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At least 145 records · Page 8Linked to original sources

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↗

PubMed1997

Compensation for spectacle lenses involves changes in proteoglycan synthesis in both the sclera and choroid.

PURPOSE: It has been demonstrated that chick eye growth compensates for defocus imposed by spectacle lenses: the eye elongates in response to hyperopic defocus imposed by negative lenses and slows its elongation in response to myopic defocus imposed by positive lenses. We ask whether the synthesis of scleral extracellular matrix, specifically glycosaminoglycans, changes in parallel with the changes in ocular elongation. In addition, there is a choroidal component to compensation for spectacle lenses; the choroid thickens in response to myopic defocus and thins in response to hyperopic defocus. We ask whether choroidal glycosaminoglycan synthesis changes in parallel with changes in choroidal thickness. METHODS: Chicks wore either a +15 diopter (D) or -15 D spectacle lens over one eye, or they wore one lens of each power over each eye for 5 days. At the end of this period, we measured refractive errors and ocular dimensions by refractometry and A-scan ultrasonography, respectively. Pieces of the scleras and choroids from these eyes were put into culture and the synthesis of glycosaminoglycans was assessed by measuring the incorporation of radioactive inorganic sulfur. RESULTS: We here report that the compensatory modulation of the length of the eye involves changes in the synthesis of glycosaminoglycans in the sclera, with synthesis increasing in eyes wearing -15 D spectacles lenses and decreasing in eyes wearing +15 D lenses. In addition, changes in the synthesis of glycosaminoglycans in the choroid are correlated with changes in choroidal thickness: eyes wearing +15 D lenses develop thicker choroids and these choroids synthesize more glycosaminoglycans than choroids from eyes wearing -15 D lenses. CONCLUSIONS: Changes in scleral glycosaminoglycan synthesis accompany lens-induced changes in the length of the eye. Furthermore, changes in the thickness of the choroid are also associated with changes in the synthesis of glycosaminoglycans. These results are consistent with the regulation of the growth of the eye being bidirectional, and with the retina being able to sense the sign of defocus.

Adaptation, Physiological↗

PubMed1989

A simple field test for assessing salt balance in heat-stressed miners.

A simple colorimetric test for urinary chloride (Fantus test) corrected for urine specific gravity (measured by refractometry) enabled 24-hour urinary sodium excretion rates to be predicted accurately from a single spot sample of urine. In 29 acclimatized miners working in an environment in excess of 40 degrees C, salt-conserving mechanisms, involving renin and aldosterone, were not active until the urinary sodium excretion rate fell below 50 mmol/24 h. A predicted sodium excretion rate greater than 50 mmol/24 h indicates that dietary sodium supplementation is not necessary.

Adult↗

PubMed1993

On the Stiles-Crawford effect and ocular imagery.

To study the modifying effect on spherical aberration of the retinal directional sensitivity (the Stiles-Crawford effect), ocular imagery was simulated by computer ray-tracing in a phakic and a pseudophakic model eye. The Stiles-Crawford effect was found to reduce the distance between the paraxial focus and the effective least blur focus. The modifying effect on spherical aberration was found to be insignificant for pupil sizes below 4 mm, and to increase in magnitude above this size. For an 8 mm pupil, the effective focus was found to move 0.3 mm and 0.2 mm toward the paraxial focus for the phakic and the pseudophakic eye, respectively. This corresponded to a shift of 1.0 D and 0.6 D in the spectacle plane, respectively. The modifying effect of the retinal directional sensitivity should be taken into account in the theory of ocular refraction and in objective keratometry and refractometry.

Cataract↗

PubMed1975

Some relations between dissolution rates and physical parameters of a drug in aqueous micellar solutions of a non-ionic surfactant.

Dissolution rates of salicylic acid from a constant surface area into a series of aqueous micellar polysorbate 20 solutions at pH 1-0 to 4-0 have been measured using two different methods; a stirred beaker and a rotating disc technique. The micellar molecular weight of polysorbate 20 has been obtained from light scattering and differential refractometry data and used with other independently determined physical data to calculate diffusion coefficients of the diffusing species. Linear multiple regression analysis was used to assess the dependence of drug dissolution rate on the diffusion coefficient and the viscosity of the dissolution medium.

Colloids↗

PubMed1966

Sweet-sensitive protein from bovine taste buds: isolation and assay.

Using refractometry and ultraviolet-difference spectroscopy to indicate interaction between proteins and coinpounds of low molecular weight, we found a protein fraction in bovine tongue extracts that coinplexes sugars and saccharin. The strengths of the coinzplexes parallel the degrees of sweetness of the compounds, and the effects of pH upon formation of complexes parallel the effects of pH upon sensitivity of taste buds to sweet compounds in vivo.

Animals↗

PubMed1971

A quantitative method for blood lipoproteins using cellulose acetate electrophoresis.

A rapid, inexpensive, and quantitative method is described for obtaining the levels of plasma very low, low, and high density lipoproteins using cellulose acetate electrophoresis and lipid assays without prior separation by ultracentrifuge or other techniques. It involves separation of the lipoproteins by cellulose acetate electrophoresis, followed by their identification with the ozone-Schiff reaction. The total lipoprotein concentration is estimated from the total plasma phospholipid, and the percentage of each component obtained by densitometric analysis of the stained electrophoretograms, using reflected light. For samples with a raised level of very low density lipoprotein, plasma triglyceride analysis is also required. The results obtained by the cellulose acetate electrophoresis method are in good agreement with those by the analytical ultracentrifuge and the preparative ultracentrifuge with refractometry. The theoretical assumptions on which the method is based have been shown to be valid.

Cellulose↗

PubMed1978

A simple estimation of the immunoglobulin content of ewe colostrum.

Use of the optical refractometer in performing a rapid assessment of the immunoglobulin content of ovine colostrum under farm conditions was investigated. Refractometer readings were compared with total protein levels and with gamma-globulin levels, determined by the ZSTT, to assess the validity of the technique. In both cases correlation coefficients were high (0.98 and 0.79 respectively). Refractometry was shown to be a valid substitute for the ZSTT in studies on colostrum gamma-globulin levels.

Animals↗

PubMed1982

Pulmonary microvascular permeability following E. coli endotoxin and hemorrhage.

The effects of hemorrhage and Escherichia coli endotoxin on vascular permeability in the lung were investigated in open-chest dogs. Systemic arterial, pulmonary artery, and left arterial pressures were monitored, and a 30-ml balloon catheter placed in the left atrium. An afferent to the left hilar lymph node was cannulated and lymph flow monitored. Lymph and plasma protein concentrations were measured by refractometry. The animals were divided into three groups: 1) a control group in which left atrial pressure was increased by inflation of the left atrial balloon; 2) a hemorrhagic shock group, bled to a systemic arterial pressure of 35-40 Torr until uptake of 20% of shed blood from the reservoir; and 3) an endotoxin shock group in which 2 or 4 mg/kg E. coli endotoxin was infused and left atrial pressure increased to 18 cmH2O for 2 hr. Permeability was determined by comparing the lymph/plasma protein ratios as a function of pulmonary lymph flow for the three groups at base line and increased left atrial pressures. There were no significant differences in lymph protein "wash down" between hemorrhage and control, and there was a minimal but significant difference between endotoxin and control groups. Postmortem extravascular lung water was not increased in the hemorrhage and endotoxin groups when compared to control. Therefore, there were no acute changes in lung vascular permeability within 2 hr after severe hemorrhage, but a minimal increase in permeability following endotoxin.

Analysis of Variance↗

PubMed1991

[Refraction by atrophine cycloplegia].

A new method for refractive measurements with atropine cycloplegia was tested in 90 children with squint. Measurements were taken by an autorefractor (Canon R 10) 90 min after application of 2 atropine eye drops and after 3 days of receiving 1 atropine eye drop 3 times daily, i.e. 9 drops per eye. Results were also compared to conventional "objective" refractometry by means of a hand refractometer (Rodenstock PR 50). According to this method, the total refraction, spherical and cylindric power and the cylinder axis are in agreement with refractive data in 80-90% of the children after 3-day atropinization. The additional cycloplegic effect of atropine given for 3 days is only 0.5 dptr compared to the application of 2 drops on the first day. So for practical purposes the refractive data evaluated after 90-min atropinization can be used as a basis for the prescription of glasses.

Atropine↗

PubMed1992

Characterization of carbonic anhydrase isozyme CA2, which is the CAH2 gene product, in Chlamydomonas reinhardtii.

From high-CO2 (5% CO2) grown unicellular green alga, Chlamydomonas reinhardtii, carbonic anhydrase (CA) was isolated by affinity chromatography and characterized. Isolated CA was identified as an isozyme (CA2) which is the product from the second gene CAH2 by peptide sequencing. The CA2 was inactivated by dithiothreitol. This treatment caused dissociation of CA2 into the large (38 kDa) and small subunits (4243 Da). The molecular mass of the CA2 holoenzyme measured by low-angle laser light-scattering photometry and precision differential refractometry combined with gel-filtration HPLC was 87.9 kDa. These results and gene structure indicate that CA2 is a heterotetramer consisting of two large and two small subunits linked by disulfide bonds like CA1, which is the CAH1 gene product. The specific activity of CA2 purified by anion-exchange HPLC was 3300 units per mg protein, which was approximately 1.6 times higher than that of CA1. Therefore, it was concluded that two structurally related isozymes, CA1 and CA2, are present in the wild type cells of C. reinhardtii and differentially regulated by the atmospheric CO2 concentration.

Amino Acid Sequence↗

PubMed1986

[Studies on the hygiene of arc-welding. (Part 8). Effects of atmospheric conditions on the chemical composition of fumes from low hydrogen welding].

Welding fumes were generated from several kinds of low hydrogen type electrodes which changed the atmosphere with use of various gases, such air, Ar, CO2 and N2, and were collected in water with an impinger. These fumes were analyzed by X-ray refractometry and chemical analysis, and pH of their collecting water was measured. Based on these results, this paper discusses the mechanism of scattering K and Na in fumes from low hydrogen welding which are considered to be the sources of respiratory tract irritation. All sample fumes from low hydrogen welding in several atmospheric conditions contained fluorite (CaF2). The pH of water in which all sample fumes were collected remarkably elevated. Chemical composition ratios of both K2O and Na2O in all sample fumes were larger than those in coating materials. The sample fumes from welding in each of both N2 and CO2 atmosphere showed higher ratios of K2O and Na2O than those in Ar. The conclusions obtained from the discussion are as follows: The potential gradient of the arc becomes larger during welding in the atmosphere with use of N2 or CO2 because the dissociation voltage of N2 and CO2 is very low. Furthermore, fluorite (CaF2) makes the slag more fluid. Then, K and Na become easily dispersed from the arc column of low hydrogen welding.

Air Pollutants, Occupational↗

PubMed1988

Relative density of urine: methods and clinical significance.

The physical properties and chemical composition of urine are highly variable and are determined in large measure by the quantity and the type of food consumed. The specific gravity is the ratio of the density to that of water, and it is dependent on the number and weight of solute particles and on the temperature of the sample. The weight of solute particles is constituted mainly of urea (73%), chloride (5.4%), sodium (5.1%), potassium (2.4%), phosphate (2.0%), uric acid (1.7%), and sulfate (1.3%). Nevertheless, urine osmolality depends only on the number of solute particles. The renal production of maximally concentrated urine and formation of dilute urine may be reduced to two basic elements: (1) generation and maintenance of a renal medullary solute concentration hypertonic to plasma and (2) a mechanism for osmotic equilibration between the inner medulla and the collecting duct fluid. The interaction of the renal medullary countercurrent system, circulating levels of antidiuretic hormone, and thirst regulates water metabolism. Renin, aldosterone, prostaglandins, and kinins also play a role. Clinical estimation of the concentrating and diluting capacity can be performed by relatively simple provocative tests. However, urinary specific gravity after taking no fluids for 12 h overnight should be 1.025 or more, so that the second urine in the morning is a useful sample for screening purposes. Many preservation procedures affect specific gravity measurements. The concentration of solids (or water) in urine can be measured by weighing, hydrometer, refractometry, surface tension, osmolality, a reagent strip, or oscillations of a capillary tube. These measurements are interrelated, not identical. Urinary density measurement is useful to assess the disorders of water balance and to discriminate between prerenal azotemia and acute tubular necrosis. The water balance regulates the serum sodium concentration, therefore disorders are revealed by hypo- and hypernatremia. The disturbances are due to renal and nonrenal diseases, mainly liver, cardiovascular, intestinal, endocrine, and iatrogenic. Fluid management is an important topic of intensive care medicine. Moreover, the usefulness of specific gravity measurement of urine lies in interpreting other findings of urinalysis, both chemical and microscopical.

Biophysical Phenomena↗

PubMed1975

Estimation of protein content in the plasma of young chickens by a refractometric method.

This study was conducted to evaluate a refractometric method for determination of protein content of chicken plasma. Comparison of the results obtained with the refractometric and the Lowry methods indicated that refractometry, when used with due caution in a typical laboratory situation, provided a simple, fast, inexpensive and valid method for determining the protein content of plasma from young chickens.

Animals↗

PubMed1982

Colostrum deficiency in mule deer fawns: identification, treatment and influence on neonatal mortality.

Glutaraldehyde coagulation test, zinc sulfate turbidity test, and total protein refractometry were adapted for use in detecting failure of passive transfer of colostral immunoglobulins to mule deer fawns (Odocoileus hemionus). The results of all three tests were similar. Serum total protein concentration was directly correlated to gamma globulin concentration and gave the best indication of morbidity and mortality. Thirteen of 13 fawns with serum total protein concentrations of 5 g/dl or less at 1 to 7 days of age developed diarrhea and died before 17 days of age. Only 1 of 14 fawns having a serum protein concentration above this level became sick and died. Seven of 13 fawns that had serum total protein concentrations of 5 g/dl or less, and that had already developed diarrhea, were given 20 ml of plasma per kg body weight. Although this increased their serum gamma globulin concentrations 0.3 g/dl, none survived. Administration of bovine colostrum to one fawn increased its serum gamma globulin concentration suggesting that mule deer fawns are able to absorb gamma globulins from bovine colostrum.

Animals↗