorefractor (VRB 200) for refractive errors, especially amblyopiogenic, in babies and infants. PATIENTS AND METHODS: Videopictures from 312 eyes of 156 babies and infants were taken, evaluated and compared with the current measurements (skiaskopy or refractometry) of the university eye hospital Erlangen-Nürnberg. RESULTS: 255 (81.7%) of 312 eyes were evaluable. The VRB 200 achieves a sensitivity of 96.1% in hyperopic eyes (219 of 228 eyes) and 94.7% in myopic eyes respectively (18 of 19 eyes). Of 8 emmetropic eyes 6 were recognized correctly negative. Astigmatism could be estimated coarsely quantitatively in power and qualitativ in the axis with a sensitivity of 80% (92 of 115 eyes) and a specificity of 86% (121 of 140). Anisometropia over 2 dpt was recognized in 5 of 6 patients. A general statement concerning the specificity is not possible with this study, because it is not a mass screening procedure. CONCLUSION: This videorefractor is able to recognize semi-quantitatively ambylopiogenic refractive errors with high sensitivity.

Amblyopia↗

PubMed1994

[How accurate is video refraction measurement in infants in comparison with skiascopy? How much do the values change within a half a year?].

BACKGROUND: Isotropic photorefraction (Atkinson et al., 1981) is a method used to screen the refraction in infants. The aim of this study is to analyze its limitations as a measuring instrument. MATERIALS AND METHODS: 215 children aged between 5 and 12 months were examined in cycloplegia. The results were subsequently compared (1) to the results of streak retinoscopy also performed at the same time and (2) to photorefraction performed a second time, 6 months later (with 145 children). RESULTS: Spherical refraction: The mean spherical values differed by 0.70 dpt through photorefraction methods, compared to retinoscopy. The standard deviation (SD) was 0.67 dpt. The values of the photorefraction differed therefore in 95% of the children within a range of 2.7 dpt (or +/- 2 SD). Compared to the second photorefractive measurement 6 months later, the average refraction showed a small myopic shift (-0.45 dpt). Astigmatism: The errors of measurement were more pronounced here. Extreme differences of up to 9 dpt were found in single cases. The mean difference, compared to retinoscopy, was 0.73 dpt. The standard deviation (SD) was 0.90 dpt. In 95% of the children, the values of photo-refraction differed therefore by a range of 3.6 dpt (or +/- 2 SD). Compared to the second photorefractive measurement 6 months later, the average refraction showed a mean change of 0.73 dpt. CONCLUSIONS: Our photorefractive measurements showed errors in the range of 1-2 dpt for the spherical refraction, and in the range of 2-3 dpt for astigmatism. In 5% of the children examined, even greater aberrations were found. As long as the aim of photorefraction is restricted to disclosing high refractive errors, this method is judged suitable for the refractive screening of infants. For more precise refraction, and for the prescription of spectacles, we believe that is should be supplemented by a second examination technique, such as retinoscopy or automated refractometry.

Astigmatism↗

PubMed1991

[Eliminating reflection of intraocular lenses].

Reflections on the refractive surfaces of intraocular lenses can be a nuisance when performing retinoscopy or refractometry. Some patients with IOLs also see reflections which disturb their vision. This article examines the conditions for coating IOLs. It also explains why conventional coating methods cannot be used for IOLs.

Humans↗

PubMed1980

[Liindner's method of cylinder retinoscopy without theory].

Brief description of Lindner's cylinder retinoscopy for practical application: The main criteria of this accurate method for checking refraction are the direction, shape, speed and brightness of the retinoscopic phenomena moving in the pupil of the examined eye. To determine astigmatism the use of plus cylinders is recommended. Difficulties may be due to the optical aberration at the periphery of a wide pupil, to a scissors phenomenon, and to optical irregularities of the senile lens, corneal opacities etc. In many cases retinoscopy can be performed well without using mydriatics and cycloplegics, respectively. Children must not be overstrained. Generally, final subjective checking is crucial for the prescription of corrective glasses. Mastery of Lindner's cylinder retinoscopy enables the eye specialist to keep refractometry with simple aids, as an essential part of the ophthalmological diagnosis, in his own hands, against the increasing claim of optometrists and opticians.

Adult↗