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Results for “Refractometry”

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At least 109 records · Page 6Linked to original sources
PubMed1993

[Prospective longitudinal studies on lens changes after vitrectomy--quantitative assessment by fluorophotometry and refractometry].

We prospectively evaluated lens changes after vitrectomy on 55 patients with vitreoretinal interface syndrome such as idiopathic epiretinal membrane, vitreomacular traction syndrome, and impending stages of idiopathic senile macular hole. Postoperative changes in crystalline lenses were assessed by fluorophotometric measurement of lens autofluorescence, measurement of refractive errors and biomicroscopic evaluation of progression of nuclear sclerosis. Examinations were repeated prior to surgery and at 1, 3, 6, and 12 months postoperatively. While autofluorescene and light transmittance of the lens were not affected by vitrectomy in patients less than 50 years old, older patients showed a significant increase of autofluorescence and decreased transmittance as early as 3 months after surgery. The refraction became myopic with time especially in the older patient group. Nuclear cataract was also found on biomicroscopic examination in the older patients as early as 1 month after surgery and progressed with time. The older the patients were, the more prominent those lens changes were.

Adult↗
PubMed2001

A short-run new analytical ultracentrifugal micromethod for determining low-density lipoprotein sub-fractions using Schlieren refractometry.

We have developed a new analytical ultracentrifugal micromethod for the determination of serum low-density lipoprotein (LDL) subclasses directly from ultracentrifugal Schlieren scans. We have used special software for the analysis of this type of single-spin density-gradient ultracentrifugation. The flotation of LDL patterns was obtained by underlayering a physiological salt solution with serum or isolated lipoprotein fractions raised to a density of 1.3 g/mL in the spinning ultracentrifugation capillary band-forming cell. The repeated analysis of Schlieren curves of the same sample from 10 to 100 microL in the 60-100 min full-speed interval time resulted in quite reproducible results. We obtained quantitative results by measuring the Schlieren areas between the sample curves and the reference baseline curve by using computerised numerical and graphic techniques. The decomposition of the integrated curve was carried out using a nonlinear regression program followed by deconvolution algorithm analysis in order to determine the parameters of the composing Gaussian subclasses. The LDL particle concentrations were calculated from the area under the integral of the Gaussian curve using a calibration data constant. The flotation range of the LDL Schlieren curves in the cell was identified with serum from which LDL had been removed by means of precipitation reagents and with centrifugation of isolated LDL aliquots. With this technique, we measured the concentration of LDL and analysed its polydispersity without the need for preceding sequential isolation of the LDL. On the basis of the Schlieren curves, the LDL samples were either physically paucidisperse, having a symmetrical peak within a narrow density range, or were polydisperse, showing an asymmetrical pattern distributed over a broader density region. The described method proved to be useful for a clear and immediate visual presentation of the concentration values of the LDL and for the identification of the heterogeneity of LDL variants without the need for the preparative isolation of that density class.

Adult↗
PubMed1985

Gel permeation chromatography with interference refractometry for the rapid assay of polydisperse dextrans in biological fluids.

A semi-automatic system incorporating an ultra-sensitive interference refractometer coupled to a dual-column gel permeation apparatus has been devised for measurement of the molecular size distribution of dextrans in small samples of serum and urine. The system was calibrated with seventeen defined dextran fractions with a range of 1200-250,000 weight average molecular weight (Mw). Urine samples were prepared for analysis by passage through small ion-exchange columns; serum was pretreated by precipitation with trichloroacetic acid and centrifuged before the ion-exchange treatment. Internal standard (dextran, 2 X 10(6) Mw) was added to each sample before pretreatment. Data were obtained in a form suitable for computerised analysis.

Body Fluids↗
PubMed2001

[Accuracy of measurements of video-refractometry in higher ametropia].

BACKGROUND: Measurement of refraction of non-cooperative patients is a real challenge for the ophthalmologist. Retinoscopy produces exact results in experienced hands, but requires practice and time. The Videorefractor VRB 200 (manufactured by Tomey, Erlangen) was especially designed for refracting children. The aim of this study is to prove the accuracy of this tool in measuring refraction. MATERIAL AND METHODS: 259 patients (age 10 month to 77 years) were measured with the VRB 200. Each patient was examined by retinoscopy in cycloplegia and refracted with the Topcon autorefraktor RM-A 6000. Ametropia was evoked at 5 emmetropic volunteers by lenses of different power, placed in a trial frame. These measurements were performed with and without use of cycloplegic drugs. RESULTS: The VRB 200 showed an average error of spherical equivalent at ametropia of the range -4 to +4 Diopters (dpt) < 2 dpt. At higher ametropia the error grew increasingly. Repeated measurements of one patient showed high variation of the results. Astigmatism was measured worse by growing magnitude, especially at diagonal axis (45 degrees and 135 degrees). Anisometropia > 2 dpt has been discovered in only 72%. It was possible to examine many infants and handicapped patients, which was impossible by using the RM-A 6000. An examination by retinoscopy was possible in all cases, but needed a lot of time and patience. CONCLUSIONS: The concept of good handling suffers especially by the increasing inaccuracy at ametropia beyond +/- 4 dpt. At this state of development the VRB 200 is no alternative in practical use to the conventional retinoscopy.

Adolescent↗
PubMed1975

Use of refractometry to determine nitrogen accumulation in close d circuits.

We have described a technique by which a portable interference refractometer may be used to determine the accumulation of nitrogen in a totally closed anaesthetic circuit. The inspired mixture contained halothane, oxygen, nitrous oxide and nitrogen. The concentrations of the first two were controlled with u.v. paramagnetic analysers respectively. It was then possible to determine the percentage of nitrous oxide replaced by nitrogen by measuring the refractive power of the mixture.

Anesthesiology↗
PubMed1984

Molecular weight and related properties of lily amylose determined by monitoring of elution from TSK-GEL PW high performance gel chromatography columns by the low-angle laser light scattering technique and precision differential refractometry.

Amylose was fractionated according to its molecular weight by high performance gel chromatography using columns of a TSK-GEL PW series. Elution from the columns was monitored with a low-angle laser light scattering photometer and a precision differential refractometer. The following results were obtained indicating that the procedure is highly efficient for characterizing an amylose preparation with respect to its molecular weight: 1) the weight-average molecular weight of lily amylose used as a test material was determined to be 786,000 +/- 26,000 (n = 7); 2) the molecular weight distribution curve of the amylose was worked out from the chromatographic data; and 3) based on the concept of the universal calibration curve, the Mark-Houwink-Sakurada equation of the amylose was presumed to be [eta] = 2.27 X 10(-4)M0.62 (dl/g). The technique saves time and sample significantly compared with the conventional ones, and consequently enables the characterization of amylose in aqueous solvents without either the degradation or association peculiar to the amylose molecule.

Amylose↗