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PubMed1990

[Objective determination of refraction].

Objective determination of refraction is basically necessary for the subjective adjustment of refraction aimed at prescribing glasses. At least as important is the use of objective determination of refraction as a basis of ophthalmological diagnosis because the best-corrected visual acuity forms basic diagnostic information. Three methods of objective determination of refraction are available. Photorefraction has only been used for screening preschool children, as it has no value for the above-mentioned purpose. Refractometry is widely being used for objective determination of refraction, and during the last few years automated refractometry has also become more and more common. This trend is supported by the possibility of delegating automated refractometry to assistant medical personnel. Retinoscopy and automated refractometry yield comparable results. Retinoscopy has some advantages: great flexibility and the fact that retinoscopy forms an image of optical aberrations of the eye, giving the ophthalmologist an idea of the optical quality of the patient's eye. Due to its flexibility retinoscopy can be used for refractioning babies and infants without any problem. The disadvantage of retinoscopy is the impossibility of delegating it to assistant medical personnel and the fact that this method must be learned by the ophthalmologist. In contrast to retinoscopy, automated refractometry can easily be learned and can be delegated to assistant medical personnel. Its drawback is that it is inflexible, making it inconvenient for refractioning babies and infants. If automated refractometry and retinoscopy are used with cycloplegia, precautions are essential to avoid errors caused by optical aberrations of the eye. The measurement must be done in the center of the pupil.(ABSTRACT TRUNCATED AT 250 WORDS)

Eyeglasses↗
PubMedDate not supplied

Evaluation of 3 assays for failure of passive transfer in calves.

This study examined the sensitivity, specificity, predictive values, and classification accuracy of 3 commonly used screening tests for failure of passive transfer: the sodium sulfite turbidity test, the zinc sulfate turbidity test, and refractometry relative to serum immunoglobulin G1 (IgG1) concentrations determined by radial immunodiffusion. Serum samples were obtained from 242 calves ranging from 1 to 8 days of age. Using a serum concentration of 1,000 mg/dL IgG1, to define adequate passive transfer, the zinc sulfate test had a sensitivity of 1.00 and a specificity of 0.52 in the detection of inadequate passive transfer. The endpoint of the test appeared to be higher than desired; calves testing negative had mean serum IgG1 concentration of 955 mg/dL and a large proportion of calves with adequate passive transfer were misclassified as positive for failure of passive transfer. Using the qualitative zinc sulfate test, the percentage of calves correctly classified with regard to passive transfer status was less than that observed with either the sodium sulfite test or refractometry. The sensitivity of the sodium sulfite assay was 0.85 at a 1+ endpoint and 1.00 at a 2 or 3+ endpoint. The specificity of the sodium sulfite assay varied from 0.87 at a 1+ endpoint and 0.56 at a 2+ endpoint. The sensitivity and specificity of refractometry varied from 0.01 to 1.00 depending on the choice of endpoint. Refractometry correctly classified the largest proportion of calves with regard to their passive transfer status at test endpoints of 5.0 and 5.5 g/dL, 83% and 82% respectively. The highest percentages of calves correctly classified occurred with the sodium sulfite test using a 1+ endpoint (86.30%) and refractometry using a 5.0 g/dL endpoint (83.00%). A regression equation was developed that permitted calculation of an optimal endpoint for refractometric determinations of total serum protein concentration. A serum protein concentration of 5.2 g/dL was equivalent to 1,000 mg/dL serum IgG1. Optimal selection of tests for passive transfer status in calves will be governed by the prevalence of failure of passive transfer, test performance, and the anticipated costs of classification errors.

Analysis of Variance↗
PubMed1993

[Urinary specific gravity--comparative measurements using reagent strips and refractometer in 340 morning urine samples].

The specific gravity of urine (SG) indicates the number and weight of solute particles in urine; its measurement is helpful in interpreting proteinuria detected by dipstick tests and in monitoring adequate hydration in patients with nephrolithiasis. Four methods for measuring SG or osmolality of urine are currently available (depression of the freezing-point, urometry, refractometry, cation exchange on a reagent strip). Using a recently developed reagent strip, we have measured SG in morning urines of 340 non-selected outpatients and compared the results with SG measurements by refractometry of the same urines. In 86.2% of all urines, a good positive correlation between SG measured by reagent strip and refractometry was noted (r = 0.913, p = 0.0001). In 13.8% of the urines, however, the SG measured by reagent strip deviated by more than +/- 5 from the value obtained by refractometry; in 90% of these urines, glucosuria (reagent strip values too low or too high), proteinuria (values too high), or bacteriuria/leukocyturia (values too low or too high) could be found. In alkaline urine (pH > 7.0), SG values obtained by reagent strip have to be corrected by +5.

Female↗
PubMed1995

Refractive index and osmolality of human tears.

Tear osmolality measurement, as a basic index of lacrimal physiology, is technically difficult. We investigated a simple, digital nanoliter technique of critical angle refractive index measurement. After initial comparison of the techniques with aqueous NaCl (0.5 to 1.4%), 3 successive tear samples were obtained from each of 40 normal, noncontact lens wearing subjects, aged 17 to 63 years, for analysis by nanoliter osmometry and digital refractometry. In addition, tear lactoferrin concentration was estimated with the Lactoplate immunoassay. For the range of NaCl concentrations tested, osmolality and refractive index measurements were highly correlated with concentration, and with each other. For 0.9% NaClaq the mean value of osmolality was 292.0 mOsm/kg and refractive index was 1.33419. For human tears average values were found to be: for osmolality, 303.7 +/- 22.9 mOsm/kg; for refractive index, 1.33698 +/- 0.00110; and for lactoferrin level, 1.64 +/- 0.47 mg/ml. No statistically significant correlation was obtained between either refractive index or lactoferrin level and osmolality, but refractive index and lactoferrin level were significantly correlated (r = 0.64, p < 0.001). The high correlation of refractometry and osmolality for aqueous NaCl indicates comparability of the techniques for this solution, but this does not apply to human tears. Unlike tear osmolality, tear refractive index is dependent to a greater extent upon composition, as is suggested by its correlation with lactoferrin level. Therefore, refractometry is not acceptable as a direct alternative to osmometry in the assessment of lacrimal function.

Adolescent↗
PubMed1995

[Evaluation of a test strip for the determination of urine specific gravity in the dog].

The specific gravity of 80 randomly chosen urine samples from healthy dogs without polyuria/polydipsia and from a few dogs with polyuria/polydipsia was measured by refractometry and by test strip method (sg test strip). Urine osmolality and pH were also measured and the urine samples were examined for the presence of glucose. In accordance with earlier observations, there was an excellent correlation between the specific gravity determined by refractory and the osmolality (r = 0.98). The results obtained with the sg test strip correlated poorly with those obtained by refractometry (r = 0.39) and poorly with the osmolality (r = 0.36). In 77.5% of the samples the specific gravity determined with the sg test strip differed by more than 0.005 from that determined by refractometry. After correction of the sg test strip results by +0.005 for urine pH > or = 6.5, this percentage decreased to 60%. The results for the refractometer and sg test strip were significantly different (P < 0.001). These results indicate that the sg test strip investigated is unsuitable for use to determination of the specific gravity of canine urine.

Animals↗
PubMed1995

Refractive indices for volatile anesthetic gases: equipment and method for calibrating vaporizers and monitors.

OBJECTIVE: The objective of our study was to establish the refractive indices and the virial coefficients of the volatile anesthetic vapors. These indices and coefficients will allow refractometry to be used by manufacturers to produce accurate calibration, without requiring expensive high-precision calibration gases. METHODS: We used a precision refractometer to measure the refractive indices for five volatile anesthetic vapors. We prepared our calibration gases by mixing a gravimetrically calibrated amount of liquid agent with a constant gas flow. RESULTS: The refractive indices for the volatile anesthetic vapors are 1,603.2 for halothane, 1,540.4 for enflurane, 1,563.3 for isoflurane, 1,538.3 for sevoflurane, and 1,211.7 for desflurane. The maximum theoretical error in our measurements, due to all sensors and all uncertainty in our measurement of apparatus and physical constants, is +/- 0.56% of the reading (+/- 0.70% for desflurane). CONCLUSIONS: If refractometry replaced calibration gases in cylinders, as a calibration standard, manufacturers might avoid errors that now occur because calibration gases manufactured by numerous companies seem to differ. We propose that our values serve as an interim database.

Anesthesia, Inhalation↗
PubMed1983

Urine specific gravity measurements: comparison of a new reagent strip method with existing methodologies, as applied to the water concentration/dilution tests.

A study was carried out to compare a new, unique chemical strip test for the measurement of urine specific gravity with the traditional methods of hydrometry and refractometry, during water concentration/dilution tests in 12 normal subjects. The pattern of specific gravity results during these serial measurements was virtually identical for the strip and for the comparative methods. Comparison of the strip results with those obtained by both hydrometry and refractometry produced acceptable linear regression data. In addition, a close relationship was demonstrated between the strip specific gravity and urine osmolality. The findings show that the strip method is an acceptable alternative to traditional methods as an indicator of urine concentration.

Adult↗
PubMed1985

Projection-simulated ametropia. A model for teaching subjective refraction.

Teaching subjective refraction techniques ("refractometry") is enhanced by having the student experience the effect of each lens change "through the eyes of the patient." A projector, positioned behind the phoropter, projects a visual acuity chart through the phoropter onto the far wall. "Unknown" refractive errors are simulated by attaching trial lenses to the lens barrel of the projector, and the student progressively clears the projected image as he learns the standard steps of subjective refractometry. The focus sensitivity of each lens change can be varied, if desired, by stopping down the projection system. This simulation, which uses equipment readily available in most ophthalmology offices, has proven useful for both demonstration and practice.

Education, Medical↗
PubMed1983

Study of urinary specific gravity by reagent strip method.

A newly developed reagent strip method for determination of urinary specific gravity is described. This reagent strip (Chemical S.G., Ames Co.) contains polyelectrolyte which is sensitive to the cation in solution. The urinary specific gravity is mainly decided by cation (Na+ and K+) concentrations in urine. As a result, the reagent strip gave measurements that corresponded to those measured by refractometry and gravimetry of NaC1 solution. Urea and glucose gave increased values by the refractometer, whereas the reagent strip did not cause changes. The values of urinary specific gravity obtained from reagent strip showed not only good correlations (r = 0.79-0.93) with the refractometry and gravimetry but also urinary osmolarity. This reagent strip method proved to be a most convenient tool for routine urinalysis because of the good reproducibility and accuracy considering its easy handling.

Contrast Media↗
PubMedDate not supplied

[Changes in clinical refraction in future pilots during the course of training].

Changes in clinical refraction parameters were followed up in 343 students of school of pilots in the town of Burguruslan in the course of vocational training. Skiascopy and laser refractometry methods were used. Dynamic follow-up of clinical refraction showed its increase in 24.3% of the examinees both with emmetropia and hypertropia or myopia. The most noticeable increase of refraction was observed during the first two years of training, which may be explained by intensive exercise of the eyes because of theoretical studies and flights. The results evidence practical advantages of laser refractometry in comparison with skiascopy.

Aerospace Medicine↗
PubMed1993

The effects of diaper brands, urine volume, and time on specific gravity measurement.

Nurses use urine specific gravity to assess fluid volume status in pediatric patients. Specific gravity of five leading brands of disposable diapers was measured to determine the effects of diaper brand, urine volume, time elapsed, and method of specific gravity measurement comparing the two methods of refractometry and N-Multistix SG (Ames Division, Miles Inc., Elkhart, IN). Immediately after a baby voided 20 mL of urine into any disposable diaper, the specific gravity by refractometer accurately compared with the control standard. Measurement accuracy by N-Multistix SG was only assured if Pampers (Procter & Gamble, Cincinnati, OH) were used. However, both methods were inaccurate at 4 hours with 20 mL of urine. Immediately after a baby voided 40 mL of urine into any disposable diaper, both methods were accurate when compared with the control. At 4 hours, only Pampers and Chux (Procter & Gamble, Cincinnati, OH) were accurate by refractometry, and Pampers alone was accurate by N-Multistix SG.

Humans↗
PubMed1983

Concentration and composition of plasma proteins in wild mammals.

Total protein concentrations from a variety of wild mammalian species were measured by the Lowry and Biuret techniques and compared with results obtained or derived by refractometry. Values obtained with the Lowry method were the highest and certain derived refractometry results, the lowest. It is suggested that the Biuret method provides the most acceptable values but that care should be exercised in using the correct standard. The percentage composition of plasma from 22 species of wild mammals is also presented and the observations discussed with relation to methodology and A/G ratio.

Animal Population Groups↗
PubMed1982

Thermodynamic characterization of hog kidney D-amino acid oxidase apoenzyme in concentrated guanidine hydrochloride solution. Preferential interaction with the solvent components and the molecular weight of the monomeric unit.

This paper describes the physical characterization of the monomeric unit of hog kidney D-amino acid oxidase apoenzyme in 6 M guanidine hydrochloride (GuHCl) solution by means of differential refractometry, densimetry, light scattering, equilibrium sedimentation, and high-speed gel filtration chromatography. In 6 M GuHCl solution, the oxidase interacts preferentially with GuHCl: the values of the preferential interaction parameter are 0.11 +/- 0.03 (S.D.) g/g of protein by densimetry and 0.14 +/- 0.04 g/g of protein by refractometry. The volume change, delta V, of the oxidase on transfer from the native to the denatured state is -350 ml/mol. The molecular weight of the monomeric apoenzyme is 39,600 +/- 1,700 by light scattering and 38,000 +/- 1,200 by high-speed equilibrium sedimentation. The values of the molecular weight estimated by the empirical methods, i.e., sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis and high-speed gel filtration chromatography in 6 M GuHCl, agree well with those obtained by the thermodynamic methods mentioned above. These results confirm definitely that the complex of the apoenzyme with SDS normally behaves in the same manner as those of standard proteins in SDS-gel electrophoresis. This is also supported in this study by the analysis of the electrophoretic data at several gel concentrations by Ferguson plots. The molecular weight of quasi-D-amino acid oxidase apoenzyme was also examined by the empirical methods.

Animals↗
PubMed1990

Subunit constitution of carbonic anhydrase from Chlamydomonas reinhardtii.

Carbonic anhydrase purified from the cell surface of Chlamydomonas reinhardtii was inactivated by treatment with dithiothreitol. This treatment caused dissociation of the holoenzyme into 35-kDa (A) and 4-kDa (B) subunits as revealed by SDS/PAGE. The 35-kDa subunit was further separated into two components A1 (35 kDa) and A2 (36.5 kDa) by SDS/PAGE using a gradient gel. These two components have the same amino acid sequence up to at least the 10th amino acid from the N-terminus. The molecular masses were estimated at 76 kDa and 35 kDa for the holoenzyme and the large subunit, respectively, and the molar ratio of the former to the latter at 1:2, by using the techniques of low-angle laser light-scattering photometry and precision differential refractometry combined with gel-filtration HPLC. The molar ratio of the 35-kDa/4-kDa subunits was estimated at 1:1 the gel-filtration HPLC monitored with precision differential refractometry. Atomic-absorption spectrophotometry revealed that the holoenzyme contains two atoms of zinc. These results suggest that the holoenzyme is a heterotetramer composed of two large subunits (A1 and A2) and two small subunits (B).

Amino Acid Sequence↗
PubMedDate not supplied

[Analysis of solutions for parenteral use under field conditions].

Methods for determination of relative density, osmolarity, then refractometry, polarymetry and conductometry as simple methods suitable for work under field conditions have been applied for the quality control of the following solutions for infusion and injections: glucose, mannitol, sodium chloride, sodium hydrogencarbonate, magnesium sulphate and potassium chloride. The results obtained in the analysis of preparations have shown the advantage of refractometry.

Infusions, Parenteral↗
PubMed1984

Influence of edge sharpness on the accommodation of the human eye.

Using a subjective method of laser refractometry, the accommodation behavior of six subjects toward real targets with various degrees of blur, dependent on the viewing distance, were investigated monocularly and binocularly. Despite the sharpness of the target, the nominal value is only reached incompletely with a lag of accommodation, because accommodation tends to be as minimal as possible. Increasing blurring leads to a drift of accommodation towards the resting position of accommodation. The resulting underaccommodation causes further physiological blurring of the retinal image of the targets. The approach of the targets to the resting position of accommodation leads to a higher precision of adjustment and less drift. Subjective components (accommodative laziness, cognitive demand) influence the accommodation and increase the phenomenons discovered.

Accommodation, Ocular↗
PubMed1991

Active and monomeric human red cell glucose transporter after high performance molecular-sieve chromatography in the presence of octyl glucoside and phosphatidylserine or phosphatidylcholine.

The human red cell glucose transporter (Glut 1) was purified by ion-exchange chromatography in the presence of octyl glucoside. The state of association of the protein was studied, and the transport activity was determined after exchange of copurified membrane lipids for phosphatidylserine (PS) or phosphatidylcholine (PC). The purpose was to analyze the Glut 1 preparation for homogeneity and activity prior to attempts at crystallization. Analyses by high performance molecular-sieve chromatography showed that the Glut 1 was monomeric immediately after the ion-exchange purification: the Mr of the Glut 1 polypeptide was estimated to be 49,000 +/- 6000 by TSKgel G3000SW chromatography monitored by low-angle laser light-scattering photometry, differential refractometry and UV photometry. This required determination of the absorption coefficient of the Glut 1, which was measured to be 1.13 +/- 0.03 ml mg-1 cm-1 at 280 nm, referring to the polypeptide concentration. The Mr value is consistent with the cDNA-deduced Mr 54,117 of the very similar HepG2 glucose transporter polypeptide. At 2 degrees C, pH 7 and an ionic strength of 0.06 M, the Glut 1 associated gradually during three days to form oligomers. These formed much more rapidly at room temperature or at high ionic strength. Freshly prepared Glut 1 retained high activity after separation from membrane lipids on a TSKgel G3000SW column in the presence of 40 mM octyl glucoside and 1 mM PS or PC. In contrast, most of the activity was lost when the membrane lipids were separated from the protein in the absence of eluent lipids. The presence of a phospholipid was thus essential for retention of high activity of the Glut 1 in octyl glucoside and PC was nearly as effective as PS.

Chromatography, Gel↗
PubMed1991

Determination of cholesterol and cortisone absorption in polyurethane. I. Methodology using size-exclusion chromatography and dual detection.

A size-exclusion chromatographic method is described for measuring the absorption of the steroid-based lipids cholesterol and cortisone into Pellethane 2363, a polyurethane used in biomedical implants. The method uses refractometry and ultraviolet diode-array detection, with tetrahydrofuran as the mobile phase. Using an injection volume of 150 microliters, the lower limit of accurate measurement for cholesterol (refractive index detection) was 6 micrograms/ml with a lower limit of detection, based on a 2:1 signal-to-noise ratio, of 0.15 micrograms (1 microgram/ml). For cortisone (ultraviolet detection), the lower accurate limit was 0.6 micrograms/ml with a lower limit of 0.015 micrograms (0.1 micrograms/ml). The results show that after 44 h, 2037 micrograms/g cholesterol and 3131 micrograms/g cortisone were absorbed by the polyurethane. The method eliminates extensive sample manipulation and is sensitive to low levels of lipid in the presence of a high-molecular-mass synthetic polymer.

Absorption↗